x86/vdso/doc: Make vDSO examples more portable (4ebbefd6) · Commits · 戴 / test

Documentation/vDSO/parse_vdso.c

+40 −27

Original line number	Diff line number	Diff line
		/*
		* parse_vdso.c: Linux reference vDSO parser
		* Written by Andrew Lutomirski, 2011.
		* Written by Andrew Lutomirski, 2011-2014.
		*
		* 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
		@@ -11,13 +11,14 @@
		* 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
		* This code is tested on x86. In principle it should work on any
		* architecture that has a vDSO.
		*/

		#include <stdbool.h>
		#include <stdint.h>
		#include <string.h>
		#include <limits.h>
		#include <elf.h>

		/*
		@@ -45,11 +46,18 @@ 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
		#ifndef ELF_BITS
		# if ULONG_MAX > 0xffffffffUL
		# define ELF_BITS 64
		# else
		# define ELF_BITS 32
		# endif
		#endif

		#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
		#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
		#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)

		static struct vdso_info
		{
		bool valid;
		@@ -59,14 +67,14 @@ static struct vdso_info
		uintptr_t load_offset; /* load_addr - recorded vaddr */

		/* Symbol table */
		Elf64_Sym *symtab;
		ELF(Sym) *symtab;
		const char *symstrings;
		Elf64_Word bucket, chain;
		Elf64_Word nbucket, nchain;
		ELF(Word) bucket, chain;
		ELF(Word) nbucket, nchain;

		/* Version table */
		Elf64_Versym *versym;
		Elf64_Verdef *verdef;
		ELF(Versym) *versym;
		ELF(Verdef) *verdef;
		} vdso_info;

		/* Straight from the ELF specification. */
		@@ -92,9 +100,14 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)

		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;
		ELF(Ehdr) hdr = (ELF(Ehdr))base;
		if (hdr->e_ident[EI_CLASS] !=
		(ELF_BITS == 32 ? ELFCLASS32 : ELFCLASS64)) {
		return; /* Wrong ELF class -- check ELF_BITS */
		}

		ELF(Phdr) pt = (ELF(Phdr))(vdso_info.load_addr + hdr->e_phoff);
		ELF(Dyn) *dyn = 0;

		/*
		* We need two things from the segment table: the load offset
		@@ -108,7 +121,7 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t 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);
		dyn = (ELF(Dyn)*)(base + pt[i].p_offset);
		}
		}

		@@ -118,7 +131,7 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
		/*
		* Fish out the useful bits of the dynamic table.
		*/
		Elf64_Word *hash = 0;
		ELF(Word) *hash = 0;
		vdso_info.symstrings = 0;
		vdso_info.symtab = 0;
		vdso_info.versym = 0;
		@@ -131,22 +144,22 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
		+ vdso_info.load_offset);
		break;
		case DT_SYMTAB:
		vdso_info.symtab = (Elf64_Sym *)
		vdso_info.symtab = (ELF(Sym) *)
		((uintptr_t)dyn[i].d_un.d_ptr
		+ vdso_info.load_offset);
		break;
		case DT_HASH:
		hash = (Elf64_Word *)
		hash = (ELF(Word) *)
		((uintptr_t)dyn[i].d_un.d_ptr
		+ vdso_info.load_offset);
		break;
		case DT_VERSYM:
		vdso_info.versym = (Elf64_Versym *)
		vdso_info.versym = (ELF(Versym) *)
		((uintptr_t)dyn[i].d_un.d_ptr
		+ vdso_info.load_offset);
		break;
		case DT_VERDEF:
		vdso_info.verdef = (Elf64_Verdef *)
		vdso_info.verdef = (ELF(Verdef) *)
		((uintptr_t)dyn[i].d_un.d_ptr
		+ vdso_info.load_offset);
		break;
		@@ -168,8 +181,8 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
		vdso_info.valid = true;
		}

		static bool vdso_match_version(Elf64_Versym ver,
		const char *name, Elf64_Word hash)
		static bool vdso_match_version(ELF(Versym) ver,
		const char *name, ELF(Word) hash)
		{
		/*
		* This is a helper function to check if the version indexed by
		@@ -188,7 +201,7 @@ static bool vdso_match_version(Elf64_Versym ver,

		/* First step: find the version definition */
		ver &= 0x7fff; /* Apparently bit 15 means "hidden" */
		Elf64_Verdef *def = vdso_info.verdef;
		ELF(Verdef) *def = vdso_info.verdef;
		while(true) {
		if ((def->vd_flags & VER_FLG_BASE) == 0
		&& (def->vd_ndx & 0x7fff) == ver)
		@@ -197,11 +210,11 @@ static bool vdso_match_version(Elf64_Versym ver,
		if (def->vd_next == 0)
		return false; /* No definition. */

		def = (Elf64_Verdef )((char )def + def->vd_next);
		def = (ELF(Verdef) )((char )def + def->vd_next);
		}

