x86/vdso/doc: Make vDSO examples more portable
This adds a new vdso_test.c that's written entirely in C. It also makes all of the vDSO examples work on 32-bit x86. Cc: Stefani Seibold <stefani@seibold.net> Signed-off-by: Andy Lutomirski <luto@amacapital.net> Link: http://lkml.kernel.org/r/62b701fc44b79f118ac2b2d64d19965fc5c291fb.1402620737.git.luto@amacapital.net Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Andy Lutomirski
H. Peter Anvin
parent
6e8f21584a
commit
4ebbefd6b9
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@ -1,6 +1,6 @@
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/*
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* parse_vdso.c: Linux reference vDSO parser
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* Written by Andrew Lutomirski, 2011.
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* Written by Andrew Lutomirski, 2011-2014.
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*
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* This code is meant to be linked in to various programs that run on Linux.
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* As such, it is available with as few restrictions as possible. This file
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@ -11,13 +11,14 @@
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* it starts a program. It works equally well in statically and dynamically
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* linked binaries.
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*
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* This code is tested on x86_64. In principle it should work on any 64-bit
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* This code is tested on x86. In principle it should work on any
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* architecture that has a vDSO.
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*/
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#include <stdbool.h>
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#include <stdint.h>
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#include <string.h>
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#include <limits.h>
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#include <elf.h>
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/*
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@ -45,11 +46,18 @@ extern void *vdso_sym(const char *version, const char *name);
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/* And here's the code. */
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#ifndef __x86_64__
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# error Not yet ported to non-x86_64 architectures
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#ifndef ELF_BITS
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# if ULONG_MAX > 0xffffffffUL
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# define ELF_BITS 64
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# else
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# define ELF_BITS 32
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# endif
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#endif
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#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
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#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
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#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
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static struct vdso_info
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{
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bool valid;
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@ -59,14 +67,14 @@ static struct vdso_info
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uintptr_t load_offset; /* load_addr - recorded vaddr */
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/* Symbol table */
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Elf64_Sym *symtab;
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ELF(Sym) *symtab;
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const char *symstrings;
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Elf64_Word *bucket, *chain;
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Elf64_Word nbucket, nchain;
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ELF(Word) *bucket, *chain;
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ELF(Word) nbucket, nchain;
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/* Version table */
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Elf64_Versym *versym;
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Elf64_Verdef *verdef;
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ELF(Versym) *versym;
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ELF(Verdef) *verdef;
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} vdso_info;
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/* Straight from the ELF specification. */
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@ -92,9 +100,14 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
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vdso_info.load_addr = base;
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Elf64_Ehdr *hdr = (Elf64_Ehdr*)base;
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Elf64_Phdr *pt = (Elf64_Phdr*)(vdso_info.load_addr + hdr->e_phoff);
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Elf64_Dyn *dyn = 0;
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ELF(Ehdr) *hdr = (ELF(Ehdr)*)base;
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if (hdr->e_ident[EI_CLASS] !=
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(ELF_BITS == 32 ? ELFCLASS32 : ELFCLASS64)) {
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return; /* Wrong ELF class -- check ELF_BITS */
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}
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ELF(Phdr) *pt = (ELF(Phdr)*)(vdso_info.load_addr + hdr->e_phoff);
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ELF(Dyn) *dyn = 0;
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/*
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* We need two things from the segment table: the load offset
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@ -108,7 +121,7 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
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+ (uintptr_t)pt[i].p_offset
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- (uintptr_t)pt[i].p_vaddr;
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} else if (pt[i].p_type == PT_DYNAMIC) {
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dyn = (Elf64_Dyn*)(base + pt[i].p_offset);
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dyn = (ELF(Dyn)*)(base + pt[i].p_offset);
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}
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}
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@ -118,7 +131,7 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
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/*
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* Fish out the useful bits of the dynamic table.
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*/
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Elf64_Word *hash = 0;
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ELF(Word) *hash = 0;
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vdso_info.symstrings = 0;
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vdso_info.symtab = 0;
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vdso_info.versym = 0;
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@ -131,22 +144,22 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
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+ vdso_info.load_offset);
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break;
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case DT_SYMTAB:
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vdso_info.symtab = (Elf64_Sym *)
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vdso_info.symtab = (ELF(Sym) *)
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((uintptr_t)dyn[i].d_un.d_ptr
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+ vdso_info.load_offset);
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break;
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case DT_HASH:
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hash = (Elf64_Word *)
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hash = (ELF(Word) *)
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((uintptr_t)dyn[i].d_un.d_ptr
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+ vdso_info.load_offset);
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break;
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case DT_VERSYM:
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vdso_info.versym = (Elf64_Versym *)
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vdso_info.versym = (ELF(Versym) *)
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((uintptr_t)dyn[i].d_un.d_ptr
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+ vdso_info.load_offset);
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break;
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case DT_VERDEF:
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vdso_info.verdef = (Elf64_Verdef *)
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vdso_info.verdef = (ELF(Verdef) *)
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((uintptr_t)dyn[i].d_un.d_ptr
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+ vdso_info.load_offset);
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break;
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@ -168,8 +181,8 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
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vdso_info.valid = true;
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}
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static bool vdso_match_version(Elf64_Versym ver,
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const char *name, Elf64_Word hash)
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static bool vdso_match_version(ELF(Versym) ver,
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const char *name, ELF(Word) hash)
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{
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/*
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* This is a helper function to check if the version indexed by
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@ -188,7 +201,7 @@ static bool vdso_match_version(Elf64_Versym ver,
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/* First step: find the version definition */
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ver &= 0x7fff; /* Apparently bit 15 means "hidden" */
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Elf64_Verdef *def = vdso_info.verdef;
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ELF(Verdef) *def = vdso_info.verdef;
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while(true) {
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if ((def->vd_flags & VER_FLG_BASE) == 0
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&& (def->vd_ndx & 0x7fff) == ver)
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@ -197,11 +210,11 @@ static bool vdso_match_version(Elf64_Versym ver,
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if (def->vd_next == 0)
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return false; /* No definition. */
