linux-kernel - [PATCH] arm64: Delete the space separator in __emit

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Date:   Sun, 12 Apr 2020 20:38:11 -0700
From:   Fangrui Song <maskray@...gle.com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        clang-built-linux@...glegroups.com,
        Fangrui Song <maskray@...gle.com>
Subject: [PATCH] arm64: Delete the space separator in __emit_inst

Many instances of __emit_inst(x) expand to a directive. In a few places
it is used as a macro argument, e.g.

  arch/arm64/include/asm/sysreg.h
  #define __emit_inst(x)                       .inst (x)

  arch/arm64/include/asm/sysreg.h
  #define SET_PSTATE_PAN(x)            __emit_inst(0xd500401f | PSTATE_PAN | ((!!x) << PSTATE_Imm_shift))

  arch/arm64/kvm/hyp/entry.S
  ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)

Clang integrated assembler parses `.inst (x)` as two arguments passing
to a macro. We delete the space separator so that `.inst(x)` will be
parsed as one argument.

Note, GNU as parsing `.inst (x)` as one argument is unintentional (for
example the x86 backend will parse the construct as two arguments).
See https://sourceware.org/bugzilla/show_bug.cgi?id=25750#c10

Link: https://github.com/ClangBuiltLinux/linux/issues/939
Cc: clang-built-linux@...glegroups.com
Signed-off-by: Fangrui Song <maskray@...gle.com>
---
 arch/arm64/include/asm/sysreg.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index ebc622432831..af21e2ec5e3e 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -49,7 +49,9 @@
 #ifndef CONFIG_BROKEN_GAS_INST
 
 #ifdef __ASSEMBLY__
-#define __emit_inst(x)			.inst (x)
+// The space separator is omitted so that __emit_inst(x) can be parsed as
+// either a directive or a macro argument.
+#define __emit_inst(x)			.inst(x)
 #else
 #define __emit_inst(x)			".inst " __stringify((x)) "\n\t"
 #endif
-- 
2.26.0.110.g2183baf09c-goog