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Date: Mon, 04 May 2015 10:37:52 +0200
From: Olivier MATZ <olivier.matz@6wind.com>
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To: "Wiles, Keith" <keith.wiles@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
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Subject: Re: [dpdk-dev] Compiling files with .S with GCC
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Hello,

On 04/26/2015 06:55 PM, Wiles, Keith wrote:
> 
> 
> On 4/26/15, 11:53 AM, "Wiles, Keith" <keith.wiles@intel.com> wrote:
> 
>> Hi All,
>>
>> I noticed in my builds with foo.S file I would get a warning from the
>> compiler the foo_s.o.tmp linker file will not be used as the code is not
>> linked. A strange error and the foo_s.o file would not be created. In the
>> mk/internal/rte.compile-pre.mk we have the following
>>
>> # command to assemble a .S file to generate an object
>> ifeq ($(USE_HOST),1)
>> S_TO_O = $(CPP) $(HOST_CPPFLAGS) $($(@)_CPPFLAGS) $(HOST_EXTRA_CPPFLAGS)
>> $< $(@).tmp && \
>>    $(HOSTAS) $(HOST_ASFLAGS) $($(@)_ASFLAGS) $(HOST_EXTRA_ASFLAGS) -o $@
>> $(@).tmp
>> S_TO_O_STR = $(subst ','\'',$(S_TO_O)) #'# fix syntax highlight
>> S_TO_O_DISP =  $(if $(V),"$(S_TO_O_STR)","  HOSTAS $(@)")
>> else
>> S_TO_O = $(CPP) $(CPPFLAGS) $($(@)_CPPFLAGS) $(EXTRA_CPPFLAGS) $< -o
>> $(@).tmp && \
>>    $(AS) $(ASFLAGS) $($(@)_ASFLAGS) $(EXTRA_ASFLAGS) -o $@ $(@).tmp
>> S_TO_O_STR = $(subst ','\'',$(S_TO_O)) #'# fix syntax highlight
>> S_TO_O_DISP =  $(if $(V),"$(S_TO_O_STR)","  AS $(@)")
>> endif
>>
>> I had to change the above Œ.tmp¹ strings to Œ.s¹ to remove this warning
>> and get the foo_s.o file created. Using the .s the file name becomes
>> foo_s.o.s
> 
> Compiler used on Ubuntu 14.04 'gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2'
> 
>>
>> Did not try this with clang or any other compiler, but I expect we can
>> safely change the Œ.tmp¹ to Œ.s¹ IMO
>>
>> Anyone else notice this problem?

I tested a similar use-case and I don't reproduce the issue.
I don't don't understand why replacing $(@).tmp by $(@).s would
solve it.

The file $(@).tmp is used as a temporary file to store the preprocessed
version of the $(@).s file. I agree that using the .s extension is not
a bad choice (see below), but to me it is not the proper solution to
your problem.

>>From https://gcc.gnu.org/onlinedocs/gcc/Overall-Options.html

  file.s
     Assembler code.
  file.S
  file.sx
     Assembler code that must be preprocessed.

Regards,
Olivier