linux-kernel - [PATCH] KVM: selftests: Add -U_FORTIFY_SOURCE to avoid some unpredictable test failures

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Message-ID: <20260122053551.548229-1-zhiquan_li@163.com>
Date: Thu, 22 Jan 2026 13:35:50 +0800
From: Zhiquan Li <zhiquan_li@....com>
To: seanjc@...gle.com,
	pbonzini@...hat.com,
	shuah@...nel.org
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	zhiquan_li@....com
Subject: [PATCH] KVM: selftests: Add -U_FORTIFY_SOURCE to avoid some unpredictable test failures

Some distributions (such as Ubuntu) configure GCC so that
_FORTIFY_SOURCE is automatically enabled at -O1 or above.  This results
in some fortified version of definitions of standard library functions
are included.  While linker resolves the symbols, the fortified versions
might override the definitions in lib/string_override.c and reference to
those PLT entries in GLIBC.  This is not a problem for the code in host,
but it is a disaster for the guest code.  E.g., if build and run
x86/nested_emulation_test on Ubuntu 24.04 will encounter a L1 #PF due to
memset() reference to __memset_chk@....

The option -fno-builtin-memset is not helpful here, because those
fortified versions are not built-in but some definitions which are
included by header, they are for different intentions.

In order to eliminate the unpredictable behaviors may vary depending on
the linker and platform, add the "-U_FORTIFY_SOURCE" into CFLAGS to
prevent from introducing the fortified definitions.

Signed-off-by: Zhiquan Li <zhiquan_li@....com>
---
 tools/testing/selftests/kvm/Makefile.kvm | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index ba5c2b643efa..d45bf4ccb3bf 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -251,6 +251,7 @@ LINUX_TOOL_INCLUDE = $(top_srcdir)/tools/include
 LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include
 CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
 	-Wno-gnu-variable-sized-type-not-at-end -MD -MP -DCONFIG_64BIT \
+	-U_FORTIFY_SOURCE \
 	-fno-builtin-memcmp -fno-builtin-memcpy \
 	-fno-builtin-memset -fno-builtin-strnlen \
 	-fno-stack-protector -fno-PIE -fno-strict-aliasing \
-- 
2.43.0