Re: [Xen-devel] [PATCH v5 19/28] build_id: Provide ld-embedded build-ids

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.04.16 at 21:23, <konrad.wilk@xxxxxxxxxx> wrote:
> On Fri, Apr 08, 2016 at 11:44:54AM -0600, Jan Beulich wrote:
>> >>> On 08.04.16 at 19:06, <konrad.wilk@xxxxxxxxxx> wrote:
>> > So that when xen.efi is linked with this build_id.o (in v5, now called 
>> > notes.o in v6)
>> > it can encapsulate __note_gnu_build_id_start and __note_gnu_build_id_end 
>> > around
>> > it. I could change for EFI builds the xen.lds.S to be:
>> > 
>> >      *(.rodata.*)
>> > +#if defined(BUILD_ID) && defined(EFI)
>> > +/*
>> > + * No mechanism to put an PT_NOTE in the EFI file - so put
>> > + * it in .data section.
>> > + */
>> > +        . = ALIGN(4);
>> > +
>> > +       __note_gnu_build_id_start = .;
>> > +       *(.rodata.note.gnu.build-id)
>> > +       __note_gnu_build_id_end = .;
>> > +       *(.note)
>> > +       *(.note.*)
>> > +#endif
>> > 
>> > But then it differes from the change for !EFI (Which would be naturally
>> > called .note.gnu.build-id).
>> 
>> But that looks to be the right approach, accounting for the
>> differences between ELF and COFF/PE. And btw., unless you did
>> changes elsewhere I don't think this inclusion of .note and .note.*
>> here would have the effect you want it to have.
> 
> We don't really have any other .note, which is good.
> 
> I tried to feed the linker a notes.o file with .rodata.note
> and have the efi.lds.S ingest it:
> 
>        __note_gnu_build_id_start = .;
>        *(.rodata.note)
>        __note_gnu_build_id_end = .;
> 
> But it ignored it (no data, and __note_gnu_build_id_start == 
> __note_gnu_build_id_end)

I don't think it ignored it - it merely got put in a place you didn't want
it to be: The earlier *(.rodata.*) consumes it afaict. So perhaps you
want to move the notes between .text and .rodata?

> @@ -57,10 +60,19 @@ SECTIONS
>         *(.lockprofile.data)
>         __lock_profile_end = .;
>  #endif
> -
> -        _erodata = .;          /* End of read-only data */
>    } :text
>  
> +#if defined(BUILD_ID)
> +  . = ALIGN(4);
> +  .note : {
> +       __note_gnu_build_id_start = .;
> +       *(.note)
> +       *(.note.*)
> +       __note_gnu_build_id_end = .;
> +  } :note :text
> +#endif

That can't be right: What if any other .note or .note.* section
appears for whatever reason? There may be distro specific
.note.* sections issued by the compiler...

Jan


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