From: Masami Hiramatsu (Google) Date: Sun, 18 Aug 2024 12:48:13 +0000 (+0900) Subject: tracing: Add a comment about ftrace_regs definition X-Git-Tag: v6.13-rc1~163^2~21 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a370b72ec7165ebe1230d0225cbe66f6526e68ef;p=thirdparty%2Fkernel%2Flinux.git tracing: Add a comment about ftrace_regs definition To clarify what will be expected on ftrace_regs, add a comment to the architecture independent definition of the ftrace_regs. Signed-off-by: Masami Hiramatsu (Google) Acked-by: Mark Rutland Signed-off-by: Steven Rostedt (Google) --- diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index fd5e84d0ec478..42106b3de3961 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -117,6 +117,32 @@ extern int ftrace_enabled; #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS +/** + * ftrace_regs - ftrace partial/optimal register set + * + * ftrace_regs represents a group of registers which is used at the + * function entry and exit. There are three types of registers. + * + * - Registers for passing the parameters to callee, including the stack + * pointer. (e.g. rcx, rdx, rdi, rsi, r8, r9 and rsp on x86_64) + * - Registers for passing the return values to caller. + * (e.g. rax and rdx on x86_64) + * - Registers for hooking the function call and return including the + * frame pointer (the frame pointer is architecture/config dependent) + * (e.g. rip, rbp and rsp for x86_64) + * + * Also, architecture dependent fields can be used for internal process. + * (e.g. orig_ax on x86_64) + * + * On the function entry, those registers will be restored except for + * the stack pointer, so that user can change the function parameters + * and instruction pointer (e.g. live patching.) + * On the function exit, only registers which is used for return values + * are restored. + * + * NOTE: user *must not* access regs directly, only do it via APIs, because + * the member can be changed according to the architecture. + */ struct ftrace_regs { struct pt_regs regs; };