commit a5b8bd47dcc57 ("bpf tools: Collect eBPF programs from their own sections")
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 <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Signed-off-by: Thomas Richter <[email protected]>
---
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)
--
2.16.4
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 <[email protected]>
> Cc: Alexei Starovoitov <[email protected]>
> Cc: Daniel Borkmann <[email protected]>
> Signed-off-by: Thomas Richter <[email protected]>
>
> 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;
On 07/26/2018 03:48 AM, Jakub Kicinski wrote:
> 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?
Yeah indeed, the issue is only in bpf-next. When I compile libbpf from
bpf tree with the below flags then it's all good.
Agree that we should rather use strerror_r() given this is a library.
>> 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:
[...]
>> @@ -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;
Sounds good to me.
> while (begin != end) {
> struct perf_event_header *ehdr;
>
On 07/27/2018 04:16 AM, Daniel Borkmann wrote:
> On 07/26/2018 03:48 AM, Jakub Kicinski wrote:
>> 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?
>
> Yeah indeed, the issue is only in bpf-next. When I compile libbpf from
> bpf tree with the below flags then it's all good>
> Agree that we should rather use strerror_r() given this is a library.
Are you sure to stick with strerror_r? I ask because it is the only
occurence of strerror_r in this file. All other error messages use strerror
as in:
pr_warning("failed to create map (name: '%s'): %s\n",
map->name,
strerror(errno));
$ fgrep strerror tools/lib/bpf/libbpf.c
strerror(errno));
issue I try to solve---> strerror_r(-err, errmsg, sizeof(errmsg));
map->name, strerror(errno), errno);
strerror(errno));
pr_warning("load bpf program failed: %s\n", strerror(errno));
pr_warning("failed to statfs %s: %s\n", dir, strerror(errno));
pr_warning("failed to pin program: %s\n", strerror(errno));
pr_warning("failed to mkdir %s: %s\n", path, strerror(-err));
pr_warning("failed to pin map: %s\n", strerror(errno));
$
The next issue with strerror_r is to assign the return value to a variable.
Then we end up with variable set but not used:
libbpf.c: In function ‘bpf_object__elf_collect’:
libbpf.c:809:35: error: variable ‘cp’ set but not used [-Werror=unused-but-set-variable]
char errmsg[STRERR_BUFSIZE], *cp;
^
cc1: all warnings being treated as errors
Here is the source:
if (err) {
char errmsg[STRERR_BUFSIZE], *cp;
cp = strerror_r(-err, errmsg, sizeof(errmsg));
pr_warning("failed to alloc program %s (%s): %s",
name, obj->path, errmsg);
}
To fix this requires something like:
pr_warning("failed to alloc program %s (%s): %s",
name, obj->path, cp);
And after pr_warning() is done, the local array errmsg is deleted.
A lot of overkill in my opinion, unless I miss something.
>>> 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:
> [...]
>>> @@ -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;
>
> Sounds good to me.
>
If you want I can send you a separate patch for this.
--
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
On Fri, 27 Jul 2018 09:22:03 +0200, Thomas-Mich Richter wrote:
> On 07/27/2018 04:16 AM, Daniel Borkmann wrote:
> > On 07/26/2018 03:48 AM, Jakub Kicinski wrote:
> >> 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?
> >
> > Yeah indeed, the issue is only in bpf-next. When I compile libbpf from
> > bpf tree with the below flags then it's all good>
> > Agree that we should rather use strerror_r() given this is a library.
>
> Are you sure to stick with strerror_r? I ask because it is the only
> occurence of strerror_r in this file. All other error messages use strerror
> as in:
> pr_warning("failed to create map (name: '%s'): %s\n",
> map->name,
> strerror(errno));
>
>
> $ fgrep strerror tools/lib/bpf/libbpf.c
> strerror(errno));
> issue I try to solve---> strerror_r(-err, errmsg, sizeof(errmsg));
> map->name, strerror(errno), errno);
> strerror(errno));
> pr_warning("load bpf program failed: %s\n", strerror(errno));
> pr_warning("failed to statfs %s: %s\n", dir, strerror(errno));
> pr_warning("failed to pin program: %s\n", strerror(errno));
> pr_warning("failed to mkdir %s: %s\n", path, strerror(-err));
> pr_warning("failed to pin map: %s\n", strerror(errno));
> $
>
> The next issue with strerror_r is to assign the return value to a variable.
