Handle EXPR_INDEX when copying expressions.

[smatch.git] / pre-process.c

/*
 * Do C preprocessing, based on a token list gathered by
 * the tokenizer.
 *
 * This may not be the smartest preprocessor on the planet.
 *
 * Copyright (C) 2003 Transmeta Corp.
 *               2003 Linus Torvalds
 *
 *  Licensed under the Open Software License version 1.1
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stddef.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>

#include "pre-process.h"
#include "lib.h"
#include "parse.h"
#include "token.h"
#include "symbol.h"
#include "expression.h"

int verbose = 0;
int preprocessing = 0;

#define MAX_NEST (256)
static int true_nesting = 0;
static int false_nesting = 0;
static struct token *unmatched_if = NULL;
static char elif_ignore[MAX_NEST];
#define if_nesting (true_nesting + false_nesting)

#define INCLUDEPATHS 32
const char *includepath[INCLUDEPATHS+1] = {
        NULL
};

const char *sys_includepath[] = {
        "/usr/include",
        "/usr/local/include",
        NULL,
};

const char *gcc_includepath[] = {
        GCC_INTERNAL_INCLUDE,
        NULL
};


/*
 * This is stupid - the tokenizer already guarantees unique
 * identifiers, so we should just compare identifier pointers
 */
int match_string_ident(struct ident *ident, const char *str)
{
        return !str[ident->len] && !memcmp(str, ident->name, ident->len);
}

static struct token *alloc_token(struct position *pos)
{
        struct token *token = __alloc_token(0);

        token->pos.stream = pos->stream;
        token->pos.line = pos->line;
        token->pos.pos = pos->pos;
        token->pos.whitespace = 1;
        return token;
}

static const char *show_token_sequence(struct token *token);

/* Expand symbol 'sym' at '*list' */
static struct token **expand(struct token **, struct symbol *);

static void replace_with_string(struct token *token, const char *str)
{
        int size = strlen(str) + 1;
        struct string *s = __alloc_string(size);

        s->length = size;
        memcpy(s->data, str, size);
        token_type(token) = TOKEN_STRING;
        token->string = s;
}

static void replace_with_integer(struct token *token, unsigned int val)
{
        char *buf = __alloc_bytes(10);
        sprintf(buf, "%d", val);
        token_type(token) = TOKEN_NUMBER;
        token->number = buf;
}

static void replace_with_defined(struct token *token)
{
        char *string[] = { "0", "1" };
        int defined = 0;
        if (token_type(token) != TOKEN_IDENT)
                warn(token->pos, "operator \"defined\" requires an identifier");
        else if (lookup_symbol(token->ident, NS_PREPROCESSOR))
                defined = 1;
        token_type(token) = TOKEN_NUMBER;
        token->number = string[defined];
}

struct token **expand_one_symbol(struct token **list)
{
        struct token *token = *list;
        struct symbol *sym;

        if (token->pos.noexpand)
                return &token->next;

        sym = lookup_symbol(token->ident, NS_PREPROCESSOR);
        if (sym)
                return expand(list, sym);
        if (token->ident == &__LINE___ident) {
                replace_with_integer(token, token->pos.line);
        } else if (token->ident == &__FILE___ident) {
                replace_with_string(token, (input_streams + token->pos.stream)->name);
        }
        return &token->next;
}

static inline struct token *scan_next(struct token **where)
{
        struct token *token = *where;
        if (token_type(token) != TOKEN_UNTAINT)
                return token;
        do {
                token->ident->tainted = 0;
                token = token->next;
        } while (token_type(token) == TOKEN_UNTAINT);
        *where = token;
        return token;
}

static struct token **expand_list(struct token **list)
{
        struct token *next;
        while (!eof_token(next = scan_next(list))) {
                if (token_type(next) == TOKEN_IDENT)
                        list = expand_one_symbol(list);
                else
                        list = &next->next;
        }
        return list;
}

static struct token *collect_arg(struct token *prev, int vararg, struct position *pos)
{
        struct token **p = &prev->next;
        struct token *next;
        int nesting = 0;

        while (!eof_token(next = scan_next(p))) {
                if (match_op(next, '(')) {
                        nesting++;
                } else if (match_op(next, ')')) {
                        if (!nesting--)
                                break;
                } else if (match_op(next, ',') && !nesting && !vararg) {
                        break;
                }
                next->pos.stream = pos->stream;
                next->pos.line = pos->line;
                next->pos.pos = pos->pos;
                p = &next->next;
        }
        *p = &eof_token_entry;
        return next;
}

