Messages in this thread Patch in this message | | | Date | Wed, 25 Jul 2018 18:48:35 -0700 | From | Jakub Kicinski <> | Subject | Re: [PATCH v2] perf build: Build error in libbpf with EXTRA_CFLAGS="-Wp,-D_FORTIFY_SOURCE=2 -O2" |
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On Wed, 25 Jul 2018 09:21:26 +0200, Thomas Richter wrote: > commit a5b8bd47dcc57 ("bpf tools: Collect eBPF programs from their own sections")
Hmm.. are you sure it's not 531b014e7a2f ("tools: bpf: make use of reallocarray") that caused the issue? That commit made us switch from XSI-compliant to GNU-specific strerror_r() implementation..
/me checks
Yes it looks like 531b014e7a2f~ builds just fine.
Daniel, did you try to apply v1 to the bpf tree? Perhaps there is a confusion about the trees here, if this is caused by my recent change it's a bpf-next material. strerror() works, but strerror_r() seems nicer, so perhaps we could keep it if the patch worked in bpf-next?
> causes a compiler error when building the perf tool in the linux-next tree. > 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" > [...] > make -f /home6/tmricht/linux-next/tools/build/Makefile.build > dir=./util/scripting-engines obj=libperf > libbpf.c: In function ‘bpf_object__elf_collect’: > libbpf.c:811:15: error: ignoring return value of ‘strerror_r’, > declared with attribute warn_unused_result [-Werror=unused-result] > strerror_r(-err, errmsg, sizeof(errmsg)); > ^ > 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 > > Since this is the only occurance of strerror_r() replace it > by strerror(). The additional functionality of strerror_r() to > copy the error message into the supplied buffer is not needed. > This is also consistant with all the other pr_warning() statements > in this file which all use strerror(). > > Also fixes a possible initialization issue. > > Cc: Wang Nan <wangnan0@huawei.com> > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Daniel Borkmann <daniel@iogearbox.net> > Signed-off-by: Thomas Richter <tmricht@linux.ibm.com> > > tools/lib/bpf/libbpf.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 955f8eafbf41..f9eb68ff2f4f 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -806,11 +806,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj) > err = bpf_object__add_program(obj, data->d_buf, > data->d_size, name, idx); > if (err) { > - char errmsg[STRERR_BUFSIZE]; > - > - strerror_r(-err, errmsg, sizeof(errmsg)); > pr_warning("failed to alloc program %s (%s): %s", > - name, obj->path, errmsg); > + name, obj->path, strerror(-err)); > } > } else if (sh.sh_type == SHT_REL) { > void *reloc = obj->efile.reloc; > @@ -2334,7 +2331,7 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, > __u64 data_tail = header->data_tail; > __u64 data_head = header->data_head; > void *base, *begin, *end; > - int ret; > + int ret = 0; > > asm volatile("" ::: "memory"); /* in real code it should be smp_rmb() */ > if (data_head == data_tail)
This looks like a separate issue. The ret variable should really be enum bpf_perf_event_ret, so could you please initialize it to one of the values of this enum?
The uninitilized condition can only happen if (data_head != data_tail) but at the same time (data_head % size == data_tail % size) which should never really happen... Perhaps initializing to LIBBPF_PERF_EVENT_ERROR would make sense?
Or better still adding:
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index f732237610e5..fa5a25945f19 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -2289,6 +2289,8 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, begin = base + data_tail % size; end = base + data_head % size; + if (being == end) + return LIBBPF_PERF_EVENT_ERROR; while (begin != end) { struct perf_event_header *ehdr;
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