Re: [PATCH 1/3] MIPS: kernel: Support extracting off-line stack traces from user-space with perf

From: Jiaxun Yang
Date: Mon Jan 04 2021 - 22:47:36 EST

在 2021/1/4 下午6:59, Peter Zijlstra 写道:
On Tue, Dec 29, 2020 at 08:55:59PM +0800, Tiezhu Yang wrote:
+u64 perf_reg_abi(struct task_struct *tsk)
+ if (test_tsk_thread_flag(tsk, TIF_32BIT_REGS))
+ else
So we recently changed this on x86 to not rely on TIF flags. IIRC the
problem is that on x86 you can change the mode of a task without the
kernel being aware of it. Is something like that possible on MIPS as

Hi all,

In MIPS world it's impossible to raise a thread to 64bit without kernel aware.
Without STATUS.UX set it will trigger reserved instruction exception when trying
to run 64bit instructions.

However it may be possible to run with 32bit ABI without TIF_32BIT_REGS if user
program didn't get ELF ABI right. I think that's out of our current consideration.

The thing x86 does today is look at it's pt_regs state to determine the
actual state.
It is possible to look at pt_regs Status.UX bit on MIPS. But it seems unnecessary
as user can't change it.


- Jiaxun