dlstart.c raw
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 }
149