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Date: Sun, 28 Jun 2015 02:48:31 +0300
From: Alexander Monakov <amonakov@...ras.ru>
To: musl@...ts.openwall.com
Subject: [PATCH v2 2/6] dynlink.c: use bloom filter in gnu hash lookup
Introduce gnu_lookup_filtered and use it to speed up symbol lookups in
find_sym (do_dlsym is left as is, based on an expectation that frequently
dlsym queries will use a dlopen handle rather than RTLD_NEXT or RTLD_DEFAULT,
and will not need to look at more than one DSO).
---
src/ldso/dynlink.c | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)
diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 0df81f2..b08596e 100644
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -200,6 +200,19 @@ static Sym *gnu_lookup(const char *s, uint32_t h1, struct dso *dso)
return 0;
}
+static Sym *gnu_lookup_filtered(const char *s, uint32_t h1, struct dso *dso, uint32_t fofs, size_t fmask)
+{
+ uint32_t *hashtab = dso->ghashtab;
+ const size_t *bloomwords = (const void *)(hashtab+4);
+ size_t f = bloomwords[fofs & (hashtab[2]-1)];
+ if (!(f & fmask)) return 0;
+
+ f >>= (h1 >> hashtab[3]) % (8 * sizeof f);
+ if (!(f & 1)) return 0;
+
+ return gnu_lookup(s, h1, dso);
+}
+
#define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON | 1<<STT_TLS)
#define OK_BINDS (1<<STB_GLOBAL | 1<<STB_WEAK | 1<<STB_GNU_UNIQUE)
@@ -209,14 +222,20 @@ static Sym *gnu_lookup(const char *s, uint32_t h1, struct dso *dso)
static struct symdef find_sym(struct dso *dso, const char *s, int need_def)
{
- uint32_t h = 0, gh = 0;
+ uint32_t h = 0, gh, gho;
+ size_t ghm = 0;
struct symdef def = {0};
for (; dso; dso=dso->next) {
Sym *sym;
if (!dso->global) continue;
if (dso->ghashtab) {
- if (!gh) gh = gnu_hash(s);
- sym = gnu_lookup(s, gh, dso);
+ if (!ghm) {
+ gh = gnu_hash(s);
+ int maskbits = 8 * sizeof ghm;
+ gho = gh / maskbits;
+ ghm = 1ul << gh % maskbits;
+ }
+ sym = gnu_lookup_filtered(s, gh, dso, gho, ghm);
} else {
if (!h) h = sysv_hash(s);
sym = sysv_lookup(s, h, dso);
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