/*
 * We store arglist as <counter> [arg1] <number of uses for arg1> ... eof
 */

struct arg {
        struct token *arg;
        struct token *expanded;
        struct token *str;
        int n_normal;
        int n_quoted;
        int n_str;
};

static int collect_arguments(struct token *start, struct token *arglist, struct arg *args, struct token *what)
{
        int wanted = arglist->count.normal;
        struct token *next = NULL;
        int count = 0;

        arglist = arglist->next;        /* skip counter */

        if (!wanted) {
                next = collect_arg(start, 0, &what->pos);
                if (eof_token(next))
                        goto Eclosing;
                if (!eof_token(start->next) || !match_op(next, ')')) {
                        count++;
                        goto Emany;
                }
        } else {
                for (count = 0; count < wanted; count++) {
                        struct argcount *p = &arglist->next->count;
                        next = collect_arg(start, p->vararg, &what->pos);
                        arglist = arglist->next->next;
                        if (eof_token(next))
                                goto Eclosing;
                        args[count].arg = start->next;
                        args[count].n_normal = p->normal;
                        args[count].n_quoted = p->quoted;
                        args[count].n_str = p->str;
                        if (match_op(next, ')')) {
                                count++;
                                break;
                        }
                        start = next;
                }
                if (count == wanted && !match_op(next, ')'))
                        goto Emany;
                if (count == wanted - 1) {
                        struct argcount *p = &arglist->next->count;
                        if (!p->vararg)
                                goto Efew;
                        args[count].arg = NULL;
                        args[count].n_normal = p->normal;
                        args[count].n_quoted = p->quoted;
                        args[count].n_str = p->str;
                }
                if (count < wanted - 1)
                        goto Efew;
        }
        what->next = next->next;
        return 1;

Efew:
        warn(what->pos, "macro \"%s\" requires %d arguments, but only %d given",
                show_token(what), wanted, count);
        goto out;
Emany:
        while (match_op(next, ',')) {
                next = collect_arg(next, 0, &what->pos);
                count++;
        }
        if (eof_token(next))
                goto Eclosing;
        warn(what->pos, "macro \"%s\" passed %d arguments, but takes just %d",
                show_token(what), count, wanted);
        goto out;
Eclosing:
        warn(what->pos, "unterminated argument list invoking macro \"%s\"",
                show_token(what));
out:
        what->next = next->next;
        return 0;
}

static struct token *dup_list(struct token *list)
{
        struct token *res;
        struct token **p = &res;

        while (!eof_token(list)) {
                struct token *newtok = __alloc_token(0);
                *newtok = *list;
                *p = newtok;
                p = &newtok->next;
                list = list->next;
        }
        return res;
}

static struct token *stringify(struct token *arg)
{
        const char *s = show_token_sequence(arg);
        int size = strlen(s)+1;
        struct token *token = __alloc_token(0);
        struct string *string = __alloc_string(size);

        memcpy(string->data, s, size);
        string->length = size;
        token->pos = arg->pos;
        token_type(token) = TOKEN_STRING;
        token->string = string;
        token->next = &eof_token_entry;
        return token;
}

static void expand_arguments(int count, struct arg *args)
{
        int i;
        for (i = 0; i < count; i++) {
                struct token *arg = args[i].arg;
                if (!arg)
                        arg = &eof_token_entry;
                if (args[i].n_str)
                        args[i].str = stringify(arg);
                if (args[i].n_normal) {
                        if (!args[i].n_quoted) {
                                args[i].expanded = arg;
                                args[i].arg = NULL;
                        } else if (eof_token(arg)) {
                                args[i].expanded = arg;
                        } else {
                                args[i].expanded = dup_list(arg);
                        }
                        expand_list(&args[i].expanded);
                }
        }
}

/*
 * Possibly valid combinations:
 *  - ident + ident -> ident
 *  - ident + number -> ident unless number contains '.', '+' or '-'.
 *  - number + number -> number
 *  - number + ident -> number
 *  - number + '.' -> number
 *  - number + '+' or '-' -> number, if number used to end on [eEpP].
 *  - '.' + number -> number, if number used to start with a digit.
 *  - special + special -> either special or an error.
 */
static enum token_type combine(struct token *left, struct token *right, char *p)
{
        int len;
        enum token_type t1 = token_type(left), t2 = token_type(right);

        if (t1 != TOKEN_IDENT && t1 != TOKEN_NUMBER && t1 != TOKEN_SPECIAL)
                return TOKEN_ERROR;

        if (t2 != TOKEN_IDENT && t2 != TOKEN_NUMBER && t2 != TOKEN_SPECIAL)
                return TOKEN_ERROR;

        strcpy(p, show_token(left));
        strcat(p, show_token(right));
        len = strlen(p);

        if (len >= 256)
                return TOKEN_ERROR;

        if (t1 == TOKEN_IDENT) {
                if (t2 == TOKEN_SPECIAL)
                        return TOKEN_ERROR;
                if (t2 == TOKEN_NUMBER && strpbrk(p, "+-."))
                        return TOKEN_ERROR;
                return TOKEN_IDENT;
        }

