diff options
Diffstat (limited to 'ldso/dlstart.c')
| -rw-r--r-- | ldso/dlstart.c | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/ldso/dlstart.c b/ldso/dlstart.c new file mode 100644 index 00000000..4482d525 --- /dev/null +++ b/ldso/dlstart.c @@ -0,0 +1,146 @@ +#include <stddef.h> +#include "dynlink.h" + +#ifndef START +#define START "_dlstart" +#endif + +#include "crt_arch.h" + +#ifndef GETFUNCSYM +#define GETFUNCSYM(fp, sym, got) do { \ + __attribute__((__visibility__("hidden"))) void sym(); \ + static void (*static_func_ptr)() = sym; \ + __asm__ __volatile__ ( "" : "+m"(static_func_ptr) : : "memory"); \ + *(fp) = static_func_ptr; } while(0) +#endif + +__attribute__((__visibility__("hidden"))) +void _dlstart_c(size_t *sp, size_t *dynv) +{ + size_t i, aux[AUX_CNT], dyn[DYN_CNT]; + size_t *rel, rel_size, base; + + int argc = *sp; + char **argv = (void *)(sp+1); + + for (i=argc+1; argv[i]; i++); + size_t *auxv = (void *)(argv+i+1); + + for (i=0; i<AUX_CNT; i++) aux[i] = 0; + for (i=0; auxv[i]; i+=2) if (auxv[i]<AUX_CNT) + aux[auxv[i]] = auxv[i+1]; + +#if DL_FDPIC + struct fdpic_loadseg *segs, fakeseg; + size_t j; + if (dynv) { + /* crt_arch.h entry point asm is responsible for reserving + * space and moving the extra fdpic arguments to the stack + * vector where they are easily accessible from C. */ + segs = ((struct fdpic_loadmap *)(sp[-1] ? sp[-1] : sp[-2]))->segs; + } else { + /* If dynv is null, the entry point was started from loader + * that is not fdpic-aware. We can assume normal fixed- + * displacement ELF loading was performed, but when ldso was + * run as a command, finding the Ehdr is a heursitic: we + * have to assume Phdrs start in the first 4k of the file. */ + base = aux[AT_BASE]; + if (!base) base = aux[AT_PHDR] & -4096; + segs = &fakeseg; + segs[0].addr = base; + segs[0].p_vaddr = 0; + segs[0].p_memsz = -1; + Ehdr *eh = (void *)base; + Phdr *ph = (void *)(base + eh->e_phoff); + size_t phnum = eh->e_phnum; + size_t phent = eh->e_phentsize; + while (phnum-- && ph->p_type != PT_DYNAMIC) + ph = (void *)((size_t)ph + phent); + dynv = (void *)(base + ph->p_vaddr); + } +#endif + + for (i=0; i<DYN_CNT; i++) dyn[i] = 0; + for (i=0; dynv[i]; i+=2) if (dynv[i]<DYN_CNT) + dyn[dynv[i]] = dynv[i+1]; + +#if DL_FDPIC + for (i=0; i<DYN_CNT; i++) { + if (i==DT_RELASZ || i==DT_RELSZ) continue; + if (!dyn[i]) continue; + for (j=0; dyn[i]-segs[j].p_vaddr >= segs[j].p_memsz; j++); + dyn[i] += segs[j].addr - segs[j].p_vaddr; + } + base = 0; + + const Sym *syms = (void *)dyn[DT_SYMTAB]; + + rel = (void *)dyn[DT_RELA]; + rel_size = dyn[DT_RELASZ]; + for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) { + if (!IS_RELATIVE(rel[1], syms)) continue; + for (j=0; rel[0]-segs[j].p_vaddr >= segs[j].p_memsz; j++); + size_t *rel_addr = (void *) + (rel[0] + segs[j].addr - segs[j].p_vaddr); + if (R_TYPE(rel[1]) == REL_FUNCDESC_VAL) { + *rel_addr += segs[rel_addr[1]].addr + - segs[rel_addr[1]].p_vaddr + + syms[R_SYM(rel[1])].st_value; + rel_addr[1] = dyn[DT_PLTGOT]; + } else { + size_t val = syms[R_SYM(rel[1])].st_value; + for (j=0; val-segs[j].p_vaddr >= segs[j].p_memsz; j++); + *rel_addr = rel[2] + segs[j].addr - segs[j].p_vaddr + val; + } + } +#else + /* If the dynamic linker is invoked as a command, its load + * address is not available in the aux vector. Instead, compute + * the load address as the difference between &_DYNAMIC and the + * virtual address in the PT_DYNAMIC program header. */ + base = aux[AT_BASE]; + if (!base) { + size_t phnum = aux[AT_PHNUM]; + size_t phentsize = aux[AT_PHENT]; + Phdr *ph = (void *)aux[AT_PHDR]; + for (i=phnum; i--; ph = (void *)((char *)ph + phentsize)) { + if (ph->p_type == PT_DYNAMIC) { + base = (size_t)dynv - ph->p_vaddr; + break; + } + } + } + + /* MIPS uses an ugly packed form for GOT relocations. Since we + * can't make function calls yet and the code is tiny anyway, + * it's simply inlined here. */ + if (NEED_MIPS_GOT_RELOCS) { + size_t local_cnt = 0; + size_t *got = (void *)(base + dyn[DT_PLTGOT]); + for (i=0; dynv[i]; i+=2) if (dynv[i]==DT_MIPS_LOCAL_GOTNO) + local_cnt = dynv[i+1]; + for (i=0; i<local_cnt; i++) got[i] += base; + } + + rel = (void *)(base+dyn[DT_REL]); + rel_size = dyn[DT_RELSZ]; + for (; rel_size; rel+=2, rel_size-=2*sizeof(size_t)) { + if (!IS_RELATIVE(rel[1], 0)) continue; + size_t *rel_addr = (void *)(base + rel[0]); + *rel_addr += base; + } + + rel = (void *)(base+dyn[DT_RELA]); + rel_size = dyn[DT_RELASZ]; + for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) { + if (!IS_RELATIVE(rel[1], 0)) continue; + size_t *rel_addr = (void *)(base + rel[0]); + *rel_addr = base + rel[2]; + } +#endif + + stage2_func dls2; + GETFUNCSYM(&dls2, __dls2, base+dyn[DT_PLTGOT]); + dls2((void *)base, sp); +} |