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Code Issues Releases Activity

Performance improvements for the ELF dynamic linker. These

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particularly help programs which load many shared libraries with
a lot of relocations.  Large C++ programs such as are found in KDE
are a prime example.

While relocating a shared object, maintain a vector of symbols
which have already been looked up, directly indexed by symbol
number.  Typically, symbols which are referenced by a relocation
entry are referenced by many of them.  This is the same optimization
I made to the a.out dynamic linker in 1995 (rtld.c revision 1.30).

Also, compare the first character of a sought-after symbol with its
symbol table entry before calling strcmp().

On a PII/400 these changes reduce the start-up time of a typical
KDE program from 833 msec (elapsed) to 370 msec.

MFC after:	5 days
This commit is contained in:
John Polstra 2001-05-05 23:21:05 +00:00
parent 12813062e3
commit c15e7faad5
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=76296
5 changed files with 60 additions and 18 deletions
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15
libexec/rtld-elf/alpha/reloc.c
View File

@ -71,6 +71,11 @@ static int
reloc_non_plt_obj(Obj_Entry *obj_rtld, Obj_Entry *obj, const Elf_Rela *rela)
{
Elf_Addr *where = (Elf_Addr *) (obj->relocbase + rela->r_offset);
SymCache *cache;
cache = (SymCache *)alloca(obj->nchains * sizeof(SymCache));
if (cache != NULL)
memset(cache, 0, obj->nchains * sizeof(SymCache));
switch (ELF_R_TYPE(rela->r_info)) {
@ -82,7 +87,7 @@ reloc_non_plt_obj(Obj_Entry *obj_rtld, Obj_Entry *obj, const Elf_Rela *rela)
const Obj_Entry *defobj;
def = find_symdef(ELF_R_SYM(rela->r_info), obj,
&defobj, false);
&defobj, false, cache);
if (def == NULL)
return -1;
store64(where,
@ -97,7 +102,7 @@ reloc_non_plt_obj(Obj_Entry *obj_rtld, Obj_Entry *obj, const Elf_Rela *rela)
Elf_Addr val;
def = find_symdef(ELF_R_SYM(rela->r_info), obj,
&defobj, false);
&defobj, false, cache);
if (def == NULL)
return -1;
val = (Elf_Addr) (defobj->relocbase + def->st_value +
@ -228,7 +233,8 @@ reloc_jmpslots(Obj_Entry *obj)
assert(ELF_R_TYPE(rel->r_info) == R_ALPHA_JMP_SLOT);
where = (Elf_Addr *)(obj->relocbase + rel->r_offset);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true,
NULL);
if (def == NULL)
return -1;
reloc_jmpslot(where,
@ -246,7 +252,8 @@ reloc_jmpslots(Obj_Entry *obj)
assert(ELF_R_TYPE(rela->r_info) == R_ALPHA_JMP_SLOT);
where = (Elf_Addr *)(obj->relocbase + rela->r_offset);
def = find_symdef(ELF_R_SYM(rela->r_info), obj, &defobj, true);
def = find_symdef(ELF_R_SYM(rela->r_info), obj, &defobj, true,
NULL);
if (def == NULL)
return -1;
reloc_jmpslot(where,

13
libexec/rtld-elf/amd64/reloc.c
View File

@ -114,6 +114,11 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
{
const Elf_Rel *rellim;
const Elf_Rel *rel;
SymCache *cache;
cache = (SymCache *)alloca(obj->nchains * sizeof(SymCache));
if (cache != NULL)
memset(cache, 0, obj->nchains * sizeof(SymCache));
rellim = (const Elf_Rel *) ((caddr_t) obj->rel + obj->relsize);
for (rel = obj->rel; rel < rellim; rel++) {
@ -130,7 +135,7 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
const Obj_Entry *defobj;
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj,
false);
false, cache);
if (def == NULL)
return -1;
@ -149,7 +154,7 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
const Obj_Entry *defobj;
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj,
false);
false, cache);
if (def == NULL)
return -1;
@ -179,7 +184,7 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
const Obj_Entry *defobj;
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj,
false);
false, cache);
if (def == NULL)
return -1;
@ -238,7 +243,7 @@ reloc_jmpslots(Obj_Entry *obj)
assert(ELF_R_TYPE(rel->r_info) == R_386_JMP_SLOT);
where = (Elf_Addr *)(obj->relocbase + rel->r_offset);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true, NULL);
if (def == NULL)
return -1;
reloc_jmpslot(where, (Elf_Addr)(defobj->relocbase + def->st_value));

