+ Linux Toolchains, Nick Clifton (author of https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107) https://lore.kernel.org/linux-block/CAKwvOdkpNRvD0kDe-j8N0Gkq+1Fdhd6=z-9ROm3gc12Sf0k-Kg@xxxxxxxxxxxxxx/ is the thread for context. On Wed, Aug 3, 2022 at 10:45 AM Jens Axboe <axboe@xxxxxxxxx> wrote: > > I ran with the below and it silences the linker warning mentioned. I do > also see the below with my build (which aren't new with the option added > obviously, but not visible since I don't get the other noise): > > axboe@r7525 ~/gi/linux-block (test)> time make -j256 -s 1.886s > ld: warning: .tmp_vmlinux.kallsyms1 has a LOAD segment with RWX permissions > ld: warning: .tmp_vmlinux.kallsyms2 has a LOAD segment with RWX permissions > ld: warning: vmlinux has a LOAD segment with RWX permissions Not sure yet about these. Looks like there's linker flags to disable warnings...but I don't recommend those. https://github.com/systemd/systemd/commit/b0e5bf0451a6bc94e6e7b2a1de668b75c63f38c8 I wonder if they go away by fixing the boot issues described below? Otherwise, I think we need to find which section is the problematic one; I suspect the segment flagged as LOAD is composed of many sections, with possibly only one or a few that needs permissions adjusted. > ld: warning: arch/x86/boot/compressed/efi_thunk_64.o: missing .note.GNU-stack section implies executable stack > ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker Right, arch/x86/boot/compressed (and arch/x86/boot/) discard/reset KBUILD_AFLAGS (via the := assignment operator). So arch/x86/boot/Makefile and arch/x86/boot/compressed/Makefile also will need changes similar to the one you did below. Finally, if those parts of the code actually expect the stack to be executable (probably depends on some inline asm), I suspect we might get some kind of fault at runtime (though I don't know how the kernel handles segment permissions or even uses ELF segments). Point being that -Wa,--noexecstack is somewhat a promise that we wont try to execute data on the stack as if it were code. -Wa,--execstack is useful if we need to be able to do so, but we should be careful to limit that to individual translation units if they really truly need that. The linker warning is more so about the current ambiguity since if the implicit default changes in the future, that could break code. Better for us to be explicit here, and disable executable stack unless strictly necessary and only as necessary IMO. Personally, I think the current implicit default is wrong, but pragmatically I recognize that people have been used to the status quo for years, and changing it could break existing codebases. If you send the below diff with the two other additions I suggest to the x86 ML, the x86 maintainers might be able to comment if they're familiar with any possible cases where the stack is expected to be executable. > ld: warning: arch/x86/boot/compressed/vmlinux has a LOAD segment with RWX permissions > ld: warning: arch/x86/boot/pmjump.o: missing .note.GNU-stack section implies executable stack > ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker ^ See above. > ld: warning: arch/x86/boot/setup.elf has a LOAD segment with RWX permissions > > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index 7854685c5f25..51824528a026 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -123,6 +123,7 @@ else > CHECKFLAGS += -D__x86_64__ > > KBUILD_AFLAGS += -m64 > + KBUILD_AFLAGS += -Wa,--noexecstack > KBUILD_CFLAGS += -m64 > > # Align jump targets to 1 byte, not the default 16 bytes: > > -- > Jens Axboe > -- Thanks, ~Nick Desaulniers
