Implement DT_GNU_HASH
DT_GNU_HASH serves the same purpose as DT_HASH, however it is a distinct and faster apprach implemented and designed in the GNU toolchain in 2006. DT_GNU_HASH is preferred whenever available. Original GNU benchmarks claim 50% faster dynamic linking time. https://www.sourceware.org/ml/binutils/2006-06/msg00418.html Code based on FreeBSD and OpenBSD, both were based on DragonFlyBSD.
This commit is contained in:
kamil
parent
4e9bea3d5d
commit
e8e477017a
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@ -1,4 +1,4 @@
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/* $NetBSD: headers.c,v 1.65 2018/12/30 11:55:15 martin Exp $ */
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/* $NetBSD: headers.c,v 1.66 2020/02/29 04:24:33 kamil Exp $ */
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/*
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* Copyright 1996 John D. Polstra.
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@ -40,7 +40,7 @@
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#include <sys/cdefs.h>
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#ifndef lint
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__RCSID("$NetBSD: headers.c,v 1.65 2018/12/30 11:55:15 martin Exp $");
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__RCSID("$NetBSD: headers.c,v 1.66 2020/02/29 04:24:33 kamil Exp $");
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#endif /* not lint */
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#include <err.h>
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@ -166,26 +166,87 @@ _rtld_digest_dynamic(const char *execname, Obj_Entry *obj)
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case DT_HASH:
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{
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uint32_t nbuckets, nchains;
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const Elf_Symindx *hashtab = (const Elf_Symindx *)
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(obj->relocbase + dynp->d_un.d_ptr);
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if (hashtab[0] > UINT32_MAX)
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obj->nbuckets = UINT32_MAX;
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nbuckets = UINT32_MAX;
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else
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obj->nbuckets = hashtab[0];
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obj->nchains = hashtab[1];
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nbuckets = hashtab[0];
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obj->nbuckets = nbuckets;
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obj->nchains = (nchains = hashtab[1]);
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obj->buckets = hashtab + 2;
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obj->chains = obj->buckets + obj->nbuckets;
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/* Validity check */
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if (!obj->buckets || !nbuckets || !nchains)
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continue;
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obj->sysv_hash = true;
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/*
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* Should really be in _rtld_relocate_objects,
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* but _rtld_symlook_obj might be used before.
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*/
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if (obj->nbuckets) {
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fast_divide32_prepare(obj->nbuckets,
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&obj->nbuckets_m,
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&obj->nbuckets_s1,
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&obj->nbuckets_s2);
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}
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fast_divide32_prepare(obj->nbuckets,
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&obj->nbuckets_m,
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&obj->nbuckets_s1,
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&obj->nbuckets_s2);
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}
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break;
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case DT_GNU_HASH:
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{
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uint32_t nmaskwords;
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uint32_t nbuckets, symndx;
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int bloom_size32;
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bool nmw_power2;
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const Elf_Symindx *hashtab = (const Elf_Symindx *)
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(obj->relocbase + dynp->d_un.d_ptr);
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if (hashtab[0] > UINT32_MAX)
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nbuckets = UINT32_MAX;
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else
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nbuckets = hashtab[0];
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obj->nbuckets_gnu = nbuckets;
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nmaskwords = hashtab[2];
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bloom_size32 = nmaskwords * (ELFSIZE / 32);
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obj->buckets_gnu = hashtab + 4 + bloom_size32;
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nmw_power2 = powerof2(nmaskwords);
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/* Validity check */
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if (!nmw_power2 || !nbuckets || !obj->buckets_gnu)
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continue;
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obj->gnu_hash = true;
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obj->mask_bm_gnu = nmaskwords - 1;
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obj->symndx_gnu = (symndx = hashtab[1]);
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obj->shift2_gnu = hashtab[3];
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obj->bloom_gnu = (const Elf_Addr *)(hashtab + 4);
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obj->chains_gnu = obj->buckets_gnu + nbuckets - symndx;
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/*
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* Should really be in _rtld_relocate_objects,
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* but _rtld_symlook_obj might be used before.
