src/lj_gdbjit.c

   1 /*
   2 ** Client for the GDB JIT API.
   3 ** Copyright (C) 2005-2016 Mike Pall. See Copyright Notice in luajit.h
   4 */
   5
   6 #define lj_gdbjit_c
   7 #define LUA_CORE
   8
   9 #include "lj_obj.h"
  10
  11 #if LJ_HASJIT
  12
  13 #include "lj_gc.h"
  14 #include "lj_err.h"
  15 #include "lj_debug.h"
  16 #include "lj_frame.h"
  17 #include "lj_jit.h"
  18 #include "lj_dispatch.h"
  19
  20 /* This is not compiled in by default.
  21 ** Enable with -DLUAJIT_USE_GDBJIT in the Makefile and recompile everything.
  22 */
  23 #ifdef LUAJIT_USE_GDBJIT
  24
  25 /* The GDB JIT API allows JIT compilers to pass debug information about
  26 ** JIT-compiled code back to GDB. You need at least GDB 7.0 or higher
  27 ** to see it in action.
  28 **
  29 ** This is a passive API, so it works even when not running under GDB
  30 ** or when attaching to an already running process. Alas, this implies
  31 ** enabling it always has a non-negligible overhead -- do not use in
  32 ** release mode!
  33 **
  34 ** The LuaJIT GDB JIT client is rather minimal at the moment. It gives
  35 ** each trace a symbol name and adds a source location and frame unwind
  36 ** information. Obviously LuaJIT itself and any embedding C application
  37 ** should be compiled with debug symbols, too (see the Makefile).
  38 **
  39 ** Traces are named TRACE_1, TRACE_2, ... these correspond to the trace
  40 ** numbers from -jv or -jdump. Use "break TRACE_1" or "tbreak TRACE_1" etc.
  41 ** to set breakpoints on specific traces (even ahead of their creation).
  42 **
  43 ** The source location for each trace allows listing the corresponding
  44 ** source lines with the GDB command "list" (but only if the Lua source
  45 ** has been loaded from a file). Currently this is always set to the
  46 ** location where the trace has been started.
  47 **
  48 ** Frame unwind information can be inspected with the GDB command
  49 ** "info frame". This also allows proper backtraces across JIT-compiled
  50 ** code with the GDB command "bt".
  51 **
  52 ** You probably want to add the following settings to a .gdbinit file
  53 ** (or add them to ~/.gdbinit):
  54 **   set disassembly-flavor intel
  55 **   set breakpoint pending on
  56 **
  57 ** Here's a sample GDB session:
  58 ** ------------------------------------------------------------------------
  59
  60 $ cat >x.lua
  61 for outer=1,100 do
  62   for inner=1,100 do end
  63 end
  64 ^D
  65
  66 $ luajit -jv x.lua
  67 [TRACE   1 x.lua:2]
  68 [TRACE   2 (1/3) x.lua:1 -> 1]
  69
  70 $ gdb --quiet --args luajit x.lua
  71 (gdb) tbreak TRACE_1
  72 Function "TRACE_1" not defined.
  73 Temporary breakpoint 1 (TRACE_1) pending.
  74 (gdb) run
  75 Starting program: luajit x.lua
  76
  77 Temporary breakpoint 1, TRACE_1 () at x.lua:2
  78 2         for inner=1,100 do end
  79 (gdb) list
  80 1       for outer=1,100 do
  81 2         for inner=1,100 do end
  82 3       end
  83 (gdb) bt
  84 #0  TRACE_1 () at x.lua:2
  85 #1  0x08053690 in lua_pcall [...]
  86 [...]
  87 #7  0x0806ff90 in main [...]
  88 (gdb) disass TRACE_1
  89 Dump of assembler code for function TRACE_1:
  90 0xf7fd9fba <TRACE_1+0>: mov    DWORD PTR ds:0xf7e0e2a0,0x1
  91 0xf7fd9fc4 <TRACE_1+10>:        movsd  xmm7,QWORD PTR [edx+0x20]
  92 [...]
  93 0xf7fd9ff8 <TRACE_1+62>:        jmp    0xf7fd2014
  94 End of assembler dump.
  95 (gdb) tbreak TRACE_2
  96 Function "TRACE_2" not defined.
  97 Temporary breakpoint 2 (TRACE_2) pending.
  98 (gdb) cont
  99 Continuing.
 100
 101 Temporary breakpoint 2, TRACE_2 () at x.lua:1
 102 1       for outer=1,100 do
 103 (gdb) info frame
 104 Stack level 0, frame at 0xffffd7c0:
 105  eip = 0xf7fd9f60 in TRACE_2 (x.lua:1); saved eip 0x8053690
 106  called by frame at 0xffffd7e0
 107  source language unknown.
