| Message ID | 1465077630-633-2-git-send-email-zlim.lnx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, Jun 04, 2016 at 03:00:29PM -0700, Zi Shen Lim wrote: > Remove superfluous stack frame, saving us 3 instructions for > every JMP_CALL. > > Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com> > --- > arch/arm64/net/bpf_jit_comp.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c > index 51abc97..7ae304e 100644 > --- a/arch/arm64/net/bpf_jit_comp.c > +++ b/arch/arm64/net/bpf_jit_comp.c > @@ -578,11 +578,8 @@ emit_cond_jmp: > const u64 func = (u64)__bpf_call_base + imm; > > emit_a64_mov_i64(tmp, func, ctx); > - emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx); > - emit(A64_MOV(1, A64_FP, A64_SP), ctx); > emit(A64_BLR(tmp), ctx); > emit(A64_MOV(1, r0, A64_R(0)), ctx); > - emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx); > break; > } Is the jitted code intended to be unwindable by standard tools? Will
Hi Will, On Mon, Jun 6, 2016 at 10:05 AM, Will Deacon <will.deacon@arm.com> wrote: > On Sat, Jun 04, 2016 at 03:00:29PM -0700, Zi Shen Lim wrote: >> Remove superfluous stack frame, saving us 3 instructions for >> every JMP_CALL. >> >> Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com> >> --- >> arch/arm64/net/bpf_jit_comp.c | 3 --- >> 1 file changed, 3 deletions(-) >> >> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c >> index 51abc97..7ae304e 100644 >> --- a/arch/arm64/net/bpf_jit_comp.c >> +++ b/arch/arm64/net/bpf_jit_comp.c >> @@ -578,11 +578,8 @@ emit_cond_jmp: >> const u64 func = (u64)__bpf_call_base + imm; >> >> emit_a64_mov_i64(tmp, func, ctx); >> - emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx); >> - emit(A64_MOV(1, A64_FP, A64_SP), ctx); >> emit(A64_BLR(tmp), ctx); >> emit(A64_MOV(1, r0, A64_R(0)), ctx); >> - emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx); >> break; >> } > > Is the jitted code intended to be unwindable by standard tools? Before this patch: bpf_prologue => push stack frame ... jmp_call => push stack frame, call bpf_helper*, pop stack frame ... bpf_epilogue => pop stack frame, ret Now: bpf_prologue => push stack frame ... jmp_call => call bpf_helper* ... bpf_epilogue => pop stack frame, ret *Note: bpf_helpers in kernel/bpf/helper.c So yes, it's still unwindable. > > Will
On Mon, Jun 06, 2016 at 09:36:03PM -0700, Z Lim wrote: > On Mon, Jun 6, 2016 at 10:05 AM, Will Deacon <will.deacon@arm.com> wrote: > > On Sat, Jun 04, 2016 at 03:00:29PM -0700, Zi Shen Lim wrote: > >> Remove superfluous stack frame, saving us 3 instructions for > >> every JMP_CALL. > >> > >> Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com> > >> --- > >> arch/arm64/net/bpf_jit_comp.c | 3 --- > >> 1 file changed, 3 deletions(-) > >> > >> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c > >> index 51abc97..7ae304e 100644 > >> --- a/arch/arm64/net/bpf_jit_comp.c > >> +++ b/arch/arm64/net/bpf_jit_comp.c > >> @@ -578,11 +578,8 @@ emit_cond_jmp: > >> const u64 func = (u64)__bpf_call_base + imm; > >> > >> emit_a64_mov_i64(tmp, func, ctx); > >> - emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx); > >> - emit(A64_MOV(1, A64_FP, A64_SP), ctx); > >> emit(A64_BLR(tmp), ctx); > >> emit(A64_MOV(1, r0, A64_R(0)), ctx); > >> - emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx); > >> break; > >> } > > > > Is the jitted code intended to be unwindable by standard tools? > > Before this patch: > bpf_prologue => push stack frame > ... > jmp_call => push stack frame, call bpf_helper*, pop stack frame > ... > bpf_epilogue => pop stack frame, ret > > Now: > bpf_prologue => push stack frame > ... > jmp_call => call bpf_helper* > ... > bpf_epilogue => pop stack frame, ret > > *Note: bpf_helpers in kernel/bpf/helper.c > > So yes, it's still unwindable. Sure, I'm not disputing that. I just wondered whether or not it needs to be unwindable at all... Will
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 51abc97..7ae304e 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -578,11 +578,8 @@ emit_cond_jmp: const u64 func = (u64)__bpf_call_base + imm; emit_a64_mov_i64(tmp, func, ctx); - emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx); - emit(A64_MOV(1, A64_FP, A64_SP), ctx); emit(A64_BLR(tmp), ctx); emit(A64_MOV(1, r0, A64_R(0)), ctx); - emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx); break; } /* tail call */
Remove superfluous stack frame, saving us 3 instructions for every JMP_CALL. Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com> --- arch/arm64/net/bpf_jit_comp.c | 3 --- 1 file changed, 3 deletions(-)