glibc added support for DT_GNU_HASH in 2006 and DT_HASH has been
obsoleted for more than one decade in many Linux distributions.
Many vDSOs support DT_GNU_HASH. This patch adds selftests support.
Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
Tested-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
--
Changes from v1:
* fix style of a multi-line comment. ignore false positive suggestions from checkpath.pl: `ELF(Word) *`
---
tools/testing/selftests/vDSO/parse_vdso.c | 105 ++++++++++++++++------
1 file changed, 79 insertions(+), 26 deletions(-)
diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
index 4ae417372e9e..dbc946dee4b1 100644
--- a/tools/testing/selftests/vDSO/parse_vdso.c
+++ b/tools/testing/selftests/vDSO/parse_vdso.c
@@ -47,6 +47,7 @@ static struct vdso_info
/* Symbol table */
ELF(Sym) *symtab;
const char *symstrings;
+ ELF(Word) *gnu_hash;
ELF(Word) *bucket, *chain;
ELF(Word) nbucket, nchain;
@@ -75,6 +76,16 @@ static unsigned long elf_hash(const char *name)
return h;
}
+static uint32_t gnu_hash(const char *name)
+{
+ const unsigned char *s = (void *)name;
+ uint32_t h = 5381;
+
+ for (; *s; s++)
+ h += h * 32 + *s;
+ return h;
+}
+
void vdso_init_from_sysinfo_ehdr(uintptr_t base)
{
size_t i;
@@ -117,6 +128,7 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
*/
ELF(Word) *hash = 0;
vdso_info.symstrings = 0;
+ vdso_info.gnu_hash = 0;
vdso_info.symtab = 0;
vdso_info.versym = 0;
vdso_info.verdef = 0;
@@ -137,6 +149,11 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
((uintptr_t)dyn[i].d_un.d_ptr
+ vdso_info.load_offset);
break;
+ case DT_GNU_HASH:
+ vdso_info.gnu_hash =
+ (ELF(Word) *)((uintptr_t)dyn[i].d_un.d_ptr +
+ vdso_info.load_offset);
+ break;
case DT_VERSYM:
vdso_info.versym = (ELF(Versym) *)
((uintptr_t)dyn[i].d_un.d_ptr
@@ -149,17 +166,26 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
break;
}
}
- if (!vdso_info.symstrings || !vdso_info.symtab || !hash)
+ if (!vdso_info.symstrings || !vdso_info.symtab ||
+ (!hash && !vdso_info.gnu_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];
+ if (vdso_info.gnu_hash) {
+ vdso_info.nbucket = vdso_info.gnu_hash[0];
+ /* The bucket array is located after the header (4 uint32) and the bloom
+ * filter (size_t array of gnu_hash[2] elements). */
+ vdso_info.bucket = vdso_info.gnu_hash + 4 +
+ sizeof(size_t) / 4 * vdso_info.gnu_hash[2];
+ } else {
+ 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;
@@ -203,6 +229,26 @@ static bool vdso_match_version(ELF(Versym) ver,
&& !strcmp(name, vdso_info.symstrings + aux->vda_name);
}
+static bool check_sym(ELF(Sym) *sym, ELF(Word) i, const char *name,
+ const char *version, unsigned long ver_hash)
+{
+ /* Check for a defined global or weak function w/ right name. */
+ if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC)
+ return false;
+ if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL &&
+ ELF64_ST_BIND(sym->st_info) != STB_WEAK)
+ return false;
+ if (strcmp(name, vdso_info.symstrings + sym->st_name))
+ return false;
+
+ /* Check symbol version. */
+ if (vdso_info.versym &&
+ !vdso_match_version(vdso_info.versym[i], version, ver_hash))
+ return false;
+
+ return true;
+}
+
void *vdso_sym(const char *version, const char *name)
{
unsigned long ver_hash;
@@ -210,29 +256,36 @@ void *vdso_sym(const char *version, const char *name)
return 0;
ver_hash = elf_hash(version);
- ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
+ ELF(Word) i;
- for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
- ELF(Sym) *sym = &vdso_info.symtab[chain];
+ if (vdso_info.gnu_hash) {
+ uint32_t h1 = gnu_hash(name), h2, *hashval;
- /* 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);
+ i = vdso_info.bucket[h1 % vdso_info.nbucket];
+ if (i == 0)
+ return 0;
+ h1 |= 1;
+ hashval = vdso_info.bucket + vdso_info.nbucket +
+ (i - vdso_info.gnu_hash[1]);
+ for (;; i++) {
+ ELF(Sym) *sym = &vdso_info.symtab[i];
+ h2 = *hashval++;
+ if (h1 == (h2 | 1) &&
+ check_sym(sym, i, name, version, ver_hash))
+ return (void *)(vdso_info.load_offset +
+ sym->st_value);
+ if (h2 & 1)
+ break;
+ }
+ } else {
+ i = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
+ for (; i; i = vdso_info.chain[i]) {
+ ELF(Sym) *sym = &vdso_info.symtab[i];
+ if (sym->st_shndx != SHN_UNDEF &&
+ check_sym(sym, i, name, version, ver_hash))
+ return (void *)(vdso_info.load_offset +
+ sym->st_value);
+ }
}
return 0;
--
2.46.0.662.g92d0881bb0-goog
