Bug: <cfloat> incude will break <cmath>

[cristianadam]

Contact Details

No response

What happened?

Given the following C++ program:

#include <cfloat>
#include <cmath>
#include <iostream>

int main()
{
    std::cout << std::boolalpha
              << "signbit(+0.0) = " << std::signbit(+0.0) << '\n'
              << "signbit(-0.0) = " << std::signbit(-0.0) << '\n'
              << "signbit(+nan) = " << std::signbit(+NAN) << '\n'
              << "signbit(-nan) = " << std::signbit(-NAN) << '\n'
              << "signbit(+inf) = " << std::signbit(+INFINITY) << '\n'
              << "signbit(-inf) = " << std::signbit(-INFINITY) << '\n';
}

Compiling the program with g++ on Linux results:

$ g++ -O2 main.cpp -o signbit && ./signbit
signbit(+0.0) = false
signbit(-0.0) = true
signbit(+nan) = false
signbit(-nan) = true
signbit(+inf) = false
signbit(-inf) = true

Compiling with cosmoc++ results in:

$ cosmoc++ -O2 main.cpp -o signbit && ./signbit
In file included from /home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:327,
                 from main.cpp:2:
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:415:20: error: 'signbit' has not been declared in 'std::__1::__math'
  415 | using std::__math::signbit;
      |                    ^~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:419:20: error: 'isfinite' has not been declared in 'std::__1::__math'
  419 | using std::__math::isfinite;
      |                    ^~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:420:20: error: 'isgreater' has not been declared in 'std::__1::__math'
  420 | using std::__math::isgreater;
      |                    ^~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:421:20: error: 'isgreaterequal' has not been declared in 'std::__1::__math'
  421 | using std::__math::isgreaterequal;
      |                    ^~~~~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:422:20: error: 'isinf' has not been declared in 'std::__1::__math'
  422 | using std::__math::isinf;
      |                    ^~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:423:20: error: 'isless' has not been declared in 'std::__1::__math'
  423 | using std::__math::isless;
      |                    ^~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:424:20: error: 'islessequal' has not been declared in 'std::__1::__math'
  424 | using std::__math::islessequal;
      |                    ^~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:425:20: error: 'islessgreater' has not been declared in 'std::__1::__math'
  425 | using std::__math::islessgreater;
      |                    ^~~~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:426:20: error: 'isnan' has not been declared in 'std::__1::__math'
  426 | using std::__math::isnan;
      |                    ^~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:427:20: error: 'isnormal' has not been declared in 'std::__1::__math'
  427 | using std::__math::isnormal;
      |                    ^~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:428:20: error: 'isunordered' has not been declared in 'std::__1::__math'
  428 | using std::__math::isunordered;
      |                    ^~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/math.h:493:20: error: 'signbit' has not been declared in 'std::__1::__math'
  493 | using std::__math::signbit;
      |                    ^~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:346:9: error: 'signbit' has not been declared in '::'
  346 | using ::signbit _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:348:9: error: 'isfinite' has not been declared in '::'
  348 | using ::isfinite _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:349:9: error: 'isinf' has not been declared in '::'
  349 | using ::isinf _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:350:9: error: 'isnan' has not been declared in '::'
  350 | using ::isnan _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:351:9: error: 'isnormal' has not been declared in '::'
  351 | using ::isnormal _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:352:9: error: 'isgreater' has not been declared in '::'
  352 | using ::isgreater _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:353:9: error: 'isgreaterequal' has not been declared in '::'
  353 | using ::isgreaterequal _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:354:9: error: 'isless' has not been declared in '::'
  354 | using ::isless _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:355:9: error: 'islessequal' has not been declared in '::'
  355 | using ::islessequal _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:356:9: error: 'islessgreater' has not been declared in '::'
  356 | using ::islessgreater _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:357:9: error: 'isunordered' has not been declared in '::'
  357 | using ::isunordered _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:358:9: error: 'isunordered' has not been declared in '::'
  358 | using ::isunordered _LIBCPP_USING_IF_EXISTS;
      |         ^~~~~~~~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath: In function 'constexpr bool std::__1::__constexpr_isnan(_A1)':
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:591:15: error: 'isnan' is not a member of 'std'
  591 |   return std::isnan(__lcpp_x);
      |               ^~~~~
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath: In function 'constexpr bool std::__1::__constexpr_isinf(_A1)':
/home/cristian/Projects/cosmopolitan/repo/cosmocc/include/third_party/libcxx/cmath:605:15: error: 'isinf' is not a member of 'std'
  605 |   return std::isinf(__lcpp_x);
      |               ^~~~~
main.cpp: In function 'int main()':
main.cpp:8:45: error: 'signbit' is not a member of 'std'
    8 |               << "signbit(+0.0) = " << std::signbit(+0.0) << '\n'
      |                                             ^~~~~~~
main.cpp:9:45: error: 'signbit' is not a member of 'std'
    9 |               << "signbit(-0.0) = " << std::signbit(-0.0) << '\n'
      |                                             ^~~~~~~
main.cpp:10:45: error: 'signbit' is not a member of 'std'
   10 |               << "signbit(+nan) = " << std::signbit(+NAN) << '\n'
      |                                             ^~~~~~~
main.cpp:11:45: error: 'signbit' is not a member of 'std'
   11 |               << "signbit(-nan) = " << std::signbit(-NAN) << '\n'
      |                                             ^~~~~~~
main.cpp:12:45: error: 'signbit' is not a member of 'std'
   12 |               << "signbit(+inf) = " << std::signbit(+INFINITY) << '\n'
      |                                             ^~~~~~~
main.cpp:13:45: error: 'signbit' is not a member of 'std'
   13 |               << "signbit(-inf) = " << std::signbit(-INFINITY) << '\n';

