[SeaBIOS] [PATCH] ld: fix .text section address alignment

[Kevin O'Connor]

On Mon, Feb 22, 2016 at 12:07:00PM +0100, Roger Pau Monné wrote:
> El 20/2/16 a les 3:41, Kevin O'Connor ha escrit:
> > On Tue, Feb 16, 2016 at 06:21:10PM +0100, Roger Pau Monné wrote:
> >> El 16/2/16 a les 17:33, Kevin O'Connor ha escrit:
> >>> On Tue, Feb 16, 2016 at 01:56:26PM +0100, Roger Pau Monne wrote:
> >>>> According to the output from readelf, the .text section should be aligned to
> >>>> 16:
> >>>>
> >>>> Section Headers:
> >>>>   [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
> >>>>   [ 0] (null)            NULL            00000000 000000 000000 00      0   0  0
> >>>>   [ 1] .text             PROGBITS        000de300 000300 021d00 00  AX  0   0 16
> >>>> [...]
> >>>>
> >>>> This however doesn't seem to be enforced when the relocations are generated.
> >>>> The following patch tries to address this by making sure the space used for
> >>>> the relocations it also aligned to the same value as the .text section.
> >>>
> >>> Thanks.  What goes wrong if the .text section is not aligned?  The
> >>> code has already been assigned physical addresses by this point, so it
> >>> should not impact the runtime code.
> >>
> >> It seems like ELF toolchain objcopy chokes if a section address is not
> >> aligned to the alignment specified by the section, see:
> >>
> >> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=207170
> >>
> >> The snippet shown above has addr aligned to 16 (which matches latest
> >> upstream), so it's not a problem, but the current SeaBIOS version
> >> shipped in Xen 4.5 (1.7.5 IIRC) ends up with an addr that's not a
> >> multiple of 16, as shown in the bug report, and objcopy complains with:
> >>
> >> objcopy: elf_update() failed: Layout constraint violation
> > 
> > Thanks.  I agree it should be fixed.  However, I think there are a few
> > other cases that could cause the ".text" section alignment to be off.
> > Are you okay with the patch below instead?
> 
> Yes, looks fine to me. AFAICT SeaBIOS packs all the sections (.text,
> .data, .rodata) ibnside of the .text section, which I didn't realize before.

Thanks, I committed the change.

-Kevin