        if (t1 == TOKEN_NUMBER) {
                if (t2 == TOKEN_SPECIAL) {
                        switch (right->special) {
                        case '.':
                                break;
                        case '+': case '-':
                                if (strchr("eEpP", p[len - 2]))
                                        break;
                        default:
                                return TOKEN_ERROR;
                        }
                }
                return TOKEN_NUMBER;
        }

        if (p[0] == '.' && isdigit(p[1]))
                return TOKEN_NUMBER;

        return TOKEN_SPECIAL;
}

static int merge(struct token *left, struct token *right)
{
        extern unsigned char combinations[][3];
        static char buffer[512];
        int n;

        switch (combine(left, right, buffer)) {
        case TOKEN_IDENT:
                left->ident = built_in_ident(buffer);
                left->pos.noexpand = 0;
                return 1;

        case TOKEN_NUMBER:
                token_type(left) = TOKEN_NUMBER;        /* could be . + num */
                left->number = __alloc_bytes(strlen(buffer) + 1);
                memcpy(left->number, buffer, strlen(buffer) + 1);
                return 1;

        case TOKEN_SPECIAL:
                if (buffer[2] && buffer[3])
                        break;
                for (n = SPECIAL_BASE; n < SPECIAL_ARG_SEPARATOR; n++) {
                        if (!memcmp(buffer, combinations[n-SPECIAL_BASE], 3)) {
                                left->special = n;
                                return 1;
                        }
                }
        default:
                ;
        }
        warn(left->pos, "'##' failed: concatenation is not a valid token");
        return 0;
}

static struct token *dup_token(struct token *token, struct position *streampos, struct position *pos)
{
        struct token *alloc = alloc_token(streampos);
        token_type(alloc) = token_type(token);
        alloc->pos.newline = pos->newline;
        alloc->pos.whitespace = pos->whitespace;
        alloc->number = token->number;
        alloc->pos.noexpand = token->pos.noexpand;
        return alloc;   
}

static struct token **copy(struct token **where, struct token *list, int *count)
{
        int need_copy = --*count;
        while (!eof_token(list)) {
                struct token *token;
                if (need_copy)
                        token = dup_token(list, &list->pos, &list->pos);
                else
                        token = list;
                if (token_type(token) == TOKEN_IDENT && token->ident->tainted)
                        token->pos.noexpand = 1;
                *where = token;
                where = &token->next;
                list = list->next;
        }
        *where = &eof_token_entry;
        return where;
}

static struct token **substitute(struct token **list, struct token *body, struct arg *args)
{
        struct token *token = *list;
        struct position *base_pos = &token->pos;
        struct position *pos = base_pos;
        int *count;
        enum {Normal, Placeholder, Concat} state = Normal;

        for (; !eof_token(body); body = body->next, pos = &body->pos) {
                struct token *added, *arg;
                struct token **tail;

                switch (token_type(body)) {
                case TOKEN_GNU_KLUDGE:
                        /*
                         * GNU kludge: if we had <comma>##<vararg>, behaviour
                         * depends on whether we had enough arguments to have
                         * a vararg.  If we did, ## is just ignored.  Otherwise
                         * both , and ## are ignored.  Comma should come from
                         * the body of macro and not be an argument of earlier
                         * concatenation.
                         */
                        if (!args[body->next->argnum].arg)
                                continue;
                        added = dup_token(body, base_pos, pos);
                        token_type(added) = TOKEN_SPECIAL;
                        tail = &added->next;
                        break;

                case TOKEN_STR_ARGUMENT:
                        arg = args[body->argnum].str;
                        count = &args[body->argnum].n_str;
                        goto copy_arg;

                case TOKEN_QUOTED_ARGUMENT:
                        arg = args[body->argnum].arg;
                        count = &args[body->argnum].n_quoted;
                        if (!arg || eof_token(arg)) {
                                if (state == Concat)
                                        state = Normal;
                                else
                                        state = Placeholder;
                                continue;
                        }
                        goto copy_arg;

                case TOKEN_MACRO_ARGUMENT:
                        arg = args[body->argnum].expanded;
                        count = &args[body->argnum].n_normal;
                        if (eof_token(arg)) {
                                state = Normal;
                                continue;
                        }
                copy_arg:
                        tail = copy(&added, arg, count);
                        added->pos.newline = pos->newline;
                        added->pos.whitespace = pos->whitespace;
                        break;

                case TOKEN_CONCAT:
                        if (state == Placeholder)
                                state = Normal;
                        else
                                state = Concat;
                        continue;

                case TOKEN_IDENT:
                        added = dup_token(body, base_pos, pos);
                        if (added->ident->tainted)
                                added->pos.noexpand = 1;
                        tail = &added->next;
                        break;

                default:
                        added = dup_token(body, base_pos, pos);
                        tail = &added->next;
                        break;
                }

