Re: [RFC PATCH v1 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable

On 4/1/21 1:53 PM, Madhavan T. Venkataraman wrote:

On 4/1/21 1:40 PM, Madhavan T. Venkataraman wrote:

quoted

quoted

quoted

So, it is only defined if CONFIG_FUNCTION_GRAPH_TRACER is defined. I can address
this as well as your comment by defining another label whose name is more meaningful
to our use:
+SYM_INNER_LABEL(ftrace_trampoline, SYM_L_GLOBAL) // checked by the unwinder
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
        nop                             // If enabled, this will be replaced
                                        // "b ftrace_graph_caller"
#endif

I'm not sure we need to bother with that, you'd still need the & I think.

I think we need to bother with that. If CONFIG_FUNCTION_GRAPH_TRACER is not on but
CONFIG_DYNAMIC_FTRACE_WITH_REGS is, then ftrace_graph_call() will not occur in the stack
trace taken from a tracer function. The unwinder still needs to recognize an ftrace frame.
I don't want to assume ftrace_common_return which is the label that currently follows
the above code. So, we need a different label outside the above ifdef.

Alternatively, I could just move the SYM_INNER_LABEL(ftrace_graph_call..) to outside the ifdef.

Madhavan

Or, even better, I could just use ftrace_call+4 because that would be the return
address for the tracer function at ftrace_call:

SYM_CODE_START(ftrace_common)
        sub     x0, x30, #AARCH64_INSN_SIZE     // ip (callsite's BL insn)
        mov     x1, x9                          // parent_ip (callsite's LR)
        ldr_l   x2, function_trace_op           // op
        mov     x3, sp                          // regs

SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
        bl      ftrace_stub

I think that would be cleaner. And, I don't need the complicated comments for ftrace_graph_call.

Is this acceptable?

Madhavan