From: Joseph Myers <joseph@codesourcery.com>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: Fengkai Sun <qcloud1014@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: why don't setjmp save MXCSR register and x87 control word?
Date: Wed, 17 Mar 2021 21:08:32 +0000 [thread overview]
Message-ID: <alpine.DEB.2.22.394.2103172104130.139917@digraph.polyomino.org.uk> (raw)
In-Reply-To: <41f234be-0fbe-0ae1-74be-084bab59bef6@linaro.org>
On Wed, 17 Mar 2021, Adhemerval Zanella via Libc-alpha wrote:
> Because afaik the C standard specify that any state of floating-point status
> flag should *not* be saved:
>
> 7.13 Nonlocal jumps <setjmp.h>
> [...]
> It does not include the state of the floating-point status flags, of open files,
> or of any other component of the abstract machine.
Indeed, the floating-point exception flags, rounding mode and any other
such state are essentially thread-local variables, and should be handled
just like such variables. setjmp and longjmp don't save and restore
thread-local or global variables, so they shouldn't save and restore
floating-point flags or control modes either.
(In psABI terms, we invented the term "limited-access bits" to describe
this state in the 32-bit Power Architecture ABI.)
--
Joseph S. Myers
joseph@codesourcery.com
prev parent reply other threads:[~2021-03-17 21:08 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAF6YOcOnWpqxsp+tbu-29HHaw7+sj=4jR-ZPcmEq=po6F5u-yg@mail.gmail.com>
2021-03-17 18:59 ` Adhemerval Zanella
2021-03-17 21:08 ` Joseph Myers [this message]
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