On Thu, Nov 17, 2016 at 2:47 AM, Carlos Chinea <carlos.chinea@xxxxxxxxx> wrote: > Hi, > > We have been trying to boot up a kernel (4.9-rc5, also tested with 4.4.31 > and 4.1.35) build with the latest binutils 2.27. > However, all those kernels fail to boot on qemu and no console logs can be > seen. > The same kernels build with binutils 2.26.1 boot without problems. > > Here some extra info: > > We have used qemu 1.6.2 to test this, with the following command: > > qemu-system-x86_64 -nographic -nodefaults -serial stdio -append > "console=ttyS0,38400" -kernel bzImage > > and we have used gcc 4.9.4 and binutils 2.27 to build the kernel. > The kernel is configure with: > > # CONFIG_RELOCATABLE is not set > > you can see the full defconfig at the end of the email. > > After bisecting binutils, we narrowed the issue to the following commit: > > commit bae420ef26f4331415b0503141c5931318025906 > Author: H.J. Lu <hjl.tools@xxxxxxxxx> > Date: Fri Feb 26 09:38:08 2016 -0800 > > Optimize x86 GOT32X/GOTPCRELX relocations > > R_386_GOT32X, R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX relocations > retrieve the symbol address via its GOT slot. If the symbol address is > known at the link-time, we can use it directly by changing instruction > encoding. Indirect branch can only be converted to PC relative direct > branch. MOV can be changed to LEA or encoded differently with signed > address. The subset of binary operations can be encoded only with > signed address. > > If undefined weak symbol is resolved to zero link-time, we can use it > as address. Zero addresss can't used with PC relative direct branch > when PIC is true since the current PC is unknown. In 64-bit, 32-bit > relocation for PC relatiave direct branch to zero may also overflow. > > If this optimization causes relocation overflow, --no-relax can be used > to work around it. > > bfd/ > > PR ld/19609 > * elf32-i386.c (elf_i386_convert_load): Convert to R_386_32 for > load with locally bound symbols if PIC is false or there is no > base register. Optimize branch to 0 if PIC is false. > (elf_i386_relocate_section): Don't generate dynamic relocations > against undefined weak symbols if PIC is false. > * elf64-x86-64.c (elf_x86_64_convert_load): Disable optimization > if we can't estimate relocation overflow with --no-relax. > Convert to R_X86_64_32S/R_X86_64_32 for load with locally bound > symbols if PIC is false. Optimize branch to 0 if PIC is false. > (elf_x86_64_relocate_section): Don't generate dynamic > relocations > against undefined weak symbols if PIC is false. > > So it seems that with the latest binutils the linker does some optimization > that breaks > the booting. > Disabling the linker relaxation with (--no-relax) fixes the issue. > The same happens whew linking with (-pie -z noreloc-overflow) options. > The compressed kernel is built with PIE/PIC and may be loaded at any address by bootloader, regardless if CONFIG_RELOCATABLE is set or not. Please try diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 536ccfc..e598a81 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -40,7 +40,6 @@ GCOV_PROFILE := n UBSAN_SANITIZE :=n LDFLAGS := -m elf_$(UTS_MACHINE) -ifeq ($(CONFIG_RELOCATABLE),y) # If kernel is relocatable, build compressed kernel as PIE. ifeq ($(CONFIG_X86_32),y) LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker) @@ -51,7 +50,6 @@ else LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \ && echo "-z noreloc-overflow -pie --no-dynamic-linker") endif -endif LDFLAGS_vmlinux := -T hostprogs-y := mkpiggy -- H.J. -- To unsubscribe from this list: send the line "unsubscribe linux-x86_64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
