On Thu, Mar 3, 2022 at 9:43 PM Nick Desaulniers ndesaulniers@google.com wrote:
On Thu, Mar 3, 2022 at 10:26 AM Nathan Chancellor nathan@kernel.org wrote:
On Thu, Mar 03, 2022 at 10:04:28AM -0800, Kees Cook wrote:
How does -mno-global-merge get KBUILD_CFLAGS in the first place? If it's arm/arm64 only, shouldn't that get relocated to those architectures?
*time travel* found it:
61163efae020 ("kbuild: LLVMLinux: Add Kbuild support for building kernel with Clang")
So I think this may have been universally true long ago, and now only arm/arm64 need it?
Looks like that's the case from LLVM sources.
<snip>
diff --git a/arch/arm/Makefile b/arch/arm/Makefile index a2391b8de5a5..dcab28c44c26 100644 --- a/arch/arm/Makefile +++ b/arch/arm/Makefile @@ -48,6 +48,13 @@ CHECKFLAGS += -D__ARMEL__ KBUILD_LDFLAGS += -EL endif
+ifdef CONFIG_CC_IS_CLANG +# CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the +# source of a reference will be _MergedGlobals and not on of the whitelisted names.
I think there's a typo in the original comment. s/on of/one of/ ?
Also, I'm not sure what's meant by _MergedGlobals. Perhaps this is an opportunity to make this clearer?
"Clang's "global-merge" pass (implemented only for arm and aarch64) may break modpost Pattern 2 if symbols are renamed and thus don't appear on modpost's allowlist.
+# See modpost pattern 2 +KBUILD_CFLAGS += -mno-global-merge +endif
I can remember on x86-64 I was able to build and boot by dropping it entirely.
- Sedat -
-- Thanks, ~Nick Desaulniers