                /*
                 * if we got to doing real concatenation, we already have
                 * added something into the list, so containing_token() is OK.
                 */
                if (state == Concat && merge(containing_token(list), added)) {
                        *list = added->next;
                        if (tail != &added->next)
                                list = tail;
                } else {
                        *list = added;
                        list = tail;
                }
                state = Normal;
        }
        *list = &eof_token_entry;
        return list;
}

static struct token **expand(struct token **list, struct symbol *sym)
{
        struct token *last;
        struct token *token = *list;
        struct ident *expanding = token->ident;
        struct token **tail;
        int nargs = sym->arglist ? sym->arglist->count.normal : 0;
        struct arg args[nargs];

        if (expanding->tainted) {
                token->pos.noexpand = 1;
                return &token->next;
        }

        if (sym->arglist) {
                if (!match_op(scan_next(&token->next), '('))
                        return &token->next;
                if (!collect_arguments(token->next, sym->arglist, args, token))
                        return &token->next;
                expand_arguments(nargs, args);
        }

        expanding->tainted = 1;

        last = token->next;
        tail = substitute(list, sym->expansion, args);
        *tail = last;

        return list;
}

static const char *token_name_sequence(struct token *token, int endop, struct token *start)
{
        struct token *last;
        static char buffer[256];
        char *ptr = buffer;

        last = token;
        while (!eof_token(token) && !match_op(token, endop)) {
                int len;
                const char *val = token->string->data;
                if (token_type(token) != TOKEN_STRING)
                        val = show_token(token);
                len = strlen(val);
                memcpy(ptr, val, len);
                ptr += len;
                token = token->next;
        }
        *ptr = 0;
        if (endop && !match_op(token, endop))
                warn(start->pos, "expected '>' at end of filename");
        return buffer;
}

static int try_include(const char *path, int plen, const char *filename, int flen, struct token **where)
{
        int fd;
        static char fullname[PATH_MAX];

        memcpy(fullname, path, plen);
        if (plen && path[plen-1] != '/') {
                fullname[plen] = '/';
                plen++;
        }
        memcpy(fullname+plen, filename, flen);
        fd = open(fullname, O_RDONLY);
        if (fd >= 0) {
                char * streamname = __alloc_bytes(plen + flen);
                memcpy(streamname, fullname, plen + flen);
                *where = tokenize(streamname, fd, *where);
                close(fd);
                return 1;
        }
        return 0;
}

static int do_include_path(const char **pptr, struct token **list, struct token *token, const char *filename, int flen)
{
        const char *path;

        while ((path = *pptr++) != NULL) {
                if (!try_include(path, strlen(path), filename, flen, list))
                        continue;
                return 1;
        }
        return 0;
}
        

static void do_include(int local, struct stream *stream, struct token **list, struct token *token, const char *filename)
{
        int flen = strlen(filename) + 1;

        /* Same directory as current stream? */
        if (local) {
                const char *path;
                char *slash;
                int plen;

                path = stream->name;
                slash = strrchr(path, '/');
                plen = slash ? slash - path : 0;

                if (try_include(path, plen, filename, flen, list))
                        return;
        }

        /* Check the standard include paths.. */
        if (do_include_path(includepath, list, token, filename, flen))
                return;
        if (do_include_path(sys_includepath, list, token, filename, flen))
                return;
        if (do_include_path(gcc_includepath, list, token, filename, flen))
                return;

        error(token->pos, "unable to open '%s'", filename);
}

static int handle_include(struct stream *stream, struct token **list, struct token *token)
{
        const char *filename;
        struct token *next;
        int expect;

        if (stream->constant == -1)
                stream->constant = 0;
        if (false_nesting)
                return 1;
        next = token->next;
        expect = '>';
        if (!match_op(next, '<')) {
                expand_list(&token->next);
                expect = 0;
                next = token;
        }
        token = next->next;
        filename = token_name_sequence(token, expect, token);
        do_include(!expect, stream, list, token, filename);
        return 1;
}

static int token_different(struct token *t1, struct token *t2)
{
        int different;

        if (token_type(t1) != token_type(t2))
                return 1;

        switch (token_type(t1)) {
        case TOKEN_IDENT:
                different = t1->ident != t2->ident;
                break;
        case TOKEN_ARG_COUNT:
        case TOKEN_UNTAINT:
        case TOKEN_CONCAT:
        case TOKEN_GNU_KLUDGE:
                different = 0;
                break;
        case TOKEN_NUMBER:
                different = strcmp(t1->number, t2->number);
                break;
        case TOKEN_SPECIAL:
                different = t1->special != t2->special;
                break;
        case TOKEN_MACRO_ARGUMENT:
        case TOKEN_QUOTED_ARGUMENT:
        case TOKEN_STR_ARGUMENT:
                different = t1->argnum != t2->argnum;
                break;
        case TOKEN_CHAR:
                different = t1->character != t2->character;
                break;
        case TOKEN_STRING: {
                struct string *s1, *s2;

