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SubjectRe: Better way to force a rebuild
On Wed, Dec 10, 2008 at 02:48:35PM -0500, Steven Rostedt wrote:
> Hi,
> In include/linux/kernel.h I currently have the following lines at the
> bottom of the file:
> /* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */
> #endif
> This is only there to force a rebuild of all files when
> CONFIG_FTRACE_MCOUNT_RECORD is modified. Since the modification of that
> config causes the build to act different, we need to rebuild all C
> objects. I added the #ifdef in kernel.h as a hack to force the rebuild by
> the config dependencies used in kbuild.
> My question is, is there a better way to force a full rebuild on a
> modification of a config?

Why is that hack required in the first place?
We rebuild if:
- target file is missing (not the case here)
- any prerequisite files are newer than target (not the case here)
- any CONFIG_* options used by any prerequisite has changed (not the case here)
[It is due to your hack]
- gcc changed (not the case here)
- options are added/deleted to gcc (this should be the case for relevant files)

Looking a bit deeper into this.
I see that we have in

define rule_cc_o_c
$(call echo-cmd,checksrc) $(cmd_checksrc) \
$(call echo-cmd,cc_o_c) $(cmd_cc_o_c); \
$(cmd_modversions) \

So you want everyting to be rebuild if the command above changes.
That should be doable - and it is indeed a bug that we do not do so.
The integration of record_mcount needs to be improved.


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