[Buildroot] [PATCH 3/3] package/qemu: host-qemu does not support XOP capable CPUs

From: Yegor Yefremov via buildroot <buildroot@buildroot.org>
To: buildroot@buildroot.org
Cc: Romain Naour <romain.naour@gmail.com>, thomas.petazzoni@bootlin.com
Subject: [Buildroot] [PATCH 3/3] package/qemu: host-qemu does not support XOP capable CPUs
Date: Thu, 17 Sep 2026 09:53:26 +0200	[thread overview]
Message-ID: <20260917075326.1256294-4-yegorslists@gmail.com> (raw)
In-Reply-To: <20260917075326.1256294-1-yegorslists@gmail.com>

From: Yegor Yefremov <yegorslists@googlemail.com>

Commit 1f7efaf89f03 ("package/qemu: do not support x86_steamroller or
x86_core_avx2") excluded BR2_x86_steamroller from
BR2_PACKAGE_HOST_QEMU_ARCH_SUPPORTS. This is still needed, but for a
different reason than AVX, and the exclusion is incomplete.

steamroller is bdver3, and what the Qemu TCG engine cannot emulate
there is not AVX, but the Bulldozer-specific XOP, FMA4, TBM and LWP
extensions. In Qemu 11.0.0 (the version we currently package) and
11.1.1, target/i386/cpu.c has:

  #define TCG_EXT3_FEATURES (CPUID_EXT3_LAHF_LM | CPUID_EXT3_SVM | \
            CPUID_EXT3_CR8LEG | CPUID_EXT3_ABM | CPUID_EXT3_SSE4A | \
            CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_KERNEL_FEATURES | \
            CPUID_EXT3_CMP_LEG)

CPUID_EXT3_XOP, CPUID_EXT3_FMA4, CPUID_EXT3_TBM and CPUID_EXT3_LWP are
defined in target/i386/cpu.h, but are not part of that mask, i.e. TCG
does not implement them. Binaries using those instructions therefore
die with:

  qemu: uncaught target signal 4 (Illegal instruction) - core dumped

This affects the whole Bulldozer family, not only steamroller:
bulldozer (bdver1), piledriver (bdver2) and excavator (bdver4) are
equally unsupported, but were never excluded.

Use the newly introduced BR2_X86_CPU_HAS_XOP symbol, which covers all
four variants, instead of listing BR2_x86_steamroller alone. As for
AVX512, this disables gobject-introspection and nodejs, which are the
two packages needing host-qemu in user mode.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Assisted-by: Claude:claude-opus-5
---
 package/qemu/Config.in.host | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/package/qemu/Config.in.host b/package/qemu/Config.in.host
index 48979fd7ce..fbc989b003 100644
--- a/package/qemu/Config.in.host
+++ b/package/qemu/Config.in.host
@@ -22,10 +22,11 @@ config BR2_PACKAGE_HOST_QEMU_ARCH_SUPPORTS
 	default y if BR2_sparc64
 	default y if BR2_xtensa
 	default y if BR2_x86_64
-	depends on !BR2_x86_steamroller
-	# The Qemu TCG engine does not implement the AVX512
-	# instruction set, so binaries built for such CPUs cannot be
-	# emulated.
+	# The Qemu TCG engine implements neither the XOP instruction set
+	# nor the other Bulldozer-specific extensions (FMA4, TBM, LWP),
+	# and it does not implement the AVX512 instruction set either,
+	# so binaries built for such CPUs cannot be emulated.
+	depends on !BR2_X86_CPU_HAS_XOP
 	depends on !BR2_X86_CPU_HAS_AVX512
 	depends on !BR2_powerpc_620 && !BR2_powerpc_630
 
-- 
2.34.1

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