Re: X86: build failure

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 2025-12-17 01:12, Grygorii Strashko wrote:
> Hi Andrew,
> 
> On 17.12.25 01:54, Andrew Cooper wrote:
>> On 16/12/2025 11:35 pm, Grygorii Strashko wrote:
>>> Hi All,
>>> 
>>> I experience build failure with following Kconfig combination:
>>>   CONFIG_DEBUG=n and CONFIG_XEN_IBT=n
>>> 
>>> with gcc:
>>>   gcc --version
>>>   gcc (Ubuntu 11.4.0-1ubuntu1~22.04.2) 11.4.0
>>>   Copyright (C) 2021 Free Software Foundation, Inc.
>>>   This is free software; see the source for copying conditions.  
>>> There
>>> is NO
>>>   warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
>>> PURPOSE.
>>> 
>>> Is this known issue?
>>> 
>>> ====== log ===============
>>>    CC      arch/x86/x86_emulate.o
>>> In file included from arch/x86/x86_emulate.c:27:
>>> arch/x86/x86_emulate/x86_emulate.c: In function ‘x86_emulate’:
>>> arch/x86/x86_emulate/x86_emulate.c:70:36: error: writing 1 byte into 
>>> a
>>> region of size 0 [-Werror=stringop-overflow=]
>>>     70 |     gcc11_wrap(ptr)[0 - PFX_BYTES] = ext < ext_8f08 ? 0xc4 :
>>> 0x8f; \
>>> arch/x86/x86_emulate/x86_emulate.c:78:9: note: in expansion of macro
>>> ‘copy_VEX’
>>>     78 |         copy_VEX(ptr, vex); \
>>>        |         ^~~~~~~~
>>> arch/x86/x86_emulate/x86_emulate.c:8140:13: note: in expansion of
>>> macro ‘copy_REX_VEX’
>>>   8140 |             copy_REX_VEX(opc, rex_prefix, vex);
>>>        |             ^~~~~~~~~~~~
>>> In file included from arch/x86/x86_emulate/x86_emulate.c:11,
>>>                   from arch/x86/x86_emulate.c:27:
>>> arch/x86/x86_emulate/private.h:691:17: note: at offset [0, 4095] into
>>> destination object of size [0, 9223372036854775807] allocated by
>>> ‘map_domain_page’
>>>    691 |     (stb).ptr = map_domain_page(_mfn(this_cpu(stubs.mfn))) + 
>>> \
>>>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> arch/x86/x86_emulate/x86_emulate.c:60:21: note: in expansion of macro
>>> ‘get_stub’
>>>     60 |     uint8_t *buf_ = get_stub(stub); \
>>>        |                     ^~~~~~~~
>>> arch/x86/x86_emulate/x86_emulate.c:3354:15: note: in expansion of
>>> macro ‘init_prefixes’
>>>   3354 |         opc = init_prefixes(stub);
>>>        |               ^~~~~~~~~~~~~
>>> arch/x86/x86_emulate/private.h:691:17: note: at offset [1, 4096] into
>>> destination object of size [0, 9223372036854775807] allocated by
>>> ‘map_domain_page’
>>>    691 |     (stb).ptr = map_domain_page(_mfn(this_cpu(stubs.mfn))) + 
>>> \
>>>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> arch/x86/x86_emulate/x86_emulate.c:94:21: note: in expansion of macro
>>> ‘get_stub’
>>>     94 |     uint8_t *buf_ = get_stub(stub); \
>>>        |                     ^~~~~~~~
>>> arch/x86/x86_emulate/x86_emulate.c:3402:15: note: in expansion of
>>> macro ‘init_evex’
>>>   3402 |         opc = init_evex(stub);
>>> [...]
>>> 
>> 
>> Hmm - that looks like more of the GCC 11 bounds bugs, but that's what
>> the gcc11_wrap() visible at the top is supposed to be fixing.
>> 
>> Neither of those CONFIG options ought to be relevant.
>> 
>> Which Ubuntu is this?  Is it something local, or from one of our CI
>> containers?  Is this on staging, or local?
> 
> Local. Nothing special - "Ubuntu 22.04.5 LTS"
> 
> ======== apt show gcc
> Package: gcc
> Version: 4:11.2.0-1ubuntu1

The minimum gcc version is 5.1 on staging, perhaps this is due to that

> Priority: optional
> Build-Essential: yes
> Section: devel
> Source: gcc-defaults (1.193ubuntu1)
> Origin: Ubuntu
> Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
> Original-Maintainer: Debian GCC Maintainers 
> <debian-gcc@lists.debian.org>
> Bugs: https://bugs.launchpad.net/ubuntu/+filebug
> Installed-Size: 51,2 kB
> Provides: c-compiler, gcc-x86-64-linux-gnu (= 4:11.2.0-1ubuntu1)
> Depends: cpp (= 4:11.2.0-1ubuntu1), gcc-11 (>= 11.2.0-1~)
> Recommends: libc6-dev | libc-dev
> Suggests: gcc-multilib, make, manpages-dev, autoconf, automake, 
> libtool, flex, bison, gdb, gcc-doc
> Conflicts: gcc-doc (<< 1:2.95.3)
> Task: ubuntustudio-video, ubuntustudio-publishing, ubuntu-mate-core, 
> ubuntu-mate-desktop
> Download-Size: 5 112 B
> APT-Manual-Installed: yes
> APT-Sources: http://ua.archive.ubuntu.com/ubuntu jammy/main amd64 
> Packages
> Description: GNU C compiler
>  This is the GNU C compiler, a fairly portable optimizing compiler for 
> C.
>  .
>  This is a dependency package providing the default GNU C compiler.

-- 
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253