Re: non-conformant ELF symbol table on MIPS?

[Jan Beulich <jbeulich@suse.com>]

On 27.07.2023 21:28, Maciej W. Rozycki wrote:
> On Thu, 27 Jul 2023, Jan Beulich wrote:
> 
>> extending the gas elf/common3.s testcase (in the context of trying to fix
>> PR gas/30688) to
>>
>> 	.comm foobar,30,4
>> 	.comm buf1, 5-1, 8
>> 	.comm buf2, 4, 9-1
>> 	.lcomm lbuf, 9-1
>>
>> I notice a violation of the ELF spec on most (all?) MIPS targets I would
>> routinely test for common code changes: "lbuf" is emitted last in the
>> symbol table. The spec is quite clear: "In each symbol table, all
>> symbols with STB_LOCAL binding precede the weak and global symbols." I
>> guess I want/need to xfail that test for mips*-*-* for the time being,
>> but it would be nice if you could shed some light on this behavior.
> 
>  Which specific MIPS target is it?

Among the 9 I test, it's mips-unknown-elf, mipsisa32r2el-unknown-elf,
mips-sgi-irix6, and mipstx39-unknown-elf.

>  There are two kinds of MIPS targets, ones that use the older IRIX symbol 
> sorting rules and ones that use the newer "traditional" symbol sorting 
> rules.  The IRIX symbol sorting rules mandate that section symbols precede 
> all other symbols, see e.g. bfd/elf32-mips.c:mips_elf_sym_is_global.  
> Mind that SGI was an early adopter of the ELF standard and things weren't 
> as settled as they are nowadays, hence e.g. the odd solution for composed 
> relocations with the n64 psABI (later n32 uses standard ELF gABI ones) and 
> other peculiarities here and there.
> 
>  Determining whether a MIPS target uses the IRIX emulation is complex, see 
> e.g. how binutils/testsuite/binutils-all/mips/mips.exp sets `irixemul'.  
> If you provide me with test case details (input and output), then I may be 
> able to give you further advice,

I've provided you the input (see context above), and you'll be able to
generate the object file from it yourself. But I don't see what this
would bring, when you already indicate that this is "expected" behavior.

> but otherwise you may want to mark the 
> test case with `notarget' or suchlike rather than `xfail', because that's 
> not a bug with the backend that the symbol ordering varies.

I'm okay making mips*-*-irix* "notarget", but I don't view this as
appropriate for e.g. mips*-unknown-elf. Instead I would prefer leaving
further tweaking (if so needed) to you. The immediate goal is to get a
regression fix (with an accompanying extension to a testcase) in
quickly, such that hopefully Nick would still be able to pick it up for
2.41 (as in principle it affects most if not all targets).

Jan