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-rw-r--r--src/ldso/dynlink.c385
-rw-r--r--src/ldso/i386/start.s19
-rw-r--r--src/ldso/x86_64/start.s8
3 files changed, 412 insertions, 0 deletions
diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
new file mode 100644
index 00000000..b4444252
--- /dev/null
+++ b/src/ldso/dynlink.c
@@ -0,0 +1,385 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <elf.h>
+#include <sys/mman.h>
+#include <limits.h>
+#include <stdint.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <limits.h>
+#include <elf.h>
+
+#include "reloc.h"
+
+#if ULONG_MAX == 0xffffffff
+typedef Elf32_Ehdr Ehdr;
+typedef Elf32_Phdr Phdr;
+typedef Elf32_Sym Sym;
+#define R_TYPE(x) ((x)&255)
+#define R_SYM(x) ((x)>>8)
+#else
+typedef Elf64_Ehdr Ehdr;
+typedef Elf64_Phdr Phdr;
+typedef Elf64_Sym Sym;
+#define R_TYPE(x) ((x)&0xffffffff)
+#define R_SYM(x) ((x)>>32)
+#endif
+
+struct dso
+{
+ struct dso *next, *prev;
+ int refcnt;
+ size_t *dynv;
+ Sym *syms;
+ size_t *hashtab;
+ char *strings;
+ unsigned char *base;
+ unsigned char *map;
+ size_t map_len;
+ dev_t dev;
+ ino_t ino;
+ int global;
+ int relocated;
+ char name[];
+};
+
+static struct dso *head, *tail, *libc;
+
+#define AUX_CNT 15
+#define DYN_CNT 34
+
+static void decode_vec(size_t *v, size_t *a, size_t cnt)
+{
+ memset(a, 0, cnt*sizeof(size_t));
+ for (; v[0]; v+=2) if (v[0]<cnt) {
+ a[0] |= 1ULL<<v[0];
+ a[v[0]] = v[1];
+ }
+}
+
+static uint32_t hash(const char *s)
+{
+ uint_fast32_t h = 0;
+ while (*s) {
+ h = 16*h + *s++;
+ h ^= h>>24 & 0xf0;
+ }
+ return h & 0xfffffff;
+}
+
+static Sym *lookup(const char *s, uint32_t h, Sym *syms, size_t *hashtab, char *strings)
+{
+ size_t i;
+ for (i=hashtab[2+h%hashtab[0]]; i; i=hashtab[2+hashtab[0]+i]) {
+ if (!strcmp(s, strings+syms[i].st_name))
+ return syms+i;
+ }
+ return 0;
+}
+
+#define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON)
+
+static void *find_sym(struct dso *dso, const char *s, int need_def)
+{
+ uint32_t h = hash(s);
+ for (; dso; dso=dso->next) {
+ Sym *sym = lookup(s, h, dso->syms, dso->hashtab, dso->strings);
+ if (sym && (!need_def || sym->st_shndx) && sym->st_value
+ && (1<<(sym->st_info&0xf) & OK_TYPES))
+ return dso->base + sym->st_value;
+ }
+ return 0;
+}
+
+static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t stride, Sym *syms, char *strings, struct dso *dso)
+{
+ Sym *sym;
+ const char *name;
+ size_t sym_val, sym_size;
+ size_t *reloc_addr;
+ void *ctx;
+ int type;
+ int sym_index;
+
+ for (; rel_size; rel+=stride, rel_size-=stride*sizeof(size_t)) {
+ reloc_addr = (void *)(base + rel[0]);
+ type = R_TYPE(rel[1]);
+ sym_index = R_SYM(rel[1]);
+ if (sym_index) {
+ sym = syms + sym_index;
+ name = strings + sym->st_name;
+ ctx = IS_COPY(type) ? dso->next : dso;
+ sym_val = (size_t)find_sym(ctx, name, 1);
+ sym_size = sym->st_size;
+ }
+ do_single_reloc(reloc_addr, type, sym_val, sym_size, base, rel[2]);
+ }
+}
+
+static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dynp)
+{
+ size_t buf[896/sizeof(size_t)];
+ size_t phsize;
+ size_t addr_min=SIZE_MAX, addr_max=0, map_len;
+ size_t this_min, this_max;
+ off_t off_start;
+ Ehdr *eh;
+ Phdr *ph;
+ unsigned prot;
+ unsigned char *map, *base;
+ size_t dyn;
+ size_t i;
+
+ ssize_t l = read(fd, buf, sizeof buf);
+ if (l<sizeof *eh) return 0;
+ eh = (void *)buf;
+ phsize = eh->e_phentsize * eh->e_phnum;
+ if (phsize + sizeof *eh > l) return 0;
+ if (eh->e_phoff + phsize > l) {
+ l = pread(fd, buf+sizeof *eh, phsize, eh->e_phoff);
+ if (l != phsize) return 0;
+ eh->e_phoff = sizeof *eh;
+ }
+ ph = (void *)((char *)buf + eh->e_phoff);
+ for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
+ if (ph->p_type == PT_DYNAMIC)
+ dyn = ph->p_vaddr;
+ if (ph->p_type != PT_LOAD) continue;
+ if (ph->p_vaddr < addr_min) {
+ addr_min = ph->p_vaddr;
+ off_start = ph->p_offset;
+ prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
+ ((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
+ ((ph->p_flags&PF_X) ? PROT_EXEC : 0));
+ }
+ if (ph->p_vaddr+ph->p_memsz > addr_max) {
+ addr_max = ph->p_vaddr+ph->p_memsz;
+ }
+ }
+ if (!dyn) return 0;
+ addr_max += PAGE_SIZE-1;
+ addr_max &= -PAGE_SIZE;
+ addr_min &= -PAGE_SIZE;
+ off_start &= -PAGE_SIZE;
+ map_len = addr_max - addr_min + off_start;
+ /* The first time, we map too much, possibly even more than
+ * the length of the file. This is okay because we will not
+ * use the invalid part; we just need to reserve the right
+ * amount of virtual address space to map over later. */
+ map = mmap(0, map_len, prot, MAP_PRIVATE, fd, off_start);
+ if (map==MAP_FAILED) return 0;
+ base = map - addr_min;
+ ph = (void *)((char *)buf + eh->e_phoff);
+ for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
+ if (ph->p_type != PT_LOAD) continue;
+ /* Reuse the existing mapping for the lowest-address LOAD */
+ if ((ph->p_vaddr & -PAGE_SIZE) == addr_min) continue;
+ this_min = ph->p_vaddr & -PAGE_SIZE;
+ this_max = ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE;
+ off_start = ph->p_offset & -PAGE_SIZE;
+ prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
+ ((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
+ ((ph->p_flags&PF_X) ? PROT_EXEC : 0));
+ if (mmap(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED) {
+ munmap(map, map_len);
+ return 0;
+ }
+ if (ph->p_memsz > ph->p_filesz) {
+ size_t brk = (size_t)base+ph->p_vaddr+ph->p_filesz;
+ size_t pgbrk = brk+PAGE_SIZE-1 & -PAGE_SIZE;
+ memset((void *)brk, 0, pgbrk-brk & PAGE_SIZE-1);