 108  Arglist at 0xffffd78c, args:
 109  Locals at 0xffffd78c, Previous frame's sp is 0xffffd7c0
 110  Saved registers:
 111   ebx at 0xffffd7ac, ebp at 0xffffd7b8, esi at 0xffffd7b0, edi at 0xffffd7b4,
 112   eip at 0xffffd7bc
 113 (gdb)
 114
 115 ** ------------------------------------------------------------------------
 116 */
 117
 118 /* -- GDB JIT API --------------------------------------------------------- */
 119
 120 /* GDB JIT actions. */
 121 enum {
 122   GDBJIT_NOACTION = 0,
 123   GDBJIT_REGISTER,
 124   GDBJIT_UNREGISTER
 125 };
 126
 127 /* GDB JIT entry. */
 128 typedef struct GDBJITentry {
 129   struct GDBJITentry *next_entry;
 130   struct GDBJITentry *prev_entry;
 131   const char *symfile_addr;
 132   uint64_t symfile_size;
 133 } GDBJITentry;
 134
 135 /* GDB JIT descriptor. */
 136 typedef struct GDBJITdesc {
 137   uint32_t version;
 138   uint32_t action_flag;
 139   GDBJITentry *relevant_entry;
 140   GDBJITentry *first_entry;
 141 } GDBJITdesc;
 142
 143 GDBJITdesc __jit_debug_descriptor = {
 144   1, GDBJIT_NOACTION, NULL, NULL
 145 };
 146
 147 /* GDB sets a breakpoint at this function. */
 148 void LJ_NOINLINE __jit_debug_register_code()
 149 {
 150   __asm__ __volatile__("");
 151 };
 152
 153 /* -- In-memory ELF object definitions ------------------------------------ */
 154
 155 /* ELF definitions. */
 156 typedef struct ELFheader {
 157   uint8_t emagic[4];
 158   uint8_t eclass;
 159   uint8_t eendian;
 160   uint8_t eversion;
 161   uint8_t eosabi;
 162   uint8_t eabiversion;
 163   uint8_t epad[7];
 164   uint16_t type;
 165   uint16_t machine;
 166   uint32_t version;
 167   uintptr_t entry;
 168   uintptr_t phofs;
 169   uintptr_t shofs;
 170   uint32_t flags;
 171   uint16_t ehsize;
 172   uint16_t phentsize;
 173   uint16_t phnum;
 174   uint16_t shentsize;
 175   uint16_t shnum;
 176   uint16_t shstridx;
 177 } ELFheader;
 178
 179 typedef struct ELFsectheader {
 180   uint32_t name;
 181   uint32_t type;
 182   uintptr_t flags;
 183   uintptr_t addr;
 184   uintptr_t ofs;
 185   uintptr_t size;
 186   uint32_t link;
 187   uint32_t info;
 188   uintptr_t align;
 189   uintptr_t entsize;
 190 } ELFsectheader;
 191
 192 #define ELFSECT_IDX_ABS         0xfff1
 193
 194 enum {
 195   ELFSECT_TYPE_PROGBITS = 1,
 196   ELFSECT_TYPE_SYMTAB = 2,
 197   ELFSECT_TYPE_STRTAB = 3,
 198   ELFSECT_TYPE_NOBITS = 8
 199 };
 200
 201 #define ELFSECT_FLAGS_WRITE     1
 202 #define ELFSECT_FLAGS_ALLOC     2
 203 #define ELFSECT_FLAGS_EXEC      4
 204
 205 typedef struct ELFsymbol {
 206 #if LJ_64
 207   uint32_t name;
 208   uint8_t info;
 209   uint8_t other;
 210   uint16_t sectidx;
 211   uintptr_t value;
 212   uint64_t size;
 213 #else
 214   uint32_t name;
 215   uintptr_t value;
 216   uint32_t size;
 217   uint8_t info;
 218   uint8_t other;
 219   uint16_t sectidx;
 220 #endif
 221 } ELFsymbol;
 222
 223 enum {
 224   ELFSYM_TYPE_FUNC = 2,
 225   ELFSYM_TYPE_FILE = 4,
 226   ELFSYM_BIND_LOCAL = 0 << 4,
 227   ELFSYM_BIND_GLOBAL = 1 << 4,
 228 };
 229
 230 /* DWARF definitions. */
 231 #define DW_CIE_VERSION  1
 232
 233 enum {
 234   DW_CFA_nop = 0x0,
 235   DW_CFA_offset_extended = 0x5,
