linux-stable.git/tools/testing/selftests/rseq, branch linux-5.15.y Linux kernel stable tree rseq/selftests: Use weak symbol reference, not definition, to link with glibc 2025-10-19T14:21:47+00:00 Sean Christopherson seanjc@google.com 2025-08-19T22:29:44+00:00 b167bfa432e3cda76fdf3197ad48adbf32da32ea commit a001cd248ab244633c5fabe4f7c707e13fc1d1cc upstream. Add "extern" to the glibc-defined weak rseq symbols to convert the rseq selftest's usage from weak symbol definitions to weak symbol _references_. Effectively re-defining the glibc symbols wreaks havoc when building with -fno-common, e.g. generates segfaults when running multi-threaded programs, as dynamically linked applications end up with multiple versions of the symbols. Building with -fcommon, which until recently has the been the default for GCC and clang, papers over the bug by allowing the linker to resolve the weak/tentative definition to glibc's "real" definition. Note, the symbol itself (or rather its address), not the value of the symbol, is set to 0/NULL for unresolved weak symbol references, as the symbol doesn't exist and thus can't have a value. Check for a NULL rseq size pointer to handle the scenario where the test is statically linked against a libc that doesn't support rseq in any capacity. Fixes: 3bcbc20942db ("selftests/rseq: Play nice with binaries statically linked against glibc 2.35+") Reported-by: Thomas Gleixner <tglx@linutronix.de> Suggested-by: Florian Weimer <fweimer@redhat.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: stable@vger.kernel.org Closes: https://lore.kernel.org/all/87frdoybk4.ffs@tglx Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit a001cd248ab244633c5fabe4f7c707e13fc1d1cc upstream.

Add "extern" to the glibc-defined weak rseq symbols to convert the rseq
selftest's usage from weak symbol definitions to weak symbol _references_.
Effectively re-defining the glibc symbols wreaks havoc when building with
-fno-common, e.g. generates segfaults when running multi-threaded programs,
as dynamically linked applications end up with multiple versions of the
symbols.

Building with -fcommon, which until recently has the been the default for
GCC and clang, papers over the bug by allowing the linker to resolve the
weak/tentative definition to glibc's "real" definition.

Note, the symbol itself (or rather its address), not the value of the
symbol, is set to 0/NULL for unresolved weak symbol references, as the
symbol doesn't exist and thus can't have a value.  Check for a NULL rseq
size pointer to handle the scenario where the test is statically linked
against a libc that doesn't support rseq in any capacity.

Fixes: 3bcbc20942db ("selftests/rseq: Play nice with binaries statically linked against glibc 2.35+")
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: Florian Weimer <fweimer@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/all/87frdoybk4.ffs@tglx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
selftests/rseq: Fix build with undefined __weak 2023-08-16T16:22:00+00:00 Mark Brown broonie@kernel.org 2023-08-04T19:22:11+00:00 b973eb76dff3f84d71ab4634a42f281e8cc4aa60 commit d5ad9aae13dcced333c1a7816ff0a4fbbb052466 upstream. Commit 3bcbc20942db ("selftests/rseq: Play nice with binaries statically linked against glibc 2.35+") which is now in Linus' tree introduced uses of __weak but did nothing to ensure that a definition is provided for it resulting in build failures for the rseq tests: rseq.c:41:1: error: unknown type name '__weak' __weak ptrdiff_t __rseq_offset; ^ rseq.c:41:17: error: expected ';' after top level declarator __weak ptrdiff_t __rseq_offset; ^ ; rseq.c:42:1: error: unknown type name '__weak' __weak unsigned int __rseq_size; ^ rseq.c:43:1: error: unknown type name '__weak' __weak unsigned int __rseq_flags; Fix this by using the definition from tools/include compiler.h. Fixes: 3bcbc20942db ("selftests/rseq: Play nice with binaries statically linked against glibc 2.35+") Signed-off-by: Mark Brown <broonie@kernel.org> Message-Id: <20230804-kselftest-rseq-build-v1-1-015830b66aa9@kernel.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit d5ad9aae13dcced333c1a7816ff0a4fbbb052466 upstream.

Commit 3bcbc20942db ("selftests/rseq: Play nice with binaries statically
linked against glibc 2.35+") which is now in Linus' tree introduced uses
of __weak but did nothing to ensure that a definition is provided for it
resulting in build failures for the rseq tests:

rseq.c:41:1: error: unknown type name '__weak'
__weak ptrdiff_t __rseq_offset;
^
rseq.c:41:17: error: expected ';' after top level declarator
__weak ptrdiff_t __rseq_offset;
                ^
                ;
rseq.c:42:1: error: unknown type name '__weak'
__weak unsigned int __rseq_size;
^
rseq.c:43:1: error: unknown type name '__weak'
__weak unsigned int __rseq_flags;

Fix this by using the definition from tools/include compiler.h.

