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x86/vdso/doc: Make vDSO examples more portable

Bladeren bron 
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
2014-06-12 17:53:10 -07:00
gecommit door H. Peter Anvin
bovenliggende 6e8f21584a
commit 4ebbefd6b9
3 gewijzigde bestanden met toevoegingen van 123 en 41 verwijderingen
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67
Documentation/vDSO/parse_vdso.c
Bestand weergeven

@@ -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 <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) {