Re: [PATCH v8 4/5] arm64: implement ftrace with regs

Julien Thierry
2019-02-13T10:30:19Z

Hi Torsten,

On 08/02/2019 15:10, Torsten Duwe wrote:
> Implement ftrace with regs, based on the new gcc flag
> -fpatchable-function-entry (=2)
>
> Now that gcc8 added 2 NOPs at the beginning of each function, replace
> the first NOP thus generated with a quick LR saver (move it to scratch
> reg x9), so the 2nd replacement insn, the call to ftrace, does not
> clobber the value. Ftrace will then generate the standard stack
> frames.
>
> Note that patchable-function-entry in GCC disables IPA-RA, which means
> ABI register calling conventions are obeyed and scratch registers such
> as x9 are available.
>
> Introduce and handle an ftrace_regs_trampoline for module PLTs, right
> after ftrace_trampoline in an ftrace_trampolines[2] array, and double
> the size of the corresponding special section.
>
> Signed-off-by: Torsten Duwe <duwe@suse.de>
>
> ---
> arch/arm64/include/asm/ftrace.h | 16 ++++
> arch/arm64/include/asm/module.h | 3
> arch/arm64/kernel/entry-ftrace.S | 125 +++++++++++++++++++++++++++++++++++++--
> arch/arm64/kernel/ftrace.c | 117 ++++++++++++++++++++++++++++--------
> arch/arm64/kernel/module-plts.c | 3
> arch/arm64/kernel/module.c | 2
> 6 files changed, 231 insertions(+), 35 deletions(-)

[...]

> --- a/arch/arm64/include/asm/module.h
> +++ b/arch/arm64/include/asm/module.h
> @@ -32,7 +32,8 @@ struct mod_arch_specific {
> struct mod_plt_sec init;
>
> /* for CONFIG_DYNAMIC_FTRACE */
> - struct plt_entry *ftrace_trampoline;
> + struct plt_entry *ftrace_trampolines;
> +#define MOD_ARCH_NR_FTRACE_TRAMPOLINES 2

Nit: I'd define this outside of the struct, just below
MODULE_ARCH_VERMAGIC, and use the prefix "MODULE_ARCH" instead of
"MOD_ARCH" as this seem to be already in use for a few other defines.

Otherwise things look good to me:

Reviewed-by: Julien Thierry <julien.thierry@arm.com>

Cheers,

--
Julien Thierry