linux-kernel - Re: {standard input}:136: Error: number (0x9000000080000000) larger than 32 bits

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Message-ID: <alpine.DEB.2.00.1604181724160.21846@tp.orcam.me.uk>
Date:	Mon, 18 Apr 2016 19:09:42 +0100
From:	"Maciej W. Rozycki" <macro@...tec.com>
To:	Ralf Baechle <ralf@...ux-mips.org>,
	Matthew Fortune <Matthew.Fortune@...tec.com>
CC:	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	kbuild test robot <fengguang.wu@...el.com>,
	Paul Burton <paul.burton@...tec.com>, <kbuild-all@...org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: {standard input}:136: Error: number (0x9000000080000000) larger
 than 32 bits

On Mon, 18 Apr 2016, Ralf Baechle wrote:

> I extracted a rather simple test case:
> 
> $ echo >> testcase .s << EOF
>         .set    mips3
>         dli     $2, 0x9000000080000000
> EOF
> $ mips-linux-as -mips3 -march=r4600 -o testcase.o testcase.s
> testcase.s: Assembler messages:
> testcase.s:2: Error: number (0x9000000080000000) larger than 32 bits
> $ mips-linux-as -mips4 -march=vr5000 -o testcase.o testcase.s
> $

 Ah, and if you use `.set mips4' instead, then the symptoms reverse.

 The thing is that to match some software's (such as ours) requirements an 
ISA override -- as a side effect -- relaxes ABI restrictions on certain 
operations.  E.g. the DLI macro and its 64-bit immediate argument are not 
valid in the o32 ABI.  When no actual override happens, such as with 
`-march=r4600' which already implies `mips3' for the ISA, the side effect 
is lost:

  /* The use of .set [arch|cpu]= historically 'fixes' the width of gp and fp
     registers based on what is supported by the arch/cpu.  */
  if (mips_opts.isa != prev_isa)

> I can trigger the error message with vanilla 2.25 and 2.26 but not 2.24.

 The regression has come with:

commit 919731affbef19fcad8dddb0a595bb05755cb345
Author: mfortune <matthew.fortune@...tec.com>
Date:   Tue May 20 13:28:20 2014 +0100

    Add MIPS .module directive

-- previously the side effect was unconditional, even if no ISA change 
resulted.

 Matthew, this functional change was not mentioned in the review: 
<https://sourceware.org/ml/binutils/2014-05/msg00179.html> -- what was the 
rationale behind it?  Do you expect any issues if we revert to old 
semantics?

  Maciej