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* [Bug math/30989] New: fesetexcept raises floating-point exception traps on i386
@ 2023-10-22 22:52 bruno at clisp dot org
2023-10-22 22:52 ` [Bug math/30989] " bruno at clisp dot org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: bruno at clisp dot org @ 2023-10-22 22:52 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=30989
Bug ID: 30989
Summary: fesetexcept raises floating-point exception traps on
i386
Product: glibc
Version: 2.35
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: math
Assignee: unassigned at sourceware dot org
Reporter: bruno at clisp dot org
Target Milestone: ---
Created attachment 15188
--> https://sourceware.org/bugzilla/attachment.cgi?id=15188&action=edit
test case foo.c
According to ISO C 23 § 7.6.4.4, fesetexcept is supposed to set floating-point
exception flags without raising a trap. (Unlike feraiseexcept, which is
supposed to raise a trap if feenableexcept() was called with the appropriate
argument.)
"This function changes the state of the floating-point exception flags, but
does not cause any other side effects that might be associated with raising
floating-point exceptions. 267)
Footnote 267) Implementation extensions like traps for floating-point
exceptions and IEC 60559 exception handling do not occur."
That's not how glibc's implementation does it on 32-bit x86.
How to reproduce:
1. Compile the attached program foo.c. On i386 hosts:
$ gcc -Wall foo.c -lm
or on x86_64 hosts:
$ i686-linux-gnu-gcc -Wall foo.c -lm
or
$ gcc -m32 -Wall foo.c -lm
2. Run it.
$ ./a.out
Floating point exception
3. Run it under gdb.
$ gdb a.out
(gdb) run
Starting program: /home/bruno/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Program received signal SIGFPE, Arithmetic exception.
0x565562a7 in main ()
(gdb) x/i $eip
=> 0x565562a7 <main+102>: fld1
I think it is a hardware limitation that on i386 CPUs, setting a
floating-point exception flag in the 387 unit triggers a trap, when
traps are enabled for the particular exception. But setting a
floating-point exception flag in the SSE unit does not have this
problem, cf. glibc/sysdeps/x86_64/fpu/fesetexcept.c.
Therefore I would expect the fesetexcept() function to operate correctly
when the hardware has an SSE unit (determined e.g. like in
sysdeps/i386/fpu/ftestexcept.c).
And only in the case where the CPU has only the 387 unit, I would expect
the fesetexcept() function to return a non-zero value (as error indicator)
and not modify the 387 floating-point control register, like I suggest
for powerpc hardware in https://sourceware.org/bugzilla/show_bug.cgi?id=30988 .
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* [Bug math/30989] fesetexcept raises floating-point exception traps on i386
2023-10-22 22:52 [Bug math/30989] New: fesetexcept raises floating-point exception traps on i386 bruno at clisp dot org
@ 2023-10-22 22:52 ` bruno at clisp dot org
2023-10-23 18:50 ` bruno at clisp dot org
2023-12-19 18:37 ` adhemerval.zanella at linaro dot org
2 siblings, 0 replies; 4+ messages in thread
From: bruno at clisp dot org @ 2023-10-22 22:52 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=30989
Bruno Haible <bruno at clisp dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Host| |i386-linux-gnu
--- Comment #1 from Bruno Haible <bruno at clisp dot org> ---
Seen on:
- glibc 2.35 (Ubuntu 22.04)
- glibc 2.33 (Slackware 15)
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* [Bug math/30989] fesetexcept raises floating-point exception traps on i386
2023-10-22 22:52 [Bug math/30989] New: fesetexcept raises floating-point exception traps on i386 bruno at clisp dot org
2023-10-22 22:52 ` [Bug math/30989] " bruno at clisp dot org
@ 2023-10-23 18:50 ` bruno at clisp dot org
2023-12-19 18:37 ` adhemerval.zanella at linaro dot org
2 siblings, 0 replies; 4+ messages in thread
From: bruno at clisp dot org @ 2023-10-23 18:50 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=30989
Bruno Haible <bruno at clisp dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://sourceware.org/bugz
| |illa/show_bug.cgi?id=30990
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* [Bug math/30989] fesetexcept raises floating-point exception traps on i386
2023-10-22 22:52 [Bug math/30989] New: fesetexcept raises floating-point exception traps on i386 bruno at clisp dot org
2023-10-22 22:52 ` [Bug math/30989] " bruno at clisp dot org
2023-10-23 18:50 ` bruno at clisp dot org
@ 2023-12-19 18:37 ` adhemerval.zanella at linaro dot org
2 siblings, 0 replies; 4+ messages in thread
From: adhemerval.zanella at linaro dot org @ 2023-12-19 18:37 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=30989
Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |FIXED
CC| |adhemerval.zanella at linaro dot o
| |rg
Target Milestone|--- |2.39
Assignee|unassigned at sourceware dot org |adhemerval.zanella at linaro dot o
| |rg
--- Comment #2 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
Fixed on 2.39 (47a9eeb9ba72fd30766bdf4faa7d46b8ca33a7fd).
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2023-10-22 22:52 [Bug math/30989] New: fesetexcept raises floating-point exception traps on i386 bruno at clisp dot org
2023-10-22 22:52 ` [Bug math/30989] " bruno at clisp dot org
2023-10-23 18:50 ` bruno at clisp dot org
2023-12-19 18:37 ` adhemerval.zanella at linaro dot org
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