[PATCH v3] LoongArch: fix missing trap for enabled exceptions on narrowing operation

[Yury Khrustalev]

On Tue, Jul 07, 2026 at 01:46:09PM +0100, Yury Khrustalev wrote:
> On Tue, Mar 24, 2026 at 03:22:59PM +0800, Xi Ruoyao wrote:
> > The libc_feupdateenv_test macro is supposed to trap when the trap for a
> > previously held exception is enabled.  But
> > libc_feupdateenv_test_loongarch wasn't doing it properly: the comment
> > claims "setting of the cause bits" would cause "the hardware to generate
> > the exception" but that's simply not true for the LoongArch movgr2fcsr
> > instruction.
> > 
> > To fix the issue, we need to call __feraiseexcept in case a held exception
> > is enabled to trap.
> > 
> > Reviewed-by: caiyinyu <caiyinyu@loongson.cn>
> > Signed-off-by: Xi Ruoyao <xry111@xry111.site>
> > ---
> >
> > ...
> >
> > diff --git a/math/test-narrowing-trap.c b/math/test-narrowing-trap.c
> > new file mode 100644
> > index 0000000000..a483c4bf1a
> > --- /dev/null
> > +++ b/math/test-narrowing-trap.c
> >
> > ...
> >
> > +static int
> > +do_test (void)
> > +{
> > +  pid_t pid;
> > +
> > +  if (!EXCEPTION_ENABLE_SUPPORTED (FE_INVALID))
> > +    FAIL_UNSUPPORTED ("feenableexcept (FE_INVALID) not supported");
> 
> On AArch64 we have
> 
>   #define EXCEPTION_ENABLE_SUPPORTED(EXCEPT)	((EXCEPT) == 0)
> 
> Which means that this test will always be unsupported even if
> 
>   feenableexcept (FE_INVALID)
> 
> would return 0 (compare with math/test-fenv-preserve.c for example).
> 
> I think this check is not correct.
> 
> Thanks,
> Yury

This simple fix should work I think.

diff --git a/math/test-narrowing-trap.c b/math/test-narrowing-trap.c
index 6d21357913..5871cb33fc 100644
--- a/math/test-narrowing-trap.c
+++ b/math/test-narrowing-trap.c
@@ -29,14 +29,14 @@ do_test (void)
 #ifdef FE_INVALID
   pid_t pid;
 
-  if (!EXCEPTION_ENABLE_SUPPORTED (FE_INVALID))
-    FAIL_UNSUPPORTED ("feenableexcept (FE_INVALID) not supported");
-
   pid = xfork ();
   if (pid == 0)
     {
       int r = feenableexcept (FE_INVALID);
 
+      if (!EXCEPTION_ENABLE_SUPPORTED (FE_INVALID) && (r == -1))
+        FAIL_UNSUPPORTED ("feenableexcept (FE_INVALID) not supported");
+
       TEST_COMPARE (r, 0);
       fdiv (0.0, 0.0);
       _exit (0);