error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]

[Leixb]

Description

When trying to build the project from source, it fails with the following error:

error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]

This seems to be caused because glibc contains its own definition of asprintf which has the warn_unused_result attribute.

If I remove -Werror and build the binary, everything works as expected and the asprintf linked
in the final binary is the one from your utility.h, so it's quite strange that gcc complains about it.

$ objdump -T headsetcontrol | grep asprint
0000000000407650 g    DF .text	00000000000000b8  Base        asprintf
0000000000407510 g    DF .text	000000000000013c  Base        vasprintf

For completeness, here is the full build log:

$ nix-shell -p cmake hidapi
$ mkdir build && cd build
$ cmake ..
$ make
[  3%] Building C object CMakeFiles/headsetcontrol.dir/src/main.c.o
/home/leix/Documents/github/HeadsetControl/src/main.c: In function ‘handle_feature’:
/home/leix/Documents/github/HeadsetControl/src/main.c:197:9: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  197 |         asprintf(&result.message, "This headset doesn't support %s", capabilities_str[cap]);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:208:13: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  208 |             asprintf(&result.message, "Could not open device. Error: %ls", hid_error(*device_handle));
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:229:13: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  229 |             asprintf(&result.message, "Battery: %d%%", battery.level);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:247:17: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  247 |                 asprintf(&result.message, "Error retrieving battery status. Error: %ls", hid_error(*device_handle));
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:249:17: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  249 |                 asprintf(&result.message, "Error retrieving battery status");
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:272:13: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  272 |             asprintf(&result.message, "Chat-Mix: %d", ret);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:327:9: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  327 |         asprintf(&result.message, "Failed to set/request %s, because of timeout", capabilities_str[cap]);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:330:9: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  330 |         asprintf(&result.message, "Failed to set/request %s. HeadsetControl Error", capabilities_str[cap]);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:333:9: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  333 |         asprintf(&result.message, "Failed to set/request %s. Provided parameter out of boundaries", capabilities_str[cap]);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:337:13: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  337 |             asprintf(&result.message, "Failed to set/request %s. Error: %d: %ls", capabilities_str[cap], ret, hid_error(*device_handle));
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/leix/Documents/github/HeadsetControl/src/main.c:339:13: error: ignoring return value of ‘asprintf’ declared with attribute ‘warn_unused_result’ [-Werror=unused-result]
  339 |             asprintf(&result.message, "Failed to set/request %s. Error: %d", capabilities_str[cap], ret);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[2]: *** [CMakeFiles/headsetcontrol.dir/build.make:76: CMakeFiles/headsetcontrol.dir/src/main.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:149: CMakeFiles/headsetcontrol.dir/all] Error 2
make: *** [Makefile:146: all] Error 2

Here are some environment details:

$ uname -a
Linux kuro 6.7.11 #1-NixOS SMP PREEMPT_DYNAMIC Tue Mar 26 22:22:50 UTC 2024 x86_64 GNU/Linux

$ cmake --version
cmake version 3.28.3

CMake suite maintained and supported by Kitware (kitware.com/cmake).

$ make --version
GNU Make 4.4.1
Built for x86_64-pc-linux-gnu
Copyright (C) 1988-2023 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

$ gcc --version
gcc (GCC) 13.2.0
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

On which OS does the problem happen?

Linux

[TheBill2001]

I'm currently the maintainer of the AUR package and can confirm this issue. Arch Linux's build system contains a lot of additional compiler flags, which triggers a bunch of warning. And with -Werror, the build just fails. The current workaround is omitting the following line in the CMake file:

HeadsetControl/CMakeLists.txt

Line 39 in 0005a0a

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Werror")

For reference, these are the flags use by Arch to compile C programs:

CFLAGS="-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions \
        -Wp,-D_FORTIFY_SOURCE=3 -Wformat -Werror=format-security \
        -fstack-clash-protection -fcf-protection \
        -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer"

---

From further investigation, the build will fail if any of these configurations are set:

• Build type is set to release with CMake flags -DCMAKE_BUILD_TYPE='Release'.
• -O2 compiler flag is set.
• -Wp,-D_FORTIFY_SOURCE=3 compiler flag is set.

Removing all three results in successful build.

[Sapd]

Thanks for your input.

Also thanks for the compilation parameters @TheBill2001
I will try to fix the resulting warnings for it. But I think I also have to get rid of the -Werror in the repo, as other Distributions can then again have other compilation parameters creating warnings and leading to an error.

For the asprintf Im not sure if I should replace it by the function in the code or check the return values. Checking the return values would be the 100% "right" way, but if something like memory allocation fails the program will crash anyway.