X86: build failure

X86: build failure

[Grygorii Strashko]

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);
[...]


-- 
Best regards,
-grygorii

Re: X86: build failure

[Andrew Cooper]

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?

~Andrew

Re: X86: build failure

[Grygorii Strashko]

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
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.



-- 
Best regards,
-grygorii

Re: X86: build failure

[Nicola Vetrini]

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

Re: X86: build failure

[Nicola Vetrini]

On 2025-12-17 08:13, Nicola Vetrini wrote:
> 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

Ah, nevermind, too early in the morning :)

> 
>> 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

Re: X86: build failure

[Jan Beulich]

On 17.12.2025 00:54, 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.

CONFIG_DEBUG=n may well matter, due to the different -O<n> settings.
CONFIG_XEN_IBT=n otoh is indeed curious.

May want experimenting some starting from the pre-processed file. Grygorii,
could you generate that in your build env and then make it available
somewhere (together with the exact options passed to gcc when you observe
the build failure)?

Jan