On 09/01/2025 3:30 pm, Frediano Ziglio wrote:
> On Thu, Jan 9, 2025 at 1:44 PM Andrew Cooper <andrew.coop...@citrix.com>
> wrote:
>> On 09/01/2025 1:23 pm, Jan Beulich wrote:
>>> On 09.01.2025 14:15, Marek Marczykowski-Górecki wrote:
>>>> Xen compiled with -mtune=generic has .text alignment set to 64-bytes.
>>>> Having text_diff non-64-bytes-aligned breaks stuff:
>>>>
>>>> Traceback (most recent call last):
>>>> File
>>>> "/builddir/build/BUILD/xen-4.20.0-build/xen-4.20.0-rc0/xen/./tools/combine_two_binaries.py",
>>>> line 96, in <module>
>>>> raise Exception('File sizes do not match')
>>>> Exception: File sizes do not match: 70160 != 4080 + 66048
>>>>
>>>> Adjust the numbers as suggested by Frediano to work with 64-bytes and
>>>> even 128-bytes alignment.
>>> And then breaking at 256? As indicated on Matrix, imo we should be able to
>>> cope with anything up to at least PAGE_SIZE. Or we should reduce .text
>>> alignment before linking.
>> Do you have a concrete proposal on how to do this?
>>
>> Because if not, we've had 2 downstreams hit by this build failure, and
>> we probably ought to take this patch as a stopgap fix, and see about
>> doing the better fix for 4.20.
>>
> I agree with this, merge this and then leave the improvements for follow
> up(s).
>
> Yesterday I checked the output object file (built-in-32.o) to find
> that the output alignment is 1 byte, which is obviously wrong!
No so. It's perfectly easy to end up with 1 byte alignment on .text,
commonly with -Os.
e.g. In my build, reloc-trampoline.32.o has:
Sections:
Idx Name Size VMA LMA File off Algn
0 .group 00000008 00000000 00000000 00000034 2**2
CONTENTS, READONLY, GROUP, LINK_ONCE_DISCARD
1 .text 00000076 00000000 00000000 0000003c 2**0
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
2 .data 00000000 00000000 00000000 000000b2 2**0
CONTENTS, ALLOC, LOAD, DATA
3 .bss 00000000 00000000 00000000 000000b2 2**0
ALLOC
4 .text.__x86.get_pc_thunk.bx 00000004 00000000 00000000 000000b2 2**0
CONTENTS, ALLOC, LOAD, READONLY, CODE
5 .comment 00000020 00000000 00000000 000000b6 2**0
CONTENTS, READONLY
6 .note.GNU-stack 00000000 00000000 00000000 000000d6 2**0
CONTENTS, READONLY
and this is entirely reasonable IMO.
That said, the fact that built-in-32.S does not have at least one .align
directive probably is an issue.
x86 will cope, and there's nothing interesting in this code that's going
to choke on being misaligned.
~Andrew
