Re: [PATCH] Add ELF note with Linux version

Jeremy Fitzhardinge
2007-09-14T21:31:38Z

Sam Ravnborg wrote:
>>> This seems outright silly.
>>> Either we should revert the notes changes or someone caring about it
>>> should sweep all archs and make sure it does not hurt there.
>>>
>> Hm, sounds like yet another binutils bug; unfortunately common when ELF
>> notes are about. Was there any further effort to isolate what was
>> causing the problem?
>>
>
> Lennart posted this:
> An ARM vmlinux kernel image built with pre-build-id binutils has:
>
> Program Header:
> LOAD off 0x00008000 vaddr 0xc0008000 paddr 0xc0008000 align 2**15
> filesz 0x002e503c memsz 0x003032c0 flags rwx
> private flags = 4000002: [Version4 EABI] [has entry point]
>
>
> Whereas a build-id binutils-built vmlinux kernel image ends up with:
>
> Program Header:
> LOAD off 0x00008000 vaddr 0x00000000 paddr 0x00000000 align 2**15
> filesz 0x00000024 memsz 0x00000024 flags r--
> LOAD off 0x00010000 vaddr 0xc0008000 paddr 0xc0008000 align 2**15
> filesz 0x002e503c memsz 0x003032c0 flags rwx
> NOTE off 0x00008000 vaddr 0x00000000 paddr 0x00000000 align 2**2
> filesz 0x00000024 memsz 0x00000024 flags r--
> private flags = 4000002: [Version4 EABI] [has entry point]
>
>
> The .note.gnu.build-id section causes objcopy to produce a 3G+
> Image file, breaking the build.
>

Hm, these phdrs seem OK though; I don't see any ~3Gish numbers here, so
it looks like objcopy is just going off into the weeds.

I don't know how ARM images are built, but I would guess that something
is trying to make the file large enough to accomodate a 3Gish kernel
virtual address address which hasn't being appropriately phys-ized. It
may be more a linker script bug than an inherent problem with either
notes or build-id themselves.

> Samuel Ortiz posted following patch:
>
>> With build-id binutils (e.g. the latest bintuils 2.18), objcopy produces
>> a 3.1 Gbytes Image file. Adding a note section fixes the problem.
>>
>> Signed-off-by: Samuel Ortiz <sameo@openedhand.com>
>> Cc: Lennert Buytenhek <buytenh@wantstofly.org>
>> Cc: Sam Ravnborg <sam@ravnborg.org>
>>
>> ---
>> arch/arm/kernel/vmlinux.lds.S | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> Index: linux-2.6.22/arch/arm/kernel/vmlinux.lds.S
>> ===================================================================
>> --- linux-2.6.22.orig/arch/arm/kernel/vmlinux.lds.S 2007-09-11 18:32:29.000000000 +0200
>> +++ linux-2.6.22/arch/arm/kernel/vmlinux.lds.S 2007-09-11 18:33:42.000000000 +0200
>> @@ -94,6 +94,7 @@
>> TEXT_TEXT
>> SCHED_TEXT
>> LOCK_TEXT
>> + *(.note.*)
>> #ifdef CONFIG_MMU
>> *(.fixup)
>> #endif
>>
>
>
> I cannot see why this should fix it since the patch does
> not discard the section. Maybe the inclusion of the section in
> some oter section does some good.
>

Yes, binutils can be pretty fragile with notes about. In this case it
seems to be a specific problem with build-id; I'm not really sure what
build-id actually does.

Though if my theory above is true, it may end up properly assigning a
value to a symbol
by putting it into the right section. Or something.
> Anyway the original submitter of the build-id should have identified such
> issues and fixed all archs.
>
> And I still do not get exactly what problem the note section solves when
> included in vmlinux....

The Note section is supposed to be a general extensible way of adding
metadata to an object file, either for a linker or a loader. There's no
inherent connection between notes and build-id (other than build-id is
one of the users of notes, I suppose).

J