ucontext functions on powerpc64

["A. Wilcox" <awilfox at adelielinux dot org>]

Dear glibc developers,

I noticed that since glibc 2.5, powerpc32 can use the swapcontext
syscall on the Linux kernel for most of the ucontext family of functions
- it was added in kernel 2.6.0.  This was actually made unconditional in
2012 for glibc 2.17.

The powerpc64 architecture does not use the Linux swapcontext syscall.
I was wondering if anyone knew the reason behind this.  I did a mailing
list archive search for "ucontext powerpc64" and "swapcontext powerpc64"
and saw no relevant threads, just threads about adding initial support
in 2002, and adding VSX extensions.

For background on this query, I'm trying to add support for ucontext
functions to an embedded C library.  Some applications are crashing when
calling setcontext on powerpc64 using the Linux swapcontext syscall.  It
works fine on powerpc32.  I was wondering if perhaps the syscall is
somehow unusable for this purpose on powerpc64, since glibc appears to
be avoiding the syscall.  If not, then it may be a slight performance
optimisation for glibc to use it instead of using rt_sigreturn.

I apologise if this may be off-topic; I didn't see any other discussion
lists that involved glibc developers.

Thank you for your time.

Best to you and yours,
--arw

-- 
A. Wilcox (awilfox)
Project Lead, Adélie Linux
https://www.adelielinux.org

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