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*/
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fast_divide32_prepare(nbuckets,
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&obj->nbuckets_m_gnu,
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&obj->nbuckets_s1_gnu,
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&obj->nbuckets_s2_gnu);
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dbg(("found GNU Hash: buckets=%p "
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"nbuckets=%lu chains=%p nchains=%u "
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"bloom=%p mask_bm=%u shift2=%u "
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"symndx=%u",
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obj->buckets_gnu, obj->nbuckets_gnu,
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obj->chains_gnu, obj->nchains_gnu,
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obj->bloom_gnu, obj->mask_bm_gnu,
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obj->shift2_gnu, obj->symndx_gnu));
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}
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break;
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@ -352,6 +413,26 @@ _rtld_digest_dynamic(const char *execname, Obj_Entry *obj)
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obj->relalim = obj->pltrela;
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}
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/* If the ELF Hash is present, "nchains" is the same in both hashes. */
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if (!obj->sysv_hash && obj->gnu_hash) {
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uint_fast32_t i, nbucket, symndx;
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/* Otherwise, count the entries from the GNU Hash chain. */
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nbucket = obj->nbuckets_gnu;
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symndx = obj->symndx_gnu;
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for (i = 0; i < nbucket; i++) {
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Elf_Word bkt = obj->buckets_gnu[i];
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if (bkt == 0)
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continue;
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const uint32_t *hashval = &obj->chains_gnu[bkt];
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do {
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symndx++;
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} while ((*hashval++ & 1U) == 0);
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}
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obj->nchains_gnu = (uint32_t)symndx;
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}
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#ifdef RTLD_LOADER
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if (init != 0)
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obj->init = (Elf_Addr) obj->relocbase + init;
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@ -1,4 +1,4 @@
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/* $NetBSD: reloc.c,v 1.115 2020/02/29 04:23:05 kamil Exp $ */
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/* $NetBSD: reloc.c,v 1.116 2020/02/29 04:24:33 kamil Exp $ */
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/*
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* Copyright 1996 John D. Polstra.
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@ -39,7 +39,7 @@
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#include <sys/cdefs.h>
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#ifndef lint
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__RCSID("$NetBSD: reloc.c,v 1.115 2020/02/29 04:23:05 kamil Exp $");
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__RCSID("$NetBSD: reloc.c,v 1.116 2020/02/29 04:24:33 kamil Exp $");
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#endif /* not lint */
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#include <err.h>
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@ -174,9 +174,8 @@ _rtld_relocate_objects(Obj_Entry *first, bool bind_now)
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int ok = 1;
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for (obj = first; obj != NULL; obj = obj->next) {
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if (obj->nbuckets == 0 || obj->nchains == 0 ||
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obj->buckets == NULL || obj->symtab == NULL ||
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obj->strtab == NULL) {
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if ((!obj->sysv_hash && !obj->gnu_hash) ||
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obj->symtab == NULL || obj->strtab == NULL) {
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_rtld_error("%s: Shared object has no run-time"
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" symbol table", obj->path);
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return -1;
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@ -1,4 +1,4 @@
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/* $NetBSD: rtld.h,v 1.137 2020/02/29 04:23:05 kamil Exp $ */
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/* $NetBSD: rtld.h,v 1.138 2020/02/29 04:24:33 kamil Exp $ */
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/*
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* Copyright 1996 John D. Polstra.
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@ -181,6 +181,7 @@ typedef struct Struct_Obj_Entry {
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Elf_Word gotsym; /* First dynamic symbol in GOT */
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#endif
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/* SysV Hash fields */
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const Elf_Symindx *buckets; /* Hash table buckets array */
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unsigned long unused1; /* Used to be nbuckets */
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const Elf_Symindx *chains; /* Hash table chain array */
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@ -221,7 +222,9 @@ typedef struct Struct_Obj_Entry {
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tls_done:1, /* True if static TLS offset
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* has been allocated */
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#endif
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ref_nodel:1; /* Refcount increased to prevent dlclose */
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ref_nodel:1, /* Refcount increased to prevent dlclose */
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sysv_hash:1, /* SysV Hash available */
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gnu_hash:1; /* GNU Hash available */
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struct link_map linkmap; /* for GDB */
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@ -234,10 +237,25 @@ typedef struct Struct_Obj_Entry {
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void *ehdr;
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/* SysV Hash fields */
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uint32_t nbuckets; /* Number of buckets */
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uint32_t nbuckets_m; /* Precomputed for fast remainder */
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uint8_t nbuckets_s1;
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uint8_t nbuckets_s2;
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/* GNU Hash fields */
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const uint32_t *buckets_gnu; /* Hash table buckets array */
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uint32_t nbuckets_gnu; /* Number of GNU hash buckets */
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uint32_t nbuckets_m_gnu; /* Precomputed for fast remainder */
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uint8_t nbuckets_s1_gnu;
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uint8_t nbuckets_s2_gnu;
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const uint32_t *chains_gnu; /* Hash table chain array */
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#define nchains_gnu nchains /* Number of symbols, shared with SysV Hash */
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const Elf_Addr *bloom_gnu;
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uint32_t symndx_gnu; /* First accessible symbol on dynsym table */
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uint32_t mask_bm_gnu; /* Bloom filter words - 1 (bitmask) */
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uint32_t shift2_gnu; /* Bloom filter shift count */
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size_t pathlen; /* Pathname length */
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SIMPLEQ_HEAD(, Struct_Name_Entry) names; /* List of names for this
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* object we know about. */
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@ -1,4 +1,4 @@
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/* $NetBSD: symbol.c,v 1.71 2020/02/29 04:23:05 kamil Exp $ */
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/* $NetBSD: symbol.c,v 1.72 2020/02/29 04:24:33 kamil Exp $ */
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/*
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* Copyright 1996 John D. Polstra.
