Hi Ludo,
Thanks for reproducing this. Did you take a look at a resolution beyond
your analysis in this message? It would seem that the attempted compilation
isn't working during the configure phase.
Erik
On Wed, Jun 10, 2020, 17:18 Ludovic Courtès <l...@gnu.org> wrote:
> Hi,
>
> Erik Garrison <erik.garri...@gmail.com> skribis:
>
> > I've run into a quirk in the various gcc toolchains that seems somewhat
> > unique to guix builds of them. I'd like to understand if this is
> > intentional.
> >
> > Initially, I found that string to numeric conversion functions that are
> > enabled by _GLIBCXX_USE_C99_STDLIB are not available on guix gcc
> toolchains
> > for gcc 8, 9, and 10.
> >
> > This is a minimal test case to reproduce the problem:
> >
> > Code:
> >
> > #include <iostream>
> > #include <string>
> >
> > uint64_t _parse_number(std::string::const_iterator& c, const
> > std::string::const_iterator& end) {
> > std::string::const_iterator s = c;
> > while (c != end and isdigit(*c)) ++c;
> > if (c > s) {
> > return std::stoull(std::string(s,c));
> > } else {
> > return 0;
> > }
> > }
> >
> > int main(int argc, char** argv) {
> > std::string s(argv[1]);
> > std::string::const_iterator b = s.begin();
> > std::string::const_iterator e = s.end();
> > std::cout << _parse_number(b, e) << std::endl;
> > return 0;
> > }
> >
> > Compiling with (g++ --version == 10.1.0),
> > /gnu/store/3kvnslc16sy7kwi2c5r7r5k6bbv2p03f-gcc-toolchain-10.1.0/bin/g++
> >
> > g++ test-stoull.cpp -o test-stoull
>
> I can reproduce it:
>
> --8<---------------cut here---------------start------------->8---
> $ guix describe
> Generacio 147 Jun 08 2020 00:30:31 (nuna)
> guix e782756
> repository URL: https://git.savannah.gnu.org/git/guix.git
> branch: master
> commit: e78275608065ef073775fabb9f1a757da65851f2
> $ guix environment --ad-hoc gcc-toolchain -C -- g++ num.cpp
> num.cpp: In function 'uint64_t
> _parse_number(std::__cxx11::basic_string<char>::const_iterator&, const
> const_iterator&)':
> num.cpp:9:33: error: invalid initialization of reference of type 'const
> wstring&' {aka 'const std::__cxx11::basic_string<wchar_t>&'} from
> expression of type 'std::string' {aka 'std::__cxx11::basic_string<char>'}
> 9 | return std::stoull(std::string(s,c));
> | ^~~~~~~~~~~
> --8<---------------cut here---------------end--------------->8---
>
> This is indeed fixed with:
>
> guix environment --ad-hoc gcc-toolchain@9 -C -- g++
> -D_GLIBCXX_USE_C99_STDLIB=1 num.cpp
>
> > This behavior appears to be similar to this issue:
> >
> http://freebsd.1045724.x6.nabble.com/base-gcc-and-GLIBCXX-USE-C99-td5781697.html
> .
> > It's also similar to this report,
> >
> https://stackoverflow.com/questions/40779611/g-compile-error-invalid-initialization-of-reference-of-type-stdstod
> > .
> >
> > It may be more correct to require wstring in these kinds of conversions.
> > However, I'm concerned that if gcc is built differently in guix than it
> > typically is in other distributions, we will need to patch many libraries
> > when building them on guix. It's probably better to match typical
> > expectations of developers about the behavior of gcc.
>
> I agree, it seems we have a misconfiguration issue leading to this in
> our c++config.h:
>
> --8<---------------cut here---------------start------------->8---
> /* Define if C99 functions or macros in <stdlib.h> should be imported in
> <cstdlib> in namespace std for C++11. */
> /* #undef _GLIBCXX11_USE_C99_STDLIB */
> --8<---------------cut here---------------end--------------->8---
>
> The check appears to be this:
>
> --8<---------------cut here---------------start------------->8---
> # Check for the existence in <stdlib.h> of lldiv_t, et. al.
> AC_MSG_CHECKING([for ISO C99 support in <stdlib.h> for C++11])
> AC_CACHE_VAL(glibcxx_cv_c99_stdlib_cxx11, [
> GCC_TRY_COMPILE_OR_LINK(
> [#include <stdlib.h>
> volatile float f;
> volatile long double ld;
> volatile unsigned long long ll;
> lldiv_t mydivt;],
> [char* tmp;
> f = strtof("gnu", &tmp);
> ld = strtold("gnu", &tmp);
> ll = strtoll("gnu", &tmp, 10);
> ll = strtoull("gnu", &tmp, 10);
> ll = llabs(10);
> mydivt = lldiv(10,1);
> ll = mydivt.quot;
> ll = mydivt.rem;
> ll = atoll("10");
> _Exit(0);
> ], [glibcxx_cv_c99_stdlib_cxx11=yes],
> [glibcxx_cv_c99_stdlib_cxx11=no])
> ])
> AC_MSG_RESULT($glibcxx_cv_c99_stdlib_cxx11)
> if test x"$glibcxx_cv_c99_stdlib_cxx11" = x"yes"; then
> AC_DEFINE(_GLIBCXX11_USE_C99_STDLIB, 1,
> [Define if C99 functions or macros in <stdlib.h> should be imported
> in <cstdlib> in namespace std for C++11.])
> fi
> --8<---------------cut here---------------end--------------->8---
>
> We should check what’s going on!
>
> Thanks,
> Ludo’.
>