                s1 = t1->string;
                s2 = t2->string;
                different = 1;
                if (s1->length != s2->length)
                        break;
                different = memcmp(s1->data, s2->data, s1->length);
                break;
        }
        default:
                different = 1;
                break;
        }
        return different;
}

static int token_list_different(struct token *list1, struct token *list2)
{
        for (;;) {
                if (list1 == list2)
                        return 0;
                if (!list1 || !list2)
                        return 1;
                if (token_different(list1, list2))
                        return 1;
                list1 = list1->next;
                list2 = list2->next;
        }
}

static inline void set_arg_count(struct token *token)
{
        token_type(token) = TOKEN_ARG_COUNT;
        token->count.normal = token->count.quoted =
        token->count.str = token->count.vararg = 0;
}

static struct token *parse_arguments(struct token *list)
{
        struct token *arg = list->next, *next = list;
        struct argcount *count = &list->count;

        set_arg_count(list);

        if (match_op(arg, ')')) {
                next = arg->next;
                list->next = &eof_token_entry;
                return next;
        }

        while (token_type(arg) == TOKEN_IDENT) {
                if (arg->ident == &__VA_ARGS___ident)
                        goto Eva_args;
                if (!++count->normal)
                        goto Eargs;
                next = arg->next;

                if (match_op(next, ',')) {
                        set_arg_count(next);
                        arg = next->next;
                        continue;
                }

                if (match_op(next, ')')) {
                        set_arg_count(next);
                        next = next->next;
                        arg->next->next = &eof_token_entry;
                        return next;
                }

                /* normal cases are finished here */

                if (match_op(next, SPECIAL_ELLIPSIS)) {
                        if (match_op(next->next, ')')) {
                                set_arg_count(next);
                                next->count.vararg = 1;
                                next = next->next;
                                arg->next->next = &eof_token_entry;
                                return next->next;
                        }

                        arg = next;
                        goto Enotclosed;
                }

                if (eof_token(next)) {
                        goto Enotclosed;
                } else {
                        arg = next;
                        goto Ebadstuff;
                }
        }

        if (match_op(arg, SPECIAL_ELLIPSIS)) {
                next = arg->next;
                token_type(arg) = TOKEN_IDENT;
                arg->ident = &__VA_ARGS___ident;
                if (!match_op(next, ')'))
                        goto Enotclosed;
                if (!++count->normal)
                        goto Eargs;
                set_arg_count(next);
                next->count.vararg = 1;
                next = next->next;
                arg->next->next = &eof_token_entry;
                return next;
        }

        if (eof_token(arg)) {
                arg = next;
                goto Enotclosed;
        }
        if (match_op(arg, ','))
                goto Emissing;
        else
                goto Ebadstuff;


Emissing:
        warn(arg->pos, "parameter name missing");
        return NULL;
Ebadstuff:
        warn(arg->pos, "\"%s\" may not appear in macro parameter list",
                show_token(arg));
        return NULL;
Enotclosed:
        warn(arg->pos, "missing ')' in macro parameter list");
        return NULL;
Eva_args:
        warn(arg->pos, "__VA_ARGS__ can only appear in the expansion of a C99 variadic macro");
        return NULL;
Eargs:
        warn(arg->pos, "too many arguments in macro definition");
        return NULL;
}

static int try_arg(struct token *token, enum token_type type, struct token *arglist)
{
        struct ident *ident = token->ident;
        int nr;

        if (!arglist || token_type(token) != TOKEN_IDENT)
                return 0;

        arglist = arglist->next;

        for (nr = 0; !eof_token(arglist); nr++, arglist = arglist->next->next) {
                if (arglist->ident == ident) {
                        struct argcount *count = &arglist->next->count;
                        int n;