 236   DW_CFA_def_cfa = 0xc,
 237   DW_CFA_def_cfa_offset = 0xe,
 238   DW_CFA_offset_extended_sf = 0x11,
 239   DW_CFA_advance_loc = 0x40,
 240   DW_CFA_offset = 0x80
 241 };
 242
 243 enum {
 244   DW_EH_PE_udata4 = 3,
 245   DW_EH_PE_textrel = 0x20
 246 };
 247
 248 enum {
 249   DW_TAG_compile_unit = 0x11
 250 };
 251
 252 enum {
 253   DW_children_no = 0,
 254   DW_children_yes = 1
 255 };
 256
 257 enum {
 258   DW_AT_name = 0x03,
 259   DW_AT_stmt_list = 0x10,
 260   DW_AT_low_pc = 0x11,
 261   DW_AT_high_pc = 0x12
 262 };
 263
 264 enum {
 265   DW_FORM_addr = 0x01,
 266   DW_FORM_data4 = 0x06,
 267   DW_FORM_string = 0x08
 268 };
 269
 270 enum {
 271   DW_LNS_extended_op = 0,
 272   DW_LNS_copy = 1,
 273   DW_LNS_advance_pc = 2,
 274   DW_LNS_advance_line = 3
 275 };
 276
 277 enum {
 278   DW_LNE_end_sequence = 1,
 279   DW_LNE_set_address = 2
 280 };
 281
 282 enum {
 283 #if LJ_TARGET_X86
 284   DW_REG_AX, DW_REG_CX, DW_REG_DX, DW_REG_BX,
 285   DW_REG_SP, DW_REG_BP, DW_REG_SI, DW_REG_DI,
 286   DW_REG_RA,
 287 #elif LJ_TARGET_X64
 288   /* Yes, the order is strange, but correct. */
 289   DW_REG_AX, DW_REG_DX, DW_REG_CX, DW_REG_BX,
 290   DW_REG_SI, DW_REG_DI, DW_REG_BP, DW_REG_SP,
 291   DW_REG_8, DW_REG_9, DW_REG_10, DW_REG_11,
 292   DW_REG_12, DW_REG_13, DW_REG_14, DW_REG_15,
 293   DW_REG_RA,
 294 #elif LJ_TARGET_ARM
 295   DW_REG_SP = 13,
 296   DW_REG_RA = 14,
 297 #elif LJ_TARGET_PPC
 298   DW_REG_SP = 1,
 299   DW_REG_RA = 65,
 300   DW_REG_CR = 70,
 301 #elif LJ_TARGET_MIPS
 302   DW_REG_SP = 29,
 303   DW_REG_RA = 31,
 304 #else
 305 #error "Unsupported target architecture"
 306 #endif
 307 };
 308
 309 /* Minimal list of sections for the in-memory ELF object. */
 310 enum {
 311   GDBJIT_SECT_NULL,
 312   GDBJIT_SECT_text,
 313   GDBJIT_SECT_eh_frame,
 314   GDBJIT_SECT_shstrtab,
 315   GDBJIT_SECT_strtab,
 316   GDBJIT_SECT_symtab,
 317   GDBJIT_SECT_debug_info,
 318   GDBJIT_SECT_debug_abbrev,
 319   GDBJIT_SECT_debug_line,
 320   GDBJIT_SECT__MAX
 321 };
 322
 323 enum {
 324   GDBJIT_SYM_UNDEF,
 325   GDBJIT_SYM_FILE,
 326   GDBJIT_SYM_FUNC,
 327   GDBJIT_SYM__MAX
 328 };
 329
 330 /* In-memory ELF object. */
 331 typedef struct GDBJITobj {
 332   ELFheader hdr;                        /* ELF header. */
 333   ELFsectheader sect[GDBJIT_SECT__MAX]; /* ELF sections. */
 334   ELFsymbol sym[GDBJIT_SYM__MAX];       /* ELF symbol table. */
 335   uint8_t space[4096];                  /* Space for various section data. */
 336 } GDBJITobj;
 337
 338 /* Combined structure for GDB JIT entry and ELF object. */
 339 typedef struct GDBJITentryobj {
 340   GDBJITentry entry;
 341   size_t sz;
 342   GDBJITobj obj;
 343 } GDBJITentryobj;
 344
 345 /* Template for in-memory ELF header. */
 346 static const ELFheader elfhdr_template = {
 347   .emagic = { 0x7f, 'E', 'L', 'F' },
 348   .eclass = LJ_64 ? 2 : 1,
 349   .eendian = LJ_ENDIAN_SELECT(1, 2),
 350   .eversion = 1,
 351 #if LJ_TARGET_LINUX
 352   .eosabi = 0,  /* Nope, it's not 3. */
 353 #elif defined(__FreeBSD__)
 354   .eosabi = 9,
 355 #elif defined(__NetBSD__)
 356   .eosabi = 2,
 357 #elif defined(__OpenBSD__)
 358   .eosabi = 12,
