summaryrefslogtreecommitdiffstats
path: root/Documentation/vDSO/parse_vdso.c
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/vDSO/parse_vdso.c')
-rw-r--r--Documentation/vDSO/parse_vdso.c256
1 files changed, 0 insertions, 256 deletions
diff --git a/Documentation/vDSO/parse_vdso.c b/Documentation/vDSO/parse_vdso.c
deleted file mode 100644
index 8587020..0000000
--- a/Documentation/vDSO/parse_vdso.c
+++ /dev/null
@@ -1,256 +0,0 @@
-/*
- * parse_vdso.c: Linux reference vDSO parser
- * Written by Andrew Lutomirski, 2011.
- *
- * This code is meant to be linked in to various programs that run on Linux.
- * As such, it is available with as few restrictions as possible. This file
- * is licensed under the Creative Commons Zero License, version 1.0,
- * available at http://creativecommons.org/publicdomain/zero/1.0/legalcode
- *
- * The vDSO is a regular ELF DSO that the kernel maps into user space when
- * it starts a program. It works equally well in statically and dynamically
- * linked binaries.
- *
- * This code is tested on x86_64. In principle it should work on any 64-bit
- * architecture that has a vDSO.
- */
-
-#include <stdbool.h>
-#include <stdint.h>
-#include <string.h>
-#include <elf.h>
-
-/*
- * To use this vDSO parser, first call one of the vdso_init_* functions.
- * If you've already parsed auxv, then pass the value of AT_SYSINFO_EHDR
- * to vdso_init_from_sysinfo_ehdr. Otherwise pass auxv to vdso_init_from_auxv.
- * Then call vdso_sym for each symbol you want. For example, to look up
- * gettimeofday on x86_64, use:
- *
- * <some pointer> = vdso_sym("LINUX_2.6", "gettimeofday");
- * or
- * <some pointer> = vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
- *
- * vdso_sym will return 0 if the symbol doesn't exist or if the init function
- * failed or was not called. vdso_sym is a little slow, so its return value
- * should be cached.
- *
- * vdso_sym is threadsafe; the init functions are not.
- *
- * These are the prototypes:
- */
-extern void vdso_init_from_auxv(void *auxv);
-extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
-extern void *vdso_sym(const char *version, const char *name);
-
-
-/* And here's the code. */
-
-#ifndef __x86_64__
-# error Not yet ported to non-x86_64 architectures
-#endif
-
-static struct vdso_info
-{
- bool valid;
-
- /* Load information */
- uintptr_t load_addr;
- uintptr_t load_offset; /* load_addr - recorded vaddr */
-
- /* Symbol table */
- Elf64_Sym *symtab;
- const char *symstrings;
- Elf64_Word *bucket, *chain;
- Elf64_Word nbucket, nchain;
-
- /* Version table */
- Elf64_Versym *versym;
- Elf64_Verdef *verdef;
-} vdso_info;
-
-/* Straight from the ELF specification. */
-static unsigned long elf_hash(const unsigned char *name)
-{
- unsigned long h = 0, g;
- while (*name)
- {
- h = (h << 4) + *name++;
- if (g = h & 0xf0000000)
- h ^= g >> 24;
- h &= ~g;
- }
- return h;
-}
-
-void vdso_init_from_sysinfo_ehdr(uintptr_t base)
-{
- size_t i;
- bool found_vaddr = false;
-
- vdso_info.valid = false;
-
- vdso_info.load_addr = base;
-
- Elf64_Ehdr *hdr = (Elf64_Ehdr*)base;
- Elf64_Phdr *pt = (Elf64_Phdr*)(vdso_info.load_addr + hdr->e_phoff);
- Elf64_Dyn *dyn = 0;
-
- /*
- * We need two things from the segment table: the load offset
- * and the dynamic table.
- */
- for (i = 0; i < hdr->e_phnum; i++)
- {
- if (pt[i].p_type == PT_LOAD && !found_vaddr) {
- found_vaddr = true;
- vdso_info.load_offset = base
- + (uintptr_t)pt[i].p_offset
- - (uintptr_t)pt[i].p_vaddr;
- } else if (pt[i].p_type == PT_DYNAMIC) {
- dyn = (Elf64_Dyn*)(base + pt[i].p_offset);
- }
- }
-
- if (!found_vaddr || !dyn)
- return; /* Failed */
-
- /*
- * Fish out the useful bits of the dynamic table.
