Re: [PATCH for-5.2 2/3] linux-user/sparc: Correct set/get_context handling of fp and i7

From: Richard Henderson <richard.henderson@linaro.org>
To: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org
Cc: Giuseppe Musacchio <thatlemon@gmail.com>,
	Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
	Laurent Vivier <laurent@vivier.eu>
Subject: Re: [PATCH for-5.2 2/3] linux-user/sparc: Correct set/get_context handling of fp and i7
Date: Thu, 5 Nov 2020 14:22:04 -0800	[thread overview]
Message-ID: <f95a1975-2fe1-5ece-56d5-3f226cb6ad98@linaro.org> (raw)
In-Reply-To: <20201105212314.9628-3-peter.maydell@linaro.org>

On 11/5/20 1:23 PM, Peter Maydell wrote:
> Because QEMU's user-mode emulation just directly accesses guest CPU
> state, for SPARC the guest register window state is not the same in
> the sparc64_get_context() and sparc64_set_context() functions as it
> is for the real kernel's versions of those functions.  Specifically,
> for the kernel it has saved the user space state such that the O*
> registers go into a pt_regs struct as UREG_I*, and the I* registers
> have been spilled onto the userspace stack.  For QEMU, we haven't
> done that, so the guest's O* registers are still in WREG_O* and the
> I* registers in WREG_I*.
> 
> The code was already accessing the O* registers correctly for QEMU,
> but had copied the kernel code for accessing the I* registers off the
> userspace stack.  Replace this with direct accesses to fp and i7 in
> the CPU state, and add a comment explaining why we differ from the
> kernel code here.
> 
> This fix is sufficient to get bash to a shell prompt.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I'm really pretty unsure about our handling of SPARC register
> windows here. This fix works, but should we instead be
> ensuring that the flush_windows() call cpu_loop() does
> before handling this trap has written the I* regs to the
> stack ???
> ---

Ach, I was so close to being right the last time I tried to clean up this code.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~