Compilation error when using the musl libc

[newbluemoon]

Hi,

I was trying to compile version 0.8.6 on Void Linux using the musl libc and ran into the following error which I would like to report:

query_sysenv_usb.c: In function 'probe_hiddev':
query_sysenv_usb.c:193:26: error: overflow in implicit constant conversion [-Werror=overflow]
           rc = ioctl(fd, HIDIOCGDEVINFO, &dev_info);
                          ^~~~~~~~~~~~~~
cc1: all warnings being treated as errors

I can make the error disappear by removing -Wpedantic from src/app_sysenv/Makefile (it isn’t set in 0.8.5), but I’d rather solve the underlying issue ;) which seems to be that glibc defines ioctl() as

extern int ioctl (int __fd, unsigned long int __request, ...) __THROW;

but the musl libc as

int ioctl (int, int, ...);

It compiles when casting to int:

rc = ioctl(fd, (int) HIDIOCGDEVINFO, &dev_info);

but I don’t know enough about the whole matter to be sure that’s safe to do.

There are a couple of instances more where a warning is issued, but not treated as an error:

make[3]: Entering directory '/builddir/ddcutil-0.8.6/src/usb'
  CC       usb_base.lo
usb_base.c: In function 'hiddev_get_device_info':
usb_base.c:188:23: warning: overflow in implicit constant conversion [-Woverflow]
    int rc = ioctl(fd, HIDIOCGDEVINFO, dev_info);
                       ^~~~~~~~~~~~~~
usb_base.c: In function 'hiddev_get_report_info':
usb_base.c:208:23: warning: overflow in implicit constant conversion [-Woverflow]
    int rc = ioctl(fd, HIDIOCGREPORTINFO, rinfo);
                       ^~~~~~~~~~~~~~~~~
usb_base.c: In function 'hiddev_get_field_info':
usb_base.c:228:23: warning: overflow in implicit constant conversion [-Woverflow]
    int rc = ioctl(fd, HIDIOCGFIELDINFO, finfo);
                       ^~~~~~~~~~~~~~~~
usb_base.c: In function 'hiddev_get_usage_code':
usb_base.c:250:23: warning: overflow in implicit constant conversion [-Woverflow]
    int rc = ioctl(fd, HIDIOCGUCODE, uref);    // Fills in usage code
                       ^~~~~~~~~~~~
usb_base.c: In function 'hiddev_get_usage_value':
usb_base.c:267:23: warning: overflow in implicit constant conversion [-Woverflow]
    int rc = ioctl(fd, HIDIOCGUSAGE, uref);
                       ^~~~~~~~~~~~
usb_base.c: In function 'hiddev_get_report':
usb_base.c:283:23: warning: overflow in implicit constant conversion [-Woverflow]
    int rc = ioctl(fd, HIDIOCGUCODE, rinfo);
                       ^~~~~~~~~~~~

...

usb_vcp.c: In function 'usb_get_usage_value_by_report_type_and_ucode':
usb_vcp.c:133:19: warning: overflow in implicit constant conversion [-Woverflow]
    rc = ioctl(fd, HIDIOCGFIELDINFO, &finfo);  // Fills in usage value
                   ^~~~~~~~~~~~~~~~

[rockowitz]

Thanks for the report.   I wasn't aware of Void Linux.  (You might want have it added to the distributions tracked at repology.org.)

Per ioctl.h, ioctl commands are encoded into 32 bits.  So assuming that your int size is at least 32 bits, the warning can be ignored.

The --pedantic option just enforces strict ISO C compatibility. It was introduced in a fruitless attempt to figure out what was triggering a known stdlib.h/floatn.h error regarding 128 bit floats (irrelevant to ddcutil) that Coverity scan was complaining about.   You can safely eliminate the option.

The reason that query_sysenv_usb.c failed to compile, but the usb_base.c just issued errors, is due to a difference in the Makefile for subdirectory app_sysenv vs that for subdirectory usb.  Files in the former are compiled with -Werror, so all warnings are treated as errors.

Sanford

On 01/21/2018 04:55 AM, newbluemoon wrote:

Hi,

I was trying to compile version 0.8.6 on Void Linux using the musl libc and ran into the following error which I would like to report:

|query_sysenv_usb.c: In function 'probe_hiddev': query_sysenv_usb.c:193:26: error: overflow in implicit constant conversion [-Werror=overflow] rc = ioctl(fd, HIDIOCGDEVINFO, &dev_info); ^~~~~~ cc1: all warnings being treated as errors |

I can make the error disappear by removing |-Wpedantic| from |src/app_sysenv/Makefile| (it isn’t set in 0.8.5), but I’d rather solve the underlying issue ;) which seems to be that glibc defines |ioctl()| as

|extern int ioctl (int fd, unsigned long int request, ...) __THROW; |

but the musl libc as

|int ioctl (int, int, ...); |

It compiles when casting to |int|:

|rc = ioctl(fd, (int) HIDIOCGDEVINFO, &dev_info); |

but I don’t know enough about the whole matter to be sure that’s safe to do.

There are a couple of instances more where a warning is issued, but not treated as an error:

|make[3]: Entering directory '/builddir/ddcutil-0.8.6/src/usb' CC usb_base.lo usb_base.c: In function 'hiddev_get_device_info': usb_base.c:188:23: warning: overflow in implicit constant conversion [-Woverflow] int rc = ioctl(fd, HIDIOCGDEVINFO, dev_info); ^~~~~~ usb_base.c: In function 'hiddev_get_report_info': usb_base.c:208:23: warning: overflow in implicit constant conversion [-Woverflow] int rc = ioctl(fd, HIDIOCGREPORTINFO, rinfo); ^~~~~ usb_base.c: In function 'hiddev_get_field_info': usb_base.c:228:23: warning: overflow in implicit constant conversion [-Woverflow] int rc = ioctl(fd, HIDIOCGFIELDINFO, finfo); ^~~~ usb_base.c: In function 'hiddev_get_usage_code': usb_base.c:250:23: warning: overflow in implicit constant conversion [-Woverflow] int rc = ioctl(fd, HIDIOCGUCODE, uref); // Fills in usage code ^~~~ usb_base.c: In function 'hiddev_get_usage_value': usb_base.c:267:23: warning: overflow in implicit constant conversion [-Woverflow] int rc = ioctl(fd, HIDIOCGUSAGE, uref); ^~~~ usb_base.c: In function 'hiddev_get_report': usb_base.c:283:23: warning: overflow in implicit constant conversion [-Woverflow] int rc = ioctl(fd, HIDIOCGUCODE, rinfo); ^~~~ ... usb_vcp.c: In function 'usb_get_usage_value_by_report_type_and_ucode': usb_vcp.c:133:19: warning: overflow in implicit constant conversion [-Woverflow] rc = ioctl(fd, HIDIOCGFIELDINFO, &finfo); // Fills in usage value ^~~~ |

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[newbluemoon]

Thank you for your reply! Yes, integer size is 32 bit and I’ll drop -Wpedandic. Didn’t know about repology.org, will check it out.

So I guess this can be closed then. Thanks again! :)