git: 19419d36cf2a - main - libc: Give __thr_jtable protected visibility

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=19419d36cf2a132a325c0a66f49c3a66043072ba

commit 19419d36cf2a132a325c0a66f49c3a66043072ba
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-05-19 14:29:12 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-05-19 14:29:12 +0000

    libc: Give __thr_jtable protected visibility
    
    This function pointer table is overwritten by libthr when it's loaded.
    libc's pthread stubs are implemented by looking up an entry in this
    table and invoking the function pointer contained in the entry.
    
    pthread calls are fairly expensive even when libthr is not loaded: each
    call involves indirection through the PLT, then through the GOT to look
    up __thr_jtable, then the function pointer itself.  We can however
    eliminate one level of indirection by disallowing preemption of the
    __thr_jtable symbol, and since the existence table is an internal
    implementation detail, disabling preemption is unlikely to break
    anything.  This gives a modest improvement in some microbenchmarks which
    call libc's pthread stubs.
    
    Reviewed by:    kib
    MFC after:      1 month
    Sponsored by:   Innovate UK
    Differential Revision:  https://reviews.freebsd.org/D50354
---
 lib/libc/gen/_pthread_stubs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/libc/gen/_pthread_stubs.c b/lib/libc/gen/_pthread_stubs.c
index 2a0cebadd5fd..d867ee4db51e 100644
--- a/lib/libc/gen/_pthread_stubs.c
+++ b/lib/libc/gen/_pthread_stubs.c
@@ -63,6 +63,7 @@ static int		stub_getname_np(pthread_t, char *, size_t);
 #define	PJT_DUAL_ENTRY(entry)	\
 	(pthread_func_t)entry, (pthread_func_t)entry
 
+__attribute__((visibility("protected")))
 pthread_func_entry_t __thr_jtable[PJT_MAX] = {
 	[PJT_ATFORK] =			{PJT_DUAL_ENTRY(stub_zero)},
 	[PJT_ATTR_DESTROY] =		{PJT_DUAL_ENTRY(stub_zero)},