Fix a problem relating to fesetenv() clobbering i387 register stack.

Details: As a side-effect of restoring a saved FP environment,
fesetenv() overwrites the tag word, which indicates which i387
registers are in use.  Normally this isn't a problem because
the calling convention requires the register stack to be empty
on function entry and exit.  However, fesetenv() is inlined, so we
need to tell gcc explicitly that the i387 registers get clobbered.

PR:	85101

1 files changed, 12 insertions, 1 deletions

diff --git a/lib/msun/i387/fenv.h b/lib/msun/i387/fenv.h
index cbe9a6b..c4eab02 100644
--- a/lib/msun/i387/fenv.h
+++ b/lib/msun/i387/fenv.h
@@ -99,6 +99,9 @@ extern const fenv_t	__fe_dfl_env;
 
 #define	__fldcw(__cw)		__asm __volatile("fldcw %0" : : "m" (__cw))
 #define	__fldenv(__env)		__asm __volatile("fldenv %0" : : "m" (__env))
+#define	__fldenvx(__env)	__asm __volatile("fldenv %0" : : "m" (__env)  \
+				: "st", "st(1)", "st(2)", "st(3)", "st(4)",   \
+				"st(5)", "st(6)", "st(7)")
 #define	__fnclex()		__asm __volatile("fnclex")
 #define	__fnstenv(__env)	__asm __volatile("fnstenv %0" : "=m" (*(__env)))
 #define	__fnstcw(__cw)		__asm __volatile("fnstcw %0" : "=m" (*(__cw)))
@@ -207,7 +210,15 @@ fesetenv(const fenv_t *__envp)
 
 	__mxcsr = __get_mxcsr(__env);
 	__set_mxcsr(__env, 0xffffffff);
-	__fldenv(__env);
+	/*
+	 * XXX Using fldenvx() instead of fldenv() tells the compiler that this
+	 * instruction clobbers the i387 register stack.  This happens because
+	 * we restore the tag word from the saved environment.  Normally, this
+	 * would happen anyway and we wouldn't care, because the ABI allows
+	 * function calls to clobber the i387 regs.  However, fesetenv() is
+	 * inlined, so we need to be more careful.
+	 */
+	__fldenvx(__env);
 	if (__HAS_SSE())
 		__ldmxcsr(__mxcsr);
 	return (0);