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

[Roger Pau Monné]

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

Roger.