                        token->argnum = nr;
                        token_type(token) = type;
                        switch (type) {
                        case TOKEN_MACRO_ARGUMENT:
                                n = ++count->normal;
                                break;
                        case TOKEN_QUOTED_ARGUMENT:
                                n = ++count->quoted;
                                break;
                        default:
                                n = ++count->str;
                        }
                        if (n)
                                return count->vararg ? 2 : 1;
                        token_type(token) = TOKEN_ERROR;
                        return -1;
                }
        }
        return 0;
}

static struct token *parse_expansion(struct token *expansion, struct token *arglist, struct ident *name)
{
        struct token *token = expansion;
        struct token **p;
        struct token *last = NULL;

        if (match_op(token, SPECIAL_HASHHASH))
                goto Econcat;

        for (p = &expansion; !eof_token(token); p = &token->next, token = *p) {
                if (match_op(token, '#')) {
                        if (arglist) {
                                struct token *next = token->next;
                                if (!try_arg(next, TOKEN_STR_ARGUMENT, arglist))
                                        goto Equote;
                                next->pos.whitespace = token->pos.whitespace;
                                token = *p = next;
                        } else {
                                token->pos.noexpand = 1;
                        }
                } else if (match_op(token, SPECIAL_HASHHASH)) {
                        struct token *next = token->next;
                        int arg = try_arg(next, TOKEN_QUOTED_ARGUMENT, arglist);
                        token_type(token) = TOKEN_CONCAT;
                        if (arg) {
                                token = next;
                                /* GNU kludge */
                                if (arg == 2 && last && match_op(last, ',')) {
                                        token_type(last) = TOKEN_GNU_KLUDGE;
                                        last->next = token;
                                }
                        } else if (match_op(next, SPECIAL_HASHHASH))
                                token = next;
                        else if (match_op(next, ','))
                                token = next;
                        else if (eof_token(next))
                                goto Econcat;
                } else if (match_op(token->next, SPECIAL_HASHHASH)) {
                        try_arg(token, TOKEN_QUOTED_ARGUMENT, arglist);
                } else {
                        try_arg(token, TOKEN_MACRO_ARGUMENT, arglist);
                }
                if (token_type(token) == TOKEN_ERROR)
                        goto Earg;
                last = token;
        }
        token = alloc_token(&expansion->pos);
        token_type(token) = TOKEN_UNTAINT;
        token->ident = name;
        token->next = *p;
        *p = token;
        return expansion;

Equote:
        warn(token->pos, "'#' is not followed by a macro parameter");
        return NULL;

Econcat:
        warn(token->pos, "'##' cannot appear at the ends of macro expansion");
        return NULL;
Earg:
        warn(token->pos, "too many instances of argument in body");
        return NULL;
}

static int handle_define(struct stream *stream, struct token **line, struct token *token)
{
        struct token *arglist, *expansion;
        struct token *left = token->next;
        struct symbol *sym;
        struct ident *name;

        if (token_type(left) != TOKEN_IDENT) {
                warn(token->pos, "expected identifier to 'define'");
                return 0;
        }
        if (false_nesting)
                return 1;
        name = left->ident;

        arglist = NULL;
        expansion = left->next;
        if (!expansion->pos.whitespace && match_op(expansion, '(')) {
                arglist = expansion;
                expansion = parse_arguments(expansion);
                if (!expansion)
                        return 1;
        }

        expansion = parse_expansion(expansion, arglist, name);
        if (!expansion)
                return 1;

        sym = lookup_symbol(name, NS_PREPROCESSOR);
        if (sym) {
                if (token_list_different(sym->expansion, expansion) || 
                    token_list_different(sym->arglist, arglist)) {
                        warn(left->pos, "preprocessor token %.*s redefined",
                                        name->len, name->name);
                        info(sym->pos, "this was the original definition");
                }
                return 1;
        }
        sym = alloc_symbol(left->pos, SYM_NODE);
        bind_symbol(sym, name, NS_PREPROCESSOR);

        sym->expansion = expansion;
        sym->arglist = arglist;
        return 1;
}

static int handle_undef(struct stream *stream, struct token **line, struct token *token)
{
        struct token *left = token->next;
        struct symbol **sym;

        if (token_type(left) != TOKEN_IDENT) {
                warn(token->pos, "expected identifier to 'undef'");
                return 0;
        }
        if (false_nesting)
                return 1;
        sym = &left->ident->symbols;
        while (*sym) {
                struct symbol *t = *sym;
                if (t->namespace == NS_PREPROCESSOR) {
                        *sym = t->next_id;
                        return 1;
                }
                sym = &t->next_id;
        }
        return 1;
}

static int preprocessor_if(struct token *token, int true)
{
        if (if_nesting == 0)
                unmatched_if = token;
        if (if_nesting >= MAX_NEST)
                error(token->pos, "Maximum preprocessor conditional level exhausted");
        elif_ignore[if_nesting] = false_nesting || true;
        if (false_nesting || !true) {
                false_nesting++;
                return 1;
        }
        true_nesting++;
        return 1;
}

static int token_defined(struct token *token)
{
        if (token_type(token) == TOKEN_IDENT)
                return lookup_symbol(token->ident, NS_PREPROCESSOR) != NULL;

        warn(token->pos, "expected identifier for #if[n]def");
        return 0;
}

static int handle_ifdef(struct stream *stream, struct token **line, struct token *token)
{
        return preprocessor_if(token, token_defined(token->next));
}

static int handle_ifndef(struct stream *stream, struct token **line, struct token *token)
{
        struct token *next = token->next;
        if (stream->constant == -1) {
                int newconstant = 0;
                if (token_type(next) == TOKEN_IDENT) {
                        if (!stream->protect || stream->protect == next->ident) {
                                newconstant = -2;
                                stream->protect = next->ident;
                                stream->nesting = if_nesting+1;
                        }
                }
                stream->constant = newconstant;
        }
        return preprocessor_if(token, !token_defined(next));
}

