[Buildroot] Passing arguments to the linker when external toolchain is used.

[Arnout Vandecappelle <arnout@mind.be>]

On 23/11/12 14:04, Ronny Meeus wrote:
> Hello
>
> I'm using buildroot to build an environment for MIPS (Cavium).
> For this I use a 64 bit toolchain provided by Cavium as an external toolchain.
>
> My buildroot configuration is as follows:
> * Buildroot 2012.05
> * Target Architecture: MIPS (big endian)
> * Target Architecture Variant: mips 64
> * Target ABI: n32
> * glibc
>
> In my application we need to create partially linked objects that will
> be linked together in a final link step.
> I see that the correct options (ABI etc) are passed to the compiler
> via the ext-toolchain-wrapper construction, but for the linker this
> technique is not used. It is directly invoked without modifying the
> command line. If I want to create this partially linked file, I need
> to pass an extra option the linker to indicate that is needs to use
> the N32 abi (-melf32btsmipn32).

  First of all, I don't understand why ld needs any option that we normally
pass to the compiler.  Do the -march, -mtune and -mfpu options even work
in ld?

  That said, if you do need the CFLAGS, then perhaps you should use
'$(CC) -nostdlib' rather than $(LD) (and of course pass ld-specific
options using -Wl,...).

>
> To make this work, I needed to make 2 changes:
> - make the linker a link to the ext-toolchain-wrapper
> - change the ext-toolchain-wrapper so that it passes to options to the
> linker (currently the option is hardcoded but this needs to be changed
> so that the BR2_TARGET_LDFLAGS are used.

  Since not all gcc flags are supported by ld, I think it should be a
separate toolchain wrapper, specific for ld.  It can be generated from
the same source code, though (using ifdefs).


  Regards,
  Arnout

-- 
Arnout Vandecappelle                               arnout at mind be
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Essensium/Mind                                     http://www.mind.be
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