Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Tue, 4 Jan 2022 11:56:38 +0100
From:   Ingo Molnar <mingo@kernel.org>
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "David S. Miller" <davem@davemloft.net>,
        Ard Biesheuvel <ardb@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Al Viro <viro@zeniv.linux.org.uk>, llvm@lists.linux.dev
Subject: [DEBUG PATCH] DO NOT MERGE: Enable SHADOW_CALL_STACK on GCC builds,
 for build testing
Message-ID: <YdQn5kTyXUJmdH9r@gmail.com>
References: <YdIfz+LMewetSaEB@gmail.com>
 <YdM4Z5a+SWV53yol@archlinux-ax161>
 <YdQlwnDs2N9a5Reh@gmail.com>
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* Ingo Molnar <mingo@kernel.org> wrote:

> > 2. Error with CONFIG_SHADOW_CALL_STACK
> 
> So this feature depends on Clang:
> 
>  # Supported by clang >= 7.0
>  config CC_HAVE_SHADOW_CALL_STACK
>          def_bool $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18)
> 
> No way to activate it under my GCC cross-build toolchain, right?
> 
> But ... I hacked the build mode on with GCC using this patch:
> 
> From: Ingo Molnar <mingo@kernel.org>
> Date: Tue, 4 Jan 2022 11:26:09 +0100
> Subject: [PATCH] DO NOT MERGE: Enable SHADOW_CALL_STACK on GCC builds, for build testing
> 
> NOT-Signed-off-by: Ingo Molnar <mingo@kernel.org>

Ok, I've attached patch again instead embedding it in the middle of a long 
discussion, for future reference.

Thanks,

	Ingo

=====================>
From: Ingo Molnar <mingo@kernel.org>
Date: Tue, 4 Jan 2022 11:26:09 +0100
Subject: [PATCH] DO NOT MERGE: Enable SHADOW_CALL_STACK on GCC builds, for build testing

NOT-Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 Makefile           | 2 +-
 arch/Kconfig       | 2 +-
 arch/arm64/Kconfig | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 16d7f83ac368..bbab462e7509 100644
--- a/Makefile
+++ b/Makefile
@@ -888,7 +888,7 @@ LDFLAGS_vmlinux += --gc-sections
 endif
 
 ifdef CONFIG_SHADOW_CALL_STACK
-CC_FLAGS_SCS	:= -fsanitize=shadow-call-stack
+CC_FLAGS_SCS	:=
 KBUILD_CFLAGS	+= $(CC_FLAGS_SCS)
 export CC_FLAGS_SCS
 endif
diff --git a/arch/Kconfig b/arch/Kconfig
index 4e56f66fdbcf..2103d9da4fe1 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -605,7 +605,7 @@ config ARCH_SUPPORTS_SHADOW_CALL_STACK
 
 config SHADOW_CALL_STACK
 	bool "Clang Shadow Call Stack"
-	depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
+	depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
 	depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
 	help
 	  This option enables Clang's Shadow Call Stack, which uses a
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index c4207cf9bb17..952f3e56e0a7 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1183,7 +1183,7 @@ config ARCH_HAS_FILTER_PGPROT
 
 # Supported by clang >= 7.0
 config CC_HAVE_SHADOW_CALL_STACK
-	def_bool $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18)
+	def_bool y
 
 config PARAVIRT
 	bool "Enable paravirtualization code"