| Message ID | 20230412210423.900851-4-song@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 2995f9a8d427b9ff6f3cf4e85c0f9d4456ef324d |
| Delegated to: | BPF |
| Headers | show |
| Series | Fix a few BPF selftests | expand |
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c index 7999476b9446..c5ad39bbe9af 100644 --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c @@ -130,7 +130,11 @@ bpf_testmod_test_btf_type_tag_percpu_2(struct bpf_testmod_btf_type_tag_3 *arg) { noinline int bpf_testmod_loop_test(int n) { - int i, sum = 0; + /* Make sum volatile, so smart compilers, such as clang, will not + * optimize the code by removing the loop. + */ + volatile int sum = 0; + int i; /* the primary goal of this test is to test LBR. Create a lot of * branches in the function, so we can catch it easily.
Some compilers (for example clang-15) optimize bpf_testmod_loop_test and remove the loop: gcc version (gdb) disassemble bpf_testmod_loop_test Dump of assembler code for function bpf_testmod_loop_test: 0x0000000000000570 <+0>: callq 0x575 <bpf_testmod_loop_test+5> 0x0000000000000575 <+5>: xor %eax,%eax 0x0000000000000577 <+7>: test %edi,%edi 0x0000000000000579 <+9>: jle 0x587 <bpf_testmod_loop_test+23> 0x000000000000057b <+11>: xor %edx,%edx 0x000000000000057d <+13>: add %edx,%eax 0x000000000000057f <+15>: add $0x1,%edx 0x0000000000000582 <+18>: cmp %edx,%edi 0x0000000000000584 <+20>: jne 0x57d <bpf_testmod_loop_test+13> 0x0000000000000586 <+22>: retq 0x0000000000000587 <+23>: retq clang-15 version (gdb) disassemble bpf_testmod_loop_test Dump of assembler code for function bpf_testmod_loop_test: 0x0000000000000450 <+0>: nopl 0x0(%rax,%rax,1) 0x0000000000000455 <+5>: test %edi,%edi 0x0000000000000457 <+7>: jle 0x46b <bpf_testmod_loop_test+27> 0x0000000000000459 <+9>: lea -0x1(%rdi),%eax 0x000000000000045c <+12>: lea -0x2(%rdi),%ecx 0x000000000000045f <+15>: imul %rax,%rcx 0x0000000000000463 <+19>: shr %rcx 0x0000000000000466 <+22>: lea -0x1(%rdi,%rcx,1),%eax 0x000000000000046a <+26>: retq 0x000000000000046b <+27>: xor %eax,%eax 0x000000000000046d <+29>: retq Note: The jne instruction is removed in clang-15 version. Force the compile to keep the loop by making sum volatile. Signed-off-by: Song Liu <song@kernel.org> --- tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)