Re: [RFC PATCH] glibc: Perform rseq(2) registration at nptl init and thread creation

----- On Sep 19, 2018, at 12:37 PM, Joseph Myers joseph@codesourcery.com wrote:

On Wed, 19 Sep 2018, Mathieu Desnoyers wrote:

quoted

Here is a rough prototype registering rseq(2) TLS for each thread
(including main), and unregistering for each thread (excluding
main). "rseq" stands for Restartable Sequences.

A final patch would need to add documentation and tests and a NEWS entry
and fix various coding style issues.

Sure,

quoted

diff --git a/nptl/Versions b/nptl/Versions
index e7f691da7a..7316c2815d 100644
--- a/nptl/Versions
+++ b/nptl/Versions

@@ -275,6 +275,7 @@ libpthread {
     mtx_init; mtx_lock; mtx_timedlock; mtx_trylock; mtx_unlock; mtx_destroy;
     call_once; cnd_broadcast; cnd_destroy; cnd_init; cnd_signal;
     cnd_timedwait; cnd_wait; tss_create; tss_delete; tss_get; tss_set;
+    __rseq_abi; __rseq_refcount;

That's the GLIBC_2.28 section, but 2.28 is already out.  New symbols would
need to go in GLIBC_2.29 or later (and the ABI test baselines would all
need updating).

OK

quoted

diff --git a/sysdeps/unix/sysv/linux/rseq.h b/sysdeps/unix/sysv/linux/rseq.h

This looks like it's coming from the Linux kernel.  Can't the relevant
uapi header just be used directly without copying into glibc (with due
care to ensure that glibc still builds if the kernel headers used for the
build are too old - you need such conditionals anyway if they don't define
the relevant syscall number)?

Something like this in pthreadP.h ?

+#ifdef __NR_rseq
+#include <sysdeps/unix/sysv/linux/rseq-internal.h>
+#else
+#include <sysdeps/nptl/rseq-internal.h>
+#endif  /* __NR_rseq.  */

where sysdeps/unix/sysv/linux/rseq-internal.h contains the linux
implementation of rseq_register_current_thread () and
rseq_unregister_current_thread (), and sysdeps/nptl/rseq-internal.h
contains stubs.

Am I on the right track ?

Thanks,

Mathieu

--
Joseph S. Myers
joseph@codesourcery.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com