S390: Fix handling of DXC-byte in FPC-register.

On s390, the DXC(data-exception-code)-byte in FPC(floating-point-control)-
register contains a code of the last occured exception.
If bits 6 and 7 of DXC-byte are zero, the bits 0-5 correspond to the
ieee-exception flag bits.
The current implementation always uses these bits as ieee-exception flag bits.
fetestexcept() reports any exception after the first usage of a
vector-instruction in a process, because it raises an "vector instruction
exception" with DXC-code 0xFE.
This patch fixes the handling of the DXC-byte. The DXC-Byte is only handled
if bits 6 and 7 are zero.

The #define _FPU_RESERVED is extended by the DXC-Byte.
Otherwise the tests math/test-fpucw-static and math/test-fpucw-ieee-static
fails, because DXC-Byte contains the vector instruction exception when reaching
main(). This exception was triggered by strrchr() call in __init_misc().
__init_misc() is called after __setfpucw () in __libc_init_first().

The field __ieee_instruction_pointer in struct fenv_t is renamed to __unused
because it is a relict from commit "Remove PTRACE_PEEKUSER"
(87b9b50) and isn´t used anymore.

ChangeLog:

	[BZ #18610]
	* sysdeps/s390/fpu/bits/fenv.h (fenv_t): Rename
	__ieee_instruction_pointer to __unused.
	* sysdeps/s390/fpu/fesetenv.c (__fesetenv): Remove usage of
	__ieee_instruction_pointer.
	* sysdeps/s390/fpu/fclrexcpt.c (feclearexcept): Fix dxc-field handling.
	* sysdeps/s390/fpu/fgetexcptflg.c (fegetexceptflag): Likewise.
	* sysdeps/s390/fpu/fsetexcptflg.c (fesetexceptflag): Likewise.
	* sysdeps/s390/fpu/ftestexcept.c (fetestexcept): Likewise.
	* sysdeps/s390/fpu/fpu_control.h (_FPU_RESERVED):
	Mark dxc-field as reserved.

ChangeLog

@@ -1,3 +1,17 @@
+2015-08-26  Stefan Liebler  <stli@linux.vnet.ibm.com>
+
+	[BZ #18610]
+	* sysdeps/s390/fpu/bits/fenv.h (fenv_t): Rename
+	__ieee_instruction_pointer to __unused.
+	* sysdeps/s390/fpu/fesetenv.c (__fesetenv): Remove usage of
+	__ieee_instruction_pointer.
+	* sysdeps/s390/fpu/fclrexcpt.c (feclearexcept): Fix dxc-field handling.
+	* sysdeps/s390/fpu/fgetexcptflg.c (fegetexceptflag): Likewise.
+	* sysdeps/s390/fpu/fsetexcptflg.c (fesetexceptflag): Likewise.
+	* sysdeps/s390/fpu/ftestexcept.c (fetestexcept): Likewise.
+	* sysdeps/s390/fpu/fpu_control.h (_FPU_RESERVED):
+	Mark dxc-field as reserved.
+
 2015-08-25  Roland McGrath  <roland@hack.frob.com>
 
 	* sysdeps/nacl/start.c (_start): Call __nacl_main instead of main

sysdeps/s390/fpu/bits/fenv.h

@@ -77,8 +77,10 @@ typedef unsigned int fexcept_t; /* size of fpc */
 typedef struct
 {
   fexcept_t __fpc;
-  void *__ieee_instruction_pointer;
-  /* failing instruction for ieee exceptions */
+  void *__unused;
+  /* The field __unused (formerly __ieee_instruction_pointer) is a relict from
+     commit "Remove PTRACE_PEEKUSER" (87b9b50f0d4b92248905e95a06a13c513dc45e59)
+     and isn´t used anymore.  */
 } fenv_t;
 
 /* If the default argument is used we use this value.  */

sysdeps/s390/fpu/fclrexcpt.c

@@ -29,7 +29,12 @@ feclearexcept (int excepts)
 
   _FPU_GETCW (temp);
   /* Clear the relevant bits.  */
-  temp &= ~((excepts << FPC_DXC_SHIFT)|(excepts << FPC_FLAGS_SHIFT));
+  temp &= ~(excepts << FPC_FLAGS_SHIFT);
+  if ((temp & FPC_NOT_FPU_EXCEPTION) == 0)
+    /* Bits 6, 7 of dxc-byte are zero,
+       thus bits 0-5 of dxc-byte correspond to the flag-bits.
+       Clear the relevant bits in flags and dxc-field.  */
+    temp &= ~(excepts << FPC_DXC_SHIFT);
 
