Re: [PATCH v3 3/4] kselftest/arm64: Add tests for SVE vector configuration

On Mon, Aug 02, 2021 at 04:36:15PM +0100, Dave Martin wrote:

On Mon, Aug 02, 2021 at 03:19:39PM +0100, Mark Brown wrote:

quoted

popen() appears to be break the _SET_VL_ONEXEC test.  Between a lack of
strace in my test filesystem and not spotting anything obvious in the
glibc sources I can't tell exactly where it's doing something different,
though it does feel like it should be a separate testcase if it's

Ah, dang, popen() will run the target program via a shell, so there will
actually be two fork-exec()s, with the VL being reset to default by the
second exec.

Oh, of course - it's basically a more useful system().  The bit where it
adds the sh invocation was buried somewhere in the glibc source I didn't
find.

This is the kind of reason why I tend not to go for it, I guess --
it looks convenient, but it's just that little bit overcooked as an API.
*sigh*

Well, if you're working at the stdio level it's fine I think but this
program is at the level below that.