		/* Now figure out whether it matches. */
		Elf64_Verdaux aux = (Elf64_Verdaux)((char *)def + def->vd_aux);
		ELF(Verdaux) aux = (ELF(Verdaux))((char *)def + def->vd_aux);
		return def->vd_hash == hash
		&& !strcmp(name, vdso_info.symstrings + aux->vda_name);
		}
		@@ -213,10 +226,10 @@ void vdso_sym(const char version, const char *name)
		return 0;

		ver_hash = elf_hash(version);
		Elf64_Word chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
		ELF(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];
		ELF(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)
		@@ -243,7 +256,7 @@ void vdso_sym(const char version, const char *name)

		void vdso_init_from_auxv(void *auxv)
		{
		Elf64_auxv_t *elf_auxv = auxv;
		ELF(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) {

Documentation/vDSO/vdso_standalone_test_x86.c

+31 −14

Original line number	Diff line number	Diff line
		/*
		* vdso_test.c: Sample code to test parse_vdso.c on x86_64
		* Copyright (c) 2011 Andy Lutomirski
		* vdso_test.c: Sample code to test parse_vdso.c on x86
		* Copyright (c) 2011-2014 Andy Lutomirski
		* Subject to the GNU General Public License, version 2
		*
		* You can amuse yourself by compiling with:
		* gcc -std=gnu99 -nostdlib
		* -Os -fno-asynchronous-unwind-tables -flto
		* -Os -fno-asynchronous-unwind-tables -flto -lgcc_s
		* vdso_standalone_test_x86.c parse_vdso.c
		* to generate a small binary with no dependencies at all.
		* to generate a small binary. On x86_64, you can omit -lgcc_s
		* if you want the binary to be completely standalone.
		*/

		#include <sys/syscall.h>
		@@ -35,21 +36,31 @@ int strcmp(const char a, const char b)
		return 0;
		}

		/* ...and two syscalls. This is x86_64-specific. */
		static inline long linux_write(int fd, const void *data, size_t len)
		/* ...and two syscalls. This is x86-specific. */
		static inline long x86_syscall3(long nr, long a0, long a1, long a2)
		{

		long ret;
		asm volatile ("syscall" : "=a" (ret) : "a" (__NR_write),
		"D" (fd), "S" (data), "d" (len) :
		#ifdef __x86_64__
		asm volatile ("syscall" : "=a" (ret) : "a" (nr),
		"D" (a0), "S" (a1), "d" (a2) :
		"cc", "memory", "rcx",
		"r8", "r9", "r10", "r11" );
		#else
		asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
		"b" (a0), "c" (a1), "d" (a2) :
		"cc", "memory" );
		#endif
		return ret;
		}

		static inline long linux_write(int fd, const void *data, size_t len)
		{
		return x86_syscall3(__NR_write, fd, (long)data, (long)len);
		}

		static inline void linux_exit(int code)
		{
		asm volatile ("syscall" : : "a" (__NR_exit), "D" (code));
		x86_syscall3(__NR_exit, code, 0, 0);
		}

		void to_base10(char *lastdig, uint64_t n)
		@@ -106,6 +117,12 @@ asm (
		".global _start\n"
		".type _start,@function\n"
		"_start:\n\t"
		#ifdef __x86_64__
		"mov %rsp,%rdi\n\t"
		"jmp c_main"
		#else
		"push %esp\n\t"
		"call c_main\n\t"
		"int $3"
		#endif
		);

Documentation/vDSO/vdso_test.c

0 → 100644

+52 −0

Original line number	Diff line number	Diff line
		/*
		* vdso_test.c: Sample code to test parse_vdso.c
		* Copyright (c) 2014 Andy Lutomirski
		* Subject to the GNU General Public License, version 2
		*
		* Compile with:
		* gcc -std=gnu99 vdso_test.c parse_vdso.c
		*
		* Tested on x86, 32-bit and 64-bit. It may work on other architectures, too.
		*/

		#include <stdint.h>
		#include <elf.h>
		#include <stdio.h>
		#include <sys/auxv.h>
		#include <sys/time.h>

		extern void vdso_sym(const char version, const char *name);
		extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
		extern void vdso_init_from_auxv(void *auxv);

		int main(int argc, char **argv)
		{
		unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
		if (!sysinfo_ehdr) {
		printf("AT_SYSINFO_EHDR is not present!\n");
		return 0;
		}

		vdso_init_from_sysinfo_ehdr(getauxval(AT_SYSINFO_EHDR));

		/* Find gettimeofday. */
		typedef long (gtod_t)(struct timeval tv, struct timezone *tz);
		gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");

		if (!gtod) {
		printf("Could not find __vdso_gettimeofday\n");
		return 1;
		}

		struct timeval tv;
		long ret = gtod(&tv, 0);

		if (ret == 0) {
		printf("The time is %lld.%06lld\n",
		(long long)tv.tv_sec, (long long)tv.tv_usec);
		} else {
		printf("__vdso_gettimeofday failed\n");
		}

		return 0;
		}

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