glibc, branch vdso

linux: Add support for getrandom vDSO

2024-09-27T18:25:36Z

Linux 6.11 has getrandom() in vDSO. It operates on a thread-local opaque state allocated with mmap using flags specified by the vDSO. Multiple states are allocated at once, as many as fit into a page, and these are held in an array of available states to be doled out to each thread upon first use, and recycled when a thread terminates. As these states run low, more are allocated. To make this procedure async-signal-safe, a simple guard is used in the LSB of the opaque state address, falling back to the syscall if there's reentrancy contention. Also, _Fork() is handled by blocking signals on opaque state allocation (so _Fork() always sees a consistent state even if it interrupts a getrandom() call) and by iterating over the thread stack cache on reclaim_stack. Each opaque state will be in the free states list (grnd_alloc.states) or allocated to a running thread. The cancellation is handled by always using GRND_NONBLOCK flags while calling the vDSO, and falling back to the cancellable syscall if the kernel returns EAGAIN (would block). Since getrandom is not defined by POSIX and cancellation is supported as an extension, the cancellation is handled as 'may occur' instead of 'shall occur' [1], meaning that if vDSO does not block (the expected behavior) getrandom will not act as a cancellation entrypoint. It avoids a pthread_testcancel call on the fast path (different than 'shall occur' functions, like sem_wait()). It is currently enabled for x86_64, which is available in Linux 6.11, and aarch64, powerpc32, powerpc64, loongarch64, and s390x, which are available in Linux 6.12. Link: https://pubs.opengroup.org/onlinepubs/9799919799/nframe.html [1] Co-developed-by: Jason A. Donenfeld Tested-by: Jason A. Donenfeld # x86_64 Tested-by: Adhemerval Zanella # x86_64, aarch64 Tested-by: Xi Ruoyao # x86_64, aarch64, loongarch64 Tested-by: Stefan Liebler # s390x

elf: Fix tst-dlopen-tlsreinit1.out test dependency

2024-09-09T19:10:23Z

Fixes commit 5097cd344fd243fb8deb6dec96e8073753f962f9 ("elf: Avoid re-initializing already allocated TLS in dlopen (bug 31717)"). Reported-by: Patsy Griffin Reviewed-by: Patsy Griffin

Add a new fwrite test for memory streams

2024-09-09T18:58:07Z

Ensure that fwrite() behaves correctly when using memory streams. Reviewed-by: Carlos O'Donell

Add a new fwrite test for read-only streams

2024-09-09T17:32:20Z

Ensure that fwrite() behaves correctly even when the stream is read-only. Reviewed-by: Carlos O'Donell

AArch64: Optimize memset

2024-09-09T14:30:00Z

Improve small memsets by avoiding branches and use overlapping stores. Use DC ZVA for copies over 128 bytes. Remove unnecessary code for ZVA sizes other than 64 and 128. Performance of random memset benchmark improves by 24% on Neoverse N1. Reviewed-by: Adhemerval Zanella

hppa: Update libm-test-ulps

2024-09-09T13:57:42Z

aarch64: Avoid redundant MOVs in AdvSIMD F32 logs

2024-09-09T12:03:49Z

Since the last operation is destructive, the first argument to the FMA also has to be the first argument to the special-case in order to avoid unnecessary MOVs. Reorder arguments and adjust special-case bounds to facilitate this. Reviewed-by: Wilco Dijkstra

io: Add FUSE-based test for fchmod

2024-09-09T07:51:50Z

Test all mode arguments, and that extra bits are ignored as required by POSIX. Reviewed-by: DJ Delorie

io: Add tst-lstat-nofollow, tst-lstat-nofollow-time64

2024-09-09T07:14:22Z

They verify that lstat, lstat64 do not follow symbolic links. Reviewed-by: DJ Delorie

Document limitations on streams passed to freopen

2024-09-06T20:38:23Z

As recently discussed, document that freopen does not work with streams opened with functions such as popen, fmemopen, open_memstream or fopencookie. I've filed to clarify this issue in POSIX. Tested with "make info" and "make html".