| Message ID | 171318535003.254850.2125783941049872788.stgit@devnote2 (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | tracing: fprobe: function_graph: Multi-function graph and fprobe on fgraph | expand |
On Mon, Apr 15, 2024 at 2:49 PM 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) Ooc, have we ever considered skipping argument registers that are not return value registers in the exit code paths ? For example, why would we want to save rdi in a return handler ? But if we want to avoid the situation of having "sparse ftrace_regs" all over again, we'd have to split ftrace_regs into a ftrace_args_regs and a ftrace_ret_regs which would make this refactoring even more painful, just to skip a few instructions. :| I don't necessarily think it's worth it, I just wanted to make sure this was considered. > + * - 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; > }; >
On Wed, Apr 24, 2024 at 2:23 PM Florent Revest <revest@chromium.org> wrote: > > On Mon, Apr 15, 2024 at 2:49 PM 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) > > Ooc, have we ever considered skipping argument registers that are not > return value registers in the exit code paths ? For example, why would > we want to save rdi in a return handler ? > > But if we want to avoid the situation of having "sparse ftrace_regs" > all over again, we'd have to split ftrace_regs into a ftrace_args_regs > and a ftrace_ret_regs which would make this refactoring even more > painful, just to skip a few instructions. :| > > I don't necessarily think it's worth it, I just wanted to make sure > this was considered. Ah, well, I just reached patch 22 and noticed that there you add add: + * Basically, ftrace_regs stores the registers related to the context. + * On function entry, registers for function parameters and hooking the + * function call are stored, and on function exit, registers for function + * return value and frame pointers are stored. So ftrace_regs can be a a sparse structure then. That's fair enough with me! ;)
On Wed, 24 Apr 2024 15:19:24 +0200 Florent Revest <revest@chromium.org> wrote: > On Wed, Apr 24, 2024 at 2:23 PM Florent Revest <revest@chromium.org> wrote: > > > > On Mon, Apr 15, 2024 at 2:49 PM 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) > > > > Ooc, have we ever considered skipping argument registers that are not > > return value registers in the exit code paths ? For example, why would > > we want to save rdi in a return handler ? > > > > But if we want to avoid the situation of having "sparse ftrace_regs" > > all over again, we'd have to split ftrace_regs into a ftrace_args_regs > > and a ftrace_ret_regs which would make this refactoring even more > > painful, just to skip a few instructions. :| > > > > I don't necessarily think it's worth it, I just wanted to make sure > > this was considered. > > Ah, well, I just reached patch 22 and noticed that there you add add: > > + * Basically, ftrace_regs stores the registers related to the context. > + * On function entry, registers for function parameters and hooking the > + * function call are stored, and on function exit, registers for function > + * return value and frame pointers are stored. > > So ftrace_regs can be a a sparse structure then. That's fair enough with me! ;) Yes, and in this patch, I explained that too :) > + * 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. So the function exit, ftrace_regs will be sparse. Thank you,
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; };