 359 #elif defined(__DragonFly__)
 360   .eosabi = 0,
 361 #elif (defined(__sun__) && defined(__svr4__))
 362   .eosabi = 6,
 363 #else
 364   .eosabi = 0,
 365 #endif
 366   .eabiversion = 0,
 367   .epad = { 0, 0, 0, 0, 0, 0, 0 },
 368   .type = 1,
 369 #if LJ_TARGET_X86
 370   .machine = 3,
 371 #elif LJ_TARGET_X64
 372   .machine = 62,
 373 #elif LJ_TARGET_ARM
 374   .machine = 40,
 375 #elif LJ_TARGET_PPC
 376   .machine = 20,
 377 #elif LJ_TARGET_MIPS
 378   .machine = 8,
 379 #else
 380 #error "Unsupported target architecture"
 381 #endif
 382   .version = 1,
 383   .entry = 0,
 384   .phofs = 0,
 385   .shofs = offsetof(GDBJITobj, sect),
 386   .flags = 0,
 387   .ehsize = sizeof(ELFheader),
 388   .phentsize = 0,
 389   .phnum = 0,
 390   .shentsize = sizeof(ELFsectheader),
 391   .shnum = GDBJIT_SECT__MAX,
 392   .shstridx = GDBJIT_SECT_shstrtab
 393 };
 394
 395 /* -- In-memory ELF object generation ------------------------------------- */
 396
 397 /* Context for generating the ELF object for the GDB JIT API. */
 398 typedef struct GDBJITctx {
 399   uint8_t *p;           /* Pointer to next address in obj.space. */
 400   uint8_t *startp;      /* Pointer to start address in obj.space. */
 401   GCtrace *T;           /* Generate symbols for this trace. */
 402   uintptr_t mcaddr;     /* Machine code address. */
 403   MSize szmcode;        /* Size of machine code. */
 404   MSize spadjp;         /* Stack adjustment for parent trace or interpreter. */
 405   MSize spadj;          /* Stack adjustment for trace itself. */
 406   BCLine lineno;        /* Starting line number. */
 407   const char *filename; /* Starting file name. */
 408   size_t objsize;       /* Final size of ELF object. */
 409   GDBJITobj obj;        /* In-memory ELF object. */
 410 } GDBJITctx;
 411
 412 /* Add a zero-terminated string. */
 413 static uint32_t gdbjit_strz(GDBJITctx *ctx, const char *str)
 414 {
 415   uint8_t *p = ctx->p;
 416   uint32_t ofs = (uint32_t)(p - ctx->startp);
 417   do {
 418     *p++ = (uint8_t)*str;
 419   } while (*str++);
 420   ctx->p = p;
 421   return ofs;
 422 }
 423
 424 /* Append a decimal number. */
 425 static void gdbjit_catnum(GDBJITctx *ctx, uint32_t n)
 426 {
 427   if (n >= 10) { uint32_t m = n / 10; n = n % 10; gdbjit_catnum(ctx, m); }
 428   *ctx->p++ = '0' + n;
 429 }
 430
 431 /* Add a ULEB128 value. */
 432 static void gdbjit_uleb128(GDBJITctx *ctx, uint32_t v)
 433 {
 434   uint8_t *p = ctx->p;
 435   for (; v >= 0x80; v >>= 7)
 436     *p++ = (uint8_t)((v & 0x7f) | 0x80);
 437   *p++ = (uint8_t)v;
 438   ctx->p = p;
 439 }
 440
 441 /* Add a SLEB128 value. */
 442 static void gdbjit_sleb128(GDBJITctx *ctx, int32_t v)
 443 {
 444   uint8_t *p = ctx->p;
 445   for (; (uint32_t)(v+0x40) >= 0x80; v >>= 7)
 446     *p++ = (uint8_t)((v & 0x7f) | 0x80);
 447   *p++ = (uint8_t)(v & 0x7f);
 448   ctx->p = p;
 449 }
 450
 451 /* Shortcuts to generate DWARF structures. */
 452 #define DB(x)           (*p++ = (x))
 453 #define DI8(x)          (*(int8_t *)p = (x), p++)
 454 #define DU16(x)         (*(uint16_t *)p = (x), p += 2)
 455 #define DU32(x)         (*(uint32_t *)p = (x), p += 4)
