| Message ID | 171509089214.162236.6201493898649663823.stgit@devnote2 (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | tracing: fprobe: function_graph: Multi-function graph and fprobe on fgraph | expand |
On Tue, 7 May 2024 23:08:12 +0900 "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote: > From: Masami Hiramatsu (Google) <mhiramat@kernel.org> > > 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) <mhiramat@kernel.org> > Acked-by: Mark Rutland <mark.rutland@arm.com> > --- > Changes in v8: > - Update that the saved registers depends on the context. > Changes in v3: > - Add instruction pointer > Changes in v2: > - newly added. > --- > include/linux/ftrace.h | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 54d53f345d14..b81f1afa82a1 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -118,6 +118,32 @@ 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. I wonder if we should also add a note about some architectures in some circumstances may store all pt_regs in ftrace_regs. For example, if an architecture supports FTRACE_WITH_REGS, it may pass the pt_regs within the ftrace_regs. If that is the case, then ftrace_get_regs() called on it will return a pointer to a valid pt_regs, or NULL if it is not supported or the ftrace_regs does not have a all the registers. -- Steve > + * > + * 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; > };
On Thu, 23 May 2024 19:10:31 -0400 Steven Rostedt <rostedt@goodmis.org> wrote: > On Tue, 7 May 2024 23:08:12 +0900 > "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote: > > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org> > > > > 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) <mhiramat@kernel.org> > > Acked-by: Mark Rutland <mark.rutland@arm.com> > > --- > > Changes in v8: > > - Update that the saved registers depends on the context. > > Changes in v3: > > - Add instruction pointer > > Changes in v2: > > - newly added. > > --- > > include/linux/ftrace.h | 26 ++++++++++++++++++++++++++ > > 1 file changed, 26 insertions(+) > > > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > > index 54d53f345d14..b81f1afa82a1 100644 > > --- a/include/linux/ftrace.h > > +++ b/include/linux/ftrace.h > > @@ -118,6 +118,32 @@ 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. > > I wonder if we should also add a note about some architectures in some > circumstances may store all pt_regs in ftrace_regs. For example, if an > architecture supports FTRACE_WITH_REGS, it may pass the pt_regs within the > ftrace_regs. If that is the case, then ftrace_get_regs() called on it will > return a pointer to a valid pt_regs, or NULL if it is not supported or the > ftrace_regs does not have a all the registers. Agreed. That case also should be noted. Thanks for pointing! > > -- Steve > > > > + * > > + * 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; > > }; >
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index 54d53f345d14..b81f1afa82a1 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -118,6 +118,32 @@ 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; };