_Unwind_Resume() references in libgcc division functions

_Unwind_Resume() references in libgcc division functions

[Sebastian Huber]

Hello,

I noticed that several division related routines provided by libgcc such 
as __divdi3, __moddi3 and __umoddi3 have references to _Unwind_Resume 
for the sparc-rtems target. For example:

	.file	"libgcc2.c"
! GNU C17 (GCC) version 13.0.0 20220621 (experimental) [master 
r13-1187-gab981aab92c] (sparc-rtems6)
!	compiled by GNU C version 12.1.1 20220517 [revision 
325d82b08696da17fb26bd2e1b6ba607649357fb], GMP version 6.1.0, MPFR 
version 3.1.4, MPC version 1.0.3, isl version isl-0.16.1-GMP

! GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
! options passed: -msoft-float -mcpu=leon3 -g -g -g -O0 -O2 -O0 
-fbuilding-libgcc -fno-stack-protector -fexceptions 
-fnon-call-exceptions -fvisibility=hidden

.LLBE7:
.LLBE6:
! /home/EB/sebastian_h/src/gcc/libgcc/libgcc2.c:1225:   w = __udivmoddi4 
(uu.ll, vv.ll, (UDWtype *) 0);
	.loc 1 1225 5
	std	%g2, [%fp-16]	! D.3900, w
! /home/EB/sebastian_h/src/gcc/libgcc/libgcc2.c:1226:   if (c)
	.loc 1 1226 6
	ld	[%fp-4], %g1	! c, tmp284
	cmp	%g1, 0	! tmp284,
	be	.LL25
	 nop		!
	b	.LL28
	 nop	!
.LL27:
	mov	%i0, %g1	!, tmp283
	mov	%g1, %o0	! D.3909,
.LLEHB2:
	call	_Unwind_Resume, 0
	 nop	!,
.LL28:

Could someone please give me a hint, why the compiler generates this 
code? I was unable to figure this out by looking at the pre-processed 
code. I tried to reproduce it with a simple division by zero test case, 
but this didn't work:

unsigned f(unsigned i)
{
         return i / 0;
}

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Re: _Unwind_Resume() references in libgcc division functions

[Jakub Jelinek]

On Tue, Jun 21, 2022 at 03:13:19PM +0200, Sebastian Huber wrote:
> Hello,
> 
> I noticed that several division related routines provided by libgcc such as
> __divdi3, __moddi3 and __umoddi3 have references to _Unwind_Resume for the
> sparc-rtems target. For example:

That is because:

ifeq ($(LIB2_DIVMOD_EXCEPTION_FLAGS),)
# Provide default flags for compiling divmod functions, if they haven't been
# set already by a target-specific Makefile fragment.
LIB2_DIVMOD_EXCEPTION_FLAGS := -fexceptions -fnon-call-exceptions
endif

which is there so that e.g. Ada or other -fnon-call-exceptions languages can
have properly working divisions.

	Jakub

Re: _Unwind_Resume() references in libgcc division functions

[Sebastian Huber]

On 21/06/2022 15:24, Jakub Jelinek wrote:
> On Tue, Jun 21, 2022 at 03:13:19PM +0200, Sebastian Huber wrote:
>> Hello,
>>
>> I noticed that several division related routines provided by libgcc such as
>> __divdi3, __moddi3 and __umoddi3 have references to _Unwind_Resume for the
>> sparc-rtems target. For example:
> 
> That is because:
> 
> ifeq ($(LIB2_DIVMOD_EXCEPTION_FLAGS),)
> # Provide default flags for compiling divmod functions, if they haven't been
> # set already by a target-specific Makefile fragment.
> LIB2_DIVMOD_EXCEPTION_FLAGS := -fexceptions -fnon-call-exceptions
> endif
> 
> which is there so that e.g. Ada or other -fnon-call-exceptions languages can
> have properly working divisions.

Thanks for the hint. It seems also the optimization level has an impact. 
The _Unwind_Resume dependency is only present if I use 
CFLAGS_FOR_TARGET="-O0 -g".

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Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
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fax:   +49-89-18 94 741 - 08

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