Messages in this thread | | | Date | Fri, 12 Oct 2012 11:24:43 -0600 | From | Stephen Warren <> | Subject | Re: dtc: import latest upstream dtc |
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On 10/10/2012 05:18 PM, David Gibson wrote: ... > And as stated elsewhere, cpp should be invoked with similar options to > the way it's done for asm files. A -D__DTS__ or something like that > would probably be a good idea too, just in case some .h needs to be > conditional on that.
Hmm. There are some problems here.
Right now, the command I proposed is basically:
$(CPP) -x c $< | dtc ...
Without "-x c", $(CPP) doesn't recognise the file extension of the input file, and defaults to assuming it's a linker script rather than an input file, even in pre-processing mode (CPP == $(CC) -E), which obviously doesn't work too well.
I chose "-x c" because *.dts syntax is closest to C.
However, related to your request above, "-x assembler" might be more appropriate, since this would presumably define __ASSEMBLY__, which is what the kernel headers currently use to determine whether to compile out anything other than #defines. However, executing $(CPP) -x assembler foo.dts yields a completely empty output! I'm not sure why that is yet.
I also tried passing to $(CPP) the exact same options that the kernel uses for compiling true assembly files, namely $(a_flags). Doing so would presumably provide complete compatibility in the pre-defined #defines between compiling *.S and *.dtsp, which would reduce the likelihood of needing to do anything different in *.h to support usage by both *.S and *.dtsp. (Note that I still need to pass a -x option, and the issue I described above still applies here too). This doesn't work out, because on ARM you get arch/arm/include/asm/unified.h force-included, which emits true assembly macros into the output, which obviously dtc can't parse. This could be avoided by editing that file to add #ifndef __DTS__ around the offending parts (and passing -D__DTS__ to $(CPP)), and that does appear to currently be the only file requiring a change. I wonder if using $(a_flags) is inviting more issues like this in the future though?
Given this, I'm not convinced we should try to make $(CPP) usage for *.dts too much like its usage for *.S. I agree it'd probably make sense to add -D__DTS__ to the command-line, but switching away from -x c or to using $(a_flags) seems like it'd increase the maintenance requirements rather than reduce them.
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