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

[Yury Khrustalev]

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