Re: [PATCH v5 09/21] modpost: pass section index to find_elf_symbol2()

Nick Desaulniers
2023-05-17T21:05:24Z

On Sun, May 14, 2023 at 8:28 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> find_elf_symbol2() converts the section index to the section name,
> then compares the two section names in each iteration. This is slow.
>
> It is faster to compare the section indices (i.e. integers) directly.

Good idea!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> scripts/mod/modpost.c | 34 +++++++++++++++-------------------
> 1 file changed, 15 insertions(+), 19 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 2cc9c2a4aadc..3b7b78e69137 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1169,19 +1169,14 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf64_Sword addr,
> * it is, but this works for now.
> **/
> static Elf_Sym *find_elf_symbol2(struct elf_info *elf, Elf_Addr addr,
> - const char *sec)
> + unsigned int secndx)
> {
> Elf_Sym *sym;
> Elf_Sym *near = NULL;
> Elf_Addr distance = ~0;
>
> for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
> - const char *symsec;
> -
> - if (is_shndx_special(sym->st_shndx))
> - continue;
> - symsec = sec_name(elf, get_secindex(elf, sym));
> - if (strcmp(symsec, sec) != 0)
> + if (get_secindex(elf, sym) != secndx)
> continue;
> if (!is_valid_name(elf, sym))
> continue;
> @@ -1203,7 +1198,8 @@ static bool is_executable_section(struct elf_info *elf, unsigned int secndx)
>
> static void default_mismatch_handler(const char *modname, struct elf_info *elf,
> const struct sectioncheck* const mismatch,
> - Elf_Rela *r, Elf_Sym *sym, const char *fromsec,
> + Elf_Rela *r, Elf_Sym *sym,
> + unsigned int fsecndx, const char *fromsec,
> const char *tosec)
> {
> Elf_Sym *to;
> @@ -1211,7 +1207,7 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
> const char *tosym;
> const char *fromsym;
>
> - from = find_elf_symbol2(elf, r->r_offset, fromsec);
> + from = find_elf_symbol2(elf, r->r_offset, fsecndx);
> fromsym = sym_name(elf, from);
>
> to = find_elf_symbol(elf, r->r_addend, sym);
> @@ -1267,7 +1263,8 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
> }
>
> static void check_section_mismatch(const char *modname, struct elf_info *elf,
> - Elf_Rela *r, Elf_Sym *sym, const char *fromsec)
> + Elf_Rela *r, Elf_Sym *sym,
> + unsigned int fsecndx, const char *fromsec)
> {
> const char *tosec = sec_name(elf, get_secindex(elf, sym));
> const struct sectioncheck *mismatch = section_mismatch(fromsec, tosec);
> @@ -1275,7 +1272,8 @@ static void check_section_mismatch(const char *modname, struct elf_info *elf,
> if (!mismatch)
> return;
>
> - default_mismatch_handler(modname, elf, mismatch, r, sym, fromsec, tosec);
> + default_mismatch_handler(modname, elf, mismatch, r, sym, fsecndx, fromsec,
> + tosec);
> }
>
> static unsigned int *reloc_location(struct elf_info *elf,
> @@ -1390,12 +1388,11 @@ static void section_rela(const char *modname, struct elf_info *elf,
> Elf_Rela *rela;
> Elf_Rela r;
> unsigned int r_sym;
> - const char *fromsec;
> -
> + unsigned int fsecndx = sechdr->sh_info;
> + const char *fromsec = sec_name(elf, fsecndx);
> Elf_Rela *start = (void *)elf->hdr + sechdr->sh_offset;
> Elf_Rela *stop = (void *)start + sechdr->sh_size;
>
> - fromsec = sec_name(elf, sechdr->sh_info);
> /* if from section (name) is know good then skip it */
> if (match(fromsec, section_white_list))
> return;
> @@ -1434,7 +1431,7 @@ static void section_rela(const char *modname, struct elf_info *elf,
> /* Skip special sections */
> if (is_shndx_special(sym->st_shndx))
> continue;
> - check_section_mismatch(modname, elf, &r, sym, fromsec);
> + check_section_mismatch(modname, elf, &r, sym, fsecndx, fromsec);
> }
> }
>
> @@ -1445,12 +1442,11 @@ static void section_rel(const char *modname, struct elf_info *elf,
> Elf_Rel *rel;
> Elf_Rela r;
> unsigned int r_sym;
> - const char *fromsec;
> -
> + unsigned int fsecndx = sechdr->sh_info;
> + const char *fromsec = sec_name(elf, fsecndx);
> Elf_Rel *start = (void *)elf->hdr + sechdr->sh_offset;
> Elf_Rel *stop = (void *)start + sechdr->sh_size;
>
> - fromsec = sec_name(elf, sechdr->sh_info);
> /* if from section (name) is know good then skip it */
> if (match(fromsec, section_white_list))
> return;
> @@ -1493,7 +1489,7 @@ static void section_rel(const char *modname, struct elf_info *elf,
> /* Skip special sections */
> if (is_shndx_special(sym->st_shndx))
> continue;
> - check_section_mismatch(modname, elf, &r, sym, fromsec);
> + check_section_mismatch(modname, elf, &r, sym, fsecndx, fromsec);
> }
> }
>
> --
> 2.39.2
>

--
Thanks,
~Nick Desaulniers