On Mon, Nov 18, 2024 at 05:18:08PM +0900, Masami Hiramatsu wrote:
> On Tue, 5 Nov 2024 14:34:01 +0100
> Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> > Putting together all the previously added pieces to support optimized
> > uprobes on top of 5-byte nop instruction.
> >
> > The current uprobe execution goes through following:
> > - installs breakpoint instruction over original instruction
> > - exception handler hit and calls related uprobe consumers
> > - and either simulates original instruction or does out of line single step
> > execution of it
> > - returns to user space
> >
> > The optimized uprobe path
> >
> > - checks the original instruction is 5-byte nop (plus other checks)
> > - adds (or uses existing) user space trampoline and overwrites original
> > instruction (5-byte nop) with call to user space trampoline
> > - the user space trampoline executes uprobe syscall that calls related uprobe
> > consumers
> > - trampoline returns back to next instruction
> >
> > This approach won't speed up all uprobes as it's limited to using nop5 as
> > original instruction, but we could use nop5 as USDT probe instruction (which
> > uses single byte nop ATM) and speed up the USDT probes.
> >
> > This patch overloads related arch functions in uprobe_write_opcode and
> > set_orig_insn so they can install call instruction if needed.
> >
> > The arch_uprobe_optimize triggers the uprobe optimization and is called after
> > first uprobe hit. I originally had it called on uprobe installation but then
> > it clashed with elf loader, because the user space trampoline was added in a
> > place where loader might need to put elf segments, so I decided to do it after
> > first uprobe hit when loading is done.
> >
> > TODO release uprobe trampoline when it's no longer needed.. we might need to
> > stop all cpus to make sure no user space thread is in the trampoline.. or we
> > might just keep it, because there's just one 4GB memory region?
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > arch/x86/include/asm/uprobes.h | 7 ++
> > arch/x86/kernel/uprobes.c | 130 +++++++++++++++++++++++++++++++++
> > include/linux/uprobes.h | 1 +
> > kernel/events/uprobes.c | 3 +
> > 4 files changed, 141 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
> > index 678fb546f0a7..84a75ed748f0 100644
> > --- a/arch/x86/include/asm/uprobes.h
> > +++ b/arch/x86/include/asm/uprobes.h
> > @@ -20,6 +20,11 @@ typedef u8 uprobe_opcode_t;
> > #define UPROBE_SWBP_INSN 0xcc
> > #define UPROBE_SWBP_INSN_SIZE 1
> >
> > +enum {
> > + ARCH_UPROBE_FLAG_CAN_OPTIMIZE = 0,
> > + ARCH_UPROBE_FLAG_OPTIMIZED = 1,
> > +};
> > +
> > struct uprobe_xol_ops;
> >
> > struct arch_uprobe {
> > @@ -45,6 +50,8 @@ struct arch_uprobe {
> > u8 ilen;
> > } push;
> > };
> > +
> > + unsigned long flags;
> > };
> >
> > struct arch_uprobe_task {
> > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> > index 02aa4519b677..50ccf24ff42c 100644
> > --- a/arch/x86/kernel/uprobes.c
> > +++ b/arch/x86/kernel/uprobes.c
> > @@ -18,6 +18,7 @@
> > #include <asm/processor.h>
> > #include <asm/insn.h>
> > #include <asm/mmu_context.h>
> > +#include <asm/nops.h>
> >
> > /* Post-execution fixups. */
> >
> > @@ -877,6 +878,33 @@ static const struct uprobe_xol_ops push_xol_ops = {
> > .emulate = push_emulate_op,
> > };
> >
> > +static int is_nop5_insns(uprobe_opcode_t *insn)
> > +{
> > + return !memcmp(insn, x86_nops[5], 5);
>
> Maybe better to use BYTES_NOP5 directly?
ok
>
> > +}
> > +
> > +static int is_call_insns(uprobe_opcode_t *insn)
> > +{
> > + return *insn == 0xe8;
>
> 0xe8 -> CALL_INSN_OPCODE
right, thanks
jirka
