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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH, RFC] Smarter compilation for target devices
Date: Tue, 28 Apr 2009 14:32:41 +0100
References: <f43fc5580904221234l22c4e5f8h7362e8e9adee0b49@mail.gmail.com>
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To: qemu-devel@nongnu.org
Cc: Blue Swirl <blauwirbel@gmail.com>

> Compile target devices only once for each endian and word size combination,
> saving a few compiles if large number of targets are enabled.

> +CPPFLAGS=-I. -I.. -I$(SRC_PATH) -MMD -MT $@ -MP -DNEED_CPU_H

> +# Warning: Do not add new files here if they have conditional code
> +# with #ifdef TARGET_xxx etc, use TARGET_PAGE_SIZE or reference
> +# CPUState

This is just asking for trouble. Anything that includes cpu.h must be rebuilt 
for every cpu.  IMO a necessary prerequisite for this change is reworking 
header files so that you can't accidentally use the wrong symbols.

Also, which bitwidth are you intending to distinguish here? target_ulong or 
target_phys_addr_t? With a few exceptions, devices don't care about the 
former. Duplicating this logic is both cpu.h and configure is also asking for 
trouble. At minimum the build should fail if they disagree.

Paul