13
libexec/rtld-elf/i386/reloc.c
View File

@ -114,6 +114,11 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
{
const Elf_Rel *rellim;
const Elf_Rel *rel;
SymCache *cache;
cache = (SymCache *)alloca(obj->nchains * sizeof(SymCache));
if (cache != NULL)
memset(cache, 0, obj->nchains * sizeof(SymCache));
rellim = (const Elf_Rel *) ((caddr_t) obj->rel + obj->relsize);
for (rel = obj->rel; rel < rellim; rel++) {
@ -130,7 +135,7 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
const Obj_Entry *defobj;
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj,
false);
false, cache);
if (def == NULL)
return -1;
@ -149,7 +154,7 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
const Obj_Entry *defobj;
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj,
false);
false, cache);
if (def == NULL)
return -1;
@ -179,7 +184,7 @@ reloc_non_plt(Obj_Entry *obj, Obj_Entry *obj_rtld)
const Obj_Entry *defobj;
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj,
false);
false, cache);
if (def == NULL)
return -1;
@ -238,7 +243,7 @@ reloc_jmpslots(Obj_Entry *obj)
assert(ELF_R_TYPE(rel->r_info) == R_386_JMP_SLOT);
where = (Elf_Addr *)(obj->relocbase + rel->r_offset);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true, NULL);
if (def == NULL)
return -1;
reloc_jmpslot(where, (Elf_Addr)(defobj->relocbase + def->st_value));

26
libexec/rtld-elf/rtld.c
View File

@ -427,7 +427,7 @@ _rtld_bind(Obj_Entry *obj, Elf_Word reloff)
rel = (const Elf_Rel *) ((caddr_t) obj->pltrela + reloff);
where = (Elf_Addr *) (obj->relocbase + rel->r_offset);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true, NULL);
if (def == NULL)
die();
@ -821,7 +821,7 @@ find_library(const char *name, const Obj_Entry *refobj)
*/
const Elf_Sym *
find_symdef(unsigned long symnum, const Obj_Entry *refobj,
const Obj_Entry **defobj_out, bool in_plt)
const Obj_Entry **defobj_out, bool in_plt, SymCache *cache)
{
const Elf_Sym *ref;
const Elf_Sym *def;
@ -829,6 +829,17 @@ find_symdef(unsigned long symnum, const Obj_Entry *refobj,
const char *name;
unsigned long hash;
/*
* If we have already found this symbol, get the information from
* the cache.
*/
if (symnum >= refobj->nchains)
return NULL; /* Bad object */
if (cache != NULL && cache[symnum].sym != NULL) {
*defobj_out = cache[symnum].obj;
return cache[symnum].sym;
}
ref = refobj->symtab + symnum;
name = refobj->strtab + ref->st_name;
hash = elf_hash(name);
@ -845,9 +856,14 @@ find_symdef(unsigned long symnum, const Obj_Entry *refobj,
defobj = obj_main;
}
if (def != NULL)
if (def != NULL) {
*defobj_out = defobj;
else
/* Record the information in the cache to avoid subsequent lookups. */
if (cache != NULL) {
cache[symnum].sym = def;
cache[symnum].obj = defobj;
}
} else
_rtld_error("%s: Undefined symbol \"%s\"", refobj->path, name);
return def;
}
@ -1926,7 +1942,7 @@ symlook_obj(const char *name, unsigned long hash, const Obj_Entry *obj,
symp = obj->symtab + symnum;
strp = obj->strtab + symp->st_name;
if (strcmp(name, strp) == 0)
if (name[0] == strp[0] && strcmp(name, strp) == 0)
return symp->st_shndx != SHN_UNDEF ||
(!in_plt && symp->st_value != 0 &&
ELF_ST_TYPE(symp->st_info) == STT_FUNC) ? symp : NULL;

11
libexec/rtld-elf/rtld.h
View File

@ -166,6 +166,15 @@ typedef struct Struct_Obj_Entry {
#define RTLD_MAGIC 0xd550b87a
#define RTLD_VERSION 1
/*
* Symbol cache entry used during relocation to avoid multiple lookups
* of the same symbol.
*/
typedef struct Struct_SymCache {
const Elf_Sym *sym; /* Symbol table entry */
const Obj_Entry *obj; /* Shared object which defines it */
} SymCache;
extern void _rtld_error(const char *, ...) __printflike(1, 2);
extern Obj_Entry *map_object(int, const char *, const struct stat *);
extern void *xcalloc(size_t);
@ -179,7 +188,7 @@ extern Elf_Addr _GLOBAL_OFFSET_TABLE_[];
int do_copy_relocations(Obj_Entry *);
unsigned long elf_hash(const char *);
const Elf_Sym *find_symdef(unsigned long, const Obj_Entry *,
const Obj_Entry **, bool);
const Obj_Entry **, bool, SymCache *);
void init_pltgot(Obj_Entry *);
void lockdflt_init(LockInfo *);
void obj_free(Obj_Entry *);