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Subject: Re: [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic
 operations
To:     Brendan Jackman <jackmanb@google.com>, <bpf@vger.kernel.org>
CC:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        KP Singh <kpsingh@chromium.org>,
        Florent Revest <revest@chromium.org>,
        <linux-kernel@vger.kernel.org>, Jann Horn <jannh@google.com>
References: <20201127175738.1085417-1-jackmanb@google.com>
 <20201127175738.1085417-13-jackmanb@google.com>
From:   Yonghong Song <yhs@fb.com>
Message-ID: <1e1656a9-6f0e-f17e-176c-37d996641e9a@fb.com>
Date:   Mon, 30 Nov 2020 19:55:02 -0800
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On 11/27/20 9:57 AM, Brendan Jackman wrote:
> This relies on the work done by Yonghong Song in
> https://reviews.llvm.org/D72184
> 
> Note the hackery in the Makefile that is necessary to avoid breaking
> tests for people who haven't yet got a version of Clang supporting
> V4. It seems like this hackery ought to be confined to
> tools/build/feature - I tried implementing that and found that it
> ballooned into an explosion of nightmares at the top of
> tools/testing/selftests/bpf/Makefile without actually improving the
> clarity of the CLANG_BPF_BUILD_RULE code at all. Hence the simple
> $(shell) call...
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   tools/testing/selftests/bpf/Makefile          |  12 +-
>   .../selftests/bpf/prog_tests/atomics_test.c   | 329 ++++++++++++++++++
>   .../selftests/bpf/progs/atomics_test.c        | 124 +++++++
>   .../selftests/bpf/verifier/atomic_and.c       |  77 ++++
>   .../selftests/bpf/verifier/atomic_cmpxchg.c   |  96 +++++
>   .../selftests/bpf/verifier/atomic_fetch_add.c | 106 ++++++
>   .../selftests/bpf/verifier/atomic_or.c        |  77 ++++
>   .../selftests/bpf/verifier/atomic_sub.c       |  44 +++
>   .../selftests/bpf/verifier/atomic_xchg.c      |  46 +++
>   .../selftests/bpf/verifier/atomic_xor.c       |  77 ++++
>   tools/testing/selftests/bpf/verifier/ctx.c    |   2 +-
>   11 files changed, 987 insertions(+), 3 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics_test.c
>   create mode 100644 tools/testing/selftests/bpf/progs/atomics_test.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_and.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_or.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_sub.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c
>   create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xor.c
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 3d5940cd110d..5eadfd09037d 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -228,6 +228,12 @@ IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
>   			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
>   MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
>   
> +# Determine if Clang supports BPF arch v4, and therefore atomics.
> +CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf -mcpu=? 2>&1)),true,)
> +ifeq ($(CLANG_SUPPORTS_V4),true)
> +	CFLAGS += -DENABLE_ATOMICS_TESTS
> +endif
> +
>   CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>   BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 			\
>   	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
> @@ -250,7 +256,9 @@ define CLANG_BPF_BUILD_RULE
>   	$(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
>   	$(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm			\
>   		-c $1 -o - || echo "BPF obj compilation failed") | 	\
> -	$(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2
> +	$(LLC) -mattr=dwarfris -march=bpf				\
> +		-mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)			\
> +		$4 -filetype=obj -o $2
>   endef
>   # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
>   define CLANG_NOALU32_BPF_BUILD_RULE
> @@ -391,7 +399,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
>   TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read				\
>   		       $(wildcard progs/btf_dump_test_case_*.c)
>   TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
> -TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
> +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)

If the compiler indeed supports cpu v4 (i.e., atomic insns), 
-DENABLE_ATOMICS_TESTS will be added to TRUNNER_BPF_FLAGS and
eventually -DENABLE_ATOMICS_TESTS is also available for
no-alu32 test and this will cause compilation error.

I did the following hack to workaround the issue, i.e., only adds
the definition to default (alu32) test run.

index 5eadfd09037d..3d1320fd93eb 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -230,9 +230,6 @@ MENDIAN=$(if 
$(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)

  # Determine if Clang supports BPF arch v4, and therefore atomics.
  CLANG_SUPPORTS_V4=$(if $(findstring v4,$(shell $(CLANG) --target=bpf 
-mcpu=? 2>&1)),true,)
-ifeq ($(CLANG_SUPPORTS_V4),true)
-       CFLAGS += -DENABLE_ATOMICS_TESTS
-endif

  CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
  BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)                  \
@@ -255,6 +252,7 @@ $(OUTPUT)/flow_dissector_load.o: flow_dissector_load.h
  define CLANG_BPF_BUILD_RULE
         $(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2)
         $(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm                     \
+               $(if $(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)      \
                 -c $1 -o - || echo "BPF obj compilation failed") |      \
         $(LLC) -mattr=dwarfris -march=bpf                               \
                 -mcpu=$(if $(CLANG_SUPPORTS_V4),v4,v3)                  \
@@ -399,7 +397,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c 
cgroup_helpers.c trace_helpers.c      \
  TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read                          \
                        $(wildcard progs/btf_dump_test_case_*.c)
  TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
-TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) $(if 
$(CLANG_SUPPORTS_V4),-DENABLE_ATOMICS_TESTS,)
+TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
  TRUNNER_BPF_LDFLAGS := -mattr=+alu32
  $(eval $(call DEFINE_TEST_RUNNER,test_progs))


