From 4ebbefd6b93c34d6da0d950b1d2e0dcca2f1e6ef Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 12 Jun 2014 17:53:10 -0700 Subject: [PATCH] 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 Signed-off-by: Andy Lutomirski Link: http://lkml.kernel.org/r/62b701fc44b79f118ac2b2d64d19965fc5c291fb.1402620737.git.luto@amacapital.net Signed-off-by: H. Peter Anvin --- Documentation/vDSO/parse_vdso.c | 67 +++++++++++-------- Documentation/vDSO/vdso_standalone_test_x86.c | 45 +++++++++---- Documentation/vDSO/vdso_test.c | 52 ++++++++++++++ 3 files changed, 123 insertions(+), 41 deletions(-) create mode 100644 Documentation/vDSO/vdso_test.c diff --git a/Documentation/vDSO/parse_vdso.c b/Documentation/vDSO/parse_vdso.c index 85870208edcf..1dbb4b87268f 100644 --- a/Documentation/vDSO/parse_vdso.c +++ b/Documentation/vDSO/parse_vdso.c @@ -1,6 +1,6 @@ /* * 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 #include #include +#include #include /* @@ -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) { diff --git a/Documentation/vDSO/vdso_standalone_test_x86.c b/Documentation/vDSO/vdso_standalone_test_x86.c index 1523f5d681f3..d46240265c50 100644 --- a/Documentation/vDSO/vdso_standalone_test_x86.c +++ b/Documentation/vDSO/vdso_standalone_test_x86.c @@ -1,13 +1,14 @@ /* - * 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 @@ -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) @@ -104,8 +115,14 @@ __attribute__((externally_visible)) void c_main(void **stack) asm ( ".text\n" ".global _start\n" - ".type _start,@function\n" - "_start:\n\t" - "mov %rsp,%rdi\n\t" - "jmp c_main" + ".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 ); diff --git a/Documentation/vDSO/vdso_test.c b/Documentation/vDSO/vdso_test.c new file mode 100644 index 000000000000..8daeb7d7032c --- /dev/null +++ b/Documentation/vDSO/vdso_test.c @@ -0,0 +1,52 @@ +/* + * 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 +#include +#include +#include +#include + +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; +} -- 2.20.1