linux-kernel - Re: [PATCH] x86/tools: Use POSIX-compliant syntax for empty regex groups

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Message-ID: <20210203120814.GB13819@zn.tnic>
Date:   Wed, 3 Feb 2021 13:08:14 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     John Millikin <john@...n-millikin.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/tools: Use POSIX-compliant syntax for empty regex
 groups

On Fri, Dec 25, 2020 at 10:30:43PM +0900, John Millikin wrote:
> The syntax for POSIX regexes technically doesn't allow empty branches in
> conditional match groups. GNU libc accepts them as equivalent to `()',
> but other libc implementations (e.g. macOS libc) reject them with a
> parse error.
> 
> Changing to compliant syntax, `(|_sym)' to `(()|_sym)', lets the `relocs'
> tool run successfully when using a non-GNU platform as a build host for
> cross-compiling the kernel.
> 
> Signed-off-by: John Millikin <john@...n-millikin.com>
> ---
> 
> Helper binary to verify behavior for the current platform:
> 
>     #include <regex.h>
>     #include <stdio.h>
>     int main(int argc, char **argv) {
>         regex_t compiled;
>         int err = regcomp(&compiled, argv[1], REG_EXTENDED|REG_NOSUB);
>         if (err != 0) {
>             char errbuf[128];
>             regerror(err, &compiled, errbuf, sizeof(errbuf));
>             printf("regcomp(\"%s\"): %s\n", argv[1], errbuf);
>            return 1;
>         }
>         printf("regcomp(\"%s\"): OK\n", argv[1]);
>         return 0;
>     }
> 
> Output from GNU libc 2.28 and a fussier non-GNU libc:
> 
>     debian:~$ ./regcomp '^a(|b)$'
>     regcomp("^a(|b)$"): OK
>     debian:~$ ./regcomp '^a(()|b)$'
>     regcomp("^a(()|b)$"): OK
> 
>     darwin:~$ ./regcomp '^a(|b)$'
>     regcomp("^a(|b)$"): empty (sub)expression
>     darwin:~$ ./regcomp '^a(()|b)$'
>     regcomp("^a(()|b)$"): OK
> 

I guess you can add those to the commit message as they explain in
detail what the situation is.

>  arch/x86/tools/relocs.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> index ce7188cbdae5..e6f28616a625 100644
> --- a/arch/x86/tools/relocs.c
> +++ b/arch/x86/tools/relocs.c
> @@ -57,12 +57,12 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = {
>      [S_REL] =

$ test-apply.sh /tmp/build.01
checking file arch/x86/tools/relocs.c
patch: **** malformed patch at line 67:      [S_REL] =

Don't tell me the apple mangles patches...

:-)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette