linux-kernel - Re: [PATCH v1] powerpc: Make setjmp/longjump signature standard

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Message-ID: <CAKwvOdmLmfJY4Uk-Atd9dT5+zQTPeoagjMZMcDqdVfKCU7_BuA@mail.gmail.com>
Date:   Fri, 27 Mar 2020 10:10:44 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Clement Courbet <courbet@...gle.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v1] powerpc: Make setjmp/longjump signature standard

On Fri, Mar 27, 2020 at 3:08 AM Clement Courbet <courbet@...gle.com> wrote:
>
> Declaring setjmp()/longjmp() as taking longs makes the signature
> non-standard, and makes clang complain. In the past, this has been
> worked around by adding -ffreestanding to the compile flags.
>
> The implementation looks like it only ever propagates the value
> (in longjmp) or sets it to 1 (in setjmp), and we only call longjmp
> with integer parameters.
>
> This allows removing -ffreestanding from the compilation flags.
>
> Context:
> https://lore.kernel.org/patchwork/patch/1214060
> https://lore.kernel.org/patchwork/patch/1216174
>
> Signed-off-by: Clement Courbet <courbet@...gle.com>

Hi Clement, thanks for the patch! Would you mind sending a V2 that
included a similar fix to arch/powerpc/xmon/Makefile?

For context, this was the original patch:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=aea447141c7e7824b81b49acd1bc78
which was then modified to:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c9029ef9c95765e7b63c4d9aa780674447db1ec0

So on your V2, if you include in the commit message, the line:

Fixes c9029ef9c957 ("powerpc: Avoid clang warnings around setjmp and longjmp")

then that will help our LTS branch maintainers back port it to the
appropriate branches.

>
> ---
>  arch/powerpc/include/asm/setjmp.h | 6 ++++--
>  arch/powerpc/kexec/Makefile       | 3 ---
>  2 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/setjmp.h b/arch/powerpc/include/asm/setjmp.h
> index e9f81bb3f83b..84bb0d140d59 100644
> --- a/arch/powerpc/include/asm/setjmp.h
> +++ b/arch/powerpc/include/asm/setjmp.h
> @@ -7,7 +7,9 @@
>
>  #define JMP_BUF_LEN    23
>
> -extern long setjmp(long *) __attribute__((returns_twice));
> -extern void longjmp(long *, long) __attribute__((noreturn));
> +typedef long *jmp_buf;
> +
> +extern int setjmp(jmp_buf env) __attribute__((returns_twice));
> +extern void longjmp(jmp_buf env, int val) __attribute__((noreturn));
>
>  #endif /* _ASM_POWERPC_SETJMP_H */
> diff --git a/arch/powerpc/kexec/Makefile b/arch/powerpc/kexec/Makefile
> index 378f6108a414..86380c69f5ce 100644
> --- a/arch/powerpc/kexec/Makefile
> +++ b/arch/powerpc/kexec/Makefile
> @@ -3,9 +3,6 @@
>  # Makefile for the linux kernel.
>  #
>
> -# Avoid clang warnings around longjmp/setjmp declarations
> -CFLAGS_crash.o += -ffreestanding
> -
>  obj-y                          += core.o crash.o core_$(BITS).o
>
>  obj-$(CONFIG_PPC32)            += relocate_32.o
> --
> 2.25.1.696.g5e7596f4ac-goog
>


-- 
Thanks,
~Nick Desaulniers