- */
- Elf64_Word *hash = 0;
- vdso_info.symstrings = 0;
- vdso_info.symtab = 0;
- vdso_info.versym = 0;
- vdso_info.verdef = 0;
- for (i = 0; dyn[i].d_tag != DT_NULL; i++) {
- switch (dyn[i].d_tag) {
- case DT_STRTAB:
- vdso_info.symstrings = (const char *)
- ((uintptr_t)dyn[i].d_un.d_ptr
- + vdso_info.load_offset);
- break;
- case DT_SYMTAB:
- vdso_info.symtab = (Elf64_Sym *)
- ((uintptr_t)dyn[i].d_un.d_ptr
- + vdso_info.load_offset);
- break;
- case DT_HASH:
- hash = (Elf64_Word *)
- ((uintptr_t)dyn[i].d_un.d_ptr
- + vdso_info.load_offset);
- break;
- case DT_VERSYM:
- vdso_info.versym = (Elf64_Versym *)
- ((uintptr_t)dyn[i].d_un.d_ptr
- + vdso_info.load_offset);
- break;
- case DT_VERDEF:
- vdso_info.verdef = (Elf64_Verdef *)
- ((uintptr_t)dyn[i].d_un.d_ptr
- + vdso_info.load_offset);
- break;
- }
- }
- if (!vdso_info.symstrings || !vdso_info.symtab || !hash)
- return; /* Failed */
-
- if (!vdso_info.verdef)
- vdso_info.versym = 0;
-
- /* Parse the hash table header. */
- vdso_info.nbucket = hash[0];
- vdso_info.nchain = hash[1];
- vdso_info.bucket = &hash[2];
- vdso_info.chain = &hash[vdso_info.nbucket + 2];
-
- /* That's all we need. */
- vdso_info.valid = true;
-}
-
-static bool vdso_match_version(Elf64_Versym ver,
- const char *name, Elf64_Word hash)
-{
- /*
- * This is a helper function to check if the version indexed by
- * ver matches name (which hashes to hash).
- *
- * The version definition table is a mess, and I don't know how
- * to do this in better than linear time without allocating memory
- * to build an index. I also don't know why the table has
- * variable size entries in the first place.
- *
- * For added fun, I can't find a comprehensible specification of how
- * to parse all the weird flags in the table.
- *
- * So I just parse the whole table every time.
- */
-
- /* First step: find the version definition */
- ver &= 0x7fff; /* Apparently bit 15 means "hidden" */
- Elf64_Verdef *def = vdso_info.verdef;
- while(true) {
- if ((def->vd_flags & VER_FLG_BASE) == 0
- && (def->vd_ndx & 0x7fff) == ver)
- break;
-
- if (def->vd_next == 0)
- return false; /* No definition. */
-
- def = (Elf64_Verdef *)((char *)def + def->vd_next);
- }
-
- /* Now figure out whether it matches. */
- Elf64_Verdaux *aux = (Elf64_Verdaux*)((char *)def + def->vd_aux);
- return def->vd_hash == hash
- && !strcmp(name, vdso_info.symstrings + aux->vda_name);
-}
-
-void *vdso_sym(const char *version, const char *name)
-{
- unsigned long ver_hash;
- if (!vdso_info.valid)
- return 0;
-
- ver_hash = elf_hash(version);
- Elf64_Word chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
-
- for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
- Elf64_Sym *sym = &vdso_info.symtab[chain];
-
- /* Check for a defined global or weak function w/ right name. */
- if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC)
- continue;
- if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL &&
- ELF64_ST_BIND(sym->st_info) != STB_WEAK)
- continue;
- if (sym->st_shndx == SHN_UNDEF)
- continue;
- if (strcmp(name, vdso_info.symstrings + sym->st_name))
- continue;
-
- /* Check symbol version. */
- if (vdso_info.versym
- && !vdso_match_version(vdso_info.versym[chain],
- version, ver_hash))
- continue;
-
- return (void *)(vdso_info.load_offset + sym->st_value);
- }
-
- return 0;
-}
-
-void vdso_init_from_auxv(void *auxv)
-{
- Elf64_auxv_t *elf_auxv = auxv;
- for (int i = 0; elf_auxv[i].a_type != AT_NULL; i++)
- {
- if (elf_auxv[i].a_type == AT_SYSINFO_EHDR) {
- vdso_init_from_sysinfo_ehdr(elf_auxv[i].a_un.a_val);
- return;
- }
- }
-
- vdso_info.valid = false;
-}