2023-07-17 20:52:02

by Jakob Koschel

Subject: [PATCH] arch: enable HAS_LTO_CLANG with KASAN and KCOV

Both KASAN and KCOV had issues with LTO_CLANG if DEBUG_INFO is enabled.
With LTO inlinable function calls are required to have debug info if
they are inlined into a function that has debug info.

Starting with LLVM 17 this will be fixed ([1],[2]) and enabling LTO with
KASAN/KCOV and DEBUG_INFO doesn't cause linker errors anymore.

Signed-off-by: Jakob Koschel <[email protected]>
Link: https://github.com/llvm/llvm-project/commit/913f7e93dac67ecff47bade862ba42f27cb68ca9
Link: https://github.com/llvm/llvm-project/commit/4a8b1249306ff11f229320abdeadf0c215a00400
---
arch/Kconfig | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index aff2746c8af2..61263ff92271 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -745,7 +745,8 @@ config HAS_LTO_CLANG
depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
depends on ARCH_SUPPORTS_LTO_CLANG
depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
- depends on !KASAN || KASAN_HW_TAGS
+ depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO
+ depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO
depends on !GCOV_KERNEL
help
The compiler and Kconfig options support building with Clang's

---
base-commit: fdf0eaf11452d72945af31804e2a1048ee1b574c
change-id: 20230717-enable-kasan-lto1-656754c76241

Best regards,
--
Jakob Koschel <[email protected]>

2023-07-17 20:54:24

by Nathan Chancellor

Subject: Re: [PATCH] arch: enable HAS_LTO_CLANG with KASAN and KCOV

Hi Jakob,

On Mon, Jul 17, 2023 at 10:09:27PM +0200, Jakob Koschel wrote:
> Both KASAN and KCOV had issues with LTO_CLANG if DEBUG_INFO is enabled.
> With LTO inlinable function calls are required to have debug info if
> they are inlined into a function that has debug info.
>
> Starting with LLVM 17 this will be fixed ([1],[2]) and enabling LTO with
> KASAN/KCOV and DEBUG_INFO doesn't cause linker errors anymore.
>
> Signed-off-by: Jakob Koschel <[email protected]>
> Link: https://github.com/llvm/llvm-project/commit/913f7e93dac67ecff47bade862ba42f27cb68ca9
> Link: https://github.com/llvm/llvm-project/commit/4a8b1249306ff11f229320abdeadf0c215a00400

Thanks for seeing this to completion, especially with the LLVM fixes in
tow! One small nit below, other than that:

Reviewed-by: Nathan Chancellor <[email protected]>

Normally, I would not say that comment alone is worth a v2 but I think
in this case, I will say it is because neither Nick nor I pick up
patches directly, so this will need to be picked up by either Kees Cook
(who has generally handled clang LTO patches because he ferried in the
initial LTO series to mainline) or Andrew Morton.

Would you mind addressing my comment and sending a v2 to them directly
(they can figure out who will take it) with us on CC in case we need to
poke them? Their addresses should be in MAINTAINERS.

Cheers,
Nathan

> ---
> arch/Kconfig | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index aff2746c8af2..61263ff92271 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -745,7 +745,8 @@ config HAS_LTO_CLANG
> depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
> depends on ARCH_SUPPORTS_LTO_CLANG
> depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
> - depends on !KASAN || KASAN_HW_TAGS

Consider linking back to either your fixes in LLVM or
https://github.com/ClangBuiltLinux/linux/issues/1721 so that we have a
paper trail of why these version checks are here :)

> + depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO
> + depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO
> depends on !GCOV_KERNEL
> help
> The compiler and Kconfig options support building with Clang's
>
> ---
> base-commit: fdf0eaf11452d72945af31804e2a1048ee1b574c
> change-id: 20230717-enable-kasan-lto1-656754c76241
>
> Best regards,
> --
> Jakob Koschel <[email protected]>
>