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SubjectRe: [PATCH 1/3] riscv: Add perf callchain support
> --- /dev/null
> +++ b/arch/riscv/kernel/perf_callchain.c
> @@ -0,0 +1,122 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2019 Hangzhou C-SKY Microsystems co.,ltd.

Please use normal /* */ Style comment for everything but the SPDX
tags.

> +static int unwind_frame_kernel(struct stackframe *frame)
> +{
> + int graph = 0;
> +
> + /* 0x3 means misalignment */
> + if (!kstack_end((void *)frame->fp) &&
> + !((unsigned long)frame->fp & 0x3) &&
> + ((unsigned long)frame->fp >= TASK_SIZE)) {
> + frame->ra = ((struct stackframe *)frame->fp - 1)->ra;
> + frame->fp = ((struct stackframe *)frame->fp - 1)->fp;
> + /* make sure CONFIG_FUNCTION_GRAPH_TRACER is turned on */
> + if (__kernel_text_address(frame->ra))
> + frame->ra = ftrace_graph_ret_addr(NULL, &graph,
> + frame->ra, NULL);
> + return 0;
> + } else {
> + return -EPERM;
> + }

Please do early exists for all the error conditions. Also no casts
are needed for using ->fp as a scalar value, and we should probably
just do a struct copy instead of copying both values individually.

The function should look something like:

static int unwind_frame_kernel(struct stackframe *frame)
{
if (!kstack_end((void *)frame->fp))
return -EPERM;
if ((frame->fp & 0x3 || frame->fp >= TASK_SIZE)
return -EPERM;

*frame = *((struct stackframe *)frame->fp - 1);
if (__kernel_text_address(frame->ra)) {
int graph = 0;

frame->ra = ftrace_graph_ret_addr(NULL, &graph, frame->ra,
NULL);
}
return 0;
}

> +static void notrace walk_stackframe(struct stackframe *fr,
> + struct perf_callchain_entry_ctx *entry)
> +{
> + while (1) {
> + int ret;
> +
> + perf_callchain_store(entry, fr->ra);
> +
> + ret = unwind_frame_kernel(fr);
> + if (ret < 0)
> + break;
> + }
> +}

Why not:

do {
perf_callchain_store(entry, fr->ra);
} while (unwind_frame_kernel(fr) >= 0);

> +/*
> + * Get the return address for a single stackframe and return a pointer to the
> + * next frame tail.
> + */
> +static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
> + unsigned long fp, unsigned long reg_ra)
> +{
> + struct stackframe buftail;
> + unsigned long ra = 0;
> + unsigned long *user_frame_tail = (unsigned long *)(fp - sizeof(struct stackframe));

Overly long line.

> + fp = user_backtrace(entry, fp, regs->ra);
> + while ((entry->nr < entry->max_stack) &&
> + fp && !((unsigned long)fp & 0x3))
> + fp = user_backtrace(entry, fp, 0);

Please don't indent the condition continuation and the loop body
by the same amount.

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