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

[Torbjorn SVENSSON <torbjorn.svensson@foss.st.com>]

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