This commit improves the section mismatch warning format when there is
no suitable symbol name to print.

The section mismatch warning prints the reference source in the form
of <symbol_name>+<offset> and the reference destination in the form
of <symbol_name>.

However, there are some corner cases where <symbol_name> becomes
"(unknown)", as reported in commit 23dfd914d2bf ("modpost: fix null
pointer dereference").

In such cases, it is better to print the symbol address.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 scripts/mod/modpost.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index d0f138803207..3e474291258c 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -705,10 +705,7 @@ static char *get_modinfo(struct elf_info *info, const char *tag)
 
 static const char *sym_name(struct elf_info *elf, Elf_Sym *sym)
 {
-	if (sym)
-		return elf->strtab + sym->st_name;
-	else
-		return "(unknown)";
+	return sym ? elf->strtab + sym->st_name : "";
 }
 
 /*
@@ -1021,6 +1018,7 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
 	Elf_Sym *from;
 	const char *tosym;
 	const char *fromsym;
+	char taddr_str[16];
 
 	from = find_fromsym(elf, faddr, fsecndx);
 	fromsym = sym_name(elf, from);
@@ -1034,10 +1032,17 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
 
 	sec_mismatch_count++;
 
-	warn("%s: section mismatch in reference: %s+0x%x (section: %s) -> %s (section: %s)\n",
-	     modname, fromsym,
-	     (unsigned int)(faddr - (from ? from->st_value : 0)),
-	     fromsec, tosym, tosec);
+	if (!tosym[0])
+		snprintf(taddr_str, sizeof(taddr_str), "0x%x", (unsigned int)taddr);
+
+	/*
+	 * The format for the reference source:      <symbol_name>+<offset> or <address>
+	 * The format for the reference destination: <symbol_name>          or <address>
+	 */
+	warn("%s: section mismatch in reference: %s%s0x%x (section: %s) -> %s (section: %s)\n",
+	     modname, fromsym, fromsym[0] ? "+" : "",
+	     (unsigned int)(faddr - (fromsym[0] ? from->st_value : 0)),
+	     fromsec, tosym[0] ? tosym : taddr_str, tosec);
 
 	if (mismatch->mismatch == EXTABLE_TO_NON_TEXT) {
 		if (match(tosec, mismatch->bad_tosec))
-- 
2.43.0

On Tue, Aug 13, 2024 at 01:54:51AM +0900, Masahiro Yamada wrote:
> This commit improves the section mismatch warning format when there is
> no suitable symbol name to print.
> 
> The section mismatch warning prints the reference source in the form
> of <symbol_name>+<offset> and the reference destination in the form
> of <symbol_name>.
> 
> However, there are some corner cases where <symbol_name> becomes
> "(unknown)", as reported in commit 23dfd914d2bf ("modpost: fix null
> pointer dereference").
> 
> In such cases, it is better to print the symbol address.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
> 
>  scripts/mod/modpost.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index d0f138803207..3e474291258c 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -705,10 +705,7 @@ static char *get_modinfo(struct elf_info *info, const char *tag)
>  
>  static const char *sym_name(struct elf_info *elf, Elf_Sym *sym)
>  {
> -	if (sym)
> -		return elf->strtab + sym->st_name;
> -	else
> -		return "(unknown)";
> +	return sym ? elf->strtab + sym->st_name : "";
>  }
>  
>  /*
> @@ -1021,6 +1018,7 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
>  	Elf_Sym *from;
>  	const char *tosym;
>  	const char *fromsym;
> +	char taddr_str[16];
>  
>  	from = find_fromsym(elf, faddr, fsecndx);
>  	fromsym = sym_name(elf, from);
> @@ -1034,10 +1032,17 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
>  
>  	sec_mismatch_count++;
>  
> -	warn("%s: section mismatch in reference: %s+0x%x (section: %s) -> %s (section: %s)\n",
> -	     modname, fromsym,
> -	     (unsigned int)(faddr - (from ? from->st_value : 0)),
> -	     fromsec, tosym, tosec);
> +	if (!tosym[0])
> +		snprintf(taddr_str, sizeof(taddr_str), "0x%x", (unsigned int)taddr);
> +
> +	/*
> +	 * The format for the reference source:      <symbol_name>+<offset> or <address>
> +	 * The format for the reference destination: <symbol_name>          or <address>
> +	 */
> +	warn("%s: section mismatch in reference: %s%s0x%x (section: %s) -> %s (section: %s)\n",
> +	     modname, fromsym, fromsym[0] ? "+" : "",
> +	     (unsigned int)(faddr - (fromsym[0] ? from->st_value : 0)),
> +	     fromsec, tosym[0] ? tosym : taddr_str, tosec);
>  
>  	if (mismatch->mismatch == EXTABLE_TO_NON_TEXT) {
>  		if (match(tosec, mismatch->bad_tosec))
> -- 
> 2.43.0
> 

Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>