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From: Fengkai Sun <qcloud1014@gmail.com>
To: libc-help@sourceware.org
Subject: why don't setjmp save MXCSR register and x87 control word?
Date: Tue, 16 Mar 2021 22:39:36 +0800	[thread overview]
Message-ID: <CAF6YOcOnWpqxsp+tbu-29HHaw7+sj=4jR-ZPcmEq=po6F5u-yg@mail.gmail.com> (raw)

Hi list,

To the best of my knowledge, setjmp have to save all the callee-saved
registers.

According to Sys V ABI:
>  The control bits of the MXCSR register are callee-saved (preserved
across calls), while the status bits are caller-saved (not preserved).
>  The x87 status word register is caller-saved, whereas the x87 control
word is callee-saved.

But in sysdeps/x86_64/setjmp.S, __sigsetjmp only saves rbx, rbp, r12-r15,
rsp.

I also found an example in FreeBSD, which makes more sense to me:
https://svnweb.freebsd.org/base/head/lib/libc/amd64/gen/_setjmp.S?view=markup

I don't know if there will be any problem if MXCSR and x87 control word are
not saved and get clobbered .


Best,
Fengkai

             reply	other threads:[~2021-03-16 14:39 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-16 14:39 Fengkai Sun [this message]
2021-03-17 18:59 ` Adhemerval Zanella
     [not found] ` <41f234be-0fbe-0ae1-74be-084bab59bef6@linaro.org>
2021-03-18 13:02   ` Fengkai Sun
2021-03-18 13:25     ` Adhemerval Zanella

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