s390: Fix undefined behaviour in feenableexcept, fedisableexcept [BZ #30960]

If feenableexcept or fedisableexcept gets excepts=FE_INVALID=0x80
as input, we have a signed left shift: 0x80 << 24 which is not
representable as int and thus is undefined behaviour according to
C standard.

This patch casts excepts as unsigned int before shifting, which is
defined.

For me, the observed undefined behaviour is that the shift is done
with "unsigned"-instructions, which is exactly what we want.
Furthermore, I don't get any exception-flags.

After the fix, the code is using the same instruction sequence as
before.

diff --git a/sysdeps/s390/fpu/fedisblxcpt.c b/sysdeps/s390/fpu/fedisblxcpt.c
index 728f103f43a0e0a10b89c57f2633bec9dc776c04..55634c299fafb17b140af67da689db66dd00ecd0 100644 (file)
--- a/sysdeps/s390/fpu/fedisblxcpt.c
+++ b/sysdeps/s390/fpu/fedisblxcpt.c
@@ -26,7 +26,8 @@ fedisableexcept (int excepts)
 
   _FPU_GETCW (temp);
   old_exc = (temp & FPC_EXCEPTION_MASK) >> FPC_EXCEPTION_MASK_SHIFT;
-  new_flags = (temp & (~((excepts & FE_ALL_EXCEPT) << FPC_EXCEPTION_MASK_SHIFT)));
+  new_flags = (temp & ~(((unsigned int) excepts & FE_ALL_EXCEPT)
+                       << FPC_EXCEPTION_MASK_SHIFT));
   _FPU_SETCW (new_flags);
 
   return old_exc;

diff --git a/sysdeps/s390/fpu/feenablxcpt.c b/sysdeps/s390/fpu/feenablxcpt.c
index 0807e610a213b1b05b0e5d64114574050268eac4..d73659f07811ea922eb67b463f78a79af5a82480 100644 (file)
--- a/sysdeps/s390/fpu/feenablxcpt.c
+++ b/sysdeps/s390/fpu/feenablxcpt.c
@@ -26,7 +26,8 @@ feenableexcept (int excepts)
 
   _FPU_GETCW (temp);
   old_exc = (temp & FPC_EXCEPTION_MASK) >> FPC_EXCEPTION_MASK_SHIFT;
-  new_flags = (temp | ((excepts & FE_ALL_EXCEPT) <<  FPC_EXCEPTION_MASK_SHIFT));
+  new_flags = (temp | (((unsigned int) excepts & FE_ALL_EXCEPT)
+                      << FPC_EXCEPTION_MASK_SHIFT));
   _FPU_SETCW (new_flags);
 
   return old_exc;