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 #ifdef ENABLE_HWASAN
22 __attribute__((no_sanitize("hwaddress")))
23 #endif
_dlstart_c(size_t * sp,size_t * dynv)24 hidden void _dlstart_c(size_t *sp, size_t *dynv)
25 {
26 size_t i, aux[AUX_CNT], dyn[DYN_CNT];
27 size_t *rel, rel_size, base;
28
29 int argc = *sp;
30 char **argv = (void *)(sp+1);
31
32 for (i=argc+1; argv[i]; i++);
33 size_t *auxv = (void *)(argv+i+1);
34
35 for (i=0; i<AUX_CNT; i++) aux[i] = 0;
36 for (i=0; auxv[i]; i+=2) if (auxv[i]<AUX_CNT)
37 aux[auxv[i]] = auxv[i+1];
38
39 #if DL_FDPIC
40 struct fdpic_loadseg *segs, fakeseg;
41 size_t j;
42 if (dynv) {
43 /* crt_arch.h entry point asm is responsible for reserving
44 * space and moving the extra fdpic arguments to the stack
45 * vector where they are easily accessible from C. */
46 segs = ((struct fdpic_loadmap *)(sp[-1] ? sp[-1] : sp[-2]))->segs;
47 } else {
48 /* If dynv is null, the entry point was started from loader
49 * that is not fdpic-aware. We can assume normal fixed-
50 * displacement ELF loading was performed, but when ldso was
51 * run as a command, finding the Ehdr is a heursitic: we
52 * have to assume Phdrs start in the first 4k of the file. */
53 base = aux[AT_BASE];
54 if (!base) base = aux[AT_PHDR] & -4096;
55 segs = &fakeseg;
56 segs[0].addr = base;
57 segs[0].p_vaddr = 0;
58 segs[0].p_memsz = -1;
59 Ehdr *eh = (void *)base;
60 Phdr *ph = (void *)(base + eh->e_phoff);
61 size_t phnum = eh->e_phnum;
62 size_t phent = eh->e_phentsize;
63 while (phnum-- && ph->p_type != PT_DYNAMIC)
64 ph = (void *)((size_t)ph + phent);
65 dynv = (void *)(base + ph->p_vaddr);
66 }
67 #endif
68
69 for (i=0; i<DYN_CNT; i++) dyn[i] = 0;
70 for (i=0; dynv[i]; i+=2) if (dynv[i]<DYN_CNT)
71 dyn[dynv[i]] = dynv[i+1];
72
73 #if DL_FDPIC
74 for (i=0; i<DYN_CNT; i++) {
75 if (i==DT_RELASZ || i==DT_RELSZ) continue;
76 if (!dyn[i]) continue;
77 for (j=0; dyn[i]-segs[j].p_vaddr >= segs[j].p_memsz; j++);
78 dyn[i] += segs[j].addr - segs[j].p_vaddr;
79 }
80 base = 0;
81
82 const Sym *syms = (void *)dyn[DT_SYMTAB];
83
84 rel = (void *)dyn[DT_RELA];
85 rel_size = dyn[DT_RELASZ];
86 for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) {
87 if (!IS_RELATIVE(rel[1], syms)) continue;
88 for (j=0; rel[0]-segs[j].p_vaddr >= segs[j].p_memsz; j++);
89 size_t *rel_addr = (void *)
90 (rel[0] + segs[j].addr - segs[j].p_vaddr);
91 if (R_TYPE(rel[1]) == REL_FUNCDESC_VAL) {
92 *rel_addr += segs[rel_addr[1]].addr
93 - segs[rel_addr[1]].p_vaddr
94 + syms[R_SYM(rel[1])].st_value;
95 rel_addr[1] = dyn[DT_PLTGOT];
96 } else {
97 size_t val = syms[R_SYM(rel[1])].st_value;
98 for (j=0; val-segs[j].p_vaddr >= segs[j].p_memsz; j++);
99 *rel_addr = rel[2] + segs[j].addr - segs[j].p_vaddr + val;
100 }
101 }
102 #else
103 /* If the dynamic linker is invoked as a command, its load
104 * address is not available in the aux vector. Instead, compute
105 * the load address as the difference between &_DYNAMIC and the
106 * virtual address in the PT_DYNAMIC program header. */
107 base = aux[AT_BASE];
108 if (!base) {
109 size_t phnum = aux[AT_PHNUM];
110 size_t phentsize = aux[AT_PHENT];
111 Phdr *ph = (void *)aux[AT_PHDR];
112 for (i=phnum; i--; ph = (void *)((char *)ph + phentsize)) {
113 if (ph->p_type == PT_DYNAMIC) {
114 base = (size_t)dynv - ph->p_vaddr;
115 break;
116 }
117 }
118 }
119
120 /* MIPS uses an ugly packed form for GOT relocations. Since we
121 * can't make function calls yet and the code is tiny anyway,
122 * it's simply inlined here. */
123 if (NEED_MIPS_GOT_RELOCS) {
124 size_t local_cnt = 0;
125 size_t *got = (void *)(base + dyn[DT_PLTGOT]);
126 for (i=0; dynv[i]; i+=2) if (dynv[i]==DT_MIPS_LOCAL_GOTNO)
127 local_cnt = dynv[i+1];
128 for (i=0; i<local_cnt; i++) got[i] += base;
129 }
130
131 rel = (void *)(base+dyn[DT_REL]);
132 rel_size = dyn[DT_RELSZ];
133 for (; rel_size; rel+=2, rel_size-=2*sizeof(size_t)) {
134 if (!IS_RELATIVE(rel[1], 0)) continue;
135 size_t *rel_addr = (void *)(base + rel[0]);
136 *rel_addr += base;
137 }
138
139 rel = (void *)(base+dyn[DT_RELA]);
140 rel_size = dyn[DT_RELASZ];
141 for (; rel_size; rel+=3, rel_size-=3*sizeof(size_t)) {
142 if (!IS_RELATIVE(rel[1], 0)) continue;
143 size_t *rel_addr = (void *)(base + rel[0]);
144 *rel_addr = base + rel[2];
145 }
146
147 rel = (void *)(base+dyn[DT_RELR]);
148 rel_size = dyn[DT_RELRSZ];
149 size_t *relr_addr = 0;
150 for (; rel_size; rel++, rel_size-=sizeof(size_t)) {
151 if ((rel[0]&1) == 0) {
152 relr_addr = (void *)(base + rel[0]);
153 *relr_addr++ += base;
154 } else {
155 for (size_t i=0, bitmap=rel[0]; bitmap>>=1; i++)
156 if (bitmap&1)
157 relr_addr[i] += base;
158 relr_addr += 8*sizeof(size_t)-1;
159 }
160 }
161 #endif
162
163 stage2_func dls2;
164 GETFUNCSYM(&dls2, __dls2, base+dyn[DT_PLTGOT]);
165 dls2((void *)base, sp);
166 }
167