Fixes: 3bcbc20942db ("selftests/rseq: Play nice with binaries statically linked against glibc 2.35+")
Signed-off-by: Mark Brown <broonie@kernel.org>
Message-Id: <20230804-kselftest-rseq-build-v1-1-015830b66aa9@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
selftests/rseq: Play nice with binaries statically linked against glibc 2.35+ 2023-08-11T13:14:00+00:00 Sean Christopherson seanjc@google.com 2023-07-21T22:33:52+00:00 c91c07ae084950622b5b3204ba1e0499d8a176d3 [ Upstream commit 3bcbc20942db5d738221cca31a928efc09827069 ] To allow running rseq and KVM's rseq selftests as statically linked binaries, initialize the various "trampoline" pointers to point directly at the expect glibc symbols, and skip the dlysm() lookups if the rseq size is non-zero, i.e. the binary is statically linked *and* the libc registered its own rseq. Define weak versions of the symbols so as not to break linking against libc versions that don't support rseq in any capacity. The KVM selftests in particular are often statically linked so that they can be run on targets with very limited runtime environments, i.e. test machines. Fixes: 233e667e1ae3 ("selftests/rseq: Uplift rseq selftests for compatibility with glibc-2.35") Cc: Aaron Lewis <aaronlewis@google.com> Cc: kvm@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20230721223352.2333911-1-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 3bcbc20942db5d738221cca31a928efc09827069 ]

To allow running rseq and KVM's rseq selftests as statically linked
binaries, initialize the various "trampoline" pointers to point directly
at the expect glibc symbols, and skip the dlysm() lookups if the rseq
size is non-zero, i.e. the binary is statically linked *and* the libc
registered its own rseq.

Define weak versions of the symbols so as not to break linking against
libc versions that don't support rseq in any capacity.

The KVM selftests in particular are often statically linked so that they
can be run on targets with very limited runtime environments, i.e. test
machines.

Fixes: 233e667e1ae3 ("selftests/rseq: Uplift rseq selftests for compatibility with glibc-2.35")
Cc: Aaron Lewis <aaronlewis@google.com>
Cc: kvm@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230721223352.2333911-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests/rseq: check if libc rseq support is registered 2023-08-11T13:13:59+00:00 Michael Jeanson mjeanson@efficios.com 2022-06-14T15:48:30+00:00 1cdb50faf7f71e05a0aeed6658d21f0cf150f0e9 [ Upstream commit d1a997ba4c1bf65497d956aea90de42a6398f73a ] When checking for libc rseq support in the library constructor, don't only depend on the symbols presence, check that the registration was completed. This targets a scenario where the libc has rseq support but it is not wired for the current architecture in 'bits/rseq.h', we want to fallback to our internal registration mechanism. Signed-off-by: Michael Jeanson <mjeanson@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Link: https://lore.kernel.org/r/20220614154830.1367382-4-mjeanson@efficios.com Stable-dep-of: 3bcbc20942db ("selftests/rseq: Play nice with binaries statically linked against glibc 2.35+") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit d1a997ba4c1bf65497d956aea90de42a6398f73a ]

When checking for libc rseq support in the library constructor, don't
only depend on the symbols presence, check that the registration was
completed.

This targets a scenario where the libc has rseq support but it is not
wired for the current architecture in 'bits/rseq.h', we want to fallback
to our internal registration mechanism.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/r/20220614154830.1367382-4-mjeanson@efficios.com
Stable-dep-of: 3bcbc20942db ("selftests/rseq: Play nice with binaries statically linked against glibc 2.35+")
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests/rseq: Change type of rseq_offset to ptrdiff_t 2022-07-07T15:53:31+00:00 Mathieu Desnoyers mathieu.desnoyers@efficios.com 2022-02-03T15:05:32+00:00 472863c7b5239ac6723e82c11bf89007e0f4d885 commit 889c5d60fbcf332c8b6ab7054d45f2768914a375 upstream. Just before the 2.35 release of glibc, the __rseq_offset userspace ABI was changed from int to ptrdiff_t. Adapt to this change in the kernel selftests. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://sourceware.org/pipermail/libc-alpha/2022-February/136024.html Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 889c5d60fbcf332c8b6ab7054d45f2768914a375 upstream.

Just before the 2.35 release of glibc, the __rseq_offset userspace ABI
was changed from int to ptrdiff_t.

Adapt to this change in the kernel selftests.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://sourceware.org/pipermail/libc-alpha/2022-February/136024.html
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
selftests/rseq: x86-32: use %gs segment selector for accessing rseq thread area 2022-07-07T15:53:31+00:00 Mathieu Desnoyers mathieu.desnoyers@efficios.com 2022-01-24T17:12:53+00:00 df2e933a53481558477d2c5dd3fb88a5f2ce25c6 commit 127b6429d235ab7c358223bbfd8a8b8d8cc799b6 upstream. Rather than use rseq_get_abi() and pass its result through a register to the inline assembler, directly access the per-thread rseq area through a memory reference combining the %gs segment selector, the constant offset of the field in struct rseq, and the rseq_offset value (in a register). Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20220124171253.22072-16-mathieu.desnoyers@efficios.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 127b6429d235ab7c358223bbfd8a8b8d8cc799b6 upstream.