+ if (pgbrk-(size_t)base < this_max && mmap((void *)pgbrk, (size_t)base+this_max-pgbrk, prot, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED) {
+ munmap(map, map_len);
+ return 0;
+ }
+ }
+ }
+ *lenp = map_len;
+ *basep = base;
+ *dynp = dyn;
+ return map;
+}
+
+static struct dso *load_library(const char *name)
+{
+ unsigned char *base, *map;
+ size_t dyno, map_len;
+ struct dso *p;
+ size_t dyn[DYN_CNT] = {0};
+ int fd;
+ struct stat st;
+
+ /* Catch and block attempts to reload the implementation itself */
+ if (name[0]=='l' && name[1]=='i' && name[2]=='b') {
+ static const char *rp, reserved[] =
+ "c\0pthread\0rt\0m\0dl\0util\0xnet\0";
+ char *z = strchr(name, '.');
+ if (z) {
+ size_t l = z-name;
+ for (rp=reserved; *rp && memcmp(name+3, rp, l-3); rp+=strlen(rp)+1);
+ if (*rp) {
+ if (!libc->prev) {
+ tail->next = libc;
+ libc->prev = tail;
+ tail = libc;
+ }
+ return libc;
+ }
+ }
+ }
+ /* Search for the name to see if it's already loaded */
+ for (p=head->next; p; p=p->next) {
+ if (!strcmp(p->name, name)) {
+ p->refcnt++;
+ return p;
+ }
+ }
+ if (name[0] == '/') {
+ fd = open(name, O_RDONLY);
+ } else {
+ static const char path[] = "/lib/\0/usr/local/lib/\0/usr/lib/\0";
+ const char *s;
+ char buf[NAME_MAX+32];
+ if (strlen(name) > NAME_MAX || strchr(name, '/')) return 0;
+ for (s=path; *s; s+=strlen(s)+1) {
+ strcpy(buf, s);
+ strcat(buf, name);
+ if ((fd = open(buf, O_RDONLY))>=0) break;
+ }
+ }
+ if (fd < 0) return 0;
+ if (fstat(fd, &st) < 0) {
+ close(fd);
+ return 0;
+ }
+ for (p=head->next; p; p=p->next) {
+ if (p->dev == st.st_dev && p->ino == st.st_ino) {
+ close(fd);
+ p->refcnt++;
+ return p;
+ }
+ }
+ map = map_library(fd, &map_len, &base, &dyno);
+ close(fd);
+ if (!map) return 0;
+ p = calloc(1, sizeof *p + strlen(name) + 1);
+ if (!p) {
+ munmap(map, map_len);
+ return 0;
+ }
+
+ p->map = map;
+ p->map_len = map_len;
+ p->base = base;
+ p->dynv = (void *)(base + dyno);
+ decode_vec(p->dynv, dyn, DYN_CNT);
+
+ p->syms = (void *)(base + dyn[DT_SYMTAB]);
+ p->hashtab = (void *)(base + dyn[DT_HASH]);
+ p->strings = (void *)(base + dyn[DT_STRTAB]);
+ p->dev = st.st_dev;
+ p->ino = st.st_ino;
+ p->global = 1;
+ p->refcnt = 1;
+ strcpy(p->name, name);
+
+ tail->next = p;
+ p->prev = tail;
+ tail = p;
+
+ return p;
+}
+
+static void load_deps(struct dso *p)
+{
+ size_t i;
+ for (; p; p=p->next) {
+ for (i=0; p->dynv[i]; i+=2) {
+ if (p->dynv[i] != DT_NEEDED) continue;
+ load_library(p->strings + p->dynv[i+1]);
+ }
+ }
+}
+
+static void reloc_all(struct dso *p)
+{
+ size_t dyn[DYN_CNT] = {0};
+ for (; p; p=p->next) {
+ if (p->relocated) continue;
+ decode_vec(p->dynv, dyn, DYN_CNT);
+ do_relocs(p->base, (void *)(p->base+dyn[DT_JMPREL]), dyn[DT_PLTRELSZ],
+ 2+(dyn[DT_PLTREL]==DT_RELA), p->syms, p->strings, p);