 456 #define DADDR(x)        (*(uintptr_t *)p = (x), p += sizeof(uintptr_t))
 457 #define DUV(x)          (ctx->p = p, gdbjit_uleb128(ctx, (x)), p = ctx->p)
 458 #define DSV(x)          (ctx->p = p, gdbjit_sleb128(ctx, (x)), p = ctx->p)
 459 #define DSTR(str)       (ctx->p = p, gdbjit_strz(ctx, (str)), p = ctx->p)
 460 #define DALIGNNOP(s)    while ((uintptr_t)p & ((s)-1)) *p++ = DW_CFA_nop
 461 #define DSECT(name, stmt) \
 462   { uint32_t *szp_##name = (uint32_t *)p; p += 4; stmt \
 463     *szp_##name = (uint32_t)((p-(uint8_t *)szp_##name)-4); } \
 464
 465 /* Initialize ELF section headers. */
 466 static void LJ_FASTCALL gdbjit_secthdr(GDBJITctx *ctx)
 467 {
 468   ELFsectheader *sect;
 469
 470   *ctx->p++ = '\0';  /* Empty string at start of string table. */
 471
 472 #define SECTDEF(id, tp, al) \
 473   sect = &ctx->obj.sect[GDBJIT_SECT_##id]; \
 474   sect->name = gdbjit_strz(ctx, "." #id); \
 475   sect->type = ELFSECT_TYPE_##tp; \
 476   sect->align = (al)
 477
 478   SECTDEF(text, NOBITS, 16);
 479   sect->flags = ELFSECT_FLAGS_ALLOC|ELFSECT_FLAGS_EXEC;
 480   sect->addr = ctx->mcaddr;
 481   sect->ofs = 0;
 482   sect->size = ctx->szmcode;
 483
 484   SECTDEF(eh_frame, PROGBITS, sizeof(uintptr_t));
 485   sect->flags = ELFSECT_FLAGS_ALLOC;
 486
 487   SECTDEF(shstrtab, STRTAB, 1);
 488   SECTDEF(strtab, STRTAB, 1);
 489
 490   SECTDEF(symtab, SYMTAB, sizeof(uintptr_t));
 491   sect->ofs = offsetof(GDBJITobj, sym);
 492   sect->size = sizeof(ctx->obj.sym);
 493   sect->link = GDBJIT_SECT_strtab;
 494   sect->entsize = sizeof(ELFsymbol);
 495   sect->info = GDBJIT_SYM_FUNC;
 496
 497   SECTDEF(debug_info, PROGBITS, 1);
 498   SECTDEF(debug_abbrev, PROGBITS, 1);
 499   SECTDEF(debug_line, PROGBITS, 1);
 500
 501 #undef SECTDEF
 502 }
 503
 504 /* Initialize symbol table. */
 505 static void LJ_FASTCALL gdbjit_symtab(GDBJITctx *ctx)
 506 {
 507   ELFsymbol *sym;
 508
 509   *ctx->p++ = '\0';  /* Empty string at start of string table. */
 510
 511   sym = &ctx->obj.sym[GDBJIT_SYM_FILE];
 512   sym->name = gdbjit_strz(ctx, "JIT mcode");
 513   sym->sectidx = ELFSECT_IDX_ABS;
 514   sym->info = ELFSYM_TYPE_FILE|ELFSYM_BIND_LOCAL;
 515
 516   sym = &ctx->obj.sym[GDBJIT_SYM_FUNC];
 517   sym->name = gdbjit_strz(ctx, "TRACE_"); ctx->p--;
 518   gdbjit_catnum(ctx, ctx->T->traceno); *ctx->p++ = '\0';
 519   sym->sectidx = GDBJIT_SECT_text;
 520   sym->value = 0;
 521   sym->size = ctx->szmcode;
 522   sym->info = ELFSYM_TYPE_FUNC|ELFSYM_BIND_GLOBAL;
 523 }
 524
 525 /* Initialize .eh_frame section. */
 526 static void LJ_FASTCALL gdbjit_ehframe(GDBJITctx *ctx)
 527 {
 528   uint8_t *p = ctx->p;
 529   uint8_t *framep = p;
 530
 531   /* Emit DWARF EH CIE. */
 532   DSECT(CIE,
 533     DU32(0);                    /* Offset to CIE itself. */
 534     DB(DW_CIE_VERSION);
 535     DSTR("zR");                 /* Augmentation. */
 536     DUV(1);                     /* Code alignment factor. */
 537     DSV(-(int32_t)sizeof(uintptr_t));  /* Data alignment factor. */
 538     DB(DW_REG_RA);              /* Return address register. */
 539     DB(1); DB(DW_EH_PE_textrel|DW_EH_PE_udata4);  /* Augmentation data. */
