diff mbox series

[bpf-next] selftests/bpf: make multi-uprobe tests work in RELEASE=1 mode

Message ID 20240329173654.3174156-1-andrii@kernel.org (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [bpf-next] selftests/bpf: make multi-uprobe tests work in RELEASE=1 mode | expand

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Commit Message

Andrii Nakryiko March 29, 2024, 5:36 p.m. UTC 
When BPF selftests are built in RELEASE=1 mode with -O2 optimization
level, uprobe_multi binary, called from multi-uprobe tests is optimized
to the point that all the thousands of target uprobe_multi_func_XXX
functions are eliminated, breaking tests.

So ensure they are preserved through noinline + asm volatile trick.

But, actually, compiling uprobe_multi binary with -O2 takes a really
long time, and is quite useless (it's not a benchmark). So in addition
to ensuring that uprobe_multi_func_XXX functions are preserved, opt-out
of -O2 explicitly in Makefile and stick to -O0. This saves a lot of
compilation time.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/Makefile       | 2 +-
 tools/testing/selftests/bpf/uprobe_multi.c | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

Comments

Alexei Starovoitov March 29, 2024, 6:21 p.m. UTC | #1 
On Fri, Mar 29, 2024 at 10:37 AM Andrii Nakryiko <andrii@kernel.org> wrote:
>
> When BPF selftests are built in RELEASE=1 mode with -O2 optimization
> level, uprobe_multi binary, called from multi-uprobe tests is optimized
> to the point that all the thousands of target uprobe_multi_func_XXX
> functions are eliminated, breaking tests.
>
> So ensure they are preserved through noinline + asm volatile trick.
>
> But, actually, compiling uprobe_multi binary with -O2 takes a really
> long time, and is quite useless (it's not a benchmark). So in addition
> to ensuring that uprobe_multi_func_XXX functions are preserved, opt-out
> of -O2 explicitly in Makefile and stick to -O0. This saves a lot of
> compilation time.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  tools/testing/selftests/bpf/Makefile       | 2 +-
>  tools/testing/selftests/bpf/uprobe_multi.c | 4 +++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 3b9eb40d6343..b0ac3dd80acf 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -759,7 +759,7 @@ $(OUTPUT)/veristat: $(OUTPUT)/veristat.o
>
>  $(OUTPUT)/uprobe_multi: uprobe_multi.c
>         $(call msg,BINARY,,$@)
> -       $(Q)$(CC) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
> +       $(Q)$(CC) $(CFLAGS) -O0 $(LDFLAGS) $^ $(LDLIBS) -o $@
>
>  EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR)                      \
>         prog_tests/tests.h map_tests/tests.h verifier/tests.h           \
> diff --git a/tools/testing/selftests/bpf/uprobe_multi.c b/tools/testing/selftests/bpf/uprobe_multi.c
> index a61ceab60b68..e38228563766 100644
> --- a/tools/testing/selftests/bpf/uprobe_multi.c
> +++ b/tools/testing/selftests/bpf/uprobe_multi.c
> @@ -9,7 +9,9 @@
>
>  #define NAME(name, idx) PASTE(name, idx)
>
> -#define DEF(name, idx)  int NAME(name, idx)(void) { return 0; }
> +#define DEF(name, idx) \
> +       int __attribute__((noinline)) \
> +       NAME(name, idx)(void) { asm volatile (""); return 0; }

