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Date:   Thu, 18 Jun 2020 11:31:16 +0200
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Subject: [PATCH 1/3] kcsan: Re-add GCC as a supported compiler
From:   Marco Elver <elver@google.com>
To:     elver@google.com, paulmck@kernel.org
Cc:     will@kernel.org, peterz@infradead.org, bp@alien8.de,
        tglx@linutronix.de, mingo@kernel.org, dvyukov@google.com,
        cai@lca.pw, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, Martin Liska <mliska@suse.cz>
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GCC version 11 recently implemented all requirements to correctly
support KCSAN:

1. Correct no_sanitize-attribute inlining behaviour:
   https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=4089df8ef4a63126b0774c39b6638845244c20d2

2. --param=tsan-distinguish-volatile
   https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=ab2789ec507a94f1a75a6534bca51c7b39037ce0

3. --param=tsan-instrument-func-entry-exit
   https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=06712fc68dc9843d9af7c7ac10047f49d305ad76

Therefore, we can re-enable GCC for KCSAN, and document the new compiler
requirements.

Signed-off-by: Marco Elver <elver@google.com>
Cc: Martin Liska <mliska@suse.cz>
---

For anyone interested to try it out before GCC 11 is released, I'd
recommend building a stable GCC 10 with the patches applied:

	git clone git://gcc.gnu.org/git/gcc.git && cd gcc
	git checkout -b gcc-10-for-kcsan releases/gcc-10.1.0
	git cherry-pick \
		4089df8ef4a63126b0774c39b6638845244c20d2 \
		ab2789ec507a94f1a75a6534bca51c7b39037ce0 \
		06712fc68dc9843d9af7c7ac10047f49d305ad76
	./configure --prefix <your-prefix> --enable-languages=c,c++
	make -j$(nproc) && make install
---
 Documentation/dev-tools/kcsan.rst | 3 ++-
 lib/Kconfig.kcsan                 | 3 ++-
 scripts/Makefile.kcsan            | 2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/dev-tools/kcsan.rst b/Documentation/dev-tools/kcsan.rst
index ce4bbd918648..8fa0dd6c8614 100644
--- a/Documentation/dev-tools/kcsan.rst
+++ b/Documentation/dev-tools/kcsan.rst
@@ -8,7 +8,8 @@ approach to detect races. KCSAN's primary purpose is to detect `data races`_.
 Usage
 -----
 
-KCSAN requires Clang version 11 or later.
+KCSAN is supported by both GCC and Clang. With GCC we require version 11 or
+later, and with Clang also require version 11 or later.
 
 To enable KCSAN configure the kernel with::
 
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 3f3b5bca7a8f..3d282d51849b 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -4,7 +4,8 @@ config HAVE_ARCH_KCSAN
 	bool
 
 config HAVE_KCSAN_COMPILER
-	def_bool CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)
+	def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)) || \
+		 (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-distinguish-volatile=1))
 	help
 	  For the list of compilers that support KCSAN, please see
 	  <file:Documentation/dev-tools/kcsan.rst>.
diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
index bd4da1af5953..dd66206f4578 100644
--- a/scripts/Makefile.kcsan
+++ b/scripts/Makefile.kcsan
@@ -6,7 +6,7 @@ ifdef CONFIG_KCSAN
 ifdef CONFIG_CC_IS_CLANG
 cc-param = -mllvm -$(1)
 else
-cc-param = --param -$(1)
+cc-param = --param $(1)
 endif
 
 # Keep most options here optional, to allow enabling more compilers if absence
-- 
2.27.0.290.gba653c62da-goog