Re: [RFC] Don't create sframes during build

[Sven Joachim <svenjoac@gmx.de>]

On 2025-09-04 10:14 -0700, Josh Poimboeuf wrote:

> On Thu, Sep 04, 2025 at 06:34:04PM +0200, Sebastian Andrzej Siewior wrote:
>> On 2025-09-04 16:02:42 [+0200], Matthias Klose wrote:
>> > [ CCing binutils@sourceware.org ]
>> > 
>> > On 9/4/25 15:18, Sebastian Andrzej Siewior wrote:
>> > > Hi,
>> > > 
>> > > gcc in Debian, starting with 15.2.0-2, 14.3.0-6 enables sframe
>> > > generation. Unless options like -ffreestanding are passed. Since this
>> > > isn't done, there are a few warnings during compile
>> > 
>> > If there are other options when sframe shouldn't be enabled, please tell.
>> 
>> No, I think this is okay.
>> 
>> …
>> > > We could drop the sframe during the final link but this does not get rid
>> > > of the objtool warnings so we would have to ignore them. But we don't
>> > > need it. So what about the following:
>> > > 
>> > > diff --git a/Makefile b/Makefile
>> > > --- a/Makefile
>> > > +++ b/Makefile
>> > > @@ -886,6 +886,8 @@ ifdef CONFIG_CC_IS_GCC
>> > >   KBUILD_CFLAGS	+= $(call cc-option,--param=allow-store-data-races=0)
>> > >   KBUILD_CFLAGS	+= $(call cc-option,-fno-allow-store-data-races)
>> > >   endif
>> > > +# No sframe generation for kernel if enabled by default
>> > > +KBUILD_CFLAGS	+= $(call cc-option,-Xassembler --gsframe=no)
>> > >   ifdef CONFIG_READABLE_ASM
>> > >   # Disable optimizations that make assembler listings hard to read.
>> > This is what I chose for package builds that need disablement of sframe.
>> 
>> I think this would work for now. Longterm we would have to allow sframe
>> creation and keep section if an architecture decides to use it for its
>> backtracing. While orc seems fine on x86, there are arm64 patches to use
>> for as a stack unwinder.
>
> This is probably fine, but... how does this interact with other kernel
> makefiles enabling sframe?  For example, x86 will soon have a patch to
> enable sframe generation for vdso.  And as you mentioned, arm64 will
> enable it kernel-wide.
>
> Removing the objtool !ENDBR warnings would be trivial (and is a good
> thing to do regardless).

What is the status of sframe support in the kernel?  With current
binutils (version 2.45.50.20260119-1) from Debian I could not build
Linux 6.18.7:

,----
| # LD      arch/x86/boot/compressed/vmlinux
|   ld -m elf_x86_64 --no-ld-generated-unwind-info  -pie  --no-dynamic-linker --orphan-handling=error -z noexecstack --no-warn-rwx-segments -T arch/x86/boot/compressed/vmlinux.lds arch/x86/boot/compressed/kernel_info.o arch/x86/boot/compressed/head_64.o arch/x86/boot/compressed/misc.o arch/x86/boot/compressed/string.o arch/x86/boot/compressed/cmdline.o arch/x86/boot/compressed/error.o arch/x86/boot/compressed/piggy.o arch/x86/boot/compressed/cpuflags.o arch/x86/boot/compressed/early_serial_console.o arch/x86/boot/compressed/kaslr.o arch/x86/boot/compressed/ident_map_64.o arch/x86/boot/compressed/idt_64.o arch/x86/boot/compressed/idt_handlers_64.o arch/x86/boot/compressed/pgtable_64.o arch/x86/boot/compressed/acpi.o arch/x86/boot/startup/lib.a -o arch/x86/boot/compressed/vmlinux
| /usr/bin/x86_64-linux-gnu-ld.bfd: error: unplaced orphan section `.sframe' from `arch/x86/boot/compressed/kernel_info.o'
| /usr/bin/x86_64-linux-gnu-ld.bfd: error: unplaced orphan section `.sframe' from `arch/x86/boot/compressed/kernel_info.o'
| make[6]: *** [arch/x86/boot/compressed/Makefile:116: arch/x86/boot/compressed/vmlinux] Error 1
| make[5]: *** [arch/x86/boot/Makefile:96: arch/x86/boot/compressed/vmlinux] Error 2
`----

Did not test mainline yet, but "git log --grep=sframe master" does not
show anything interesting.

Cheers,
       Sven