While executing tools/iio_generic_buffer i was getting this fault:
beagle /usr/src/linux/tools/iio # ./iio_generic_buffer -a -c 10 -N 0 -T 0
iio device number being used is 0
iio trigger number being used is 0
Auto-channels selected but some channels are already activated in sysfs
Proceeding without activating any channels
/sys/bus/iio/devices/iio:device0 mytmr
Floating point exception
The FPE was generated due to a modulo zero in size_from_channelarray()
(all channels[].bytes were zero because channels[] were never populated).
The root of the cause is the seekdir() function within
build_channel_array().
On my system I can observe a clear difference between these two functions:
seekdir(dp, 0);
printf("location = %lu\n", telldir(dp)); // location == 4294967295
rewinddir(dp);
printf("location = %lu\n", telldir(dp)); // location == 1
The attached patch fixed the bug for me.
I'm using a BeagleBone Black devboard with an up-to-date stable branch
Gentoo Linux OS on top of it.
CHOST: armv7a-unknown-linux-gnueabihf
kernel: mainline 6.7.0-rc6
glibc: 2.37-r7:2.2::gentoo USE="caps gd multiarch ssp static-libs -audit
-cet -compile-locales -crypt -custom-cflags -doc -hash-sysv-compat
-headers-only -multilib -multilib-bootstrap -nscd -perl -profile
(-selinux) -stack-realign -suid -systemd -systemtap -test -vanilla"
(+ contains Gentoo specific patches)
Fixes: <e58537ccce733> ("staging: iio: update example application.")
Signed-off-by: Petre Rodan <[email protected]>
Petre Rodan (1):
tools: iio: fix iio_generic_buffer
tools/iio/iio_utils.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--
2.41.0
Fix code flow problem and floating point exception caused by improper
directory stream positioning.
Fixes: <e58537ccce733> ("staging: iio: update example application.")
Signed-off-by: Petre Rodan <[email protected]>
---
tools/iio/iio_utils.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/iio/iio_utils.c b/tools/iio/iio_utils.c
index 6a00a6eecaef..c5c5082cb24e 100644
--- a/tools/iio/iio_utils.c
+++ b/tools/iio/iio_utils.c
@@ -376,7 +376,7 @@ int build_channel_array(const char *device_dir, int buffer_idx,
goto error_close_dir;
}
- seekdir(dp, 0);
+ rewinddir(dp);
while (ent = readdir(dp), ent) {
if (strcmp(ent->d_name + strlen(ent->d_name) - strlen("_en"),
"_en") == 0) {
--
2.41.0
On Thu, 4 Jan 2024 12:12:45 +0200
Petre Rodan <[email protected]> wrote:
> Fix code flow problem and floating point exception caused by improper
> directory stream positioning.
>
> Fixes: <e58537ccce733> ("staging: iio: update example application.")
> Signed-off-by: Petre Rodan <[email protected]>
Hi Petre,
This doesn't really explain 'why' seeekdir(dp, 0) is wrong.
My assumption is that telldir() would not have returned 0 on this particular
system? Could you confirm that and update the message to explain why
seekdir(dp, 0) is not equivalent to rewinddir(dp).
Thanks,
Jonathan
> ---
> tools/iio/iio_utils.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/iio/iio_utils.c b/tools/iio/iio_utils.c
> index 6a00a6eecaef..c5c5082cb24e 100644
> --- a/tools/iio/iio_utils.c
> +++ b/tools/iio/iio_utils.c
> @@ -376,7 +376,7 @@ int build_channel_array(const char *device_dir, int buffer_idx,
> goto error_close_dir;
> }
>
> - seekdir(dp, 0);
> + rewinddir(dp);
> while (ent = readdir(dp), ent) {
> if (strcmp(ent->d_name + strlen(ent->d_name) - strlen("_en"),
> "_en") == 0) {
> --
> 2.41.0
>
Hi Jonathan,
On Sun, Jan 07, 2024 at 03:53:33PM +0000, Jonathan Cameron wrote:
> On Thu, 4 Jan 2024 12:12:45 +0200
> Petre Rodan <[email protected]> wrote:
>
> > Fix code flow problem and floating point exception caused by improper
> > directory stream positioning.
> >
> > Fixes: <e58537ccce733> ("staging: iio: update example application.")
> > Signed-off-by: Petre Rodan <[email protected]>
> Hi Petre,
>
> This doesn't really explain 'why' seeekdir(dp, 0) is wrong.
> My assumption is that telldir() would not have returned 0 on this particular
> system? Could you confirm that and update the message to explain why
> seekdir(dp, 0) is not equivalent to rewinddir(dp).
it looks like there is a 32-bit specific bug in one of the glibc patches that
the stable Gentoo Linux is using [1]. telldir returns (u32)(-1) if seekdir is
used which ends up in a floating point exception.
it so happens that the rewinddir() function (which is equivalent) works
correctly. so it is a fix for Gentoo users and should not impact anyone else.
