On Mon, Dec 16, 2024 at 12:32 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > On Fri, Dec 13, 2024 at 01:58:33PM -0800, Andrii Nakryiko wrote: > > On Wed, Dec 11, 2024 at 5:35 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > > > Using 5-byte nop for x86 usdt probes so we can switch > > > to optimized uprobe them. > > > > > > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> > > > --- > > > tools/testing/selftests/bpf/sdt.h | 9 ++++++++- > > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > > > > This change will make it impossible to run latest selftests on older > > kernels. Let's do what we did with -DENABLE_ATOMICS_TESTS and allow to > > disable this through Makefile, ok? > > ok, I wanted to start addressing this after this version > > so the problem is using this macro with nop5 in application running > on older kernels that do not have nop5 emulation and uprobe syscall > optimization, because uprobe/usdt on top of nop5 (single-stepped) > will be slower than on top of current nop1 (emulated) > > AFAICS selftests should still work, just bit slower due to nop5 emulation ah, fair enough, it won't break anything, true > > one part of the solution would be to backport [1] to stable kernels > which is an easy fix (even though it needs changes now) > > if that's not enough we'd need to come up with that nop1/nop5 macro > solution, where tooling (libbpf with extra data in usdt note) would > install uprobe on top of nop1 on older kernels and on top of nop5 on > new ones.. but that'd need more work of course yes, I think that's the way we should go, but as you said, that's outside of kernel and we should work on that as a follow up to this series > > jirka > > > [1] patch#7 - uprobes/x86: Add support to emulate nop5 instruction > > > > > > > > > diff --git a/tools/testing/selftests/bpf/sdt.h b/tools/testing/selftests/bpf/sdt.h > > > index ca0162b4dc57..7ac9291f45f1 100644 > > > --- a/tools/testing/selftests/bpf/sdt.h > > > +++ b/tools/testing/selftests/bpf/sdt.h > > > @@ -234,6 +234,13 @@ __extension__ extern unsigned long long __sdt_unsp; > > > #define _SDT_NOP nop > > > #endif > > > > > > +/* Use 5 byte nop for x86_64 to allow optimizing uprobes. */ > > > +#if defined(__x86_64__) > > > +# define _SDT_DEF_NOP _SDT_ASM_5(990: .byte 0x0f, 0x1f, 0x44, 0x00, 0x00) > > > +#else > > > +# define _SDT_DEF_NOP _SDT_ASM_1(990: _SDT_NOP) > > > +#endif > > > + > > > #define _SDT_NOTE_NAME "stapsdt" > > > #define _SDT_NOTE_TYPE 3 > > > > > > @@ -286,7 +293,7 @@ __extension__ extern unsigned long long __sdt_unsp; > > > > > > #define _SDT_ASM_BODY(provider, name, pack_args, args, ...) \ > > > _SDT_DEF_MACROS \ > > > - _SDT_ASM_1(990: _SDT_NOP) \ > > > + _SDT_DEF_NOP \ > > > _SDT_ASM_3( .pushsection .note.stapsdt,_SDT_ASM_AUTOGROUP,"note") \ > > > _SDT_ASM_1( .balign 4) \ > > > _SDT_ASM_3( .4byte 992f-991f, 994f-993f, _SDT_NOTE_TYPE) \ > > > -- > > > 2.47.0 > > >
