Messages in this thread Patch in this message | | | Subject | Re: [PATCH] perf build: Build error in libbpf missing initialization | From | Daniel Borkmann <> | Date | Fri, 27 Jul 2018 21:31:01 +0200 |
| |
On 07/27/2018 07:59 PM, Jakub Kicinski wrote: > On Fri, 27 Jul 2018 10:21:26 +0200, Thomas Richter wrote: >> In linux-next tree compiling the perf tool with additional make flags >> "EXTRA_CFLAGS="-Wp,-D_FORTIFY_SOURCE=2 -O2" >> causes a compiler error. It is the warning >> 'variable may be used uninitialized' >> which is treated as error: >> >> I compile it using a FEDORA 28 installation, my gcc compiler version: >> gcc (GCC) 8.0.1 20180324 (Red Hat 8.0.1-0.20) >> >> The file that causes the error is tools/lib/bpf/libbpf.c >> >> Here is the error message: >> >> [root@p23lp27] # make V=1 EXTRA_CFLAGS="-Wp,-D_FORTIFY_SOURCE=2 -O2" >> [...] >> Makefile.config:849: No openjdk development package found, please >> install JDK package, e.g. openjdk-8-jdk, java-1.8.0-openjdk-devel >> Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h' >> differs from latest version at 'include/uapi/linux/if_link.h' >> CC libbpf.o >> libbpf.c: In function ‘bpf_perf_event_read_simple’: >> libbpf.c:2342:6: error: ‘ret’ may be used uninitialized in this >> function [-Werror=maybe-uninitialized] >> int ret; >> ^ >> cc1: all warnings being treated as errors >> mv: cannot stat './.libbpf.o.tmp': No such file or directory >> /home6/tmricht/linux-next/tools/build/Makefile.build:96: recipe for target 'libbpf.o' failed >> >> Fix this warning and add an addition check at the beginning >> of the while loop. >> >> Cc: Alexei Starovoitov <ast@kernel.org> >> Cc: Daniel Borkmann <daniel@iogearbox.net> >> >> Suggested-by: Jakub Kicinski <jakub.kicinski@netronome.com> >> Signed-off-by: Thomas Richter <tmricht@linux.ibm.com> > > Ah, you already sent this, LGTM, thanks Thomas! > >> tools/lib/bpf/libbpf.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >> index 73465caa33ba..66965ca96113 100644 >> --- a/tools/lib/bpf/libbpf.c >> +++ b/tools/lib/bpf/libbpf.c >> @@ -2349,6 +2349,8 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, >> >> begin = base + data_tail % size; >> end = base + data_head % size; >> + if (begin == end) >> + return LIBBPF_PERF_EVENT_ERROR; >> >> while (begin != end) { >> struct perf_event_header *ehdr;
One question though, any objections to go for something like the below instead? I doubt we ever hit this in a 'normal' situation, and given we already test for the begin and end anyway, we could just avoid the extra test altogether. I could change it to the below if you're good as well (no need to resend anything):
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index d881d37..1aafdbe 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -2273,8 +2273,8 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, volatile struct perf_event_mmap_page *header = mem; __u64 data_tail = header->data_tail; __u64 data_head = header->data_head; + int ret = LIBBPF_PERF_EVENT_ERROR; void *base, *begin, *end; - int ret;
asm volatile("" ::: "memory"); /* in real code it should be smp_rmb() */ if (data_head == data_tail) Thanks, Daniel
| |