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outelf: hash sections for performance

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Use a hash table to look up sections by name, and an RAA to look up
sections by index; thus remove O(n) searches. This becomes important
since ELF uses sections for dead code elimination.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2019-01-12 00:35:20 -08:00
parent 52266ad424
commit 69fa3c2e8e
3 changed files with 56 additions and 28 deletions
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75
output/outelf.c
View File

@ -1,6 +1,6 @@
/* ----------------------------------------------------------------------- *
*
* Copyright 1996-2018 The NASM Authors - All Rights Reserved
* Copyright 1996-2019 The NASM Authors - All Rights Reserved
* See the file AUTHORS included with the NASM distribution for
* the specific copyright holders.
*
@ -50,6 +50,7 @@
#include "outform.h"
#include "outlib.h"
#include "rbtree.h"
#include "hashtbl.h"
#include "ver.h"
#include "dwarf.h"
@ -77,6 +78,9 @@ static struct RAA *bsym;
static struct SAA *strs;
static uint32_t strslen;
static struct RAAPTR *section_by_index;
static struct hash_table section_by_name;
static struct elf_symbol *fwds;
static char elf_module[FILENAME_MAX];
@ -375,6 +379,11 @@ elf_directive(enum directive directive, char *value, int pass)
static void elf_init(void)
{
static const char * const reserved_sections[] = {
".shstrtab", ".strtab", ".symtab", ".symtab_shndx", NULL
};
const char * const *p;
strlcpy(elf_module, inname, sizeof(elf_module));
sects = NULL;
nsects = sectlen = 0;
@ -391,11 +400,23 @@ static void elf_init(void)
fwds = NULL;
hash_init(&section_by_name, HASH_MEDIUM);
section_by_index = raa_init_ptr();
/*
* Add reserved section names to the section hash, with NULL
* as the data pointer
*/
for (p = reserved_sections; *p; p++) {
struct hash_insert hi;
hash_find(&section_by_name, *p, &hi);
hash_add(&hi, *p, NULL);
}
/*
* FIXME: tlsie is Elf32 only and
* gottpoff is Elfx32|64 only.
*/
elf_gotpc_sect = seg_alloc();
backend_label("..gotpc", elf_gotpc_sect + 1, 0L);
elf_gotoff_sect = seg_alloc();
@ -431,6 +452,8 @@ static void elf_cleanup(void)
nasm_free(r);
}
}
hash_free(&section_by_name);
raa_free_ptr(section_by_index);
nasm_free(sects);
saa_free(syms);
raa_free(bsym);
@ -449,7 +472,8 @@ static void add_sectname(const char *firsthalf, const char *secondhalf)
shstrtablen += len + 1;
}
static int elf_make_section(char *name, int type, int flags, uint64_t align)
static struct elf_section *
elf_make_section(char *name, int type, int flags, uint64_t align)
{
struct elf_section *s;
@ -468,12 +492,13 @@ static int elf_make_section(char *name, int type, int flags, uint64_t align)
s->type = type;
s->flags = flags;
s->align = align;
s->shndx = nsects + 1;
if (nsects >= sectlen)
sects = nasm_realloc(sects, (sectlen += SECT_DELTA) * sizeof(*sects));
sects[nsects++] = s;
return nsects - 1;
return s;
}
static int32_t elf_section_names(char *name, int pass, int *bits)
@ -481,8 +506,10 @@ static int32_t elf_section_names(char *name, int pass, int *bits)
char *p;
uint32_t flags, flags_and, flags_or;
uint64_t align, entsize;
void **hp;
struct elf_section *s;
int type, i;
struct hash_insert hi;
int type;
if (!name) {
*bits = ofmt->maxbits;
@ -497,18 +524,15 @@ static int32_t elf_section_names(char *name, int pass, int *bits)
elf_section_attrib(name, p, pass, &flags_and,
&flags_or, &align, &entsize, &type);
if (!strcmp(name, ".shstrtab") ||
!strcmp(name, ".symtab") ||
!strcmp(name, ".strtab")) {
nasm_error(ERR_NONFATAL, "attempt to redefine reserved section"
"name `%s'", name);
return NO_SEG;
}
for (i = 0; i < nsects; i++)
if (!strcmp(name, sects[i]->name))
break;
if (i == nsects) {
hp = hash_find(&section_by_name, name, &hi);
if (hp) {
s = *hp;
if (!s) {
nasm_error(ERR_NONFATAL, "attempt to redefine reserved section"
"name `%s'", name);
return NO_SEG;
}
} else {
const struct elf_known_section *ks = elf_known_sections;
while (ks->name) {
@ -521,11 +545,11 @@ static int32_t elf_section_names(char *name, int pass, int *bits)
align = align ? align : ks->align;
flags = (ks->flags & ~flags_and) | flags_or;
i = elf_make_section(name, type, flags, align);
s = elf_make_section(name, type, flags, align);
hash_add(&hi, s->name, s);
section_by_index = raa_write_ptr(section_by_index, s->index >> 1, s);
}
s = sects[i];
if (pass == 1) {
if ((type && s->type != type)
|| ((s->flags & flags_and) != flags_or)
@ -628,7 +652,7 @@ static void elf_deflabel(char *name, int32_t segment, int64_t offset,
if (segment == NO_SEG)
sym->section = SHN_ABS;
else {
int i;
const struct elf_section *s;
sym->section = SHN_UNDEF;
if (segment == def_seg) {
/* we have to be sure at least text section is there */
@ -636,12 +660,9 @@ static void elf_deflabel(char *name, int32_t segment, int64_t offset,
if (segment != elf_section_names(".text", 2, &tempint))
nasm_panic(0, "strange segment conditions in ELF driver");
}
for (i = 0; i < nsects; i++) {
if (segment == sects[i]->index) {
sym->section = i + 1;
break;
}
}
s = raa_read_ptr(section_by_index, segment >> 1);
if (s)
sym->section = s->shndx;
}
if (is_global == 2) {

3
output/outelf.h
View File

@ -137,7 +137,8 @@ struct elf_section {
uint64_t len;
uint64_t size;
uint64_t nrelocs;
int32_t index;
int32_t index; /* NASM index */
int shndx; /* ELF index */
int type; /* SHT_PROGBITS or SHT_NOBITS */
uint64_t align; /* alignment: power of two */
uint64_t flags; /* section flags */

6
test/manysecs.asm Normal file
View File

@ -0,0 +1,6 @@
%assign n 0
%rep 10000
section .text %+ n progbits exec
nop
%assign n n+1
%endrep