   /* Put the new data in effect.  */
   _FPU_SETCW (temp);

sysdeps/s390/fpu/fesetenv.c

@@ -32,12 +32,10 @@ __fesetenv (const fenv_t *envp)
   if (envp == FE_DFL_ENV)
     {
       env.__fpc = _FPU_DEFAULT;
-      env.__ieee_instruction_pointer = 0;
     }
   else if (envp == FE_NOMASK_ENV)
     {
       env.__fpc = FPC_EXCEPTION_MASK;
-      env.__ieee_instruction_pointer = 0;
     }
   else
     env = (*envp);

sysdeps/s390/fpu/fgetexcptflg.c

@@ -27,7 +27,13 @@ fegetexceptflag (fexcept_t *flagp, int excepts)
 
   /* Get the current exceptions.  */
   _FPU_GETCW (temp);
-  newexcepts = (excepts << FPC_DXC_SHIFT) | (excepts << FPC_FLAGS_SHIFT);
+  newexcepts = excepts << FPC_FLAGS_SHIFT;
+  if ((temp & FPC_NOT_FPU_EXCEPTION) == 0)
+    /* Bits 6, 7 of dxc-byte are zero,
+       thus bits 0-5 of dxc-byte correspond to the flag-bits.
+       Evaluate flags and last dxc-exception-code.  */
+    newexcepts |= excepts << FPC_DXC_SHIFT;
+
   *flagp = temp & newexcepts;
 
   /* Success.  */

sysdeps/s390/fpu/fpu_control.h

@@ -19,12 +19,12 @@
    <http://www.gnu.org/licenses/>.  */
 
 #ifndef _FPU_CONTROL_H
-# define _FPU_CONTROL_H
+#define _FPU_CONTROL_H
 
-# include <features.h>
+#include <features.h>
 
 /* These bits are reserved are not changed.  */
-# define _FPU_RESERVED 0x070700FC
+#define _FPU_RESERVED 0x0707FFFC
 
 /* The fdlibm code requires no interrupts for exceptions.  Don't
    change the rounding mode, it would break long double I/O!  */

sysdeps/s390/fpu/fsetexcptflg.c

@@ -24,16 +24,25 @@
 int
 fesetexceptflag (const fexcept_t *flagp, int excepts)
 {
-  fexcept_t temp,newexcepts;
+  fexcept_t temp, newexcepts;
 
   /* Get the current environment.  We have to do this since we cannot
      separately set the status word.  */
   _FPU_GETCW (temp);
   /* Install the new exception bits in the Accrued Exception Byte.  */
   excepts = excepts & FE_ALL_EXCEPT;
-  newexcepts = (excepts << FPC_DXC_SHIFT) | (excepts << FPC_FLAGS_SHIFT);
+  newexcepts = excepts << FPC_FLAGS_SHIFT;
   temp &= ~newexcepts;
-  temp |= *flagp & newexcepts;
+  if ((temp & FPC_NOT_FPU_EXCEPTION) == 0)
+    /* Bits 6, 7 of dxc-byte are zero,
+       thus bits 0-5 of dxc-byte correspond to the flag-bits.
+       Clear given exceptions in dxc-field.  */
+    temp &= ~(excepts << FPC_DXC_SHIFT);
+
+  /* Integrate dxc-byte of flagp into flags. The dxc-byte of flagp contains
+     either an ieee-exception or 0 (see fegetexceptflag).  */
+  temp |= (*flagp | ((*flagp >> FPC_DXC_SHIFT) << FPC_FLAGS_SHIFT))
+    & newexcepts;
 
   /* Store the new status word (along with the rest of the environment.
      Possibly new exceptions are set but they won't get executed unless

sysdeps/s390/fpu/ftestexcept.c

@@ -23,11 +23,17 @@
 int
 fetestexcept (int excepts)
 {
-  fexcept_t temp;
+  fexcept_t temp, res;
 
   /* Get current exceptions.  */
   _FPU_GETCW (temp);
-  temp = (temp >> FPC_DXC_SHIFT) | (temp >> FPC_FLAGS_SHIFT);
-  return temp & excepts & FE_ALL_EXCEPT;
+  res = temp >> FPC_FLAGS_SHIFT;
+  if ((temp & FPC_NOT_FPU_EXCEPTION) == 0)
+    /* Bits 6, 7 of dxc-byte are zero,
+       thus bits 0-5 of dxc-byte correspond to the flag-bits.
+       Evaluate flags and last dxc-exception-code.  */
+    res |= temp >> FPC_DXC_SHIFT;
+
+  return res & excepts & FE_ALL_EXCEPT;
 }
 libm_hidden_def (fetestexcept)