* what is the difference with and without crc extension support
@ 2022-03-03 13:41 Dongjiu Geng
2022-03-03 13:48 ` Martin Liška
2022-03-04 18:20 ` Richard Earnshaw
0 siblings, 2 replies; 5+ messages in thread
From: Dongjiu Geng @ 2022-03-03 13:41 UTC (permalink / raw)
To: gcc
Hi,
My program does not use CRC instructions,but I find the compiled
binary has much difference between using "-march=armv8-a+crc" and
using "-march=armv8-a". Even stranger, when I use
"-march=armv8-a+crc", I find my compiled binary can not run. but when
I change -O2 to -O0 based on "-march=armv8-a+crc", it can run. I do
not know what is the reason.. can you answer it? Thanks.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: what is the difference with and without crc extension support
2022-03-03 13:41 what is the difference with and without crc extension support Dongjiu Geng
@ 2022-03-03 13:48 ` Martin Liška
2022-03-03 13:52 ` Dongjiu Geng
2022-03-04 18:20 ` Richard Earnshaw
1 sibling, 1 reply; 5+ messages in thread
From: Martin Liška @ 2022-03-03 13:48 UTC (permalink / raw)
To: Dongjiu Geng, gcc
On 3/3/22 14:41, Dongjiu Geng via Gcc wrote:
> Hi,
> My program does not use CRC instructions,but I find the compiled
> binary has much difference between using "-march=armv8-a+crc" and
> using "-march=armv8-a". Even stranger, when I use
> "-march=armv8-a+crc", I find my compiled binary can not run. but when
> I change -O2 to -O0 based on "-march=armv8-a+crc", it can run. I do
> not know what is the reason.. can you answer it? Thanks.
Hello.
Please report bug here:
https://gcc.gnu.org/bugzilla/
and attach a pre-processed source file:
https://gcc.gnu.org/bugs/
Martin
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: what is the difference with and without crc extension support
2022-03-03 13:48 ` Martin Liška
@ 2022-03-03 13:52 ` Dongjiu Geng
2022-03-04 13:05 ` Martin Liška
0 siblings, 1 reply; 5+ messages in thread
From: Dongjiu Geng @ 2022-03-03 13:52 UTC (permalink / raw)
To: Martin Liška; +Cc: gcc
Thanks for the answer, my source file is complex,it is not convenient
attach, because it is company code. According to your experience,
what is the reason about it?
Martin Liška <mliska@suse.cz> 于2022年3月3日周四 21:48写道:
>
> On 3/3/22 14:41, Dongjiu Geng via Gcc wrote:
> > Hi,
> > My program does not use CRC instructions,but I find the compiled
> > binary has much difference between using "-march=armv8-a+crc" and
> > using "-march=armv8-a". Even stranger, when I use
> > "-march=armv8-a+crc", I find my compiled binary can not run. but when
> > I change -O2 to -O0 based on "-march=armv8-a+crc", it can run. I do
> > not know what is the reason.. can you answer it? Thanks.
>
> Hello.
>
> Please report bug here:
> https://gcc.gnu.org/bugzilla/
>
> and attach a pre-processed source file:
> https://gcc.gnu.org/bugs/
>
> Martin
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: what is the difference with and without crc extension support
2022-03-03 13:52 ` Dongjiu Geng
@ 2022-03-04 13:05 ` Martin Liška
0 siblings, 0 replies; 5+ messages in thread
From: Martin Liška @ 2022-03-04 13:05 UTC (permalink / raw)
To: Dongjiu Geng; +Cc: gcc
On 3/3/22 14:52, Dongjiu Geng wrote:
> Thanks for the answer, my source file is complex,it is not convenient
> attach, because it is company code.
I see. So then you can try -fdump-tree-optimized and compare the corresponding dump file.
Or you can use -fdump-tree-all -fdump-rtl-all and do the same.
> According to your experience,
> what is the reason about it?
Dunno.
Cheers,
Martin
>
> Martin Liška <mliska@suse.cz> 于2022年3月3日周四 21:48写道:
>>
>> On 3/3/22 14:41, Dongjiu Geng via Gcc wrote:
>>> Hi,
>>> My program does not use CRC instructions,but I find the compiled
>>> binary has much difference between using "-march=armv8-a+crc" and
>>> using "-march=armv8-a". Even stranger, when I use
>>> "-march=armv8-a+crc", I find my compiled binary can not run. but when
>>> I change -O2 to -O0 based on "-march=armv8-a+crc", it can run. I do
>>> not know what is the reason.. can you answer it? Thanks.
>>
>> Hello.
>>
>> Please report bug here:
>> https://gcc.gnu.org/bugzilla/
>>
>> and attach a pre-processed source file:
>> https://gcc.gnu.org/bugs/
>>
>> Martin
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: what is the difference with and without crc extension support
2022-03-03 13:41 what is the difference with and without crc extension support Dongjiu Geng
2022-03-03 13:48 ` Martin Liška
@ 2022-03-04 18:20 ` Richard Earnshaw
1 sibling, 0 replies; 5+ messages in thread
From: Richard Earnshaw @ 2022-03-04 18:20 UTC (permalink / raw)
To: Dongjiu Geng, gcc
On 03/03/2022 13:41, Dongjiu Geng via Gcc wrote:
> Hi,
> My program does not use CRC instructions,but I find the compiled
> binary has much difference between using "-march=armv8-a+crc" and
> using "-march=armv8-a". Even stranger, when I use
> "-march=armv8-a+crc", I find my compiled binary can not run. but when
> I change -O2 to -O0 based on "-march=armv8-a+crc", it can run. I do
> not know what is the reason.. can you answer it? Thanks.
The most common reason for a program failing to run when the optimizer
is turned on is that it contains undefined behaviour. Make sure that
you turn on GCC's warning options and fix anything that these report.
It's very unlikely that the change of -march=armv8-a to
-march=armv8-a+crc is the reason for the differences in compiled code
that you are seeing. Something else to try here is to identify an
object file that is different between the two options and then rebuild
it both ways, but add "-g". You can then use
readelf -debug-dump=str <object-file>
to print out the real options used by the compiler (there may be some
additional strings reported in the dump, but the options are the bit
that is interesting). The only difference should be the -march option
you mentioned above.
R.
^ permalink raw reply [flat|nested] 5+ messages in thread
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2022-03-03 13:41 what is the difference with and without crc extension support Dongjiu Geng
2022-03-03 13:48 ` Martin Liška
2022-03-03 13:52 ` Dongjiu Geng
2022-03-04 13:05 ` Martin Liška
2022-03-04 18:20 ` Richard Earnshaw
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