summaryrefslogtreecommitdiff
path: root/ldso/dlstart.c
diff options
context:
space:
mode:
authorRich Felker <dalias@aerifal.cx>2016-01-25 19:29:55 -0500
committerRich Felker <dalias@aerifal.cx>2016-01-25 19:29:55 -0500
commit5552ce52000855906a5cb4f08f2e456573cca51f (patch)
tree7a6bd7fb987116843bfa9bd985dfb51f726cdd01 /ldso/dlstart.c
parent16f70388d4a876c216cbf1d829782ace41a07634 (diff)
downloadmusl-5552ce52000855906a5cb4f08f2e456573cca51f.tar.gz
move dynamic linker to its own top-level directory, ldso
this eliminates the last need for the SHARED macro to control how files in the src tree are compiled. the same code is used for both libc.a and libc.so, with additional code for the dynamic linker (from the new ldso tree) being added to libc.so but not libc.a. separate .o and .lo object files still exist for the src tree, but the only difference is that the .lo files are built as PIC. in the future, if/when we add dlopen support for static-linked programs, much of the code in dynlink.c may be moved back into the src tree, but properly factored into separate source files. in that case, the code in the ldso tree will be reduced to just the dynamic linker entry point, self-relocation, and loading of libraries needed by the main application.
Diffstat (limited to 'ldso/dlstart.c')
-rw-r--r--ldso/dlstart.c146
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);
+}