Re: Unable to link C++ application with libstdc++ when newlib is used (gcc 13 and perhaps also 12)

Hi Christophe,

Thanks for the fast reply! :)

Looking at one of the the config.log, it appears that the 
GCC_TRY_COMPILE_OR_LINK trick does not do AC_TRY_LINK for the 
arm-none-eabi build that I'm trying, but instead just does the 
AC_TRY_COMPILE that would succeed due to that the unistd.h file contains 
the definition...

Here is a snippet from on of the config.log related to getentropy and 
arc4random:

configure:69582: checking for getentropy
configure:69601:  /build/src/build-native/gcc-final/./gcc/xgcc 
-shared-libgcc -B/build/src/build-native/gcc-final/./gcc -nostdinc++ 
-L/build/src/build-native/gcc-final/arm-none-eabi/libstdc++-v3/src 
-L/build/src/build-native/gcc-final/arm-none-eabi/libstdc++-v3/src/.libs 
-L/build/src/build-native/gcc-final/arm-none-eabi/libstdc++-v3/libsupc++/.libs 
-B/build/src/install-native/arm-none-eabi/bin/ 
-B/build/src/install-native/arm-none-eabi/lib/ -isystem 
/build/src/install-native/arm-none-eabi/include -isystem 
/build/src/install-native/arm-none-eabi/sys-include    -c -g -O2 
conftest.cpp >&5
configure:69601: $? = 0
configure:69633: result: yes
configure:69657: checking for arc4random
configure:69675:  /build/src/build-native/gcc-final/./gcc/xgcc 
-shared-libgcc -B/build/src/build-native/gcc-final/./gcc -nostdinc++ 
-L/build/src/build-native/gcc-final/arm-none-eabi/libstdc++-v3/src 
-L/build/src/build-native/gcc-final/arm-none-eabi/libstdc++-v3/src/.libs 
-L/build/src/build-native/gcc-final/arm-none-eabi/libstdc++-v3/libsupc++/.libs 
-B/build/src/install-native/arm-none-eabi/bin/ 
-B/build/src/install-native/arm-none-eabi/lib/ -isystem 
/build/src/install-native/arm-none-eabi/include -isystem 
/build/src/install-native/arm-none-eabi/sys-include    -c -g -O2 
conftest.cpp >&5
configure:69675: $? = 0
configure:69706: result: yes
configure:69737: checking for unistd.h
configure:69737: result: yes



Based on this snippet, I think there is not much that can be done in the 
GCC end on this issue, but rather that newlib should not provide the 
definition _or_ it should provide a basic implementation of the function.
I'm just not sure what is the prefered solution here...


