From: Catalin Marinas <catalin.marinas@arm.com>
To: Fangrui Song <maskray@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Ilie Halip <ilie.halip@gmail.com>,
Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org, Jian Cai <jiancai@google.com>,
clang-built-linux@googlegroups.com, Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] arm64: Delete the space separator in __emit_inst
Date: Wed, 15 Apr 2020 13:07:52 +0100 [thread overview]
Message-ID: <20200415120752.GD6526@gaia> (raw)
In-Reply-To: <20200414163255.66437-1-maskray@google.com>
On Tue, Apr 14, 2020 at 09:32:55AM -0700, Fangrui Song wrote:
> In assembly, many instances of __emit_inst(x) expand to a directive. In
> a few places __emit_inst(x) is used as an assembler macro argument. For
> example, in arch/arm64/kvm/hyp/entry.S
>
> ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)
>
> expands to the following by the C preprocessor:
>
> alternative_insn nop, .inst (0xd500401f | ((0) << 16 | (4) << 5) | ((!!1) << 8)), 4, 1
>
> Both comma and space are separators, with an exception that content
> inside a pair of parentheses/quotes is not split, so the clang
> integrated assembler splits the arguments to:
>
> nop, .inst, (0xd500401f | ((0) << 16 | (4) << 5) | ((!!1) << 8)), 4, 1
>
> GNU as preprocesses the input with do_scrub_chars(). Its arm64 backend
> (along with many other non-x86 backends) sees:
>
> alternative_insn nop,.inst(0xd500401f|((0)<<16|(4)<<5)|((!!1)<<8)),4,1
> # .inst(...) is parsed as one argument
>
> while its x86 backend sees:
>
> alternative_insn nop,.inst (0xd500401f|((0)<<16|(4)<<5)|((!!1)<<8)),4,1
> # The extra space before '(' makes the whole .inst (...) parsed as two arguments
>
> The non-x86 backend's behavior is considered unintentional
> (https://sourceware.org/bugzilla/show_bug.cgi?id=25750).
> So drop the space separator inside `.inst (...)` to make the clang
> integrated assembler work.
>
> Suggested-by: Ilie Halip <ilie.halip@gmail.com>
> Signed-off-by: Fangrui Song <maskray@google.com>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/939
Queued for 5.7. Thanks.
--
Catalin
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prev parent reply other threads:[~2020-04-15 12:08 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 16:32 [PATCH v2] arm64: Delete the space separator in __emit_inst Fangrui Song
2020-04-15 12:07 ` Catalin Marinas [this message]
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