[arm-gnu] gcc-arm Compiler produce different object file for the same source file

[Ricardo Anguiano]

Hello Abudurahman,

We'll need more information.  The GCC bug reporting instructions
(under the _What we need_ heading) are a good template to use when
reporting possible problems or difficulties with GCC:

      http://gcc.gnu.org/bugs/

Do you have a small preprocessed test case file (-save-temps, *.i*
output) you can send to the list?

Thanks,
-- 
Ricardo Anguiano
Mentor Graphics
+1-510-354-6774

On 6/13/2013 2:47 AM, Abdurahman Alfeky wrote:
> there is no chnagein source code , and there no use of __DATE__ or time macros , no regenerated headers and by looking into the output of objdump on object file which is compiled without debugging information i can see too many differences in assembly instructions. i heard about using -frandom-seed=string to avoid this but it is not clear how the compiler deal with it ?
>
> copied from man page "http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html"
>
>     |-frandom-seed=|string
>         This option provides a seed that GCC uses in place of random numbers in generating certain symbol names that have to be different in every compiled file. It is also used to place unique stamps in coverage data files and the object files that produce them. You can use the -frandom-seed option to produce reproducibly identical object files.
>
>         The string should be different for every file you compile
>
>
>
>
> On Thu, Jun 13, 2013 at 9:30 AM, David Brown <david at westcontrol.com <mailto:david at westcontrol.com>> wrote:
>
>     On 12/06/13 17:59, Abdurahman Alfeky wrote:
>      > Hi All ,
>      >
>      > Have anyone face the following problem before:
>      >
>      > Using the GCC compiler for ARM (windows) :
>      >
>      >     /arm-none-eabi-gcc.exe (Sourcery CodeBench Lite 2012.09-63) 4.7.2/
>      >     version
>      >
>      > I have got different object file produced every ~5 times i compiled the
>      > same source file.
>      >
>      > The optimization level 3 is used (aggressive) is used, compiler options
>      > used:
>      >
>      >     -O3 -mcpu=cortex-a8 -mfpu=neon -mfloat-abi=softfp -fshort-wchar
>      >     -fshort-enums  -funsafe-math-optimizations -mvectorize-with-neon-quad
>      >
>      > The dump of the different object files shows too many differences in
>      > assembly instructions , registers and addresses used.
>      >
>      >   *
>      >
>      >     Is it normal that compiler optimize/compile exactly the same source
>      >     file differently and produce different object files ?! is it a
>      >     compiler bug ?
>      >
>      >   *
>      >
>      >     How to avoid this behavior without turning off aggressive optimization ?
>      >
>      > Thanks
>      >
>
>     There are usually differences in the object file, because it includes
>     things like compilation date in the debugging information.  But I don't
>     think you should get differences in the actual generated code.  Are you
>     sure there is nothing changing, like headers, use of __DATE__ macros,
>     etc.?  Minor changes in the source code can sometimes lead to apparently
>     large changes in the object code such as different register choices or
>     different ordering of code (the behaviour of such code is identical, but
>     it can look very different).
>
>     If you are looking at the final linked code, then remember that the
>     order of the object files in the link can often affect the order of the
>     generated code.
>
>
>     _______________________________________________
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>
>
>
>
> --
> Abdurahman Alfeky,
> Software Engineer
>
>
>
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