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Date: Wed, 1 Apr 2020 09:14:02 -0500 From: Josh Poimboeuf <jpoimboe@...hat.com> To: Peter Zijlstra <peterz@...radead.org> Cc: tglx@...utronix.de, linux-kernel@...r.kernel.org, x86@...nel.org, mhiramat@...nel.org, mbenes@...e.cz, Steven Rostedt <rostedt@...dmis.org> Subject: Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET On Wed, Apr 01, 2020 at 12:27:03AM +0200, Peter Zijlstra wrote: > On Tue, Mar 31, 2020 at 04:20:40PM -0500, Josh Poimboeuf wrote: > > On Tue, Mar 31, 2020 at 04:17:58PM -0500, Josh Poimboeuf wrote: > > > > I'm not against adding a second/separate hint for this. In fact, I > > > > almost considered teaching objtool how to interpret the whole IRET frame > > > > so that we can do it without hints. It's just that that's too much code > > > > for this one case. > > > > > > > > HINT_IRET_SELF ? > > > > > > Despite my earlier complaint about stack size knowledge, we could just > > > forget the hint and make "iretq in C code" equivalent to "reduce stack > > > size by arch_exception_stack_size()" and keep going. There's > > > file->c_file which tells you it's a C file. > > > > Or maybe "iretq in an STT_FUNC" is better since this pattern could > > presumably happen in a callable asm function. > > Like so then? I'd suggest a patch split like: 1) objtool: automagic IRET-in-func 2) objtool: add RET_OFFSET 3) ftrace: re-organize asm (and use RET_OFFSET hint) 4) objtool: remove now-unused SAVE/RESTORE > --- a/arch/x86/include/asm/orc_types.h > +++ b/arch/x86/include/asm/orc_types.h > @@ -58,8 +58,13 @@ > #define ORC_TYPE_CALL 0 > #define ORC_TYPE_REGS 1 > #define ORC_TYPE_REGS_IRET 2 > -#define UNWIND_HINT_TYPE_SAVE 3 > -#define UNWIND_HINT_TYPE_RESTORE 4 > + > +/* > + * RET_OFFSET: Used on instructions that terminate a function; mostly RETURN > + * and sibling calls. On these, sp_offset denotes the expected offset from > + * initial_func_cfi. > + */ > +#define UNWIND_HINT_TYPE_RET_OFFSET 3 I think this comment belongs at the UNWIND_HINT_RET_OFFSET macro definition. > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -282,7 +282,8 @@ static inline void tramp_free(void *tram > > /* Defined as markers to the end of the ftrace default trampolines */ > extern void ftrace_regs_caller_end(void); > -extern void ftrace_epilogue(void); > +extern void ftrace_regs_caller_ret(void); > +extern void ftrace_caller_end(void); > extern void ftrace_caller_op_ptr(void); > extern void ftrace_regs_caller_op_ptr(void); > > @@ -334,7 +335,7 @@ create_trampoline(struct ftrace_ops *ops > call_offset = (unsigned long)ftrace_regs_call; > } else { > start_offset = (unsigned long)ftrace_caller; > - end_offset = (unsigned long)ftrace_epilogue; > + end_offset = (unsigned long)ftrace_caller_end; > op_offset = (unsigned long)ftrace_caller_op_ptr; > call_offset = (unsigned long)ftrace_call; > } > @@ -366,6 +367,13 @@ create_trampoline(struct ftrace_ops *ops > if (WARN_ON(ret < 0)) > goto fail; > > + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > + ip = ftrace_regs_caller_ret; > + ret = probe_kernel_read(ip, (void *)retq, RET_SIZE); > + if (WARN_ON(ret < 0)) > + goto fail; > + } > + Hm? This function creates a trampoline but it looks like this change is overwriting the original ftrace_64 code itself? > --- a/tools/objtool/Makefile > +++ b/tools/objtool/Makefile > @@ -31,7 +31,7 @@ INCLUDES := -I$(srctree)/tools/include \ > -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi \ > -I$(srctree)/tools/arch/$(SRCARCH)/include > WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed > -CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS) > +CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -ggdb3 $(INCLUDES) $(LIBELF_FLAGS) > LDFLAGS += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS) Why? Smells like a separate patch at least. -- Josh
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