 540     DB(DW_CFA_def_cfa); DUV(DW_REG_SP); DUV(sizeof(uintptr_t));
 541 #if LJ_TARGET_PPC
 542     DB(DW_CFA_offset_extended_sf); DB(DW_REG_RA); DSV(-1);
 543 #else
 544     DB(DW_CFA_offset|DW_REG_RA); DUV(1);
 545 #endif
 546     DALIGNNOP(sizeof(uintptr_t));
 547   )
 548
 549   /* Emit DWARF EH FDE. */
 550   DSECT(FDE,
 551     DU32((uint32_t)(p-framep)); /* Offset to CIE. */
 552     DU32(0);                    /* Machine code offset relative to .text. */
 553     DU32(ctx->szmcode);         /* Machine code length. */
 554     DB(0);                      /* Augmentation data. */
 555     /* Registers saved in CFRAME. */
 556 #if LJ_TARGET_X86
 557     DB(DW_CFA_offset|DW_REG_BP); DUV(2);
 558     DB(DW_CFA_offset|DW_REG_DI); DUV(3);
 559     DB(DW_CFA_offset|DW_REG_SI); DUV(4);
 560     DB(DW_CFA_offset|DW_REG_BX); DUV(5);
 561 #elif LJ_TARGET_X64
 562     DB(DW_CFA_offset|DW_REG_BP); DUV(2);
 563     DB(DW_CFA_offset|DW_REG_BX); DUV(3);
 564     DB(DW_CFA_offset|DW_REG_15); DUV(4);
 565     DB(DW_CFA_offset|DW_REG_14); DUV(5);
 566     /* Extra registers saved for JIT-compiled code. */
 567     DB(DW_CFA_offset|DW_REG_13); DUV(9);
 568     DB(DW_CFA_offset|DW_REG_12); DUV(10);
 569 #elif LJ_TARGET_ARM
 570     {
 571       int i;
 572       for (i = 11; i >= 4; i--) { DB(DW_CFA_offset|i); DUV(2+(11-i)); }
 573     }
 574 #elif LJ_TARGET_PPC
 575     {
 576       int i;
 577       DB(DW_CFA_offset_extended); DB(DW_REG_CR); DUV(55);
 578       for (i = 14; i <= 31; i++) {
 579         DB(DW_CFA_offset|i); DUV(37+(31-i));
 580         DB(DW_CFA_offset|32|i); DUV(2+2*(31-i));
 581       }
 582     }
 583 #elif LJ_TARGET_MIPS
 584     {
 585       int i;
 586       DB(DW_CFA_offset|30); DUV(2);
 587       for (i = 23; i >= 16; i--) { DB(DW_CFA_offset|i); DUV(26-i); }
 588       for (i = 30; i >= 20; i -= 2) { DB(DW_CFA_offset|32|i); DUV(42-i); }
 589     }
 590 #else
 591 #error "Unsupported target architecture"
 592 #endif
 593     if (ctx->spadjp != ctx->spadj) {  /* Parent/interpreter stack frame size. */
 594       DB(DW_CFA_def_cfa_offset); DUV(ctx->spadjp);
 595       DB(DW_CFA_advance_loc|1);  /* Only an approximation. */
 596     }
 597     DB(DW_CFA_def_cfa_offset); DUV(ctx->spadj);  /* Trace stack frame size. */
 598     DALIGNNOP(sizeof(uintptr_t));
 599   )
 600
 601   ctx->p = p;
 602 }
 603
 604 /* Initialize .debug_info section. */
 605 static void LJ_FASTCALL gdbjit_debuginfo(GDBJITctx *ctx)
 606 {
 607   uint8_t *p = ctx->p;
 608
 609   DSECT(info,
 610     DU16(2);                    /* DWARF version. */
 611     DU32(0);                    /* Abbrev offset. */
 612     DB(sizeof(uintptr_t));      /* Pointer size. */
 613
 614     DUV(1);                     /* Abbrev #1: DW_TAG_compile_unit. */
 615     DSTR(ctx->filename);        /* DW_AT_name. */
 616     DADDR(ctx->mcaddr);         /* DW_AT_low_pc. */
 617     DADDR(ctx->mcaddr + ctx->szmcode);  /* DW_AT_high_pc. */
 618     DU32(0);                    /* DW_AT_stmt_list. */
 619   )
 620
 621   ctx->p = p;
 622 }
 623
 624 /* Initialize .debug_abbrev section. */
 625 static void LJ_FASTCALL gdbjit_debugabbrev(GDBJITctx *ctx)
 626 {
