On 8/3/22 11:38 AM, Nick Desaulniers wrote:
> On Wed, Aug 3, 2022 at 9:53 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
>>
>> On 8/3/22 10:51 AM, Nick Desaulniers wrote:
>>> On Wed, Aug 3, 2022 at 9:26 AM Linus Torvalds
>>> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>>>
>>>> On Wed, Aug 3, 2022 at 8:16 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
>>>>>
>>>>> On the topic of warnings, on my new build box I get a lot of these:
>>>>>
>>>>> ld: warning: arch/x86/lib/putuser.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
>>>>>
>>>>> which ends up polluting the output quite a bit.
>>>>>
>>>>> axboe@r7525 ~> ld --version
>>>>> GNU ld (GNU Binutils for Debian) 2.38.90.20220713
>>>>
>>>> Ok, I have binutils 2.37, so it may be new to 2.38.
>>>>
>>>> Some googling around seems to imply that we'd need to so something like this
>>>>
>>>> .section .note.GNU-stack,"",%progbits
>>>>
>>>> in all our *.S files.
>>>>
>>>> We do have some signs of that in our tooling, because apparently it
>>>> has hit user-space, but I wonder what has triggered the need on the
>>>> kernel side for you.
>>>>
>>>> I'd hate to add that pointless line to every asm file, but maybe we
>>>> could so something like this
>>>>
>>>> #ifdef __ASSEMBLY_
>>>> #ifdef OUTPUT_PROGBITS
>>>> .section .note.GNU-stack,"",%progbits
>>>> #undef OUTPUT_PROGBITS
>>>> #endif
>>>> #endif
>>>>
>>>> and then change our 'AS' command line to do '-DOUTPUT_PROGBITS' in our
>>>> makefiles.
>>>>
>>>> *Most* asm files should include <linux/linkage.h> just for all the
>>>> macros that declare variables externally, so that might catch the bulk
>>>> of it.
>>>>
>>>> Somebody who knows the rules better than I would be a good idea.
>>>
>>> $ as --help | grep exec
>>> --execstack require executable stack for this object
>>> --noexecstack don't require executable stack for this object
>>> --statistics print various measured statistics from execution
>>>
>>> Does adding `--noexecstack` to KBUILD_ASFLAGS for these architectures
>>> help, rather than modifying every assembler source?
>>
>> I can try whatever here, but a quick grep doesn't find anything for
>> KBUILD_ASFLAGS or anything close to it. What am I missing?
>
> Sorry, I'm running between many meetings today...so suggestions aren't
> tested and may not be fully coherent...
>
> KBUILD_AFLAGS += -Wa,--noexecstack
>
> There's also as-option Make macro in case older binutils doesn't
> support that flag outright.
>
> tools/perf/Makefile.config also uses noexecstack as a linker flag.
> That might be an option, too. It is the linker producing the
> warnings, not the assembler, but the assembler flag is probably the
> way to go to fix the warnings since it sounds like these are assembler
> sources exclusively causing the issue.
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
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
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
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
