linux-kernel - Re: [PATCH v3 3/5] arm64: vdso32: Fix compilation warning

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Message-ID: <20191001132108.jx2x7quyk2p2vyfw@willie-the-truck>
Date:   Tue, 1 Oct 2019 14:21:09 +0100
From:   Will Deacon <will@...nel.org>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        ard.biesheuvel@...aro.org, ndesaulniers@...gle.com,
        catalin.marinas@....com, tglx@...utronix.de
Subject: Re: [PATCH v3 3/5] arm64: vdso32: Fix compilation warning

On Thu, Sep 26, 2019 at 10:43:40PM +0100, Vincenzo Frascino wrote:
> As reported by Will Deacon the following compilation warning appears
> during the compilation of the vdso32:
> 
> In file included from ./arch/arm64/include/asm/thread_info.h:17:0,
>                  from ./include/linux/thread_info.h:38,
>                  from ./arch/arm64/include/asm/preempt.h:5,
>                  from ./include/linux/preempt.h:78,
>                  from ./include/linux/spinlock.h:51,
>                  from ./include/linux/seqlock.h:36,
>                  from ./include/linux/time.h:6,
>                  from .../work/linux/lib/vdso/gettimeofday.c:7,
>                  from <command-line>:0:
> ./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
> ./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer to
> integer of different size [-Wpointer-to-int-cast]
>   u64 __addr = (u64)addr & ~__tag_shifted(0xff);
>                ^
> In file included from ./arch/arm64/include/asm/pgtable-hwdef.h:8:0,
>                  from ./arch/arm64/include/asm/processor.h:34,
>                  from ./arch/arm64/include/asm/elf.h:118,
>                  from ./include/linux/elf.h:5,
>                  from ./include/linux/elfnote.h:62,
>                  from arch/arm64/kernel/vdso32/note.c:11:
> ./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
> ./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer to
> integer of different size [-Wpointer-to-int-cast]
>   u64 __addr = (u64)addr & ~__tag_shifted(0xff);
>                ^
> 
> This happens because few 64 bit compilation headers are included during
> the generation of vdso32.
> 
> Fix the issue redefining the __tag_set function.
> 
> Note: This fix is meant to be temporary, a more comprehensive solution
> based on the refactoring of the generic headers will be provided with a
> future patch set. At that point it will be possible to revert this patch.
> 
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> ---
>  arch/arm64/include/asm/memory.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index b61b50bf68b1..c61b2eb50a3b 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -228,11 +228,14 @@ static inline unsigned long kaslr_offset(void)
>  #define __tag_get(addr)		0
>  #endif /* CONFIG_KASAN_SW_TAGS */
>  
> +#ifdef __aarch64__
> +/* Do not attempt to compile this code with compat vdso */
>  static inline const void *__tag_set(const void *addr, u8 tag)
>  {
>  	u64 __addr = (u64)addr & ~__tag_shifted(0xff);
>  	return (const void *)(__addr | __tag_shifted(tag));
>  }
> +#endif

Sorry, but I'm not taking this.

I know you're trying to fix the issues I reported as quickly as you can (and
thank you for that), but I'm sure that you agree this needs more thought to
develop a proper solution to what is a much bigger issue than can be solved
by sprinkling #ifdefs. I can live with the warning on the basis that a
proper fix is in the pipeline, but in the meantime it can serve as a
reminder that we're not done here.

Will