Re: X86: build failure

[Andrew Cooper <andrew.cooper3@citrix.com>]

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