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From: Arjun Shankar <arjun@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/release/2.36/master] nptl: Unconditionally use a 32-byte rseq area Date: Mon, 18 Mar 2024 17:49:40 +0000 (GMT) [thread overview] Message-ID: <20240318174940.7DCA2385840D@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=54e812100df2a6f1d75fbef4e3b45c076599842f commit 54e812100df2a6f1d75fbef4e3b45c076599842f Author: Florian Weimer <fweimer@redhat.com> Date: Fri Jul 21 16:18:18 2023 +0200 nptl: Unconditionally use a 32-byte rseq area If the kernel headers provide a larger struct rseq, we used that size as the argument to the rseq system call. As a result, rseq registration would fail on older kernels which only accept size 32. (cherry picked from commit 2c6b4b272e6b4d07303af25709051c3e96288f2d) Diff: --- nptl/descr.h | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/nptl/descr.h b/nptl/descr.h index 70cf4b639a..ff634dac33 100644 --- a/nptl/descr.h +++ b/nptl/descr.h @@ -34,7 +34,6 @@ #include <bits/types/res_state.h> #include <kernel-features.h> #include <tls-internal-struct.h> -#include <sys/rseq.h> #include <internal-sigset.h> #ifndef TCB_ALIGNMENT @@ -402,14 +401,25 @@ struct pthread /* Used on strsignal. */ struct tls_internal_t tls_state; - /* rseq area registered with the kernel. */ - struct rseq rseq_area; + /* rseq area registered with the kernel. Use a custom definition + here to isolate from kernel struct rseq changes. The + implementation of sched_getcpu needs acccess to the cpu_id field; + the other fields are unused and not included here. */ + union + { + struct + { + uint32_t cpu_id_start; + uint32_t cpu_id; + }; + char pad[32]; /* Original rseq area size. */ + } rseq_area __attribute__ ((aligned (32))); /* Amount of end padding, if any, in this structure. This definition relies on rseq_area being last. */ #define PTHREAD_STRUCT_END_PADDING \ (sizeof (struct pthread) - offsetof (struct pthread, rseq_area) \ - + sizeof (struct rseq)) + + sizeof ((struct pthread) {}.rseq_area)) } __attribute ((aligned (TCB_ALIGNMENT))); static inline bool
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