On Tue, 23 Nov 2021 at 17:40, Richard Henderson
<richard.henderson@linaro.org> wrote:
We don't need a register that can live across the syscall;
we only need a register that can live until the syscall.
What about the case where:
* we execute the sc instruction (r11 trashed)
* the syscall is one that from the host kernel point of
view is restartable
* the kernel arranges to restart the syscall by rewinding the
PC to point to the start of the 'sc' instruction
* our rewind_if_in_safe_syscall() rewinds PC further to
point at safe_syscall_start
* we want to use r11 again, but it was trashed in step 1
?
Put another way, this patch is effectively a revert of
commit 5d9f3ea081721, which was a fix to an observed bug.