[Bug gas/28762] New: [z80-unknown-elf-as]: assembly fails, but fixed with a blank line

[petemoore at gmx dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=28762

            Bug ID: 28762
           Summary: [z80-unknown-elf-as]: assembly fails, but fixed with a
                    blank line
           Product: binutils
           Version: 2.36.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: petemoore at gmx dot net
                CC: nickc at redhat dot com, sergey.belyashov at gmail dot com
  Target Milestone: ---

Created attachment 13898
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13898&action=edit
Bogus assembly failure fixed by introduction of arbitrary whitespace

Attached (rom1.s) is valid assembly code that won't assemble under
z80-unknown-elf-as version 2.36.1 on macOS and Linux, yet will assemble with
the introduction of almost any (innocuous) change, including non-code changes
such as a blank line or a .global directive, anywhere above the reported
failure line (10290) of the source code.

Since the bogus failure disappears if I delete lines, it is difficult to
provide a smaller test case than the full file. However, since I've been able
to reproduce it independently on both macOS and Linux, I assume it is nothing
to do with my environment, and it should be reasonably easy to reproduce with
the exact version of the attached file.

To reproduce, download the attached file rom1.s, and run the following:

```
$ # Gas version
$ z80-unknown-elf-as --version
GNU assembler (GNU Binutils) 2.36.1
Copyright (C) 2021 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 `z80-unknown-elf'.
$ z80-unknown-elf-as rom1.s
rom1.s: Assembler messages:
rom1.s:10290: Error: bad instruction syntax
$ # Insert blank line at top of file...
$ (echo; cat rom1.s) > rom1_fixed.s
$ # Assembly now passes, despite no code change!
$ z80-unknown-elf-as rom1_fixed.s
$ echo $?
0
$ # Show the lines around the reported failure...
$ sed -n 10287,10293p rom1.s

randomize:
        CALL    find_int2                 ; routine FIND-INT2 puts parameter in
BC.
        LD      A,B                       ; test this
        OR      C                         ; for zero.
        JR      NZ,rand_1                 ; forward to RAND-1 if not zero.

$ 
```

As you see above, the failure "rom1.s:10290: Error: bad instruction syntax"
appears to be bogus, since the instruction "LD A,B" is valid, and as shown in
the console output above, just inserting a blank line at the top of the file
fixes the issue.

I haven't yet tried assembling with z80-unknown-elf-as version 2.37, I can do
that too, if that is useful.

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