> Then we end up with variable set but not used:
> libbpf.c: In function ‘bpf_object__elf_collect’:
> libbpf.c:809:35: error: variable ‘cp’ set but not used [-Werror=unused-but-set-variable]
> char errmsg[STRERR_BUFSIZE], *cp;
> ^
> cc1: all warnings being treated as errors
The GNU-specific strerror_r() returns a pointer to a string containing
the error message. This may be either a pointer to a string that the
function stores in buf, or a pointer to some (immutable) static string
(in which case buf is unused). If the function stores a string in buf,
then at most buflen bytes are stored (the string may be truncated if
buflen is too small and errnum is unknown). The string always includes
a terminating null byte ('\0').
IOW you gotta use the return value.
> Here is the source:
> if (err) {
> char errmsg[STRERR_BUFSIZE], *cp;
>
> cp = strerror_r(-err, errmsg, sizeof(errmsg));
> pr_warning("failed to alloc program %s (%s): %s",
> name, obj->path, errmsg);
> }
>
> To fix this requires something like:
> pr_warning("failed to alloc program %s (%s): %s",
> name, obj->path, cp);
This looks correct.
> And after pr_warning() is done, the local array errmsg is deleted.
>
> A lot of overkill in my opinion, unless I miss something.
IMO using potentially mutli-thread unsafe functions in a library is not
optimal, we should strive to convert the other instances of strerror()
rather than move the other way.
> >>> 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:
> > [...]
> >>> @@ -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;
> >
> > Sounds good to me.
> >
>
> If you want I can send you a separate patch for this.
As far as I'm concerned - yes, please!
On 07/27/2018 07:57 PM, Jakub Kicinski wrote:
> On Fri, 27 Jul 2018 09:22:03 +0200, Thomas-Mich Richter wrote:
>> On 07/27/2018 04:16 AM, Daniel Borkmann wrote:
>>> On 07/26/2018 03:48 AM, Jakub Kicinski wrote:
>>>> 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?
>>>
>>> Yeah indeed, the issue is only in bpf-next. When I compile libbpf from
>>> bpf tree with the below flags then it's all good>
>>> Agree that we should rather use strerror_r() given this is a library.
>>
>> Are you sure to stick with strerror_r? I ask because it is the only
>> occurence of strerror_r in this file. All other error messages use strerror
>> as in:
>> pr_warning("failed to create map (name: '%s'): %s\n",
>> map->name,
>> strerror(errno));
>>
>> $ fgrep strerror tools/lib/bpf/libbpf.c
>> strerror(errno));
>> issue I try to solve---> strerror_r(-err, errmsg, sizeof(errmsg));
>> map->name, strerror(errno), errno);
>> strerror(errno));
>> pr_warning("load bpf program failed: %s\n", strerror(errno));
>> pr_warning("failed to statfs %s: %s\n", dir, strerror(errno));
>> pr_warning("failed to pin program: %s\n", strerror(errno));
>> pr_warning("failed to mkdir %s: %s\n", path, strerror(-err));
>> pr_warning("failed to pin map: %s\n", strerror(errno));
>> $
>>
>> The next issue with strerror_r is to assign the return value to a variable.
>> Then we end up with variable set but not used:
>> libbpf.c: In function ‘bpf_object__elf_collect’:
>> libbpf.c:809:35: error: variable ‘cp’ set but not used [-Werror=unused-but-set-variable]
>> char errmsg[STRERR_BUFSIZE], *cp;
>> ^
>> cc1: all warnings being treated as errors
>
> The GNU-specific strerror_r() returns a pointer to a string containing
> the error message. This may be either a pointer to a string that the
> function stores in buf, or a pointer to some (immutable) static string
> (in which case buf is unused). If the function stores a string in buf,
> then at most buflen bytes are stored (the string may be truncated if
> buflen is too small and errnum is unknown). The string always includes
> a terminating null byte ('\0').
>
> IOW you gotta use the return value.
>
>> Here is the source:
>> if (err) {
>> char errmsg[STRERR_BUFSIZE], *cp;
>>
>> cp = strerror_r(-err, errmsg, sizeof(errmsg));
>> pr_warning("failed to alloc program %s (%s): %s",
>> name, obj->path, errmsg);
>> }
>>
>> To fix this requires something like:
>> pr_warning("failed to alloc program %s (%s): %s",
>> name, obj->path, cp);
>
> This looks correct.
>
>> And after pr_warning() is done, the local array errmsg is deleted.
>>
>> A lot of overkill in my opinion, unless I miss something.
>
> IMO using potentially mutli-thread unsafe functions in a library is not
> optimal, we should strive to convert the other instances of strerror()
> rather than move the other way.
Yeah, fully agree. We should convert the other ones as well over to use
strerror_r().
Thanks,
Daniel