On Wed, 28 Oct 2020 20:08:16 -0400 Steven Rostedt <rost...@goodmis.org> wrote:
> This is something I wanted to implement a long time ago, but held off until > there was a good reason to do so. Now it appears that having access to the > arguments of the function by default is very useful. As a bonus, because > arguments must be saved regardless before calling a callback, because they > need to be restored before returning back to the start of the traced > function, there's not much work to do to have them always be there for > normal function callbacks. > > The basic idea is that if CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS is set, then > all callbacks registered to ftrace can use the regs parameter for the stack > and arguments (kernel_stack_pointer(regs), regs_get_kernel_argument(regs, n)), > without the need to set REGS that causes overhead by saving all registers as > REGS simulates a breakpoint. > > This could be extended to move the REGS portion to kprobes itself, and > remove the SAVE_REGS flag completely, but for now, kprobes still uses the > full SAVE_REGS support. Yeah, I would like to keep using the SAVE_REGS support until SAVE_ARGS implemented on all arch. But in parallel, I will prepare generic kprobe-on-ftrace handler. > The last patch extends the WITH_ARGS to allow default function tracing to > modify the instruction pointer, where livepatching for x86 no longer needs > to save all registers. > > The idea of this approach is to give enough information to a callback that > it could retrieve all arguments, which includes the stack pointer and > instruction pointer. > > This can also be extended to modify the function graph tracer to use the > function tracer instead of having a separate trampoline. Anyway, this series (3 patches) looks good to me. Reviewed-by: Masami Hiramatsu <mhira...@kernel.org> Thank you! > > Changes since v2: > > - Change all callback args to use struct ftrace_regs, and if something > requires the full regs, it must use the ftrace_get_regs() helper macro, > which will return NULL if the regs isn't full (FL_SAVE_REGS set). > This addresses a concern by both Peter Zijlsta and Thomas Gleixner that > a partially filled pt_regs may be used inappropriately. > > - No test patch in this version. > > - Use case using livepatching is added. This passes the test_livepatch.sh > selftest. > > Steven Rostedt (VMware) (3): > ftrace: Have the callbacks receive a struct ftrace_regs instead of > pt_regs > ftrace/x86: Allow for arguments to be passed in to ftrace_regs by > default > livepatching: Use the default ftrace_ops instead of REGS when ARGS is > available > > ---- > arch/powerpc/include/asm/livepatch.h | 4 +++- > arch/s390/include/asm/livepatch.h | 5 ++++- > arch/x86/Kconfig | 1 + > arch/x86/include/asm/ftrace.h | 18 ++++++++++++++++++ > arch/x86/include/asm/livepatch.h | 4 ++-- > arch/x86/kernel/ftrace_64.S | 15 +++++++++++++-- > arch/x86/kernel/kprobes/ftrace.c | 3 ++- > include/linux/ftrace.h | 28 ++++++++++++++++++++++++++-- > include/linux/kprobes.h | 2 +- > kernel/livepatch/patch.c | 10 ++++++---- > kernel/trace/Kconfig | 9 +++++++++ > kernel/trace/ftrace.c | 27 +++++++++++++++------------ > kernel/trace/trace_event_perf.c | 2 +- > kernel/trace/trace_functions.c | 9 ++++----- > kernel/trace/trace_irqsoff.c | 2 +- > kernel/trace/trace_sched_wakeup.c | 2 +- > kernel/trace/trace_selftest.c | 20 +++++++++++--------- > kernel/trace/trace_stack.c | 2 +- > 18 files changed, 119 insertions(+), 44 deletions(-) -- Masami Hiramatsu <mhira...@kernel.org>