I prefer to use __weak to avoid inlining and compiler optimizations.
It's less work for compiler as well,
since noinline doesn't tell compiler to stop analyzing the body
of the function, while __weak does have such an effect.
And asm won't be necessary as well.
Andrii Nakryiko March 29, 2024, 6:30 p.m. UTC | #2 
On Fri, Mar 29, 2024 at 11:21 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Fri, Mar 29, 2024 at 10:37 AM Andrii Nakryiko <andrii@kernel.org> wrote:
> >
> > When BPF selftests are built in RELEASE=1 mode with -O2 optimization
> > level, uprobe_multi binary, called from multi-uprobe tests is optimized
> > to the point that all the thousands of target uprobe_multi_func_XXX
> > functions are eliminated, breaking tests.
> >
> > So ensure they are preserved through noinline + asm volatile trick.
> >
> > But, actually, compiling uprobe_multi binary with -O2 takes a really
> > long time, and is quite useless (it's not a benchmark). So in addition
> > to ensuring that uprobe_multi_func_XXX functions are preserved, opt-out
> > of -O2 explicitly in Makefile and stick to -O0. This saves a lot of
> > compilation time.
> >
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> > ---
> >  tools/testing/selftests/bpf/Makefile       | 2 +-
> >  tools/testing/selftests/bpf/uprobe_multi.c | 4 +++-
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > index 3b9eb40d6343..b0ac3dd80acf 100644
> > --- a/tools/testing/selftests/bpf/Makefile
> > +++ b/tools/testing/selftests/bpf/Makefile
> > @@ -759,7 +759,7 @@ $(OUTPUT)/veristat: $(OUTPUT)/veristat.o
> >
> >  $(OUTPUT)/uprobe_multi: uprobe_multi.c
> >         $(call msg,BINARY,,$@)
> > -       $(Q)$(CC) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
> > +       $(Q)$(CC) $(CFLAGS) -O0 $(LDFLAGS) $^ $(LDLIBS) -o $@
> >
> >  EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR)                      \
> >         prog_tests/tests.h map_tests/tests.h verifier/tests.h           \
> > diff --git a/tools/testing/selftests/bpf/uprobe_multi.c b/tools/testing/selftests/bpf/uprobe_multi.c
> > index a61ceab60b68..e38228563766 100644
> > --- a/tools/testing/selftests/bpf/uprobe_multi.c
> > +++ b/tools/testing/selftests/bpf/uprobe_multi.c
> > @@ -9,7 +9,9 @@
> >
> >  #define NAME(name, idx) PASTE(name, idx)
> >
> > -#define DEF(name, idx)  int NAME(name, idx)(void) { return 0; }
> > +#define DEF(name, idx) \
> > +       int __attribute__((noinline)) \
> > +       NAME(name, idx)(void) { asm volatile (""); return 0; }
>
> I prefer to use __weak to avoid inlining and compiler optimizations.
> It's less work for compiler as well,
> since noinline doesn't tell compiler to stop analyzing the body
> of the function, while __weak does have such an effect.
> And asm won't be necessary as well.


makes sense, will do __weak, maybe it will make -O0 unnecessary as well
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 3b9eb40d6343..b0ac3dd80acf 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -759,7 +759,7 @@  $(OUTPUT)/veristat: $(OUTPUT)/veristat.o
 
 $(OUTPUT)/uprobe_multi: uprobe_multi.c
 	$(call msg,BINARY,,$@)
-	$(Q)$(CC) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
+	$(Q)$(CC) $(CFLAGS) -O0 $(LDFLAGS) $^ $(LDLIBS) -o $@
 
 EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR)			\
 	prog_tests/tests.h map_tests/tests.h verifier/tests.h		\
diff --git a/tools/testing/selftests/bpf/uprobe_multi.c b/tools/testing/selftests/bpf/uprobe_multi.c
index a61ceab60b68..e38228563766 100644
--- a/tools/testing/selftests/bpf/uprobe_multi.c
+++ b/tools/testing/selftests/bpf/uprobe_multi.c
@@ -9,7 +9,9 @@ 
 
 #define NAME(name, idx) PASTE(name, idx)
 
-#define DEF(name, idx)  int NAME(name, idx)(void) { return 0; }
+#define DEF(name, idx) \
+	int __attribute__((noinline)) \
+	NAME(name, idx)(void) { asm volatile (""); return 0; }
 #define CALL(name, idx) NAME(name, idx)();
 
 #define F(body, name, idx) body(name, idx)