/*
 * Expression handling for #if and #elif; it differs from normal expansion
 * due to special treatment of "defined".
 */
static int expression_value(struct token **where)
{
        struct expression *expr;
        struct token *p;
        struct token **list = where, **beginning = NULL;
        long long value;
        int state = 0;

        while (!eof_token(p = scan_next(list))) {
                switch (state) {
                case 0:
                        if (token_type(p) == TOKEN_IDENT) {
                                if (p->ident != &defined_ident) {
                                        list = expand_one_symbol(list);
                                        continue;
                                }
                                state = 1;
                                beginning = list;
                        }
                        break;
                case 1:
                        if (match_op(p, '(')) {
                                state = 2;
                        } else {
                                state = 0;
                                replace_with_defined(p);
                                *beginning = p;
                        }
                        break;
                case 2:
                        if (token_type(p) == TOKEN_IDENT)
                                state = 3;
                        else
                                state = 0;
                        replace_with_defined(p);
                        *beginning = p;
                        break;
                case 3:
                        state = 0;
                        if (!match_op(p, ')'))
                                warn(p->pos, "missing ')' after \"defined\"");
                        *list = p->next;
                        continue;
                }
                list = &p->next;
        }

        p = constant_expression(*where, &expr);
        if (!eof_token(p))
                warn(p->pos, "garbage at end: %s", show_token_sequence(p));
        value = get_expression_value(expr);
        return value != 0;
}

static int handle_if(struct stream *stream, struct token **line, struct token *token)
{
        int value = 0;
        if (!false_nesting)
                value = expression_value(&token->next);
        return preprocessor_if(token, value);
}

static int handle_elif(struct stream * stream, struct token **line, struct token *token)
{
        if (stream->nesting == if_nesting)
                stream->constant = 0;
        if (false_nesting) {
                /* If this whole if-thing is if'ed out, an elif cannot help */
                if (elif_ignore[if_nesting-1])
                        return 1;
                if (expression_value(&token->next)) {
                        false_nesting--;
                        true_nesting++;
                        elif_ignore[if_nesting-1] = 1;
                }
                return 1;
        }
        if (true_nesting) {
                false_nesting = 1;
                true_nesting--;
                return 1;
        }
        warn(token->pos, "unmatched '#elif'");
        return 1;
}

static int handle_else(struct stream *stream, struct token **line, struct token *token)
{
        if (stream->nesting == if_nesting)
                stream->constant = 0;
        if (false_nesting) {
                /* If this whole if-thing is if'ed out, an else cannot help */
                if (elif_ignore[if_nesting-1])
                        return 1;
                false_nesting--;
                true_nesting++;
                elif_ignore[if_nesting-1] = 1;
                return 1;
        }
        if (true_nesting) {
                true_nesting--;
                false_nesting = 1;
                return 1;
        }
        warn(token->pos, "unmatched #else");
        return 1;
}

static int handle_endif(struct stream *stream, struct token **line, struct token *token)
{
        if (stream->constant == -2 && stream->nesting == if_nesting)
                stream->constant = -1;

        if (false_nesting) {
                false_nesting--;
                return 1;
        }
        if (true_nesting) {
                true_nesting--;
                return 1;
        }
        warn(token->pos, "unmatched #endif");
        return 1;
}

static const char *show_token_sequence(struct token *token)
{
        static char buffer[1024];
        char *ptr = buffer;
        int whitespace = 0;

        if (!token)
                return "<none>";
        while (!eof_token(token)) {
                const char *val = show_token(token);
                int len = strlen(val);

                if (ptr + whitespace + len > buffer + sizeof(buffer)) {
                        warn(token->pos, "too long token expansion");
                        break;
                }

                if (whitespace)
                        *ptr++ = ' ';
                memcpy(ptr, val, len);
                ptr += len;
                token = token->next;
                whitespace = token->pos.whitespace;
        }
        *ptr = 0;
        return buffer;
}

static int handle_warning(struct stream *stream, struct token **line, struct token *token)
{
        if (false_nesting)
                return 1;
        warn(token->pos, "%s", show_token_sequence(token->next));
        return 1;
}

