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Re: More ARM binutils fuckage


On 12/7/06, Nicolas Pitre <nico@cam.org> wrote:
There is the "toolchain", ant there is the "compiler".  The kernel only
needs a "compiler" (well and a linker of course).  You don't need glibc
to compile a kernel. The compiler can select between both ABIs at
runtime.  At least enough of the ABI differences the kernel cares about
can be selected at runtime.  So any gcc with EABI support can do
regardless of how it was configured.

Judging from the code in gcc/config/arm/arm.c (prefaced with "This has now turned into a maze"), completely specifying the code generation parameters involves: -march -mcpu (overrides -march, with a warning if they conflict) -mtune (overrides tunings implied by -march and -mcpu, but does not alter the __ARM_ARCH_xxx__ macro) or if none of the above are specified, interworking, thumb, and mode26/32 selectors, which can result in selection of a different CPU tuning from the compile-time default; followed by some more Thumb, PIC, and frame register related flags, and then: -mabi -mfpe -mfpu -mfloat-abi -mtp followed by structure alignment and the choice of PIC register. Endianness seems to be handled elsewhere, and aliases like -macps and -msoft-float appear to be mapped into the above.

The OABI build of 2.6.19 that I just did has (among others):
   -macps -mabi=apcs-gnu -march=armv5te -mtune=xscale
-Wa,-mcpu=xscale  -msoft-float
It does not have FPE, FPU, and TP selectors.  Does this mean that I
get the compiler's default float format (FPA vs. VFP)?  Are the FPE
and TP selectors irrelevant to kernel compilation?

Cheers,
- Michael

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