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MIPS multigot at linker

Rafael Martínez Torres rmartine@fdi.ucm.es
Thu Mar 27 13:43:00 GMT 2003 
Hi:

I apologize if this is not the list to deal with this. I'm a newbie and my
message may seem a bit fuzzy.

1.- gcc-2.95
=============
I'm running gcc-2.95.3 on mips-sgi-irix65. GNU Binutils then were not
supported at this platform, so this tar.gz was prepared to be integrated
with
native (as and ld) MipsPro .

My applcation runs finely when no "multigot" is invoked.

However , some times MipsPro ld invokes automatically MULTIGOT . As far as
I know, GOT ( Global Offset table) is a special way to access data using
economical 16-bit addressing mode, by using the $gp register pointing into
".sdata" region. MULTI-GOT splits this region into several ones when some
thing bigger than 64K is detected.

If I'm not wrong , "const struct" data are allocated inside "section
.rodata" in gcc-2.95 . When assembling and linking, this remains so:

nm foo

...
[22]	| 270909440|  266108|SECT |LOCL |DEFAULT  |MIPS_DATA|.rodata
[23]	| 271175552|   39236|SECT |LOCL |DEFAULT  |MIPS_DATA|.data
[136]	| 270909440|       0|SECT |GLOB |DEFAULT  |MIPS_DATA|fdata
[137]	| 270909440|       0|SECT |GLOB |DEFAULT  |MIPS_DATA|_fdata
...


Since no reference into ".sdata" and ".rsdata", it crashes when trying to
use MULTIGOT ( and may be GOT ? )

2.- gcc-3.0
====================================
gcc-3.0 solved this problem by allocating "const struct" into ".data"
instead of "section .rodata" .

diff foo.s.gcc-2.95	diff foo.s.gcc-3.0

>	.data
	.align	3
	.size	aMi_id34,16
	aMi_id34:
	.word	aMi_srt

>.section	.rodata
	.align	3
	.size 	aMi_id34,16
	aMi_id34:
	.word	aMi_srt

BTW, when

nm foo

[25]	| 271286272|   69268|SECT |LOCL |DEFAULT  |MIPS_DATA|.rodata
[26]	| 271355544|  236268|SECT |LOCL |DEFAULT  |MIPS_DATA|.data
[31]	| 271618896|       3|SECT |LOCL |DEFAULT  |MIPS_DATA|.srdata


A new region is included ...".srdata", this makes MULTIGOT run sucessfull.
May be gcc-2.95 doesn't handle $gp addressing properly ...



3.= WHAT I'M ASKING FOR
=========================

I need to run gcc-2.95/gcc-3.0 without GP/MULTIGOT addressing mode,
(hacking some piece
that needs to know if a pointer belongs to ".rodata" section ).


Which flag should apply to gcc ( or pass to MipsPro ld) to disable
MULTIGOT and GOT addressing mode...?

LARGE_GOT is discard.


Best Regards.

Rafael Martinez Torres . Univeridad Complutense de Madrid (Spain)
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