On Mon, May 4, 2020 at 1:16 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > 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 drop the .llvm_addrsig section explicitly as well, to work around > this behavior. > > [0] https://sourceware.org/bugzilla/show_bug.cgi?id=23817 This page also has info about the extension: https://llvm.org/docs/Extensions.html#sht-llvm-addrsig-section-address-significance-table Peter, do you know if it's possible to prevent the emission of this section from clang? Scanning through the sources, it looks like it's set unconditionally during LTO, but I couldn't find where else? Is this section required for more than LTO? We need a generic way to disable LLVM extensions when we're not using the LLVM binutils. We have a couple cases where `-no-integrated-as` will prevent AsmStreamer from not using assembler extensions, but in this case it's the linker+objcopy+strip that don't work with the extensions. > > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Reported-by: Arnd Bergmann <arnd@xxxxxxxx> Do you have a link to the configs or report so we can repro? Also, scripts/get_maintainer.pl should recommend our list for patches mentioning clang or llvm, which is a wider audience that can help test and review. I've been out sick much of the past week, so I appreciate the shared help with code review. Of course if your intention was to be more discreet, I'm sorry I may have just messed that up. > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > drivers/firmware/efi/libstub/Makefile | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile > index 8d246b51bd49..4d137615a666 100644 > --- a/drivers/firmware/efi/libstub/Makefile > +++ b/drivers/firmware/efi/libstub/Makefile > @@ -66,7 +66,8 @@ CFLAGS_arm64-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET) > # .data section of the compressed kernel to ensure initialization. Rename the > # .bss section here so it's easy to pick out in the linker script. > # > -STUBCOPY_FLAGS-$(CONFIG_X86) += --rename-section .bss=.bss.efistub,load,alloc > +STUBCOPY_FLAGS-$(CONFIG_X86) += -R .llvm_addrsig \ > + --rename-section .bss=.bss.efistub,load,alloc Do we only observe this for x86, not ARM? > STUBCOPY_RELOC-$(CONFIG_X86_32) := R_386_32 > STUBCOPY_RELOC-$(CONFIG_X86_64) := R_X86_64_64 > > @@ -111,7 +112,7 @@ $(obj)/%.stub.o: $(obj)/%.o FORCE > # > quiet_cmd_stubcopy = STUBCPY $@ > cmd_stubcopy = \ > - $(STRIP) --strip-debug -o $@ $<; \ > + $(STRIP) --strip-debug -R .llvm_addrsig -o $@ $<; \ > if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then \ > echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \ > /bin/false; \ > -- > 2.17.1 > In the absence of a linker script where we can use `DISCARD` rules, this looks like the best approach, though I'm still curious about ARM. Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> -- Thanks, ~Nick Desaulniers
