* [PATCH] nptl: Unconditionally use a 32-byte rseq area
@ 2023-07-20 10:39 Florian Weimer
2023-07-20 10:40 ` Florian Weimer
0 siblings, 1 reply; 2+ messages in thread
From: Florian Weimer @ 2023-07-20 10:39 UTC (permalink / raw)
To: libc-alpha; +Cc: Mathieu Desnoyers
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.
Tested on x86_64-linux-gnu. Built with build-many-glibcs.py.
This needs to be backported all the way to glibc 2.35.
---
nptl/descr.h | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/nptl/descr.h b/nptl/descr.h
index d06abd6ad9..abc9282ef7 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -405,8 +405,19 @@ 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. */
base-commit: 3edc4ff2ceff4a59587ebecb94148d3bcfa1df62
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] nptl: Unconditionally use a 32-byte rseq area
2023-07-20 10:39 [PATCH] nptl: Unconditionally use a 32-byte rseq area Florian Weimer
@ 2023-07-20 10:40 ` Florian Weimer
0 siblings, 0 replies; 2+ messages in thread
From: Florian Weimer @ 2023-07-20 10:40 UTC (permalink / raw)
To: libc-alpha; +Cc: Mathieu Desnoyers
* Florian Weimer:
> 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.
>
> Tested on x86_64-linux-gnu. Built with build-many-glibcs.py.
> This needs to be backported all the way to glibc 2.35.
>
> ---
> nptl/descr.h | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/nptl/descr.h b/nptl/descr.h
> index d06abd6ad9..abc9282ef7 100644
> --- a/nptl/descr.h
> +++ b/nptl/descr.h
> @@ -405,8 +405,19 @@ 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. */
>
> base-commit: 3edc4ff2ceff4a59587ebecb94148d3bcfa1df62
Meh, disregard that, the patch is buggy.
Thanks,
Florian
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2023-07-20 10:40 ` Florian Weimer
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