I was literally just looking at this. I originally commented out the removal of debug (which I though was really annoying) but ran into the absolute relocations warning for symbols that it need not apply to. Your two-pass solution is a nice one. > -----Original Message----- > From: Ard Biesheuvel [mailto:ard.biesheuvel@xxxxxxxxxx] > Sent: Wednesday, October 19, 2016 5:41 AM > To: linux-efi@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Cc: mark.rutland@xxxxxxx; leif.lindholm@xxxxxxxxxx; Cohen, Eugene > <eugene@xxxxxx>; matt@xxxxxxxxxxxxxxxxxxx; Ard Biesheuvel > <ard.biesheuvel@xxxxxxxxxx> > Subject: [RFC PATCH 1/2] efi: libstub: preserve .debug sections after absolute > relocation check > > The build commands for the ARM and arm64 EFI stubs strips the .debug > sections and other sections that my legally contain absolute relocations, > in order to inspect the remaining sections for the presence of such > relocations. > > This leaves us without debugging symbols in the stub for no good reason, > given that these sections are omitted from the kernel binary, and that > these relocations are thus only interpreted by the debugger. > > So if the relocation check succeeds, invoke objcopy again, but this time, > leave the .debug sections in place. Note that these sections may refer > to ksymtab/kcrctab contents, so leave those in place as well. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> Reviewed-by: Eugene Cohen <eugene@xxxxxx> > --- > drivers/firmware/efi/libstub/Makefile | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > diff --git a/drivers/firmware/efi/libstub/Makefile > b/drivers/firmware/efi/libstub/Makefile > index c06945160a41..66584f173123 100644 > --- a/drivers/firmware/efi/libstub/Makefile > +++ b/drivers/firmware/efi/libstub/Makefile > @@ -60,7 +60,7 @@ CFLAGS_arm64-stub.o := - > DTEXT_OFFSET=$(TEXT_OFFSET) > extra-$(CONFIG_EFI_ARMSTUB) := $(lib-y) > lib-$(CONFIG_EFI_ARMSTUB) := $(patsubst %.o,%.stub.o,$(lib-y)) > > -STUBCOPY_FLAGS-y := -R .debug* -R *ksymtab* -R *kcrctab* > +STUBCOPY_RM := -R .debug* -R *ksymtab* -R *kcrctab* > STUBCOPY_FLAGS-$(CONFIG_ARM64) += --prefix-alloc-sections=.init \ > --prefix-symbols=__efistub_ > STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS > @@ -68,11 +68,20 @@ STUBCOPY_RELOC-$(CONFIG_ARM64) := > R_AARCH64_ABS > $(obj)/%.stub.o: $(obj)/%.o FORCE > $(call if_changed,stubcopy) > > +# > +# This calls objcopy twice: the first time it includes STUBCOPY_RM, and inspects > +# the result to ensure that the actual code itself does not contain any absolute > +# references. If this succeeds, the objcopy is performed a second time, but this > +# time the .debug and other sections are retained, given that we know that the > +# absolute relocations they may contain are harmless. > +# > quiet_cmd_stubcopy = STUBCPY $@ > - cmd_stubcopy = if $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@; then \ > - $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y) \ > - && (echo >&2 "$@: absolute symbol references not allowed in > the EFI stub"; \ > - rm -f $@; /bin/false); else /bin/false; fi > + cmd_stubcopy = if $(OBJCOPY) $(STUBCOPY_FLAGS-y) $(STUBCOPY_RM) $< > $@; \ > + then if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); \ > + then (echo >&2 "$@: absolute symbol references not allowed > in the EFI stub"; \ > + rm -f $@; /bin/false); \ > + else $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@; fi \ > + else /bin/false; fi > > # > # ARM discards the .data section because it disallows r/w data in the > -- > 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