Kind regards,
Torbjörn


On 2022-09-17 22:47, Christophe Lyon wrote:
> Hi Torbjorn,
> I think there's additional context in:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103166 
> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103166>
> 
> 
> Le sam. 17 sept. 2022, 19:45, Torbjorn SVENSSON 
> <[email protected] <mailto:[email protected]>> a 
> écrit :
> 
>     Hello,
> 
>     I've just tried to run the DejaGNU testsuite on GCC master
>     (9ac9fde961f76879f0379ff3b2494a2f9ac915f7) with a rather recent commit
>     of newlib (the package was patched by Arm and provided in their
>     11.3.rel1 release).
>     Running the testsuite on arm-none-eabi produces a few hundred
>     UNRESOLVED
>     test cases, all related to the absence of an implementation of
>     getentropy.
> 
>     Looking at the current master of newlib
>     (eb5c631ead537ac5640d7e4b1ea0edbef344d6d9), there is still no
>     implementation, so I suspect that the same error would be visible if I
>     switched to the official newlib tree.
> 
>     In commit 3439657b02869299685d259c3a77aa38714565b7, the use of
>     getentropy was introduced in GCC and the changeset enables the use
>     after
>     checking that the getentropy function is defined in unistd.h. In the
>     case of newlib, the definition exists in unistd.h, but there is no
>     common implementation for it. There are 2 specific implementations for
>     RTEMS and cygwin, but nothing common.
> 
> 
>     I suppose the origin of the problem is the definition of the getentropy
>     function in the newlib provided unistd.h, but what is the appropriate
>     fix for it?
>     - Create a stub function that just returns -1 and sets errno=ENOSYS?
>     - Remove the getentropy definition from common unistd.h and place it in
>     a fragment for cygwin and RTEMS?
>     - Any other solution that I've overlooked?
> 
> 
> 
>     Here is an example of how the error looks like for the GCC testsuite:
>     Testing g++.robertl/eb77.C,  -std=c++20
>     doing compile
>     Executing on host:
>     /build/gcc-13-2709-g9ac9fde961f/bin/arm-none-eabi-g++
>        /build/src/gcc/gcc/testsuite/g++.old-deja/g++.robertl/eb77.C 
>     -mthumb
>     -march=armv6s-m -mcpu=cortex-m0 -mfloat-abi=soft
>     -fdiagnostics-plain-output   -fmessage-length=0  -std=c++20
>     -pedantic-errors -Wno-long-long        -Wl,--start-group -lc -lm
>     -Wl,--end-group --specs=nosys.specs -Wl,--allow-multiple-definition
>     -Wl,-u,_isatty,-u,_fstat   -Wl,-wrap,exit -Wl,-wrap,_exit
>     -Wl,-wrap,main
>     -Wl,-wrap,abort -Wl,g++_tg.o -lm -o ./eb77.exe    (timeout = 800)
>     spawn -ignore SIGHUP
>     /build/gcc-13-2709-g9ac9fde961f/bin/arm-none-eabi-g++
>     /build/src/gcc/gcc/testsuite/g++.old-deja/g++.robertl/eb77.C -mthumb
>     -march=armv6s-m -mcpu=cortex-m0 -mfloat-abi=soft
>     -fdiagnostics-plain-output -fmessage-length=0 -std=c++20
>     -pedantic-errors -Wno-long-long -Wl,--start-group -lc -lm
>     -Wl,--end-group --specs=nosys.specs -Wl,--allow-multiple-definition
>     -Wl,-u,_isatty,-u,_fstat -Wl,-wrap,exit -Wl,-wrap,_exit -Wl,-wrap,main
>     -Wl,-wrap,abort -Wl,g++_tg.o -lm -o ./eb77.exe
>     pid is 28414 -28414
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/bin/ld:
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libstdc++.a(random.o):
>     in function `std::(anonymous namespace)::__libc_getentropy(void*)':
>     (.text._ZNSt12_GLOBAL__N_117__libc_getentropyEPv+0x8): undefined
>     reference to `getentropy'
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/bin/ld:
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libstdc++.a(random.o):
>     in function
>     `std::random_device::_M_init(std::__cxx11::basic_string<char,
>     std::char_traits<char>, std::allocator<char> > const&)':
>     (.text._ZNSt13random_device7_M_initERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE+0x58):
>     undefined reference to `getentropy'
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/bin/ld:
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libc.a(libc_a-arc4random.o):
>     in function `_rs_stir':
>     (.text._rs_stir+0x8): undefined reference to `getentropy'
>     collect2: error: ld returned 1 exit status
>     pid is -1
>     close result is 28414 exp6 0 1
>     output is
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/bin/ld:
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libstdc++.a(random.o):
>     in function `std::(anonymous namespace)::__libc_getentropy(void*)':
>     (.text._ZNSt12_GLOBAL__N_117__libc_getentropyEPv+0x8): undefined
>     reference to `getentropy'
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/bin/ld:
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libstdc++.a(random.o):
>     in function
>     `std::random_device::_M_init(std::__cxx11::basic_string<char,
>     std::char_traits<char>, std::allocator<char> > const&)':
>     (.text._ZNSt13random_device7_M_initERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE+0x58):
>     undefined reference to `getentropy'
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/bin/ld:
>     /build/gcc-13-2709-g9ac9fde961f/bin/../lib/gcc/arm-none-eabi/13.0.0/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/libc.a(libc_a-arc4random.o):
>     in function `_rs_stir':
>     (.text._rs_stir+0x8): undefined reference to `getentropy'
>     collect2: error: ld returned 1 exit status
>        status 1
>     compiler exited with status 1
>     FAIL: g++.old-deja/g++.robertl/eb77.C  -std=c++20 (test for excess
>     errors)
>     Excess errors:
>     (.text._ZNSt12_GLOBAL__N_117__libc_getentropyEPv+0x8): undefined
>     reference to `getentropy'
>     (.text._ZNSt13random_device7_M_initERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE+0x58):
>     undefined reference to `getentropy'
>     (.text._rs_stir+0x8): undefined reference to `getentropy'
>     UNRESOLVED: g++.old-deja/g++.robertl/eb77.C  -std=c++20 compilation
>     failed to produce executable
> 
> 
>     Kind regards,
>     Torbjörn
>