linux-kernel - Re: [PATCH 1/2] riscv: ptrace: Use the correct API for `fcsr' access

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Date:   Wed, 5 Aug 2020 11:25:11 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@....com>
To:     Al Viro <viro@...iv.linux.org.uk>
cc:     Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv: ptrace: Use the correct API for `fcsr'
 access

On Wed, 5 Aug 2020, Al Viro wrote:

> > I'm not sure I understand what you're saying, but given that branch replaces
> > all of this I guess it's best to just do nothing on our end here?
> 
> It doesn't replace ->put() (for now); it _does_ replace ->get() and AFAICS the
> replacement is much saner:
> 
> static int riscv_fpr_get(struct task_struct *target,
>                          const struct user_regset *regset,
>                          struct membuf to)
> {
> 	struct __riscv_d_ext_state *fstate = &target->thread.fstate;
> 
> 	membuf_write(&to, fstate, offsetof(struct __riscv_d_ext_state, fcsr));
> 	membuf_store(&to, fstate->fcsr);
> 	return membuf_zero(&to, 4);     // explicitly pad
> }

 I'm glad to see the old interface go, it was cumbersome.

> user_regset_copyout() calling conventions are atrocious and so are those of
> regset ->get().  The best thing to do with both is to take them out of their
> misery and be done with that.  Do you see any problems with riscv gdbserver
> on current linux-next?  If not, I'd rather see that "API" simply go away...
> If there are problems, I would very much prefer fixes on top of what's done
> in that branch.

 I can push linux-next through regression-testing with RISC-V gdbserver 
and/or native GDB if that would help.  This is also used with core dumps, 
but honestly I don't know what state RISC-V support is in in the BFD/GDB's 
core dump interpreter, as people tend to forget about the core dump 
feature nowadays.

  Maciej