[1] https://sourceware.org/bugzilla/show_bug.cgi?id=31212
my very best regards,
peter
> Thanks,
>
> Jonathan
>
> > ---
> > tools/iio/iio_utils.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/iio/iio_utils.c b/tools/iio/iio_utils.c
> > index 6a00a6eecaef..c5c5082cb24e 100644
> > --- a/tools/iio/iio_utils.c
> > +++ b/tools/iio/iio_utils.c
> > @@ -376,7 +376,7 @@ int build_channel_array(const char *device_dir, int buffer_idx,
> > goto error_close_dir;
> > }
> >
> > - seekdir(dp, 0);
> > + rewinddir(dp);
> > while (ent = readdir(dp), ent) {
> > if (strcmp(ent->d_name + strlen(ent->d_name) - strlen("_en"),
> > "_en") == 0) {
> > --
> > 2.41.0
On Sun, 7 Jan 2024 18:28:52 +0200
Petre Rodan <[email protected]> wrote:
> Hi Jonathan,
>
> On Sun, Jan 07, 2024 at 03:53:33PM +0000, Jonathan Cameron wrote:
> > On Thu, 4 Jan 2024 12:12:45 +0200
> > Petre Rodan <[email protected]> wrote:
> >
> > > Fix code flow problem and floating point exception caused by improper
> > > directory stream positioning.
> > >
> > > Fixes: <e58537ccce733> ("staging: iio: update example application.")
> > > Signed-off-by: Petre Rodan <[email protected]>
> > Hi Petre,
> >
> > This doesn't really explain 'why' seeekdir(dp, 0) is wrong.
> > My assumption is that telldir() would not have returned 0 on this particular
> > system? Could you confirm that and update the message to explain why
> > seekdir(dp, 0) is not equivalent to rewinddir(dp).
>
> it looks like there is a 32-bit specific bug in one of the glibc patches that
> the stable Gentoo Linux is using [1]. telldir returns (u32)(-1) if seekdir is
> used which ends up in a floating point exception.
>
> it so happens that the rewinddir() function (which is equivalent) works
> correctly. so it is a fix for Gentoo users and should not impact anyone else.
>
> [1] https://sourceware.org/bugzilla/show_bug.cgi?id=31212
>
> my very best regards,
> peter
I'd be happy to take the same change as a cleanup if you want to resubmit it
with a different patch description.
Thanks,
Jonathan
>
> > Thanks,
> >
> > Jonathan
> >
> > > ---
> > > tools/iio/iio_utils.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/tools/iio/iio_utils.c b/tools/iio/iio_utils.c
> > > index 6a00a6eecaef..c5c5082cb24e 100644
> > > --- a/tools/iio/iio_utils.c
> > > +++ b/tools/iio/iio_utils.c
> > > @@ -376,7 +376,7 @@ int build_channel_array(const char *device_dir, int buffer_idx,
> > > goto error_close_dir;
> > > }
> > >
> > > - seekdir(dp, 0);
> > > + rewinddir(dp);
> > > while (ent = readdir(dp), ent) {
> > > if (strcmp(ent->d_name + strlen(ent->d_name) - strlen("_en"),
> > > "_en") == 0) {
> > > --
> > > 2.41.0
Hi Jonathan,
On Sun, Jan 07, 2024 at 05:00:26PM +0000, Jonathan Cameron wrote:
> > On Sun, Jan 07, 2024 at 03:53:33PM +0000, Jonathan Cameron wrote:
> > > On Thu, 4 Jan 2024 12:12:45 +0200
> > > Petre Rodan <[email protected]> wrote:
> > >
> > > > Fix code flow problem and floating point exception caused by improper
> > > > directory stream positioning.
> > > >
> > > > Fixes: <e58537ccce733> ("staging: iio: update example application.")
> > > > Signed-off-by: Petre Rodan <[email protected]>
> > > Hi Petre,
> > >
> > > This doesn't really explain 'why' seeekdir(dp, 0) is wrong.
> > > My assumption is that telldir() would not have returned 0 on this particular
> > > system? Could you confirm that and update the message to explain why
> > > seekdir(dp, 0) is not equivalent to rewinddir(dp).
> >
> > it looks like there is a 32-bit specific bug in one of the glibc patches that
> > the stable Gentoo Linux is using [1]. telldir returns (u32)(-1) if seekdir is
> > used which ends up in a floating point exception.
> >
> > it so happens that the rewinddir() function (which is equivalent) works
> > correctly. so it is a fix for Gentoo users and should not impact anyone else.
> >
> > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=31212
> >
> > my very best regards,
> > peter
>
> I'd be happy to take the same change as a cleanup if you want to resubmit it
> with a different patch description.
sure, I will resubmit it, but tomorrow morning.
best regards,
peter