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def = (Elf64_Verdef *)((char *)def + def->vd_next);
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def = (ELF(Verdef) *)((char *)def + def->vd_next);
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}
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/* Now figure out whether it matches. */
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Elf64_Verdaux *aux = (Elf64_Verdaux*)((char *)def + def->vd_aux);
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ELF(Verdaux) *aux = (ELF(Verdaux)*)((char *)def + def->vd_aux);
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return def->vd_hash == hash
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&& !strcmp(name, vdso_info.symstrings + aux->vda_name);
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}
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@ -213,10 +226,10 @@ void *vdso_sym(const char *version, const char *name)
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return 0;
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ver_hash = elf_hash(version);
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Elf64_Word chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
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ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
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for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
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Elf64_Sym *sym = &vdso_info.symtab[chain];
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ELF(Sym) *sym = &vdso_info.symtab[chain];
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/* Check for a defined global or weak function w/ right name. */
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if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC)
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@ -243,7 +256,7 @@ void *vdso_sym(const char *version, const char *name)
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void vdso_init_from_auxv(void *auxv)
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{
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Elf64_auxv_t *elf_auxv = auxv;
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ELF(auxv_t) *elf_auxv = auxv;
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for (int i = 0; elf_auxv[i].a_type != AT_NULL; i++)
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{
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if (elf_auxv[i].a_type == AT_SYSINFO_EHDR) {
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@ -1,13 +1,14 @@
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/*
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* vdso_test.c: Sample code to test parse_vdso.c on x86_64
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* Copyright (c) 2011 Andy Lutomirski
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* vdso_test.c: Sample code to test parse_vdso.c on x86
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* Copyright (c) 2011-2014 Andy Lutomirski
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* Subject to the GNU General Public License, version 2
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*
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* You can amuse yourself by compiling with:
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* gcc -std=gnu99 -nostdlib
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* -Os -fno-asynchronous-unwind-tables -flto
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* -Os -fno-asynchronous-unwind-tables -flto -lgcc_s
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* vdso_standalone_test_x86.c parse_vdso.c
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* to generate a small binary with no dependencies at all.
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* to generate a small binary. On x86_64, you can omit -lgcc_s
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* if you want the binary to be completely standalone.
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*/
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#include <sys/syscall.h>
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@ -35,21 +36,31 @@ int strcmp(const char *a, const char *b)
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return 0;
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}
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/* ...and two syscalls. This is x86_64-specific. */
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static inline long linux_write(int fd, const void *data, size_t len)
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/* ...and two syscalls. This is x86-specific. */
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static inline long x86_syscall3(long nr, long a0, long a1, long a2)
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{
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long ret;
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asm volatile ("syscall" : "=a" (ret) : "a" (__NR_write),
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"D" (fd), "S" (data), "d" (len) :
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#ifdef __x86_64__
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asm volatile ("syscall" : "=a" (ret) : "a" (nr),
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"D" (a0), "S" (a1), "d" (a2) :
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"cc", "memory", "rcx",
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"r8", "r9", "r10", "r11" );
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#else
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asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
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"b" (a0), "c" (a1), "d" (a2) :
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"cc", "memory" );
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#endif
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return ret;
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}
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static inline long linux_write(int fd, const void *data, size_t len)
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{
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return x86_syscall3(__NR_write, fd, (long)data, (long)len);
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}
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static inline void linux_exit(int code)
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{
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asm volatile ("syscall" : : "a" (__NR_exit), "D" (code));
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x86_syscall3(__NR_exit, code, 0, 0);
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}
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void to_base10(char *lastdig, uint64_t n)
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asm (
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".text\n"
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".global _start\n"
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".type _start,@function\n"
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"_start:\n\t"
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"mov %rsp,%rdi\n\t"
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"jmp c_main"
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".type _start,@function\n"
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"_start:\n\t"
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#ifdef __x86_64__
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"mov %rsp,%rdi\n\t"
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"jmp c_main"
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#else
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"push %esp\n\t"
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"call c_main\n\t"
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"int $3"
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#endif
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);
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@ -0,0 +1,52 @@
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/*
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* vdso_test.c: Sample code to test parse_vdso.c
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* Copyright (c) 2014 Andy Lutomirski
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* Subject to the GNU General Public License, version 2
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*
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* Compile with:
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* gcc -std=gnu99 vdso_test.c parse_vdso.c
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*
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* Tested on x86, 32-bit and 64-bit. It may work on other architectures, too.
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*/
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#include <stdint.h>
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#include <elf.h>
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#include <stdio.h>
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#include <sys/auxv.h>
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#include <sys/time.h>
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extern void *vdso_sym(const char *version, const char *name);
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extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
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extern void vdso_init_from_auxv(void *auxv);
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int main(int argc, char **argv)
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{
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unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
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if (!sysinfo_ehdr) {
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printf("AT_SYSINFO_EHDR is not present!\n");
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return 0;
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}
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vdso_init_from_sysinfo_ehdr(getauxval(AT_SYSINFO_EHDR));
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/* Find gettimeofday. */
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typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
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gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
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if (!gtod) {
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printf("Could not find __vdso_gettimeofday\n");
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return 1;
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}
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struct timeval tv;
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long ret = gtod(&tv, 0);
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if (ret == 0) {
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printf("The time is %lld.%06lld\n",
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(long long)tv.tv_sec, (long long)tv.tv_usec);
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} else {
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printf("__vdso_gettimeofday failed\n");
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}
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return 0;
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}
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