linux-kernel - Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf

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Date: Wed, 1 May 2024 19:54:35 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Edward Liaw <edliaw@...gle.com>
Cc: linux-kernel@...r.kernel.org, Shuah Khan <shuah@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, "H. Peter Anvin" <hpa@...ux.intel.com>, 
	Andy Lutomirski <luto@....edu>, linux-kselftest@...r.kernel.org, kernel-team@...roid.com, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for
 elf_hash

Hi,

On Wed, May 01, 2024 at 06:06:18PM +0000, Edward Liaw wrote:
> Fixes clang compilation warnings by adding explicit unsigned conversion:
> 
> parse_vdso.c:206:22: warning: passing 'const char *' to parameter of
>  type 'const unsigned char *' converts between pointers to integer types
>  where one is of the unique plain 'char' type and the other is not
>  [-Wpointer-sign]
>         ver_hash = elf_hash(version);
>                             ^~~~~~~
> parse_vdso.c:59:52: note: passing argument to parameter 'name' here
> static unsigned long elf_hash(const unsigned char *name)
>                                                    ^
> parse_vdso.c:207:46: warning: passing 'const char *' to parameter of
>  type 'const unsigned char *' converts between pointers to integer types
>  where one is of the unique plain 'char' type and the other is not
>  [-Wpointer-sign]
>         ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
>                                                     ^~~~
> parse_vdso.c:59:52: note: passing argument to parameter 'name' here
> static unsigned long elf_hash(const unsigned char *name)
> 
> Fixes: 98eedc3a9dbf ("Document the vDSO and add a reference parser")
> Signed-off-by: Edward Liaw <edliaw@...gle.com>

> ---
> v2: update commit message with correct compiler warning
> v3: fix checkpatch errors and indentation
> ---
>  tools/testing/selftests/vDSO/parse_vdso.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
> index 413f75620a35..9e29ff0657ea 100644
> --- a/tools/testing/selftests/vDSO/parse_vdso.c
> +++ b/tools/testing/selftests/vDSO/parse_vdso.c
> @@ -203,8 +203,9 @@ void *vdso_sym(const char *version, const char *name)

Is it possible to just change the types of the parameters of vdso_sym()
or does that trigger even more warnings on the callsites of vdso_sym()?

Either way, this looks ok to me.

Acked-by: Justin Stitt <justinstitt@...gle.com>

>  	if (!vdso_info.valid)
>  		return 0;
> 
> -	ver_hash = elf_hash(version);
> -	ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
> +	ver_hash = elf_hash((const unsigned char *)version);
> +	ELF(Word) chain = vdso_info.bucket[
> +		elf_hash((const unsigned char *)name) % vdso_info.nbucket];
> 
>  	for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
>  		ELF(Sym) *sym = &vdso_info.symtab[chain];
> --
> 2.45.0.rc0.197.gbae5840b3b-goog
> 

Thanks
Justin