From d79069d2ff163397ed83fd90c97ae778977274fb Mon Sep 17 00:00:00 2001 From: "J.H. van de Water" Date: Fri, 3 Aug 2018 01:45:12 +0200 Subject: [PATCH] Cygwin: fegetenv() should not disable exceptions fnstenv MUST be followed by fldenv in fegetenv(), as the former disables all exceptions in the x87 FPU, which is not appropriate here (fegetenv() ). fldenv after fnstenv should reload the x87 FPU w/ the configuration that was saved by fnstenv, i.e. a configuration that might have exceptions enabled. Note: x86_64 uses SSE for floating-point, not the x87 FPU. However, because feraiseexcept() attempts to provoke an exception using the x87 FPU, the bug in fegetenv() will make this attempt futile here (x86_64). Note: WoW uses the x87 FPU for floating-point, not SSE. Here anything that would normally result in triggering an exception, not only feraiseexcept(), will not be able to, as result of the bug in fegetenv(). --- winsup/cygwin/fenv.cc | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/winsup/cygwin/fenv.cc b/winsup/cygwin/fenv.cc index bd3f90495..066704b40 100644 --- a/winsup/cygwin/fenv.cc +++ b/winsup/cygwin/fenv.cc @@ -141,7 +141,11 @@ fegetexcept (void) int fegetenv (fenv_t *envp) { - __asm__ volatile ("fnstenv %0" : "=m" (envp->_fpu) : ); + /* fnstenv disables all exceptions in the x87 FPU; as this is not what is + desired here, reload the cfg saved from the x87 FPU, back to the FPU */ + __asm__ volatile ("fnstenv %0\n\ + fldenv %0" + : "=m" (envp->_fpu) : ); if (use_sse) __asm__ volatile ("stmxcsr %0" : "=m" (envp->_sse_mxcsr) : ); return 0;