Re: [PATCH v8] xen: Strip xen.efi by default

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Sat, Nov 15, 2025 at 06:23:08AM +0000, Frediano Ziglio wrote:
> On Fri, 14 Nov 2025 at 19:18, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
> >
> > On 14/11/2025 3:40 pm, Oleksii Kurochko wrote:
> > >
> > >
> > > On 11/13/25 4:43 PM, Frediano Ziglio wrote:
> > >> From: Frediano Ziglio <frediano.ziglio@cloud.com>
> > >>
> > >> For xen.gz file we strip all symbols and have an additional
> > >> xen-syms.efi file version with all symbols.
> > >> Make xen.efi more coherent stripping all symbols too.
> > >> xen-syms.efi can be used for debugging.
> > >>
> > >> Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
> > > Release-Acked-By: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> > >
> > > Thanks.
> >
> > Thanks.  Unfortunately CI says no.
> >
> > Ubuntu's 20.04, 18.04 and 16.04 all fail:
> > https://gitlab.com/xen-project/hardware/xen-staging/-/pipelines/2159622869
> >
> > From 16.04:
> >
> > 2025-11-14T18:01:51.192964Z 01O strip xen-syms.efi -o xen.efi
> > 2025-11-14T18:01:51.198151Z 01O strip:xen-syms.efi[.init]: relocation count is negative: File truncated
> > 2025-11-14T18:01:51.198166Z 01O strip: xen.efi: Failed to read debug data section
> > 2025-11-14T18:01:51.198169Z 01O strip:xen.efi: error copying private BFD data: File truncated
> > 2025-11-14T18:01:51.198932Z 01O arch/x86/Makefile:207: recipe for target 'xen.efi' failed
> > 2025-11-14T18:01:51.198937Z 01O make[3]: *** [xen.efi] Error 1
> > 2025-11-14T18:01:51.199616Z 01O build.mk:90: recipe for target 'xen' failed
> > 2025-11-14T18:01:51.199619Z 01O make[2]: *** [xen] Error 2
> > 2025-11-14T18:01:51.200402Z 01O Makefile:600: recipe for target 'xen' failed
> > 2025-11-14T18:01:51.200409Z 01O make[1]: *** [xen] Error 2
> >
> >
> > I find it hard to believe that the relocation count is really negative,
> > and given that newer binuitls works, I expect this is a binutils bug.
> >
> 
> Unless the message is just misleading I find it hard to have a
> negative number of items in a container.
> 
> > Nevertheless, we need some workaround.  Given that the previous
> > behaviour was not to strip, I think we can reuse that for broken toolchains?
> >
> 
> Something like that ?
> 
> diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
> index a154ffe6b2..c465eb12e2 100644
> --- a/xen/arch/x86/Makefile
> +++ b/xen/arch/x86/Makefile
> @@ -236,7 +236,9 @@ ifeq ($(CONFIG_DEBUG_INFO),y)
>         $(if $(filter --strip-debug,$(EFI_LDFLAGS)),:$(space))$(OBJCOPY) \
>                 -O elf64-x86-64 $(TARGET)-syms.efi $@.elf
>  endif
> -       $(STRIP) $(TARGET)-syms.efi -o $@
> +       $(STRIP) $(TARGET)-syms.efi -o $@ || { \
> +               LANG=C strip $(TARGET)-syms.efi -o $@ 2>&1 | grep -q \
> +               "relocation count is negative" && mv -f $(TARGET)-syms.efi $@; }
>  ifneq ($(CONFIG_DEBUG_INFO),y)
>         rm -f $(TARGET)-syms.efi
>  endif

On Ubuntu 20.04 it fails different way:

    strip: xen.efi: Data Directory size (1c) exceeds space left in section (18)
    strip: xen.efi: error copying private BFD data: file in wrong format

Looks similar to:
https://lore.kernel.org/all/3TMd7J2u5gCA8ouIG_Xfcw7s5JKMG06XsDIesEB3Fi9htUJ43Lfl057wXohlpCHcszqoCmicpIlneEDO26ZqT8QfC2Y39VxBuqD3nS1j5Q4=@trmm.net/

Qubes has this patch:
https://github.com/QubesOS/qubes-vmm-xen/blob/main/0608-Fix-buildid-alignment.patch

    diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
    index 9a1dfe1b340a..26a23a7b0651 100644
    --- a/xen/arch/x86/xen.lds.S
    +++ b/xen/arch/x86/xen.lds.S
    @@ -171,6 +171,7 @@ SECTIONS
            __note_gnu_build_id_end = .;
       } PHDR(note) PHDR(text)
     #elif defined(BUILD_ID_EFI)
    +  . = ALIGN(32);
       DECL_SECTION(.buildid) {
            __note_gnu_build_id_start = .;
            *(.buildid)

Lets see if that helps:
https://gitlab.com/xen-project/people/marmarek/xen/-/pipelines/2167783980

And few lines earlier there is also:

    ld: xen-syms.efi: warning: section .init: alignment 2**15 not representable

> It will fall back to not stripping in case that bug is detected. I
> don't know how to test it.
> (the LANG=C is to always force the English message).

If going this way, use LC_ALL=C (otherwise LC_ALL=something present in
the env would override your LANG=C). But given there are different
messages, this may not be the best option.

And TBH, I don't like silent behavior change based on (unknown) version
of binutils. Lets see if the alignment adjustment helps. While it
shouldn't be necessary on newer binutils (thanks to Jan's fix there -
see thread linked above), IMO it isn't too bad to add it, to keep older
versions happy. And it can be dropped, once we raise toolchain base
version next time.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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