Rather than use rseq_get_abi() and pass its result through a register to
the inline assembler, directly access the per-thread rseq area through a
memory reference combining the %gs segment selector, the constant offset
of the field in struct rseq, and the rseq_offset value (in a register).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220124171253.22072-16-mathieu.desnoyers@efficios.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
selftests/rseq: x86-64: use %fs segment selector for accessing rseq thread area 2022-07-07T15:53:31+00:00 Mathieu Desnoyers mathieu.desnoyers@efficios.com 2022-01-24T17:12:52+00:00 f5a656b4ab48bb3b4d17dc603d4f3d80dbb61fd5 commit 4e15bb766b6c6e963a4d33629034d0ec3b7637df upstream. Rather than use rseq_get_abi() and pass its result through a register to the inline assembler, directly access the per-thread rseq area through a memory reference combining the %fs segment selector, the constant offset of the field in struct rseq, and the rseq_offset value (in a register). Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20220124171253.22072-15-mathieu.desnoyers@efficios.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 4e15bb766b6c6e963a4d33629034d0ec3b7637df upstream.

Rather than use rseq_get_abi() and pass its result through a register to
the inline assembler, directly access the per-thread rseq area through a
memory reference combining the %fs segment selector, the constant offset
of the field in struct rseq, and the rseq_offset value (in a register).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220124171253.22072-15-mathieu.desnoyers@efficios.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
selftests/rseq: Fix: work-around asm goto compiler bugs 2022-07-07T15:53:31+00:00 Mathieu Desnoyers mathieu.desnoyers@efficios.com 2022-01-24T17:12:51+00:00 4633aa6fadc68396637b464f01e9ab98249ca2ba commit b53823fb2ef854222853be164f3b1e815f315144 upstream. gcc and clang each have their own compiler bugs with respect to asm goto. Implement a work-around for compiler versions known to have those bugs. gcc prior to 4.8.2 miscompiles asm goto. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670 gcc prior to 8.1.0 miscompiles asm goto at O1. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103908 clang prior to version 13.0.1 miscompiles asm goto at O2. https://github.com/llvm/llvm-project/issues/52735 Work around these issues by adding a volatile inline asm with memory clobber in the fallthrough after the asm goto and at each label target. Emit this for all compilers in case other similar issues are found in the future. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20220124171253.22072-14-mathieu.desnoyers@efficios.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit b53823fb2ef854222853be164f3b1e815f315144 upstream.

gcc and clang each have their own compiler bugs with respect to asm
goto. Implement a work-around for compiler versions known to have those
bugs.

gcc prior to 4.8.2 miscompiles asm goto.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670

gcc prior to 8.1.0 miscompiles asm goto at O1.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103908

clang prior to version 13.0.1 miscompiles asm goto at O2.
https://github.com/llvm/llvm-project/issues/52735

Work around these issues by adding a volatile inline asm with
memory clobber in the fallthrough after the asm goto and at each
label target.  Emit this for all compilers in case other similar
issues are found in the future.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220124171253.22072-14-mathieu.desnoyers@efficios.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
selftests/rseq: Remove arm/mips asm goto compiler work-around 2022-07-07T15:53:31+00:00 Mathieu Desnoyers mathieu.desnoyers@efficios.com 2022-01-24T17:12:50+00:00 786bd3511934157f88e141d0a8494fcfb02b02f6 commit 94c5cf2a0e193afffef8de48ddc42de6df7cac93 upstream. The arm and mips work-around for asm goto size guess issues are not properly documented, and lack reference to specific compiler versions, upstream compiler bug tracker entry, and reproducer. I can only find a loosely documented patch in my original LKML rseq post refering to gcc < 7 on ARM, but it does not appear to be sufficient to track the exact issue. Also, I am not sure MIPS really has the same limitation. Therefore, remove the work-around until we can properly document this. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/lkml/20171121141900.18471-17-mathieu.desnoyers@efficios.com/ Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 94c5cf2a0e193afffef8de48ddc42de6df7cac93 upstream.

The arm and mips work-around for asm goto size guess issues are not
properly documented, and lack reference to specific compiler versions,
upstream compiler bug tracker entry, and reproducer.

I can only find a loosely documented patch in my original LKML rseq post
refering to gcc < 7 on ARM, but it does not appear to be sufficient to
track the exact issue. Also, I am not sure MIPS really has the same
limitation.

Therefore, remove the work-around until we can properly document this.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/20171121141900.18471-17-mathieu.desnoyers@efficios.com/
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
selftests/rseq: Fix warnings about #if checks of undefined tokens 2022-07-07T15:53:31+00:00 Mathieu Desnoyers mathieu.desnoyers@efficios.com 2022-01-24T17:12:49+00:00 33307f2afd8579ccb41ef77dfcab7e148e82e5fd commit d7ed99ade3e62b755584eea07b4e499e79240527 upstream. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20220124171253.22072-12-mathieu.desnoyers@efficios.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit d7ed99ade3e62b755584eea07b4e499e79240527 upstream.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220124171253.22072-12-mathieu.desnoyers@efficios.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>