linux-kernel - [PATCH 13/15] efi/libstub/x86: Work around LLVM ELF quirk build regression

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Date:   Fri,  8 May 2020 20:01:55 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Guenter Roeck <linux@...ck-us.net>,
        Joe Perches <joe@...ches.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 13/15] efi/libstub/x86: Work around LLVM ELF quirk build regression

When building the x86 EFI stub with Clang, the libstub Makefile rules
that manipulate the ELF object files may throw an error like:

    STUBCPY drivers/firmware/efi/libstub/efi-stub-helper.stub.o
  strip: drivers/firmware/efi/libstub/efi-stub-helper.stub.o: Failed to find link section for section 10
  objcopy: drivers/firmware/efi/libstub/efi-stub-helper.stub.o: Failed to find link section for section 10

This is the result of a LLVM feature [0] where symbol references are
stored in a LLVM specific .llvm_addrsig section in a non-transparent way,
causing generic ELF tools such as strip or objcopy to choke on them.

So force the compiler not to emit these sections, by passing the
appropriate command line option.

[0] https://sourceware.org/bugzilla/show_bug.cgi?id=23817

Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Peter Collingbourne <pcc@...gle.com>
Cc: Sami Tolvanen <samitolvanen@...gle.com>
Reported-by: Arnd Bergmann <arnd@...db.de>
Suggested-by: Fangrui Song <maskray@...gle.com>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 drivers/firmware/efi/libstub/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 8d246b51bd49..e5a49dc8e9bc 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -30,6 +30,7 @@ KBUILD_CFLAGS			:= $(cflags-y) -DDISABLE_BRANCH_PROFILING \
 				   -D__NO_FORTIFY \
 				   $(call cc-option,-ffreestanding) \
 				   $(call cc-option,-fno-stack-protector) \
+				   $(call cc-option,-fno-addrsig) \
 				   -D__DISABLE_EXPORTS
 
 GCOV_PROFILE			:= n
-- 
2.17.1