+ do_relocs(p->base, (void *)(p->base+dyn[DT_REL]), dyn[DT_RELSZ],
+ 2, p->syms, p->strings, p);
+ do_relocs(p->base, (void *)(p->base+dyn[DT_RELA]), dyn[DT_RELASZ],
+ 3, p->syms, p->strings, p);
+ }
+}
+
+void *__dynlink(int argc, char **argv, size_t *got)
+{
+ size_t *auxv, aux[AUX_CNT] = {0};
+ size_t app_dyn[DYN_CNT] = {0};
+ size_t lib_dyn[DYN_CNT] = {0};
+ size_t i;
+ Phdr *phdr;
+ struct dso lib, app;
+
+ /* Find aux vector just past environ[] */
+ for (i=argc+1; argv[i]; i++);
+ auxv = (void *)(argv+i+1);
+
+ decode_vec(auxv, aux, AUX_CNT);
+
+ /* Relocate ldso's DYNAMIC pointer and load vector */
+ decode_vec((void *)(got[0] += aux[AT_BASE]), lib_dyn, DYN_CNT);
+
+ /* Find the program image's DYNAMIC section and decode it */
+ phdr = (void *)aux[AT_PHDR];
+ for (i=aux[AT_PHNUM]; i--; phdr=(void *)((char *)phdr + aux[AT_PHENT])) {
+ if (phdr->p_type == PT_DYNAMIC) {
+ decode_vec((void *)phdr->p_vaddr, app_dyn, DYN_CNT);
+ break;
+ }
+ }
+
+ app = (struct dso){
+ .base = 0,
+ .strings = (void *)(app_dyn[DT_STRTAB]),
+ .hashtab = (void *)(app_dyn[DT_HASH]),
+ .syms = (void *)(app_dyn[DT_SYMTAB]),
+ .dynv = (void *)(phdr->p_vaddr),
+ .next = &lib
+ };
+
+ lib = (struct dso){
+ .base = (void *)aux[AT_BASE],
+ .strings = (void *)(aux[AT_BASE]+lib_dyn[DT_STRTAB]),
+ .hashtab = (void *)(aux[AT_BASE]+lib_dyn[DT_HASH]),
+ .syms = (void *)(aux[AT_BASE]+lib_dyn[DT_SYMTAB]),
+ .dynv = (void *)(got[0]),
+ .relocated = 1
+ };
+
+ /* Relocate the dynamic linker/libc */
+ do_relocs((void *)aux[AT_BASE], (void *)(aux[AT_BASE]+lib_dyn[DT_REL]),
+ lib_dyn[DT_RELSZ], 2, lib.syms, lib.strings, &app);
+ do_relocs((void *)aux[AT_BASE], (void *)(aux[AT_BASE]+lib_dyn[DT_RELA]),
+ lib_dyn[DT_RELASZ], 3, lib.syms, lib.strings, &app);
+
+ /* At this point the standard library is fully functional */
+
+ head = tail = &app;
+ libc = &lib;
+ app.next = 0;
+ load_deps(head);
+
+ reloc_all(head);
+
+ errno = 0;
+ return (void *)aux[AT_ENTRY];
+}
diff --git a/src/ldso/i386/start.s b/src/ldso/i386/start.s
new file mode 100644
index 00000000..47c2748b
--- /dev/null
+++ b/src/ldso/i386/start.s
@@ -0,0 +1,19 @@
+.text
+.global _start
+_start:
+ xorl %ebp,%ebp
+ popl %ecx
+ movl %esp,%eax
+ andl $-16,%esp
+ movl %eax,%esi
+ movl %ecx,%edi
+ pushl %ebp
+ call 1f
+1: addl $_GLOBAL_OFFSET_TABLE_,(%esp)
+ pushl %eax
+ pushl %ecx
+ call __dynlink
+ movl %esi,%esp
+ pushl %edi
+ xorl %edx,%edx
+ jmp *%eax
diff --git a/src/ldso/x86_64/start.s b/src/ldso/x86_64/start.s
new file mode 100644
index 00000000..efb27454
--- /dev/null
+++ b/src/ldso/x86_64/start.s
@@ -0,0 +1,8 @@
+.text
+.global _start
+_start:
+ mov (%rsp),%rdi
+ lea 8(%rsp),%rsi
+ lea _GLOBAL_OFFSET_TABLE_(%rip),%rdx
+ call __dynlink
+ jmp *%rax
generated by cgit v1.2.1 (git 2.18.0) at 2024-11-10 21:40:42 +0000