From 7a9669e977e5f750cf72ccbd2614f8b72ce02c4c Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Tue, 22 Sep 2015 03:54:42 +0000 Subject: add general fdpic support in dynamic linker and arch support for sh at this point not all functionality is complete. the dynamic linker itself, and main app if it is also loaded by the kernel, take advantage of fdpic and do not need constant displacement between segments, but additional libraries loaded by the dynamic linker follow normal ELF semantics for mapping still. this fully works, but does not admit shared text on nommu. in terms of actual functional correctness, dlsym's results are presently incorrect for function symbols, RTLD_NEXT fails to identify the caller correctly, and dladdr fails almost entirely. with the dynamic linker entry point working, support for static pie is automatically included, but linking the main application as ET_DYN (pie) probably does not make sense for fdpic anyway. ET_EXEC is equally relocatable but more efficient at representing relocations. --- src/ldso/dlstart.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 63 insertions(+), 2 deletions(-) (limited to 'src/ldso/dlstart.c') diff --git a/src/ldso/dlstart.c b/src/ldso/dlstart.c index e84e073e..46f50114 100644 --- a/src/ldso/dlstart.c +++ b/src/ldso/dlstart.c @@ -33,10 +33,70 @@ void _dlstart_c(size_t *sp, size_t *dynv) for (i=0; auxv[i]; i+=2) if (auxv[i]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= 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 @@ -68,7 +128,7 @@ void _dlstart_c(size_t *sp, size_t *dynv) 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])) continue; + if (!IS_RELATIVE(rel[1], 0)) continue; size_t *rel_addr = (void *)(base + rel[0]); *rel_addr += base; } @@ -76,10 +136,11 @@ void _dlstart_c(size_t *sp, size_t *dynv) 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])) continue; + 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]); -- cgit v1.2.1