On Mon, 21 Oct 2019 16:10:38 +0200 Borislav Petkov <bp@xxxxxxxxx> wrote: > From: Borislav Petkov <bp@xxxxxxx> > > function_hook is used as a better name than the default __fentry__ > which is the profiling counter which gcc adds before every function's > prologue. Thus, it is not called from C and cannot have the same > semantics as a pure C function - it saves/restores regs so that a C > function can be called. > > Drop the function_hook symbol and use __fentry__ directly for better > alignment with gcc's documentation. > > Switch the marking to SYM_CODE_START/_END which is reserved for > non-standard, special functions. I would break this into two patches. One that removes the function_hook name, and the other to convert to the SYM_CODE_START/END. For the removal of the function_hook patch, be sure to state some of the history for why the function_hook was created in the first place. Which would be something like this: "When ftrace first was introduced to the kernel, it used gcc's mcount profiling mechanism. The mcount mechanism would add a call to "mcount" at the start of every function but after the stack frame was set up. Later, in gcc 4.6, gcc introduced -mfentry, that would create a call to "__fentry__" instead of "mcount", before the stack frame was set up. In order to handle both cases, ftrace defined a macro "function_hook" that would be either "mcount" or "__fentry__" depending on which one was being used. The Linux kernel no longer supports the "mcount" method, thus there's no reason to keep the "function_hook" define around. Simply use "__fentry__", as there is no ambiguity to the name anymore." -- Steve > > Signed-off-by: Borislav Petkov <bp@xxxxxxx> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Jiri Slaby <jslaby@xxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > Cc: linux-doc@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: x86@xxxxxxxxxx > --- > Documentation/asm-annotations.rst | 4 ++-- > arch/x86/kernel/ftrace_32.S | 8 +++----- > arch/x86/kernel/ftrace_64.S | 13 ++++++------- > 3 files changed, 11 insertions(+), 14 deletions(-) >