Commenting the first #include <cfloat> fixes the errors.

Version

$ cosmoc++ --version
cosmoc++ (GCC) 14.1.0

What operating system are you seeing the problem on?

Linux

Relevant log output

No response

[ahgamut]

The error goes away if I comment out this check: https://github.com/jart/cosmopolitan/blob/master/third_party/libcxx/float.h#L79

[ahgamut]

Okay the macro undefs in cmath (or rather third_party/libcxx/math.h) are being overwritten

[jart]

This was a little tricky to figure out. The key insight is if you take these lines from your example:

#include <cfloat>
#include <cmath>

And reorder them:

#include <cmath>
#include <cfloat>

Then things work.

So @ahgamut proposed a PR that adds #undef statements to third_party/libcxx/__math/traits.h, to get rid of the macros like fpclassify and signbit that are defined by libc/math.h. However, such #undef statements already exist in third_party/libcxx/math.h which is a wrapper around libc/math.h when compiling in c++ mode.

To see what's happening, I can add your example to the examples folder as a file name wut.cc and say make o//examples/wut.cc, copy and paste the build command that's outputted, and add a -E flag to invoke the preprocessor instead.

.cosmocc/3.9.2/bin/x86_64-linux-cosmo-g++ -Wall -Werror -frecord-gcc-switches -O2 -fno-code-hoisting -fno-schedule-insns2 -fno-optimize-sibling-calls -mno-omit-leaf-frame-pointer -fpatchable-function-entry=18,16 -g -ggdb -Wa,-W -Wa,-I. -Wa,--noexecstack -std=gnu++23 -fuse-cxa-atexit -Wno-int-in-bool-context -Wno-narrowing -Wno-literal-suffix -isystem third_party/libcxx -fno-inline-functions-called-once -D_COSMO_SOURCE -DMODE="" -Wno-prio-ctor-dtor -Wno-unknown-pragmas -nostdinc -iquote. -isystem libc/isystem -DSYSDEBUG -DFTRACE -include libc/integral/normalize.inc -fno-ident -fno-common -fno-gnu-unique -fstrict-aliasing -fstrict-overflow -fno-semantic-interposition -mno-tls-direct-seg-refs -E examples/wut.cc -fdiagnostics-color=always -mno-red-zone -D__MNO_RED_ZONE__ -fno-omit-frame-pointer -D__FNO_OMIT_FRAME_POINTER__ >hog2.i

Then, peeking into this file, I can see code that's clearly wrong, like:

template <class _A1, __enable_if_t<is_floating_point<_A1>::value, int> = 0>
[[__nodiscard__]] inline __attribute__((__always_inline__)) bool __builtin_signbit(_A1 __x) noexcept {
  return __builtin_signbit(__x);
}

Which was supposed to be our C++ signbit() function, except it got mangled by libc/math.h's signbit() macro.

#define signbit(x) __builtin_signbit(x)

If we follow the chain of includes, it seems the cfloat header is doing this:

# 1 "third_party/libcxx/float.h" 1 3 4
# 80 "third_party/libcxx/float.h" 3 4
# 1 "libc/isystem/float.h" 1 3 4
# 1 "./libc/math.h" 1 3 4
# 132 "./libc/math.h" 3 4

Because libc/isystem/float.h has this code:

#ifndef _FLOAT_H
#define _FLOAT_H
#include "libc/math.h"
#include "libc/runtime/fenv.h"
#endif /* _FLOAT_H */

Which causes C math.h to be included before C++ math.h. Since libcxx seems to be sensitive to this happening, the solution appears to be using <math.h> instead of "libc/math.h" in our isystem headers.

[cristianadam]

Thank you 🙏

[jart]

Glad I could help!