Re: [PATCH v4 3/9] bpf/btf: Add a function to search a member of a struct/union
From: Florent Revest <hidden>
Date: 2023-08-02 14:49:14
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On Wed, Aug 2, 2023 at 3:56 PM Masami Hiramatsu [off-list ref] wrote:
On Tue, 1 Aug 2023 20:40:54 -0400 Steven Rostedt [off-list ref] wrote:quoted
On Wed, 2 Aug 2023 09:21:46 +0900 Masami Hiramatsu (Google) [off-list ref] wrote:quoted
quoted
Then use kprobes. When I asked Masami what the difference between fprobes and kprobes was, he told me that it would be that it would no longer rely on the slower FTRACE_WITH_REGS. But currently, it still does.kprobes needs to keep using pt_regs because software-breakpoint exception handler gets that. And fprobe is used for bpf multi-kprobe interface, but I think it can be optional. So until user-land tool supports the ftrace_regs, you can just disable using fprobes if CONFIG_DYNAMIC_FTRACE_WITH_REGS=nI'm confused. I asked about the difference between kprobes on ftrace and fprobes, and you said it was to get rid of the requirement of FTRACE_WITH_REGS. https://lore.kernel.org/all/20230120205535.98998636329ca4d5f8325bc3@kernel.org/ (local)Yes, it is for enabling fprobe (and fprobe-event) on more architectures. I don't think it's possible to change everything at once. So, it will be changed step by step. At the first step, I will replace pt_regs with ftrace_regs, and make bpf_trace.c and fprobe_event depends on FTRACE_WITH_REGS.
Just a small note that, strictly speaking, CONFIG_DYNAMIC_FTRACE_WITH_REGS=y is not enough. fprobe_init() would also need a way to set FTRACE_OPS_FL_SAVE_REGS conditionally. (you could be on an arch that supports saving either regs or args and if you don't set FTRACE_OPS_FL_SAVE_REGS you'd go through the args trampoline and get a ftrace_regs that doesn't hold a pt_regs)