Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 3 Nov 2015 10:44:11 -0600

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Hi Ben,

On 11/03/2015 08:30 AM, Benjamin Franksen wrote:
> There is one small problem in the build system (probably in all
> 3.15 versions) and it concerns dependency generation when a
> generated header file is included. This can cause error messages
> from gcc when using parallel make, such as
> 
>> ../builtin.c:11:17: fatal error: snl.h: No such file or
>> directory #include "snl.h"
>> 
>> compilation terminated.
> 
> The solution is to add -MG to the compiler flags when generating 
> dependencies (see the attached patch). According to the gcc man
> page, "-MG assumes missing header files are generated files and
> adds them to the dependency list without raising an error."

Your -MG solution assumes that we only use gcc to build Base, which is
not true for some targets, and it doesn't always result in the correct
dependency information being output.

The correct solution is to make snl.h an explicit dependency of the
builtin$(DEP) and any similar targets in your Makefile, for example:

...
include $(TOP)/configure/RULES

ifdef BASE_3_15
  builtin$(DEP): $(COMMON_DIR)/snl.h
endif

This tells GNUmake to create the snl.h file before trying to generate
the builtin.d file, which is where your errors are coming from.

You can see other examples in the std/filters/test/Makefile and
ioc/db/test/Makefile of Base-3.15, although they don't need to have
the version check in them. This is mentioned in the Release Notes
under the Parallel Builds heading.

Are you trying to fix Peter Heesterman's sequencer build problem? The
- -MG flag wouldn't help him anyway since he's building on Windows, but
the above $(DEP): fix should.

- - Andrew

- -- 
Light thinks it travels faster than anything but it is wrong.
No matter how fast light travels, it finds the darkness has
always got there first, and is waiting for it.
    -- Terry Pratchett, Reaper Man
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System