Messages in this thread | | | Date | Wed, 1 Apr 2020 09:39:16 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET |
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On Wed, Apr 01, 2020 at 04:22:26PM +0200, Peter Zijlstra wrote: > > > --- 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. > > Humph, ok, but there's two of those :/
Just commenting the asm one should be fine I think.
That way a reader of code using the macro is more likely to understand its purpose.
> > > --- 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? > > Ahh. So if you look at what the trampoline copies, you'll note we'll > copy until -- but *NOT* including -- the jmp ftrace_epilogue. Instead > we'll write a RET at the end. > > However, due to splitting the return path, such that each instruction > has a unique stack offset, we now have a second jmp ftrace_epilogue in > the middle of the function. That too needs to be overwritten by a RET.
Right, but 'ip' needs to point to the trampoline's version of 'ftrace_regs_caller_ret', not the original ftrace_64 version.
> > > --- 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. > > Oh, whoops :-) I keep doing this every time I need to run gdb on it. > I'll make it go away.
Ha, I do something similar, I just add -O0 to CFLAGS.
-- Josh
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