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@ -40,7 +40,7 @@
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#include <sys/cdefs.h>
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#ifndef lint
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__RCSID("$NetBSD: symbol.c,v 1.71 2020/02/29 04:23:05 kamil Exp $");
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__RCSID("$NetBSD: symbol.c,v 1.72 2020/02/29 04:24:33 kamil Exp $");
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#endif /* not lint */
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#include <err.h>
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@ -327,18 +327,17 @@ _rtld_symlook_obj_matched_symbol(const char *name,
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* the given name. Returns a pointer to the symbol, or NULL if no
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* definition was found.
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*
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* The symbol's hash value is passed in for efficiency reasons; that
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* eliminates many recomputations of the hash value.
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* SysV Hash version.
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*/
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const Elf_Sym *
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_rtld_symlook_obj(const char *name, Elf_Hash *hash,
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static const Elf_Sym *
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_rtld_symlook_obj_sysv(const char *name, unsigned long hash,
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const Obj_Entry *obj, u_int flags, const Ver_Entry *ventry)
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{
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unsigned long symnum;
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const Elf_Sym *vsymp = NULL;
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int vcount = 0;
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for (symnum = obj->buckets[fast_remainder32(hash->sysv, obj->nbuckets,
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for (symnum = obj->buckets[fast_remainder32(hash, obj->nbuckets,
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obj->nbuckets_m, obj->nbuckets_s1, obj->nbuckets_s2)];
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symnum != ELF_SYM_UNDEFINED;
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symnum = obj->chains[symnum]) {
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return NULL;
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}
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/*
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* Search the symbol table of a single shared object for a symbol of
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* the given name. Returns a pointer to the symbol, or NULL if no
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* definition was found.
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*
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* GNU Hash version.
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*/
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static const Elf_Sym *
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_rtld_symlook_obj_gnu(const char *name, unsigned long hash,
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const Obj_Entry *obj, u_int flags, const Ver_Entry *ventry)
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{
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unsigned long symnum;
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const Elf_Sym *vsymp = NULL;
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const Elf32_Word *hashval;
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Elf_Addr bloom_word;
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Elf32_Word bucket;
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int vcount = 0;
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unsigned int h1, h2;
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/* Pick right bitmask word from Bloom filter array */
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bloom_word = obj->bloom_gnu[(hash / ELFSIZE) & obj->mask_bm_gnu];
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/* Calculate modulus word size of gnu hash and its derivative */
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h1 = hash & (ELFSIZE - 1);
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h2 = ((hash >> obj->shift2_gnu) & (ELFSIZE - 1));
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/* Filter out the "definitely not in set" queries */
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if (((bloom_word >> h1) & (bloom_word >> h2) & 1) == 0)
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return NULL;
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/* Locate hash chain and corresponding value element*/
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bucket = obj->buckets_gnu[fast_remainder32(hash, obj->nbuckets_gnu,
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obj->nbuckets_m_gnu, obj->nbuckets_s1_gnu, obj->nbuckets_s2_gnu)];
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if (bucket == 0)
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return NULL;
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hashval = &obj->chains_gnu[bucket];
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do {
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if (((*hashval ^ hash) >> 1) == 0) {
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symnum = hashval - obj->chains_gnu;
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if (_rtld_symlook_obj_matched_symbol(name, obj, flags,
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ventry, symnum, &vsymp, &vcount)) {
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return vsymp;
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}
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}
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} while ((*hashval++ & 1) == 0);
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if (vcount == 1)
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return vsymp;
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return NULL;
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}
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/*
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* Search the symbol table of a single shared object for a symbol of
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* the given name. Returns a pointer to the symbol, or NULL if no
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* definition was found.
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*
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* The symbol's hash value is passed in for efficiency reasons; that
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* eliminates many recomputations of the hash value.
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*
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* Redirect to either GNU Hash (whenever available) or ELF Hash.
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*/
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const Elf_Sym *
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_rtld_symlook_obj(const char *name, Elf_Hash *hash,
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const Obj_Entry *obj, u_int flags, const Ver_Entry *ventry)
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{
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assert(obj->sysv_hash || obj->gnu_hash);
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/* Always prefer the GNU Hash as it is faster. */
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if (obj->gnu_hash)
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return _rtld_symlook_obj_gnu(name, hash->gnu, obj, flags, ventry);
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else
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return _rtld_symlook_obj_sysv(name, hash->sysv, obj, flags, ventry);
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}
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/*
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* Given a symbol number in a referencing object, find the corresponding
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* definition of the symbol. Returns a pointer to the symbol, or NULL if
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