linux-kernel - Re: [PATCH v2 09/14] objtool: Extract elf_strtab

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Message-ID: <20210319021038.6mfpnbel67yhyapw@treble>
Date:   Thu, 18 Mar 2021 21:10:38 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, jgross@...e.com, mbenes@...e.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/14] objtool: Extract elf_strtab_concat()

On Thu, Mar 18, 2021 at 06:11:12PM +0100, Peter Zijlstra wrote:
> Create a common helper to append strings to a strtab.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  tools/objtool/elf.c |   73 +++++++++++++++++++++++++++++-----------------------
>  1 file changed, 42 insertions(+), 31 deletions(-)
> 
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -676,13 +676,51 @@ struct elf *elf_open_read(const char *na
>  	return NULL;
>  }
>  
> +static int elf_strtab_concat(struct elf *elf, char *name, const char *strtab_name)
> +{
> +	struct section *strtab = NULL;
> +	Elf_Data *data;
> +	Elf_Scn *s;
> +	int len;
> +
> +	if (strtab_name)
> +		strtab = find_section_by_name(elf, strtab_name);
> +	if (!strtab)
> +		strtab = find_section_by_name(elf, ".strtab");
> +	if (!strtab) {
> +		WARN("can't find %s or .strtab section", strtab_name);
> +		return -1;
> +	}

This part's a bit mysterious (and it loses the Clang comment).  Maybe we
can leave the section finding logic in elf_create_section()?

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index b85db6efb9d3..db9ad54894d8 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -676,19 +676,17 @@ struct elf *elf_open_read(const char *name, int flags)
 	return NULL;
 }
 
-static int elf_strtab_concat(struct elf *elf, char *name, const char *strtab_name)
+static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
 {
 	struct section *strtab = NULL;
 	Elf_Data *data;
 	Elf_Scn *s;
 	int len;
 
-	if (strtab_name)
-		strtab = find_section_by_name(elf, strtab_name);
 	if (!strtab)
 		strtab = find_section_by_name(elf, ".strtab");
 	if (!strtab) {
-		WARN("can't find %s or .strtab section", strtab_name);
+		WARN("can't find .strtab section");
 		return -1;
 	}
 
@@ -718,7 +716,7 @@ static int elf_strtab_concat(struct elf *elf, char *name, const char *strtab_nam
 struct section *elf_create_section(struct elf *elf, const char *name,
 				   unsigned int sh_flags, size_t entsize, int nr)
 {
-	struct section *sec;
+	struct section *sec, *shstrtab;
 	size_t size = entsize * nr;
 	Elf_Scn *s;
 
@@ -777,7 +775,15 @@ struct section *elf_create_section(struct elf *elf, const char *name,
 	sec->sh.sh_addralign = 1;
 	sec->sh.sh_flags = SHF_ALLOC | sh_flags;
 
-	sec->sh.sh_name = elf_strtab_concat(elf, sec->name, ".shstrtab");
+	/* Add section name to .shstrtab (or .strtab for Clang) */
+	shstrtab = find_section_by_name(elf, ".shstrtab");
+	if (!shstrtab)
+		shstrtab = find_section_by_name(elf, ".strtab");
+	if (!shstrtab) {
+		WARN("can't find .shstrtab or .strtab section");
+		return NULL;
+	}
+	sec->sh.sh_name = elf_add_string(elf, sec->name, shstrtab);
 	if (sec->sh.sh_name == -1)
 		return NULL;