Re: [PATCH 0/1] MIPS SDE-compatible bare metal target

["Yann E. MORIN" <yann dot morin dot 1998 at anciens dot enib dot fr>]

On Monday 26 September 2011 00:49:15 Kevin Cernekee wrote:
> I ran into a couple of semi-obscure issues linking objects generated
> from the mips-unknown-elf sample toolchain into a program built with
> Sourcery G++ (now Sourcery CodeBench), and I wanted to pitch the idea of
> including an SDE-compatible sample config in the release.
> 
> I have not performed enough testing to be confident that I know about
> all of the changes needed for 100% SDE compatibility, but maybe this
> will get the ball rolling and somebody more knowledgeable can help fill
> in the gaps...
> 
> Problem #1:
> 
> mips-unknown-elf uses SGI-compatible symbol ordering:
[--SNIP--]
> In SGI mode, sh_info in the symtab's section header entry points to line
> 18.
> 
> By contrast, a copy of binutils that had been built as an SDE or Linux
> toolchain assumes that sh_info points to the first global symbol, and
> that all local symbols (such as $LC0) have an index lower than sh_info
> (in this case, 20):
[--SNIP--]
> A non-SGI ld may report the former case as a malformed object file:
> 
> mipsel-linux-ld: error: _fixunssfsi-sgi.o contains a reloc
> (0x0000000000001705) for section .text that references a non-existent
> global symbol
> mipsel-linux-ld: final link failed: Bad value
> 
> Fix: use "sde" instead of "unknown" for CT_TARGET_VENDOR.  If the tuple
> is mips-sde-elf, binutils will disable the SGI/IRIX quirks.

Oh, so we have a case where the vendor part of the tuple *is* actually
meaningful. Sigh...

> Problem #2:
> 
> In my test runs, CT_CC_GCC_ENABLE_TARGET_OPTSPACE caused libgcc to be
> built with the MIPS SDA data model.  i.e. it assumes that $gp always
> points to a "small data area" which can access items in the .sdata and
> .sbss sections using just a signed 16-bit offset.  Many embedded
> programs do use SDA, but some do not and this could cause
> incompatibilities.
> 
> Fix: disable CT_CC_GCC_ENABLE_TARGET_OPTSPACE

OK.

Thank you for documenting all of this. :-)

Regards,
Yann E. MORIN.

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