Re: [PATCH 0/2] riscv: ftrace: make stack walk more robust.

From: "Björn Töpel" <bjorn@kernel.org>
To: "Puranjay Mohan" <puranjay12@gmail.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	"Björn Töpel" <bjorn@rivosinc.com>
Cc: puranjay12@gmail.com
Subject: Re: [PATCH 0/2] riscv: ftrace: make stack walk more robust.
Date: Tue, 02 Apr 2024 15:18:48 +0200	[thread overview]
Message-ID: <8734s3sy13.fsf@all.your.base.are.belong.to.us> (raw)
In-Reply-To: <20240328184020.34278-1-puranjay12@gmail.com>

Puranjay Mohan <puranjay12@gmail.com> writes:

> The current stack walker in riscv implemented in walk_stackframe() provides
> the PC to a callback function when it unwinds the stacks. This doesn't
> allow implementing stack walkers that need access to more information like
> the frame pointer, etc.
>
> This series makes walk_stackframe() provide a unwinde_state structure to
> callback functions. This structure has all the information that
> walk_stackframe() can provide.
>
> Currently, there are four users of walk_stackframe(): return_address(),
> perf_callchain_kernel(), dump_backtrace(), and __get_wchan(). All of these
> have been converted to use arch_stack_walk() rather than calling
> walk_stackframe() directly.
>
> We need this to implement arch_bpf_stack_walk() that provides a callback
> that needs the FP, SP, and PC. This will be needed for implementing BFP
> exceptions for RISCV.

Hmm, I wonder if it's easier to have these two patches as part of the
BPF exception series, instead of having the dependencies be cross-tree?

> There are no functional changes in this series.
>
> I have tested this by crashing the kernel and looking at the stack trace
> with and without CONFIG_FRAME_POINTER

I have two really minor style nits, but regardless if they're fixed or
not:

Reviewed-by: Björn Töpel <bjorn@rivosinc.com>