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

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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.
This commit is contained in:
Stefan Liebler 2023-10-18 15:08:40 +02:00
parent c06e10c813
commit 97a58d885b
2 changed files with 4 additions and 2 deletions
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3
sysdeps/s390/fpu/fedisblxcpt.c
View File

@ -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;

3
sysdeps/s390/fpu/feenablxcpt.c
View File

@ -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;