linux-kernel - [PATCH 5.4 271/411] Kconfig: add config option for asm goto w/ outputs

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Message-Id: <20220613094936.886224146@linuxfoundation.org>
Date:   Mon, 13 Jun 2022 12:09:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nick Desaulniers <ndesaulniers@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.4 271/411] Kconfig: add config option for asm goto w/ outputs

From: Nick Desaulniers <ndesaulniers@...gle.com>

commit 587f17018a2c6c414e41a312b002faaef60cf423 upstream.

This allows C code to make use of compilers with support for output
variables along the fallthrough path via preprocessor define:

  CONFIG_CC_HAS_ASM_GOTO_OUTPUT

[ This is not used anywhere yet, and currently released compilers don't
  support this yet, but it's coming, and I have some local experimental
  patches to take advantage of it when it does   - Linus ]

Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 init/Kconfig |    4 ++++
 1 file changed, 4 insertions(+)

--- a/init/Kconfig
+++ b/init/Kconfig
@@ -38,6 +38,10 @@ config CC_HAS_ASM_GOTO_TIED_OUTPUT
 	# Detect buggy gcc and clang, fixed in gcc-11 clang-14.
 	def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)
 
+config CC_HAS_ASM_GOTO_OUTPUT
+	depends on CC_HAS_ASM_GOTO
+	def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
+
 config TOOLS_SUPPORT_RELR
 	def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)