[Buildroot] ccache problem when compiling with different toolchains in different projects

[Danomi Manchego]

On Fri, Apr 19, 2013 at 4:54 PM, Arnout Vandecappelle <arnout at mind.be>wrote:

> On 19/04/13 13:41, Mathias De Maré wrote:
>
>>
>> wouldn't an alternative possibility be to change the CCACHE_COMPILERCHECK
>> to:
>> export CCACHE_COMPILERCHECK=%**compiler% -v
>>
>> You don't rely on the timestamp that way, but you still have a check. I
>> believe this resolves the clearing of ccache also (see also
>> http://lists.busybox.net/**pipermail/buildroot/2012-**March/051187.html<http://lists.busybox.net/pipermail/buildroot/2012-March/051187.html>).
>>
>
>  That sounds like a very good idea!
>
>  It still has a few shortcomings, but it's definitely better than the
> current situation. At least the following are not solved yet.
>
> - Options included in the external toolchain wrapper are not included. For
> instance, if you switch to Thumb on the Sourcery ARM toolchain, that will
> be recorded in the additional cflags in the wrapper and won't be visible to
> ccache.
>
> - The output of gcc -v contains the absolute path, so if you change the
> output directory (or share the ccache between several developers) it won't
> work. But it would be feasible to strip off the $(O) part.
>
> - For internal/crosstool-NG toolchains, when toolchain parameters are
> changed this is still not detected. For instance, some configure script
> checks for wchar, it fails, you change your configuration to include WCHAR
> and rebuild, and it still fails because the cached test is used...
>


I think that the "%**compiler% -v" suggestion is definitely more robust
that the current "none" setting, and my CCACHE_HASHDIR idea.  Glad I asked!

Regarding the settings hidden by the ext-toolchan wrapper and the built
toolchain configuration options - what if we took a hash of the
ext-toolchain wrapper or built compiler itself, and the -v info, and used
that directly in the ccache check.  We could do a one-time hash when the
toolchain is set up:

    $(TARGET_CC_NOCCACHE) -v > $(STAMP_DIR)/toolchain-config-info
    md5sum -b $(TARGET_CC_NOCCACHE) >> $(STAMP_DIR)/toolchain-config-info
    md5sum $(STAMP_DIR)/toolchain-config-info >
$(STAMP_DIR)/toolchain-config-info.md5sum

and then set the CCACHE_COMPILERCHECK to "echo
$(STAMP_DIR)/toolchain-config-info.md5sum".  Then, the effects of all the
hidden variables are in some way accounted for without grepping for them in
the .config.

Is that crazy talk?

Danomi -
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