Automatic dependency resolution on generated python file

DISCUSSION Kieran Bingham 2 participants 3 messages May 23, 2016 – Jun 21, 2016 Kbuild

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Kieran Bingham

author

2016-05-23 23:02 UTC #0 lore raw

Hi Kbuild / Michal,

I've been working through a problem that Jan has reported whereby if we modify a file included by our template for constants.py, the generated file is not rebuilt.

The rule/cmd [0] to generate the python constants is cmd_gen_constants_py which uses the $(CPP) with $(c_flags) to create the output.

One benefit of this is that it already creates the $(depfile) through the addition of the flags provided by $(c_flags), however as yet it would seem that my efforts to understand how the $(depfile) gets included have failed.

From what I can tell, the $(call if_changed...) rule is generating my targets .constants.py.cmd, but the .d file is not being utilised.

By swapping $(call if_changed, ) to $(call if_changed_dep,...) I can see that my .constants.py.cmd [1] file now has (apparently) correct dependency rules being generated. However they still don't take actual effect. If I 'touch/modify' one of the files I have added to the #includes, then my target is not rebuilt (I have added include/linux/kieran.h for testing this specifically without rebuilding all other objects)

I can see at the bottom of my .constants.py.cmd :
scripts/gdb/linux/constants.py: $(deps_scripts/gdb/linux/constants.py) $(deps_scripts/gdb/linux/constants.py):

which looks like it's doing the right thing to me ... except it's not actually allowing the rule to run if a dependency is updated.

Is this failing because it is being called from the top Kbuild, as part of making sure it is built after bounds.h, or is it because I'm not generating from the builtin rules?

I'm hoping perhaps I've missed a stage or something obvious that will make this automatic dependency resolution 'just-work' for recreating the constants file.

Signature · 9 lines

Regards

Kieran Bingham


[0]
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/scripts/gdb/linux/Makefile

[1] http://paste.ubuntu.com/16645481/

Michal Marek

2016-06-20 15:05 UTC #1 lore raw

Quoted 18 lines · Kieran Bingham

Hi Kbuild / Michal,
I've been working through a problem that Jan has reported whereby if we modify a file included by our template for constants.py, the generated file is not rebuilt.
The rule/cmd [0] to generate the python constants is cmd_gen_constants_py which uses the $(CPP) with $(c_flags) to create the output.
One benefit of this is that it already creates the $(depfile) through the addition of the flags provided by $(c_flags), however as yet it would seem that my efforts to understand how the $(depfile) gets included have failed.
From what I can tell, the $(call if_changed...) rule is generating my targets .constants.py.cmd, but the .d file is not being utilised.

Quoted 7 lines

By swapping $(call if_changed, ) to $(call if_changed_dep,...) I can see that my .constants.py.cmd [1] file now has (apparently) correct dependency rules being generated. However they still don't take actual effect. If I 'touch/modify' one of the files I have added to the #includes, then my target is not rebuilt (I have added include/linux/kieran.h for testing this specifically without rebuilding all other objects)

Hi Kieran,

sorry for the late reply. In case this is still relevant: For if_changed/if_changed_dep to work, you must list the target in the $(targets) list (without the $(obj) prefix) and add FORCE as a prerequisite of the rule.

Michal

Kieran Bingham

author

2016-06-21 22:03 UTC #2 lore raw

Quoted 27 lines · Michal Marek

Quoted 18 lines · Kieran Bingham
Hi Kbuild / Michal,
I've been working through a problem that Jan has reported whereby if we modify a file included by our template for constants.py, the generated file is not rebuilt.
The rule/cmd [0] to generate the python constants is cmd_gen_constants_py which uses the $(CPP) with $(c_flags) to create the output.
One benefit of this is that it already creates the $(depfile) through the addition of the flags provided by $(c_flags), however as yet it would seem that my efforts to understand how the $(depfile) gets included have failed.
From what I can tell, the $(call if_changed...) rule is generating my targets .constants.py.cmd, but the .d file is not being utilised.
Quoted 7 lines
By swapping $(call if_changed, ) to $(call if_changed_dep,...) I can see that my .constants.py.cmd [1] file now has (apparently) correct dependency rules being generated. However they still don't take actual effect. If I 'touch/modify' one of the files I have added to the #includes, then my target is not rebuilt (I have added include/linux/kieran.h for testing this specifically without rebuilding all other objects)

Quoted 3 lines

Hi Kieran,
sorry for the late reply.

No problem, still useful!

Quoted 4 lines

In case this is still relevant: For if_changed/if_changed_dep to work, you must list the target in the $(targets) list (without the $(obj) prefix) and add FORCE as a prerequisite of the rule.

Thankyou! - It works!

Now my generate rule is only called when it is supposed to be.

I'll hopefully get this fix sent in with the rest of my series by the weekend.

Quoted 1 line

Michal

Thankyou for your support

Signature · 3 lines

Regards

Kieran Bingham