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

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Message-ID: <20200327182708.GA13308@ubuntu-m2-xlarge-x86>
Date:   Fri, 27 Mar 2020 11:27:08 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Clement Courbet <courbet@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.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>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v1] powerpc: Make setjmp/longjump signature standard

On Fri, Mar 27, 2020 at 06:45:21PM +0100, Christophe Leroy wrote:
> Subject line, change longjump to longjmp
> 
> Le 27/03/2020 à 11:07, Clement Courbet a écrit :
> > 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>
> > ---
> >   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;
> 
> Do we need that new opaque typedef ? Why not just keep long * ?

Yes, otherwise the warning comes back:

In file included from arch/powerpc/kexec/crash.c:25:
arch/powerpc/include/asm/setjmp.h:10:12: error: declaration of built-in function 'setjmp' requires the declaration of the 'jmp_buf' type, commonly provided in the header <setjmp.h>. [-Werror,-Wincomplete-setjmp-declaration]
extern int setjmp(long *env) __attribute__((returns_twice));
           ^
arch/powerpc/include/asm/setjmp.h:11:13: error: declaration of built-in function 'longjmp' requires the declaration of the 'jmp_buf' type, commonly provided in the header <setjmp.h>. [-Werror,-Wincomplete-setjmp-declaration]
extern void longjmp(long *env, int val) __attribute__((noreturn));
            ^
2 errors generated.

> > +
> > +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
> > 
> 
> Christophe