 627   uint8_t *p = ctx->p;
 628
 629   /* Abbrev #1: DW_TAG_compile_unit. */
 630   DUV(1); DUV(DW_TAG_compile_unit);
 631   DB(DW_children_no);
 632   DUV(DW_AT_name);      DUV(DW_FORM_string);
 633   DUV(DW_AT_low_pc);    DUV(DW_FORM_addr);
 634   DUV(DW_AT_high_pc);   DUV(DW_FORM_addr);
 635   DUV(DW_AT_stmt_list); DUV(DW_FORM_data4);
 636   DB(0); DB(0);
 637
 638   ctx->p = p;
 639 }
 640
 641 #define DLNE(op, s)     (DB(DW_LNS_extended_op), DUV(1+(s)), DB((op)))
 642
 643 /* Initialize .debug_line section. */
 644 static void LJ_FASTCALL gdbjit_debugline(GDBJITctx *ctx)
 645 {
 646   uint8_t *p = ctx->p;
 647
 648   DSECT(line,
 649     DU16(2);                    /* DWARF version. */
 650     DSECT(header,
 651       DB(1);                    /* Minimum instruction length. */
 652       DB(1);                    /* is_stmt. */
 653       DI8(0);                   /* Line base for special opcodes. */
 654       DB(2);                    /* Line range for special opcodes. */
 655       DB(3+1);                  /* Opcode base at DW_LNS_advance_line+1. */
 656       DB(0); DB(1); DB(1);      /* Standard opcode lengths. */
 657       /* Directory table. */
 658       DB(0);
 659       /* File name table. */
 660       DSTR(ctx->filename); DUV(0); DUV(0); DUV(0);
 661       DB(0);
 662     )
 663
 664     DLNE(DW_LNE_set_address, sizeof(uintptr_t)); DADDR(ctx->mcaddr);
 665     if (ctx->lineno) {
 666       DB(DW_LNS_advance_line); DSV(ctx->lineno-1);
 667     }
 668     DB(DW_LNS_copy);
 669     DB(DW_LNS_advance_pc); DUV(ctx->szmcode);
 670     DLNE(DW_LNE_end_sequence, 0);
 671   )
 672
 673   ctx->p = p;
 674 }
 675
 676 #undef DLNE
 677
 678 /* Undef shortcuts. */
 679 #undef DB
 680 #undef DI8
 681 #undef DU16
 682 #undef DU32
 683 #undef DADDR
 684 #undef DUV
 685 #undef DSV
 686 #undef DSTR
 687 #undef DALIGNNOP
 688 #undef DSECT
 689
 690 /* Type of a section initializer callback. */
 691 typedef void (LJ_FASTCALL *GDBJITinitf)(GDBJITctx *ctx);
 692
 693 /* Call section initializer and set the section offset and size. */
 694 static void gdbjit_initsect(GDBJITctx *ctx, int sect, GDBJITinitf initf)
 695 {
 696   ctx->startp = ctx->p;
 697   ctx->obj.sect[sect].ofs = (uintptr_t)((char *)ctx->p - (char *)&ctx->obj);
 698   initf(ctx);
 699   ctx->obj.sect[sect].size = (uintptr_t)(ctx->p - ctx->startp);
 700 }
 701
 702 #define SECTALIGN(p, a) \
 703   ((p) = (uint8_t *)(((uintptr_t)(p) + ((a)-1)) & ~(uintptr_t)((a)-1)))
 704
 705 /* Build in-memory ELF object. */
 706 static void gdbjit_buildobj(GDBJITctx *ctx)
 707 {
 708   GDBJITobj *obj = &ctx->obj;
 709   /* Fill in ELF header and clear structures. */
 710   memcpy(&obj->hdr, &elfhdr_template, sizeof(ELFheader));
 711   memset(&obj->sect, 0, sizeof(ELFsectheader)*GDBJIT_SECT__MAX);
 712   memset(&obj->sym, 0, sizeof(ELFsymbol)*GDBJIT_SYM__MAX);
 713   /* Initialize sections. */
 714   ctx->p = obj->space;
 715   gdbjit_initsect(ctx, GDBJIT_SECT_shstrtab, gdbjit_secthdr);
 716   gdbjit_initsect(ctx, GDBJIT_SECT_strtab, gdbjit_symtab);
 717   gdbjit_initsect(ctx, GDBJIT_SECT_debug_info, gdbjit_debuginfo);
 718   gdbjit_initsect(ctx, GDBJIT_SECT_debug_abbrev, gdbjit_debugabbrev);
