On Fri, 18 Oct 2019 19:13:54 +0200 Borislav Petkov <bp@xxxxxxx> wrote: > On Fri, Oct 18, 2019 at 12:49:56PM -0400, Steven Rostedt wrote: > > On Fri, 18 Oct 2019 12:48:00 -0400 > > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > > > Relabel function_hook to be marked really as a function. It is called > > > > from C and has the same expectations towards the stack etc. > > > > > > > And to go even further, it *does not* have the same expectations > > towards the stack. > > > > I think this patch should not be applied. > > There are a couple more markings like that now: > > $ git grep function_hook > Documentation/asm-annotations.rst:120: SYM_FUNC_START(function_hook) > Documentation/asm-annotations.rst:122: SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_32.S:15:# define function_hook __fentry__ > arch/x86/kernel/ftrace_32.S:24:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_32.S:26:SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_64.S:17:# define function_hook __fentry__ > arch/x86/kernel/ftrace_64.S:135:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_64.S:137:SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_64.S:251:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_64.S:282:SYM_FUNC_END(function_hook) > > Frankly, I wouldn't mark this function at all as it is special and I see > a little sense to have it in stack traces but maybe Jiri has another > angle here. I'll let him comment. It just needs to be visible by modules and what not, otherwise linking will fail. > > I guess with the new nomenclature that can be SYM_CODE_* now... > > Then, this magic "function" or a global symbol with an address or > whatever that is (oh, there's #define trickery too) definitely deserves > a comment above it to explain what it is. I even have to build the .s > file to see what it turns into: The #define was because we use to support mcount or __fentry__, now we just support __fentry__, and function_hook describes it better ;-) > > .globl __fentry__ ; .p2align 4, 0x90 ; __fentry__: > retq > .type __fentry__, @function ; .size __fentry__, .-__fentry__ > > Yeah, it is called on every function entry: > > callq ffffffff81a01760 <__fentry__> > > but can we please explain with a comment above it what it is? Heh, I guess we could, which would probably be quite a long comment as it's the key behind ftrace itself. -- Steve
