kernel/linux.git/tools/testing/selftests/rseq/rseq.c, branch v6.1.168

rseq/selftests: Use weak symbol reference, not definition, to link with glibc

2025-10-19T14:23:16+00:00

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 Suggested-by: Florian Weimer Signed-off-by: Sean Christopherson Signed-off-by: Thomas Gleixner Reviewed-by: Mathieu Desnoyers Cc: stable@vger.kernel.org Closes: https://lore.kernel.org/all/87frdoybk4.ffs@tglx Signed-off-by: Greg Kroah-Hartman

selftests/rseq: Fix build with undefined __weak

2023-08-16T16:27:25+00:00

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 Message-Id: <20230804-kselftest-rseq-build-v1-1-015830b66aa9@kernel.org> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman

selftests/rseq: Play nice with binaries statically linked against glibc 2.35+

2023-08-11T10:08:26+00:00

[ 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 Cc: kvm@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20230721223352.2333911-1-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin

selftests/rseq: check if libc rseq support is registered

2022-06-28T07:08:28+00:00

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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Mathieu Desnoyers Link: https://lore.kernel.org/r/20220614154830.1367382-4-mjeanson@efficios.com

selftests/rseq: Change type of rseq_offset to ptrdiff_t

2022-02-11T22:30:08+00:00

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 Signed-off-by: Peter Zijlstra (Intel) Link: https://sourceware.org/pipermail/libc-alpha/2022-February/136024.html

selftests/rseq: Uplift rseq selftests for compatibility with glibc-2.35

2022-02-02T12:11:35+00:00

glibc-2.35 (upcoming release date 2022-02-01) exposes the rseq per-thread data in the TCB, accessible at an offset from the thread pointer, rather than through an actual Thread-Local Storage (TLS) variable, as the Linux kernel selftests initially expected. The __rseq_abi TLS and glibc-2.35's ABI for per-thread data cannot actively coexist in a process, because the kernel supports only a single rseq registration per thread. Here is the scheme introduced to ensure selftests can work both with an older glibc and with glibc-2.35+: - librseq exposes its own "rseq_offset, rseq_size, rseq_flags" ABI. - librseq queries for glibc rseq ABI (__rseq_offset, __rseq_size, __rseq_flags) using dlsym() in a librseq library constructor. If those are found, copy their values into rseq_offset, rseq_size, and rseq_flags. - Else, if those glibc symbols are not found, handle rseq registration from librseq and use its own IE-model TLS to implement the rseq ABI per-thread storage. Signed-off-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220124171253.22072-8-mathieu.desnoyers@efficios.com

selftests/rseq: Remove volatile from __rseq_abi

2022-02-02T12:11:34+00:00

This is done in preparation for the selftest uplift to become compatible with glibc-2.35. All accesses to the __rseq_abi fields are volatile, but remove the volatile from the TLS variable declaration, otherwise we are stuck with volatile for the upcoming rseq_get_abi() helper. Signed-off-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220124171253.22072-5-mathieu.desnoyers@efficios.com

selftests/rseq: introduce own copy of rseq uapi header

2022-02-02T12:11:33+00:00

The Linux kernel rseq uapi header has a broken layout for the rseq_cs.ptr field on 32-bit little endian architectures. The entire rseq_cs.ptr field is planned for removal, leaving only the 64-bit rseq_cs.ptr64 field available. Both glibc and librseq use their own copy of the Linux kernel uapi header, where they introduce proper union fields to access to the 32-bit low order bits of the rseq_cs pointer on 32-bit architectures. Introduce a copy of the Linux kernel uapi headers in the Linux kernel selftests. Signed-off-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220124171253.22072-2-mathieu.desnoyers@efficios.com

selftests/rseq: remove ARRAY_SIZE define from individual tests

2021-12-11T00:51:03+00:00

ARRAY_SIZE is defined in several selftests. Remove definitions from individual test files and include header file for the define instead. ARRAY_SIZE define is added in a separate patch to prepare for this change. Remove ARRAY_SIZE from rseq tests and pickup the one defined in kselftest.h. Signed-off-by: Shuah Khan

rseq/selftests: Use __rseq_handled symbol to coexist with glibc

2019-05-07T21:31:46+00:00

In order to integrate rseq into user-space applications, expose a __rseq_handled symbol so many rseq users can be linked into the same application (e.g. librseq and glibc). The __rseq_refcount TLS variable is static to the librseq library. It ensures that rseq syscall registration/unregistration happens only for the most early/late caller to rseq_{,un}register_current_thread for each thread, thus ensuring that rseq is registered across the lifetime of all rseq users for a given thread. Signed-off-by: Mathieu Desnoyers CC: Shuah Khan CC: Carlos O'Donell CC: Florian Weimer CC: Joseph Myers CC: Szabolcs Nagy CC: Thomas Gleixner CC: Ben Maurer CC: Peter Zijlstra CC: "Paul E. McKenney" CC: Boqun Feng CC: Will Deacon CC: Dave Watson CC: Paul Turner CC: linux-api@vger.kernel.org Signed-off-by: Shuah Khan