 719   gdbjit_initsect(ctx, GDBJIT_SECT_debug_line, gdbjit_debugline);
 720   SECTALIGN(ctx->p, sizeof(uintptr_t));
 721   gdbjit_initsect(ctx, GDBJIT_SECT_eh_frame, gdbjit_ehframe);
 722   ctx->objsize = (size_t)((char *)ctx->p - (char *)obj);
 723   lua_assert(ctx->objsize < sizeof(GDBJITobj));
 724 }
 725
 726 #undef SECTALIGN
 727
 728 /* -- Interface to GDB JIT API -------------------------------------------- */
 729
 730 /* Add new entry to GDB JIT symbol chain. */
 731 static void gdbjit_newentry(lua_State *L, GDBJITctx *ctx)
 732 {
 733   /* Allocate memory for GDB JIT entry and ELF object. */
 734   MSize sz = (MSize)(sizeof(GDBJITentryobj) - sizeof(GDBJITobj) + ctx->objsize);
 735   GDBJITentryobj *eo = lj_mem_newt(L, sz, GDBJITentryobj);
 736   memcpy(&eo->obj, &ctx->obj, ctx->objsize);  /* Copy ELF object. */
 737   eo->sz = sz;
 738   ctx->T->gdbjit_entry = (void *)eo;
 739   /* Link new entry to chain and register it. */
 740   eo->entry.prev_entry = NULL;
 741   eo->entry.next_entry = __jit_debug_descriptor.first_entry;
 742   if (eo->entry.next_entry)
 743     eo->entry.next_entry->prev_entry = &eo->entry;
 744   eo->entry.symfile_addr = (const char *)&eo->obj;
 745   eo->entry.symfile_size = ctx->objsize;
 746   __jit_debug_descriptor.first_entry = &eo->entry;
 747   __jit_debug_descriptor.relevant_entry = &eo->entry;
 748   __jit_debug_descriptor.action_flag = GDBJIT_REGISTER;
 749   __jit_debug_register_code();
 750 }
 751
 752 /* Add debug info for newly compiled trace and notify GDB. */
 753 void lj_gdbjit_addtrace(jit_State *J, GCtrace *T)
 754 {
 755   GDBJITctx ctx;
 756   GCproto *pt = &gcref(T->startpt)->pt;
 757   TraceNo parent = T->ir[REF_BASE].op1;
 758   const BCIns *startpc = mref(T->startpc, const BCIns);
 759   ctx.T = T;
 760   ctx.mcaddr = (uintptr_t)T->mcode;
 761   ctx.szmcode = T->szmcode;
 762   ctx.spadjp = CFRAME_SIZE_JIT +
 763                (MSize)(parent ? traceref(J, parent)->spadjust : 0);
 764   ctx.spadj = CFRAME_SIZE_JIT + T->spadjust;
 765   lua_assert(startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc);
 766   ctx.lineno = lj_debug_line(pt, proto_bcpos(pt, startpc));
 767   ctx.filename = proto_chunknamestr(pt);
 768   if (*ctx.filename == '@' || *ctx.filename == '=')
 769     ctx.filename++;
 770   else
 771     ctx.filename = "(string)";
 772   gdbjit_buildobj(&ctx);
 773   gdbjit_newentry(J->L, &ctx);
 774 }
 775
 776 /* Delete debug info for trace and notify GDB. */
 777 void lj_gdbjit_deltrace(jit_State *J, GCtrace *T)
 778 {
 779   GDBJITentryobj *eo = (GDBJITentryobj *)T->gdbjit_entry;
 780   if (eo) {
 781     if (eo->entry.prev_entry)
 782       eo->entry.prev_entry->next_entry = eo->entry.next_entry;
 783     else
 784       __jit_debug_descriptor.first_entry = eo->entry.next_entry;
 785     if (eo->entry.next_entry)
 786       eo->entry.next_entry->prev_entry = eo->entry.prev_entry;
 787     __jit_debug_descriptor.relevant_entry = &eo->entry;
 788     __jit_debug_descriptor.action_flag = GDBJIT_UNREGISTER;
 789     __jit_debug_register_code();
 790     lj_mem_free(J2G(J), eo, eo->sz);
 791   }
 792 }
 793
 794 #endif
 795 #endif