[PATCH 15/23] perf test llvm: Avoid error when PROFILE_ALL_BRANCHES is set

Arnaldo Carvalho de Melo
2017-06-20T01:58:01Z

From: Wang Nan <wangnan0@huawei.com>

The 'if' keyword is a define that expands to complex code when
CONFIG_PROFILE_ALL_BRANCHES is selected, which causes a 'perf test LLVM'
failure like:

$ ./perf test LLVM
35: LLVM search and compile :
35.1: Basic BPF llvm compile : Ok
35.2: kbuild searching : Ok
35.3: Compile source for BPF prologue generation: FAILED!
35.4: Compile source for BPF relocation : Skip

The only affected test case is bpf-script-test-prologue.c
because it uses kernel headers and has 'if' inside.

This patch undefines 'if' to make it passes perf test.

More detailed analysis from a message in this thread, also by Wang:

The problem is caused by following relocation information:

$ readelf -a ./llvmsubtest3
...
[ 5] _ftrace_branch PROGBITS 0000000000000000 00000260
00000000000000a0 0000000000000000 WA 0 0 4
...
Relocation section '.relfunc=null_lseek file->f_mode offset orig' at
offset 0x490 contains 4 entries:
Offset Info Type Sym. Value Sym. Name
000000000038 000b00000001 unrecognized: 1 0000000000000000 _ftrace_branch
0000000000b0 000b00000001 unrecognized: 1 0000000000000000 _ftrace_branch
000000000128 000b00000001 unrecognized: 1 0000000000000000 _ftrace_branch
0000000001c0 000b00000001 unrecognized: 1 0000000000000000 _ftrace_branch

Relocation section '.rel_ftrace_branch' at offset 0x4d0 contains 8 entries:
Offset Info Type Sym. Value Sym. Name
000000000000 000200000001 unrecognized: 1 0000000000000000 .L__func__.bpf_func__n
000000000008 000100000001 unrecognized: 1 0000000000000015 .L.str
000000000028 000200000001 unrecognized: 1 0000000000000000 .L__func__.bpf_func__n
000000000030 000100000001 unrecognized: 1 0000000000000015 .L.str
000000000050 000200000001 unrecognized: 1 0000000000000000 .L__func__.bpf_func__n
000000000058 000100000001 unrecognized: 1 0000000000000015 .L.str
000000000078 000200000001 unrecognized: 1 0000000000000000 .L__func__.bpf_func__n
000000000080 000100000001 unrecognized: 1 0000000000000015 .L.str
...

So I think the failure is because you enabled CONFIG_PROFILE_ALL_BRANCHES.

I can reproduce your buggy result by selecting
CONFIG_PROFILE_ALL_BRANCHES in my kbuild:

$ ./perf test LLVM
35: LLVM search and compile :
35.1: Basic BPF llvm compile : Ok
35.2: kbuild searching : Ok
35.3: Compile source for BPF prologue generation: FAILED!
35.4: Compile source for BPF relocation : Skip

Simply undef CONFIG_PROFILE_ALL_BRANCHES in clang opts not working
because it is introduced by "#include <uapi/linux/fs.h>", which override
cmdline options. So I think the best way is to undefine 'if' inside BPF
script.

Reported-and-Tested-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/20170620183203.2517-1-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/tests/bpf-script-test-prologue.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/tools/perf/tests/bpf-script-test-prologue.c b/tools/perf/tests/bpf-script-test-prologue.c
index 7230e62c70fc..b4ebc75e25ae 100644
--- a/tools/perf/tests/bpf-script-test-prologue.c
+++ b/tools/perf/tests/bpf-script-test-prologue.c
@@ -10,6 +10,15 @@

#include <uapi/linux/fs.h>

+/*
+ * If CONFIG_PROFILE_ALL_BRANCHES is selected,
+ * 'if' is redefined after include kernel header.
+ * Recover 'if' for BPF object code.
+ */
+#ifdef if
+# undef if
+#endif
+
#define FMODE_READ 0x1
#define FMODE_WRITE 0x2

--
2.9.4