static int handle_error(struct stream *stream, struct token **line, struct token *token)
{
        if (false_nesting)
                return 1;
        warn(token->pos, "%s", show_token_sequence(token->next));
        return 1;
}

static int handle_nostdinc(struct stream *stream, struct token **line, struct token *token)
{
        if (false_nesting)
                return 1;
        includepath[0] = NULL;
        return 1;
}

static void add_path_entry(struct token *token, const char *path)
{
        int i;

        for (i = 0; i < INCLUDEPATHS; i++) {
                if (!includepath[i]) {
                        includepath[i] = path;
                        includepath[i+1] = NULL;
                        return;
                }
        }
        warn(token->pos, "too many include path entries");
}

static int handle_add_include(struct stream *stream, struct token **line, struct token *token)
{
        for (;;) {
                token = token->next;
                if (eof_token(token))
                        return 1;
                if (token_type(token) != TOKEN_STRING) {
                        warn(token->pos, "expected path string");
                        return 1;
                }
                add_path_entry(token, token->string->data);
        }
}

/*
 * We replace "#pragma xxx" with "__pragma__" in the token
 * stream. Just as an example.
 *
 * We'll just #define that away for now, but the theory here
 * is that we can use this to insert arbitrary token sequences
 * to turn the pragma's into internal front-end sequences for
 * when we actually start caring about them.
 *
 * So eventually this will turn into some kind of extended
 * __attribute__() like thing, except called __pragma__(xxx).
 */
static int handle_pragma(struct stream *stream, struct token **line, struct token *token)
{
        struct token *next = *line;

        token->ident = &pragma_ident;
        token->pos.newline = 1;
        token->pos.whitespace = 1;
        token->pos.pos = 1;
        *line = token;
        token->next = next;
        return 1;
}

static int handle_preprocessor_command(struct stream *stream, struct token **line, struct ident *ident, struct token *token)
{
        int i;
        static struct {
                const char *name;
                int (*handler)(struct stream *, struct token **, struct token *);
        } handlers[] = {
                { "define",     handle_define },
                { "undef",      handle_undef },
                { "ifdef",      handle_ifdef },
                { "ifndef",     handle_ifndef },
                { "else",       handle_else },
                { "endif",      handle_endif },
                { "if",         handle_if },
                { "elif",       handle_elif },
                { "warning",    handle_warning },
                { "error",      handle_error },
                { "include",    handle_include },
                { "pragma",     handle_pragma },

                // our internal preprocessor tokens
                { "nostdinc",   handle_nostdinc },
                { "add_include", handle_add_include },
        };

        for (i = 0; i < (sizeof (handlers) / sizeof (handlers[0])); i++) {
                if (match_string_ident(ident, handlers[i].name))
                        return handlers[i].handler(stream, line, token);
        }
        return 0;
}

static void handle_preprocessor_line(struct stream *stream, struct token **line, struct token *token)
{
        if (!token)
                return;

        if (token_type(token) == TOKEN_IDENT)
                if (handle_preprocessor_command(stream, line, token->ident, token))
                        return;
        warn(token->pos, "unrecognized preprocessor line '%s'", show_token_sequence(token));
}

static void preprocessor_line(struct stream *stream, struct token **line)
{
        struct token *start = *line, *next;
        struct token **tp = &start->next;

        for (;;) {
                next = *tp;
                if (next->pos.newline)
                        break;
                tp = &next->next;
        }
        *line = next;
        *tp = &eof_token_entry;
        handle_preprocessor_line(stream, line, start->next);
}

static void do_preprocess(struct token **list)
{
        struct token *next;

        while (!eof_token(next = scan_next(list))) {
                struct stream *stream = input_streams + next->pos.stream;

                if (next->pos.newline && match_op(next, '#')) {
                        if (!next->pos.noexpand) {
                                preprocessor_line(stream, list);
                                continue;
                        }
                }

                if (false_nesting) {
                        *list = next->next;
                        continue;
                }

                switch (token_type(next)) {
                case TOKEN_STREAMEND:
                        if (stream->constant == -1 && stream->protect) {
                                stream->constant = 1;
                        }
                        /* fallthrough */
                case TOKEN_STREAMBEGIN:
                        *list = next->next;
                        continue;

                case TOKEN_IDENT:
                        list = expand_one_symbol(list);
                        break;
                default:
                        list = &next->next;
                }
                /*
                 * Any token expansion (even if it ended up being an
                 * empty expansion) in this stream implies it can't
                 * be constant.
                 */
                stream->constant = 0;
        }
}

struct token * preprocess(struct token *token)
{
        preprocessing = 1;
        do_preprocess(&token);
        if (if_nesting)
                warn(unmatched_if->pos, "unmatched preprocessor conditional");

        // Drop all expressions from pre-processing, they're not used any more.
        clear_expression_alloc();
        preprocessing = 0;

        return token;
}