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

[Christophe Lyon <christophe.lyon.oss@gmail.com>]

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Hi Torbjorn,
I think there's additional context in:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103166


Le sam. 17 sept. 2022, 19:45, Torbjorn SVENSSON <
torbjorn.svensson@foss.st.com> 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
>