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Date: Wed, 15 Apr 2020 13:07:52 +0100 From: Catalin Marinas <catalin.marinas@....com> To: Fangrui Song <maskray@...gle.com> Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Nick Desaulniers <ndesaulniers@...gle.com>, clang-built-linux@...glegroups.com, Ilie Halip <ilie.halip@...il.com>, Jian Cai <jiancai@...gle.com> Subject: Re: [PATCH v2] arm64: Delete the space separator in __emit_inst 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@...il.com> > Signed-off-by: Fangrui Song <maskray@...gle.com> > Reviewed-by: Mark Rutland <mark.rutland@....com> > Link: https://github.com/ClangBuiltLinux/linux/issues/939 Queued for 5.7. Thanks. -- Catalin
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