Re: [PATCH 10/20] MIPS/GAS: Fail on 64-bit addresses used with LI

[Richard Sandiford <rdsandiford@googlemail.com>]

"Maciej W. Rozycki" <macro@codesourcery.com> writes:
> On Tue, 7 Dec 2010, Richard Sandiford wrote:
>> Not OK.  This trivially triggers for:
>> 
>> 	li.d	$f2,1.1
>> 
>> assembled with -mabi=64 -G0.
>
>  And rightfully so, broken code is produced:
>
> $ cat li_d.s
> 	li.d	$f2, 1.1
> $ mips-sde-elf-as -mabi=64 -G0 -o li_d.o li_d.s
> $ mips-sde-elf-ld -m elf64btsmip -e0 -o li_d li_d.o
> $ mips-sde-elf-objdump -dt li_d
>
> li_d:     file format elf64-tradbigmips
>
> SYMBOL TABLE:
> 0000000120000078 l    d  .MIPS.options	0000000000000000 .MIPS.options
> 0000000120000078 l    d  .text	0000000000000000 .text
> 0000000120000080 l    d  .rodata	0000000000000000 .rodata
> 0000000120010088 g       .rodata	0000000000000000 _fdata
> 0000000120018080 g       *ABS*	0000000000000000 _gp
> 0000000120000078 g       .text	0000000000000000 _ftext
> 0000000120010088 g       *ABS*	0000000000000000 __bss_start
> 0000000120010088 g       *ABS*	0000000000000000 _edata
> 0000000120010088 g       *ABS*	0000000000000000 _end
> 0000000120010088 g       *ABS*	0000000000000000 _fbss
>
>
>
> Disassembly of section .text:
>
> 0000000120000078 <_ftext>:
>    120000078:	3c012000 	lui	at,0x2000
>    12000007c:	d4220080 	ldc1	$f2,128(at)
> $
>
> I don't think the code above gets at .rodata, do you?

You're just repeating what the FIXME already says: that the code doesn't
work correctly with addresses whose values exceed the 32-bit range.
I wasn't disputing that.

>  With some tweaking we should be able to reuse code from M_L_DAB to handle 
> this case (i.e. jump to there with some prearrangements), but I may not 
> have the time to implement this stuff properly now.  Why do you think 
> silently making broken code is better than signalling an internal error 
> (which it is) here?

An assertion failure is also a bug.  Assertion failures are for
conditions that we think should never occur, so we shouldn't add
an assertion failure for a condition that is known to trigger.
We should either fix the FIXME or issue a proper diagnostic.

Richard