>   TRUNNER_BPF_LDFLAGS := -mattr=+alu32
>   $(eval $(call DEFINE_TEST_RUNNER,test_progs))
>   
> diff --git a/tools/testing/selftests/bpf/prog_tests/atomics_test.c b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> new file mode 100644
> index 000000000000..8ecc0392fdf9
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/atomics_test.c
> @@ -0,0 +1,329 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <test_progs.h>
> +
> +#ifdef ENABLE_ATOMICS_TESTS
> +
> +#include "atomics_test.skel.h"
> +
> +static void test_add(void)
[...]
> +
> +#endif /* ENABLE_ATOMICS_TESTS */
> diff --git a/tools/testing/selftests/bpf/progs/atomics_test.c b/tools/testing/selftests/bpf/progs/atomics_test.c
> new file mode 100644
> index 000000000000..3139b00937e5
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/atomics_test.c
> @@ -0,0 +1,124 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +#ifdef ENABLE_ATOMICS_TESTS
> +
> +__u64 add64_value = 1;
> +__u64 add64_result = 0;
> +__u32 add32_value = 1;
> +__u32 add32_result = 0;
> +__u64 add_stack_value_copy = 0;
> +__u64 add_stack_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(add, int a)
> +{
> +	__u64 add_stack_value = 1;
> +
> +	add64_result = __sync_fetch_and_add(&add64_value, 2);
> +	add32_result = __sync_fetch_and_add(&add32_value, 2);
> +	add_stack_result = __sync_fetch_and_add(&add_stack_value, 2);
> +	add_stack_value_copy = add_stack_value;
> +
> +	return 0;
> +}
> +
> +__s64 sub64_value = 1;
> +__s64 sub64_result = 0;
> +__s32 sub32_value = 1;
> +__s32 sub32_result = 0;
> +__s64 sub_stack_value_copy = 0;
> +__s64 sub_stack_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(sub, int a)
> +{
> +	__u64 sub_stack_value = 1;
> +
> +	sub64_result = __sync_fetch_and_sub(&sub64_value, 2);
> +	sub32_result = __sync_fetch_and_sub(&sub32_value, 2);
> +	sub_stack_result = __sync_fetch_and_sub(&sub_stack_value, 2);
> +	sub_stack_value_copy = sub_stack_value;
> +
> +	return 0;
> +}
> +
> +__u64 and64_value = (0x110ull << 32);
> +__u64 and64_result = 0;
> +__u32 and32_value = 0x110;
> +__u32 and32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(and, int a)
> +{
> +
> +	and64_result = __sync_fetch_and_and(&and64_value, 0x011ull << 32);
> +	and32_result = __sync_fetch_and_and(&and32_value, 0x011);
> +
> +	return 0;
> +}
> +
> +__u64 or64_value = (0x110ull << 32);
> +__u64 or64_result = 0;
> +__u32 or32_value = 0x110;
> +__u32 or32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(or, int a)
> +{
> +	or64_result = __sync_fetch_and_or(&or64_value, 0x011ull << 32);
> +	or32_result = __sync_fetch_and_or(&or32_value, 0x011);
> +
> +	return 0;
> +}
> +
> +__u64 xor64_value = (0x110ull << 32);
> +__u64 xor64_result = 0;
> +__u32 xor32_value = 0x110;
> +__u32 xor32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(xor, int a)
> +{
> +	xor64_result = __sync_fetch_and_xor(&xor64_value, 0x011ull << 32);
> +	xor32_result = __sync_fetch_and_xor(&xor32_value, 0x011);
> +
> +	return 0;
> +}

All above __sync_fetch_and_{add, sub, and, or, xor} produces a return
value used later. To test atomic_<op> instructions, it will be good if
you can add some tests which ignores the return value.

> +
> +__u64 cmpxchg64_value = 1;
> +__u64 cmpxchg64_result_fail = 0;
> +__u64 cmpxchg64_result_succeed = 0;
> +__u32 cmpxchg32_value = 1;
> +__u32 cmpxchg32_result_fail = 0;
> +__u32 cmpxchg32_result_succeed = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(cmpxchg, int a)
> +{
> +	cmpxchg64_result_fail = __sync_val_compare_and_swap(
> +		&cmpxchg64_value, 0, 3);
> +	cmpxchg64_result_succeed = __sync_val_compare_and_swap(
> +		&cmpxchg64_value, 1, 2);
> +
> +	cmpxchg32_result_fail = __sync_val_compare_and_swap(
> +		&cmpxchg32_value, 0, 3);
> +	cmpxchg32_result_succeed = __sync_val_compare_and_swap(
> +		&cmpxchg32_value, 1, 2);
> +
> +	return 0;
> +}
> +
> +__u64 xchg64_value = 1;
> +__u64 xchg64_result = 0;
> +__u32 xchg32_value = 1;
> +__u32 xchg32_result = 0;
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(xchg, int a)
> +{
> +	__u64 val64 = 2;
> +	__u32 val32 = 2;
> +
> +	__atomic_exchange(&xchg64_value, &val64, &xchg64_result, __ATOMIC_RELAXED);
> +	__atomic_exchange(&xchg32_value, &val32, &xchg32_result, __ATOMIC_RELAXED);
> +
> +	return 0;
> +}
> +
> +#endif /* ENABLE_ATOMICS_TESTS */
[...]