From: ori@eigenstate.org
To: 9fans@9fans.net
Subject: [9fans] non-interruptible temporary: why do we care?
Date: Sun, 03 Jan 2021 19:32:22 -0800 [thread overview]
Message-ID: <41FE44BF416FFB4B9ED729FE2AB1A4DE@eigenstate.org> (raw)
Our compilers will sometimes produce a warning about
a non-interruptible temporary:
#include <u.h>
#include <libc.h>
void
f(vlong a)
{
vlong x, y, z;
x = y = z = a;
}
cpu% 5c -w test.c
warning: /fd/0:7 non-interruptable temporary
warning: /fd/0:7 non-interruptable temporary
I know this means that the intermediate values
cannot be assigned atomically, but I don't see
why this rates a warning. From what I understand,
the uninterruptability of the temporaries should
be unobservable as long as our note handlers
save and restore registers correctly.
The only case I can think of is that a note
handler may see "tearing" of a register, but
that doesn't require a non-interruptible
temporary -- this kind of code will suffice:
vlong x;
int
use_x(){ return x; }
void
main(void)
{
atnotify(use_x, 1);
while(1)
x++;
}
Why do we warn about non-interruptible
temporaries? What issues am I missing?
------------------------------------------
9fans: 9fans
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next reply other threads:[~2021-01-04 3:32 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-04 3:32 ori [this message]
2021-06-16 20:23 ` unobe
2021-06-16 20:28 ` ori
2021-06-17 19:32 ` Charles Forsyth
2021-06-16 21:10 ` Anthony Martin
2021-06-16 21:28 ` unobe
2021-06-20 14:53 ` [9fans] help Spock via 9fans
2021-06-20 15:32 ` Marshall Conover
2021-06-20 18:46 ` U Cirello
2021-06-20 21:14 ` Ethan Gardener
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