linux-kernel - Re: [PATCH] arm64: define BUG() instruction without CONFIG

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Date:   Wed, 15 Feb 2017 12:37:22 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Will Deacon <will.deacon@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH] arm64: define BUG() instruction without CONFIG_BUG

On Wed, Feb 15, 2017 at 12:22 PM, Will Deacon <will.deacon@....com> wrote:
> On Tue, Feb 14, 2017 at 10:39:28PM +0100, Arnd Bergmann wrote:
>> @@ -57,6 +58,14 @@ _BUGVERBOSE_LOCATION(__FILE__, __LINE__)           \
>>
>>  #define __WARN_TAINT(taint) _BUG_FLAGS(BUGFLAG_TAINT(taint))
>>
>> +#else
>> +
>> +#define BUG() do {                                   \
>> +     asm volatile("brk %[imm]"                       \
>> +                  :: [imm] "i" (BUG_BRK_IMM));       \
>> +     unreachable();                                  \
>> +} while (0)
>
> Do we need to duplicate the asm, or can we reuse the existing BUG
> definition in this header? The only extra thing we do is push a __bug_table
> entry, but I can't see why that would be a problem.

The only reason for turning off CONFIG_BUG is to save a little extra space
in the kernel image, so I think we really don't want the __bug_table to be
generated.

However, we could split the existing asm in two and have only one definition
for the asm containing the brk instruction.

     Arnd