On 03/16/2011 09:41 AM, Sebastian Huber wrote:
> On 03/14/2011 03:14 PM, Andrew Haley wrote:
>> On 03/14/2011 12:02 PM, Sebastian Huber wrote:
>>> Hello,
>>>
>>> the object file bpabi.o is part of libgcc. It is compiled with the option
>>> -fexceptions. Does anyone know why we need exceptions here?
>>
>> __divdi3 can throw an exception. I don't know whether it does on ARM,
>> but it does on other processors.
>>
>> Andrew.
>
> Thanks for the hint. How can an assembler or C function throw an exception? I
> am absolutely not sure how this low-level stuff works in detail, but it seems
> to me from a look at libgcc/Makefile.in that this -fexceptions is used for all
> targets? I currently try to prepare a RTEMS GCC for ARM to use the ARM EABI
> version 5. Now I have the problem that an innocent looking
>
> int64_t f(int64_t a, int64_t b)
> {
> return a / b;
> }
>
> will pull in the hole unwind mechanic that accounts for 10kByte of Thumb code.
> This might be a problem for small target systems.
>
In "gcc/config/arm/lib1funcs.asm" is this the code that is supposed to throw an
exception:
/* ------------------------------------------------------------------------ */
#ifdef L_dvmd_tls
#ifdef __ARM_EABI__
WEAK aeabi_idiv0
WEAK aeabi_ldiv0
FUNC_START aeabi_idiv0
FUNC_START aeabi_ldiv0
RET
FUNC_END aeabi_ldiv0
FUNC_END aeabi_idiv0
#else
FUNC_START div0
RET
FUNC_END div0
#endif
#endif /* L_divmodsi_tools */
/* ------------------------------------------------------------------------ */
#ifdef L_dvmd_lnx
@ GNU/Linux division-by zero handler. Used in place of L_dvmd_tls
/* Constant taken from <asm/signal.h>. */
#define SIGFPE 8
#ifdef __ARM_EABI__
WEAK aeabi_idiv0
WEAK aeabi_ldiv0
ARM_FUNC_START aeabi_idiv0
ARM_FUNC_START aeabi_ldiv0
#else
ARM_FUNC_START div0
#endif
do_push {r1, lr}
mov r0, #SIGFPE
bl SYM(raise) __PLT__
RETLDM r1
#ifdef __ARM_EABI__
FUNC_END aeabi_ldiv0
FUNC_END aeabi_idiv0
#else
FUNC_END div0
#endif
?
Does this mean that only on GNU/Linux we need this unwind stuff?
--
Sebastian Huber, embedded brains GmbH
Address : Obere Lagerstr. 30, D-82178 Puchheim, Germany
Phone : +49 89 18 90 80 79-6
Fax : +49 89 18 90 80 79-9
E-Mail : sebastian.huber@xxxxxxxxxxxxxxxxxx
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