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elf: Tidy section headers

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Don't emit useless section headers and also sort them in allocated
order.  Doesn't change behaviour except makes the resulting files
a tiny bit smaller (though at the expense of some very tiny compile
time and code size increase of tcc itself; not 100% it's worth it).
This commit is contained in:
Michael Matz 2017-01-23 01:11:38 +01:00
parent 3c39cb5cd8
commit 24420bb5c0
1 changed files with 51 additions and 2 deletions
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53
tccelf.c
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@ -1406,7 +1406,6 @@ static void alloc_sec_names(TCCState *s1, int file_type, Section *strsec)
/* Allocate strings for section names */
for(i = 1; i < s1->nb_sections; i++) {
s = s1->sections[i];
s->sh_name = put_elf_str(strsec, s->name);
/* when generating a DLL, we include relocations but we may
patch them */
if (file_type == TCC_OUTPUT_DLL &&
@ -1420,11 +1419,14 @@ static void alloc_sec_names(TCCState *s1, int file_type, Section *strsec)
} else if (s1->do_debug ||
file_type == TCC_OUTPUT_OBJ ||
(s->sh_flags & SHF_ALLOC) ||
i == (s1->nb_sections - 1)) {
i == (s1->nb_sections - 1)) {
/* we output all sections if debug or object file */
s->sh_size = s->data_offset;
}
if (s->sh_size || (s->sh_flags & SHF_ALLOC))
s->sh_name = put_elf_str(strsec, s->name);
}
strsec->sh_size = strsec->data_offset;
}
/* Info to be copied in dynamic section */
@ -1898,6 +1900,51 @@ static int tcc_write_elf_file(TCCState *s1, const char *filename, int phnum,
return 0;
}
/* Sort section headers by assigned sh_addr, remove sections
that we aren't going to output. */
static void tidy_section_headers(TCCState *s1, int *sec_order)
{
int i, nnew, l, *backmap;
Section **snew, *s;
ElfW(Sym) *sym;
snew = tcc_malloc(s1->nb_sections * sizeof(snew[0]));
backmap = tcc_malloc(s1->nb_sections * sizeof(backmap[0]));
for (i = 0, nnew = 0, l = s1->nb_sections; i < s1->nb_sections; i++) {
s = s1->sections[sec_order[i]];
if (!i || s->sh_name) {
backmap[sec_order[i]] = nnew;
snew[nnew] = s;
++nnew;
} else {
backmap[sec_order[i]] = 0;
snew[--l] = s;
}
}
for (i = 0; i < nnew; i++) {
s = snew[i];
if (s) {
s->sh_num = i;
if (s->sh_type == SHT_RELX)
s->sh_info = backmap[s->sh_info];
}
}
for_each_elem(symtab_section, 1, sym, ElfW(Sym))
if (sym->st_shndx != SHN_UNDEF && sym->st_shndx < SHN_LORESERVE)
sym->st_shndx = backmap[sym->st_shndx];
for_each_elem(s1->dynsym, 1, sym, ElfW(Sym))
if (sym->st_shndx != SHN_UNDEF && sym->st_shndx < SHN_LORESERVE)
sym->st_shndx = backmap[sym->st_shndx];
for (i = 0; i < s1->nb_sections; i++)
sec_order[i] = i;
tcc_free(s1->sections);
s1->sections = snew;
s1->nb_sections = nnew;
tcc_free(backmap);
}
/* Output an elf, coff or binary file */
/* XXX: suppress unneeded sections */
static int elf_output_file(TCCState *s1, const char *filename)
@ -2068,6 +2115,7 @@ static int elf_output_file(TCCState *s1, const char *filename)
ret = final_sections_reloc(s1);
if (ret)
goto the_end;
tidy_section_headers(s1, sec_order);
}
/* Perform relocation to GOT or PLT entries */
@ -2076,6 +2124,7 @@ static int elf_output_file(TCCState *s1, const char *filename)
/* Create the ELF file with name 'filename' */
ret = tcc_write_elf_file(s1, filename, phnum, phdr, file_offset, sec_order);
s1->nb_sections = shnum;
the_end:
tcc_free(sec_order);
tcc_free(phdr);