linux-kernel - [PATCH v4 09/21] modpost: pass section index to find_elf

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Date:   Sun, 14 May 2023 05:44:50 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Pitre <npitre@...libre.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: [PATCH v4 09/21] modpost: pass section index to find_elf_symbol2()

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.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.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