[libc][fenv] Add missing FE_* definitions for some environment.

[lntue]

No description provided.

[llvmbot]

@llvm/pr-subscribers-libc

Author: None (lntue)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/91519.diff

1 Files Affected:

• (modified) libc/hdr/fenv_macros.h (+24)

diff --git a/libc/hdr/fenv_macros.h b/libc/hdr/fenv_macros.h
index 041fca5f224b3..2ebff4caba90d 100644
--- a/libc/hdr/fenv_macros.h
+++ b/libc/hdr/fenv_macros.h
@@ -17,10 +17,34 @@
 
 #include <fenv.h>
 
+// In some environment, FE_ALL_EXCEPT is set to 0 and the remaining exceptions
+// FE_* are missing.
+#if (FE_ALL_EXCEPT == 0)
+#ifndef FE_DIVBYZERO
+#define FE_DIVBYZERO 0
+#endif // FE_DIVBYZERO
+
+#ifndef FE_INEXACT
+#define FE_INEXACT 0
+#endif // FE_INEXACT
+
+#ifndef FE_INVALID
+#define FE_INVALID 0
+#endif // FE_INVALID
+
+#ifndef FE_OVERFLOW
+#define FE_OVERFLOW 0
+#endif // FE_OVERFLOW
+
+#ifndef FE_UNDERFLOW
+#define FE_UNDERFLOW 0
+#endif // FE_UNDERFLOW
+#else
 // If this is not provided by the system, define it for use internally.
 #ifndef __FE_DENORM
 #define __FE_DENORM (1 << 6)
 #endif
+#endif
 
 #endif // LLVM_LIBC_FULL_BUILD
 

[nickdesaulniers]

"some environment" ? Got any more details?

[zibi2]

This is not a valid preprocessor constant expression. On z/OS this caused hard error as the following:

cat t.C && clang++ -c t.C

#define FE_ALL_EXCEPT   ((unsigned int) 0x000000F8)

#if (FE_ALL_EXCEPT == 0)
#ifndef FE_DIVBYZERO
#define FE_DIVBYZERO 0
#endif // FE_DIVBYZERO
#endif
t.C:3:6: error: token is not a valid binary operator in a preprocessor subexpression
    3 | #if (FE_ALL_EXCEPT == 0)
      |      ^~~~~~~~~~~~~
t.C:1:36: note: expanded from macro 'FE_ALL_EXCEPT'
    1 | #define FE_ALL_EXCEPT   ((unsigned int) 0x000000F8)
      |                           ~~~~~~~~ ^
1 error generated.

We are currently using #ifndef FE_ALL_EXCEPT as hack.

Will you be able to provide a proper fix?

[lntue]

I think we can remove the outer #if (FE_ALL_EXCEPT == 0) entirely, just directly check for exception macros individually and set them to 0 if not defined, WDYT ? @nickdesaulniers

[nickdesaulniers]

Yeah, seems like we can just remove this outer conditional.

[lntue]

@zibi2 #114446