From: Florian Weimer <fw@deneb.enyo.de>
To: Godmar Back via Libc-help <libc-help@sourceware.org>
Cc: Godmar Back <godmar@gmail.com>
Subject: Re: curiosity question about swapcontext libc implementation on x86_64
Date: Sun, 25 Feb 2024 12:27:25 +0100 [thread overview]
Message-ID: <87bk84eqci.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <CAB4+JYKx0+6r=pVzymV24O3LHSdVBCZUXJKM9LAmVkwEEgAJeA@mail.gmail.com> (Godmar Back via Libc-help's message of "Thu, 1 Feb 2024 10:23:37 -0500")
* Godmar Back via Libc-help:
> The implementation of the obsolescent makecontext/getcontext/swapcontext
> family of functions on x86_64 [1] appears to save a selection of registers.
>
> These include callee-saved regs like rbx, rbp, r12-r15, but also
> caller-saved regs like rdi, rsi, rdx, rcx. On the floating point side, it
> saves mxcsr, the x87 FPU state via fnstenv, but not the xmm SSE register.
> All of these floating point registers are callee-saved based on the AMD64
> ABI [2].
%rdi, %rsi, %rdx, %rcx are argument registers and need to be restored
for makecontext to work correctly. As far as I can see, getcontext
wouldn't need to save them, but they need to be restored.
The handling of what is now considered per-thread state (such as
floating point control words or signal masks) is inconsistent. I
think this is just due to the age of these interfaces, and not
something that was designed explicitly.
prev parent reply other threads:[~2024-02-25 11:27 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-01 15:23 Godmar Back
2024-02-25 11:27 ` Florian Weimer [this message]
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