[Bug math/30998] New: fesetexceptflag clears too many floating-point exception flags on alpha

[Bug math/30998] New: fesetexceptflag clears too many floating-point exception flags on alpha

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30998

            Bug ID: 30998
           Summary: fesetexceptflag clears too many floating-point
                    exception flags on alpha
           Product: glibc
           Version: 2.36
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: bruno at clisp dot org
  Target Milestone: ---

Created attachment 15196
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15196&action=edit
test case foo.c

On Linux/alpha, the function fesetexceptflag() clears some exception flags that
are outside the EXCEPTS argument. This violates ISO C 23 § 7.6.4.5, which says:
  "The fesetexceptflag function attempts to set the floating-point status flags
indicated by the argument excepts to the states stored in the object pointed to
by flagp."

How to reproduce:
Compile and run the attached program.
$ gcc -Wall foo.c -lm
$ ./a.out

Expected: It terminates with exit code 0.
Actual:
a.out: foo.c:58: main: Assertion `fetestexcept (FE_DIVBYZERO) == FE_DIVBYZERO'
failed.
Aborted

When you compare the program's lines 49 and 58, you see that the invocation
  fesetexceptflag (&saved_flags_2, FE_OVERFLOW)
not only modified the FE_OVERFLOW flag bit, but also cleared the FE_DIVBYZERO
flag bit.

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[Bug math/30998] fesetexceptflag clears too many floating-point exception flags on alpha

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30998

Bruno Haible <bruno at clisp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Host|                            |alpha-linux-gnu

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[Bug math/30998] fesetexceptflag clears too many floating-point exception flags on alpha

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30998

--- Comment #1 from Bruno Haible <bruno at clisp dot org> ---
Seen on Debian 12.0/alpha.

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[Bug math/30998] fesetexceptflag clears too many floating-point exception flags on alpha

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30998

--- Comment #2 from Bruno Haible <bruno at clisp dot org> ---
Created attachment 15197
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15197&action=edit
proposed fix

Find attached a proposed fix.

The bug is obviously in glibc/sysdeps/alpha/fpu/fsetexcptflg.c .
The line

  tmp = (tmp & ~SWCR_STATUS_MASK) | (*flagp & excepts & SWCR_STATUS_MASK);

needs to be changed to

  tmp = (tmp & ~(excepts & SWCR_STATUS_MASK)) | (*flagp & excepts &
SWCR_STATUS_MASK);

A optimized expression (produces one less instruction when compiled by
"alpha-linux-gnu-gcc -O2") is:

  tmp ^= (tmp ^ *flagp) & excepts & SWCR_STATUS_MASK;

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[Bug math/30998] fesetexceptflag clears too many floating-point exception flags on alpha

[adhemerval.zanella at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30998

Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |2.39
                 CC|                            |adhemerval.zanella at linaro dot o
                   |                            |rg
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #3 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
Fixed on 2.39 (80a40a9e14d9a01e3f70c5b37ecd1da83033b6de).

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