ldso/dlstart.c

   1 #include <stddef.h>
   2 #include "dynlink.h"
   3 #include "libc.h"
   4
   5 #ifndef START
   6 #define START "_dlstart"
   7 #endif
   8
   9 #define SHARED
  10
  11 #include "crt_arch.h"
  12
  13 #ifndef GETFUNCSYM
  14 #define GETFUNCSYM(fp, sym, got) do { \
  15         hidden void sym(); \
  16         static void (*static_func_ptr)() = sym; \
  17         __asm__ __volatile__ ( "" : "+m"(static_func_ptr) : : "memory"); \
  18         *(fp) = static_func_ptr; } while(0)
  19 #endif
  20
  21 hidden void _dlstart_c(size_t *sp, size_t *dynv)
  22 {
  23         size_t i, aux[AUX_CNT], dyn[DYN_CNT];
  24         size_t *rel, rel_size, base;
  25
  26         int argc = *sp;
  27         char **argv = (void *)(sp+1);
  28
  29         for (i=argc+1; argv[i]; i++);
  30         size_t *auxv = (void *)(argv+i+1);
  31
  32         for (i=0; i<AUX_CNT; i++) aux[i] = 0;
  33         for (i=0; auxv[i]; i+=2) if (auxv[i]<AUX_CNT)
  34                 aux[auxv[i]] = auxv[i+1];
  35
  36 #if DL_FDPIC
  37         struct fdpic_loadseg *segs, fakeseg;
  38         size_t j;
  39         if (dynv) {
  40                 /* crt_arch.h entry point asm is responsible for reserving
  41                  * space and moving the extra fdpic arguments to the stack
  42                  * vector where they are easily accessible from C. */
  43                 segs = ((struct fdpic_loadmap *)(sp[-1] ? sp[-1] : sp[-2]))->segs;
  44         } else {
  45                 /* If dynv is null, the entry point was started from loader
  46                  * that is not fdpic-aware. We can assume normal fixed-
  47                  * displacement ELF loading was performed, but when ldso was
  48                  * run as a command, finding the Ehdr is a heursitic: we
  49                  * have to assume Phdrs start in the first 4k of the file. */
  50                 base = aux[AT_BASE];
  51                 if (!base) base = aux[AT_PHDR] & -4096;
  52                 segs = &fakeseg;
  53                 segs[0].addr = base;
  54                 segs[0].p_vaddr = 0;
  55                 segs[0].p_memsz = -1;
  56                 Ehdr *eh = (void *)base;
  57                 Phdr *ph = (void *)(base + eh->e_phoff);
  58                 size_t phnum = eh->e_phnum;
  59                 size_t phent = eh->e_phentsize;
  60                 while (phnum-- && ph->p_type != PT_DYNAMIC)
  61                         ph = (void *)((size_t)ph + phent);
  62                 dynv = (void *)(base + ph->p_vaddr);
  63         }
  64 #endif
  65
  66         for (i=0; i<DYN_CNT; i++) dyn[i] = 0;
  67         for (i=0; dynv[i]; i+=2) if (dynv[i]<DYN_CNT)
  68                 dyn[dynv[i]] = dynv[i+1];
  69
  70 #if DL_FDPIC
  71         for (i=0; i<DYN_CNT; i++) {
  72                 if (i==DT_RELASZ || i==DT_RELSZ) continue;
  73                 if (!dyn[i]) continue;
  74                 for (j=0; dyn[i]-segs[j].p_vaddr >= segs[j].p_memsz; j++);
  75                 dyn[i] += segs[j].addr - segs[j].p_vaddr;
  76         }
  77         base = 0;
  78
  79         const Sym *syms = (void *)dyn[DT_SYMTAB];
  80
  81         rel = (void *)dyn[DT_RELA];
  82         rel_size = dyn[DT_RELASZ];
  83         for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) {
  84                 if (!IS_RELATIVE(rel[1], syms)) continue;
  85                 for (j=0; rel[0]-segs[j].p_vaddr >= segs[j].p_memsz; j++);
  86                 size_t *rel_addr = (void *)
  87                         (rel[0] + segs[j].addr - segs[j].p_vaddr);
  88                 if (R_TYPE(rel[1]) == REL_FUNCDESC_VAL) {
  89                         *rel_addr += segs[rel_addr[1]].addr
  90                                 - segs[rel_addr[1]].p_vaddr
  91                                 + syms[R_SYM(rel[1])].st_value;
  92                         rel_addr[1] = dyn[DT_PLTGOT];
  93                 } else {
  94                         size_t val = syms[R_SYM(rel[1])].st_value;
  95                         for (j=0; val-segs[j].p_vaddr >= segs[j].p_memsz; j++);
  96                         *rel_addr = rel[2] + segs[j].addr - segs[j].p_vaddr + val;
  97                 }
  98         }
  99 #else
 100         /* If the dynamic linker is invoked as a command, its load
 101          * address is not available in the aux vector. Instead, compute
 102          * the load address as the difference between &_DYNAMIC and the
 103          * virtual address in the PT_DYNAMIC program header. */
 104         base = aux[AT_BASE];
 105         if (!base) {
 106                 size_t phnum = aux[AT_PHNUM];
 107                 size_t phentsize = aux[AT_PHENT];
 108                 Phdr *ph = (void *)aux[AT_PHDR];
 109                 for (i=phnum; i--; ph = (void *)((char *)ph + phentsize)) {
 110                         if (ph->p_type == PT_DYNAMIC) {
 111                                 base = (size_t)dynv - ph->p_vaddr;
 112                                 break;
 113                         }
 114                 }
 115         }
 116
 117         /* MIPS uses an ugly packed form for GOT relocations. Since we
 118          * can't make function calls yet and the code is tiny anyway,
 119          * it's simply inlined here. */
 120         if (NEED_MIPS_GOT_RELOCS) {
 121                 size_t local_cnt = 0;
 122                 size_t *got = (void *)(base + dyn[DT_PLTGOT]);
 123                 for (i=0; dynv[i]; i+=2) if (dynv[i]==DT_MIPS_LOCAL_GOTNO)
 124                         local_cnt = dynv[i+1];
 125                 for (i=0; i<local_cnt; i++) got[i] += base;
 126         }
 127
 128         rel = (void *)(base+dyn[DT_REL]);
 129         rel_size = dyn[DT_RELSZ];
 130         for (; rel_size; rel+=2, rel_size-=2*sizeof(size_t)) {
 131                 if (!IS_RELATIVE(rel[1], 0)) continue;
 132                 size_t *rel_addr = (void *)(base + rel[0]);
 133                 *rel_addr += base;
 134         }
 135
 136         rel = (void *)(base+dyn[DT_RELA]);
 137         rel_size = dyn[DT_RELASZ];
 138         for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) {
 139                 if (!IS_RELATIVE(rel[1], 0)) continue;
 140                 size_t *rel_addr = (void *)(base + rel[0]);
 141                 *rel_addr = base + rel[2];
 142         }
 143 #endif
 144
 145         stage2_func dls2;
 146         GETFUNCSYM(&dls2, __dls2, base+dyn[DT_PLTGOT]);
 147         dls2((void *)base, sp);
 148 }