Bug 31319

Summary: [2.42 regression]: `.arch i386` is rejected by `x86_64` target: 4bit mode not supported on `i386'.
Product: binutils Reporter: Sergei Trofimovich <slyich>
Component: gasAssignee: Not yet assigned to anyone <unassigned>
Status: RESOLVED NOTABUG    
Severity: normal CC: jbeulich
Priority: P2    
Version: unspecified   
Target Milestone: ---   
Host: Target:
Build: Last reconfirmed: 2024-01-31 00:00:00
Attachments: entry32-16-debug.s

Description Sergei Trofimovich 2024-01-30 22:46:31 UTC 
Created attachment 15346 [details]
entry32-16-debug.s

Initially observed the failure on kexec-tools-2.0.27 package at https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git/tree/purgatory/arch/i386/entry32-16-debug.S#n28

Attached self-contained `entry32-16-debug.s` file.

binutils-2.40 and 2.41 worked:

    $ as-2.40  --64 -o entry32-16-debug.o entry32-16-debug.s
    # ok

binutils-2.42 fails as:

    $ as-2.42 --64 -o entry32-16-debug.o entry32-16-debug.s
    purgatory/arch/i386/entry32-16-debug.S: Assembler messages:
    purgatory/arch/i386/entry32-16-debug.S:28: Error: 64bit mode not supported on `i386'.

$ as --version
GNU assembler (GNU Binutils) 2.42
Copyright (C) 2024 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or later.
This program has absolutely no warranty.
This assembler was configured for a target of `x86_64-unknown-linux-gnu'.

Configured as:

--prefix=/<<NIX>>/binutils-2.42 --bindir=/<<NIX>>/binutils-2.42/bin --sbindir=/<<NIX>>/binutils-2.42/sbin --includedir=/<<NIX>>/binutils-2.42-dev/include --oldincludedir=/<<NIX>>/binutils-2.42-dev/include --mandir=/<<NIX>>/binutils-2.42-man/share/man --infodir=/<<NIX>>/binutils-2.42-info/share/info --docdir=/<<NIX>>/binutils-2.42/share/doc/binutils --libdir=/<<NIX>>/binutils-2.42-lib/lib --libexecdir=/<<NIX>>/binutils-2.42-lib/libexec --localedir=/<<NIX>>/binutils-2.42-lib/share/locale --enable-64-bit-bfd --with-system-zlib --enable-deterministic-archives --disable-werror --enable-fix-loongson2f-nop --enable-new-dtags --program-prefix= --disable-gprofng --with-lib-path=: --enable-gold --enable-plugins --enable-shared --disable-static --build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu --target=x86_64-unknown-linux-gnu
Comment 2 Jan Beulich 2024-01-31 09:33:26 UTC 
So this is precisely the case that the new behavior is intended to catch: It is meaningless to restrict ISA to i386 when trying to build 64-bit code. In the kexec example, the .code32 comes too late anyway (would have wanted to be at least before the label already before); wants moving ahead of the .arch.

IOW for now I view this as neither a bug nor a regression; earlier gas simply was to lax. I'm open to be convinced otherwise ...
Comment 3 Sergei Trofimovich 2024-01-31 09:46:33 UTC 
Aha, adapting kexec-tools sounds fine as well.

Does the `.code16` use look fine in the rest of the file?

SO far I made it build as:

--- a/entry32-16-debug.s
+++ b/entry32-16-debug.s
@@ -18,10 +18,10 @@
  .globl entry16_debug_pre32
  .globl entry16_debug_first32
  .globl entry16_debug_old_first32
+ .code32
  .arch i386
  .balign 16
 entry16_debug:
- .code32

  call 1f
 1: popl %ebx

Does it look about right?
Comment 4 Jan Beulich 2024-01-31 10:07:29 UTC 
(In reply to Sergei Trofimovich from comment #3)
> Aha, adapting kexec-tools sounds fine as well.
> 
> Does the `.code16` use look fine in the rest of the file?

They're all okay, as there's no other .arch directive. Ordering there would be a problem only if you had e.g. ".arch i286" ahead of ".code16".

> SO far I made it build as:
>[...]
> Does it look about right?

Yes.
Comment 5 Sergei Trofimovich 2024-01-31 10:23:55 UTC 
Thank you!

Proposed kexec-tools fix as http://lists.infradead.org/pipermail/kexec/2024-January/029349.html

Let's close as NOTABUG.