cmake: silence "LOAD segment with RWX permissions" warning

[marckleinebudde]

Link: #106

[marckleinebudde]

@fenugrec my compiler doesn't support --no-warn-rwx-segments and cmake doesn't use the new option. Does it fix the warning with your compiler?

[marckleinebudde]

Debian stable ("bullseye") uses cmake-3.18, Debian oldstable ("buster") is still on cmake-3.13, but "buster-backports" has cmake-3.18, too.

[fenugrec]

I think bumping required to 3.18 is reasonable; distros with really old cmake have a simple workaround of just reverting this commit.

[fenugrec]

Oops, actual test doesn't quite work as is, two issues - cmake invokes gcc for the link step, so the arg needs to be -Wl,--no-warn-rwx-segments . Second issue is trickier, cmake fails its compile test :

        Run Build Command(s): /usr/bin/cmake -E env VERBOSE=1 /usr/bin/make -f Makefile cmTC_318a8/fast
        make[1]: Entering directory '/home/q/d/can/candleLight_fw/build/CMakeFiles/CMakeScratch/TryCompile-nTjHd2'
        /usr/bin/make  -f CMakeFiles/cmTC_318a8.dir/build.make CMakeFiles/cmTC_318a8.dir/build
        make[2]: Entering directory '/home/q/d/can/candleLight_fw/build/CMakeFiles/CMakeScratch/TryCompile-nTjHd2'
        Building C object CMakeFiles/cmTC_318a8.dir/src.c.obj
        /usr/bin/arm-none-eabi-gcc -DLINKER_SUPPORTS_NO_WARN_RWX_SEGMENTS   -o CMakeFiles/cmTC_318a8.dir/src.c.obj -c /home/q/d/can/candleLight_fw/build/CMakeFiles/CMakeScratch/TryCompile-nTjHd2/src.c
        Linking C executable cmTC_318a8
        /usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_318a8.dir/link.txt --verbose=1
        /usr/bin/arm-none-eabi-gcc -Wl,--no-warn-rwx-segments CMakeFiles/cmTC_318a8.dir/src.c.obj -o cmTC_318a8 
        /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/lib/libc.a(libc_a-exit.o): in function `exit':
        /build/arm-none-eabi-newlib/src/build-newlib/arm-none-eabi/newlib/../../../newlib-4.3.0.20230120/newlib/libc/stdlib/exit.c:65:(.text.exit+0x28): undefined reference to `_exit'
        /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/lib/libc.a(libc_a-closer.o): in function `_close_r':
        /build/arm-none-eabi-newlib/src/build-newlib/arm-none-eabi/newlib/../../../newlib-4.3.0.20230120/newlib/libc/reent/closer.c:47:(.text._close_r+0x18): undefined reference to `_close'
        /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/lib/libc.a(libc_a-lseekr.o): in function `_lseek_r':
        /build/arm-none-eabi-newlib/src/build-newlib/arm-none-eabi/newlib/../../../newlib-4.3.0.20230120/newlib/libc/reent/lseekr.c:49:(.text._lseek_r+0x24): undefined reference to `_lseek'
        /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/lib/libc.a(libc_a-readr.o): in function `_read_r':
        /build/arm-none-eabi-newlib/src/build-newlib/arm-none-eabi/newlib/../../../newlib-4.3.0.20230120/newlib/libc/reent/readr.c:49:(.text._read_r+0x24): undefined reference to `_read'
        /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/lib/libc.a(libc_a-writer.o): in function `_write_r':
        /build/arm-none-eabi-newlib/src/build-newlib/arm-none-eabi/newlib/../../../newlib-4.3.0.20230120/newlib/libc/reent/writer.c:49:(.text._write_r+0x24): undefined reference to `_write'
        /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/13.2.0/../../../../arm-none-eabi/lib/libc.a(libc_a-sbrkr.o): in function `_sbrk_r':
        /build/arm-none-eabi-newlib/src/build-newlib/arm-none-eabi/newlib/../../../newlib-4.3.0.20230120/newlib/libc/reent/sbrkr.c:51:(.text._sbrk_r+0x18): undefined reference to `_sbrk'
        collect2: error: ld returned 1 exit status
        make[2]: *** [CMakeFiles/cmTC_318a8.dir/build.make:99: cmTC_318a8] Error 1
        make[2]: Leaving directory '/home/q/d/can/candleLight_fw/build/CMakeFiles/CMakeScratch/TryCompile-nTjHd2'
        make[1]: *** [Makefile:127: cmTC_318a8/fast] Error 2
        make[1]: Leaving directory '/home/q/d/can/candleLight_fw/build/CMakeFiles/CMakeScratch/TryCompile-nTjHd2'

We're also getting those super annoying warnings about _write etc. not being implemented on master as well but seems here they are causing a link failure. No time to mess with this atm.

[marckleinebudde]

Thanks for testing! Fixed the first issue, add missing LINKER:.

I see a undefined reference to _exit'` here, too:

        /usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_5ff6a.dir/link.txt --verbose=1
        /usr/lib/ccache/arm-none-eabi-gcc -Wl,--no-warn-rwx-segments CMakeFiles/cmTC_5ff6a.dir/src.c.obj -o cmTC_5ff6a
        /usr/lib/gcc/arm-none-eabi/13.2.1/../../../arm-none-eabi/bin/ld: /usr/lib/gcc/arm-none-eabi/13.2.1/../../../arm-none-eabi/lib/libc.a(lib_a-exit.o): in function `exit':
        /build/newlib-afIbHz/newlib-3.3.0/build/arm-none-eabi/newlib/libc/stdlib/../../../../../newlib/libc/stdlib/exit.c:64:(.text+0x2c): undefined reference to `_exit'

but it correctly detects support for --no-warn-rwx-segments:

    buildResult:
      variable: "LINKER_SUPPORTS_NO_WARN_RWX_SEGMENTS"
      cached: true

[fenugrec]

Fixed.

Thanks, youǜve fixed the passing-wrong-arg problem, but since the test compilation fails, cmake still thinks the flag is "not supported"

[marckleinebudde]

Just noticed, too. But why does it say cached: true.

[fenugrec]

But why does it say cached: true.

AFAIK because https://cmake.org/cmake/help/latest/module/CheckLinkerFlag.html

Stores the result in an internal cache entry named <var>