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[Bug gas/20364] New: Data-based padding causes current address evaluatio

From: contact at paulk dot fr
Subject: [Bug gas/20364] New: Data-based padding causes current address evaluation to be non-constant on aarch64
Date: Wed, 13 Jul 2016 08:30:00 +0000


            Bug ID: 20364
           Summary: Data-based padding causes current address evaluation
                    to be non-constant on aarch64
           Product: binutils
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: contact at paulk dot fr
  Target Milestone: ---

It appears that starting with binutils 2.26, evaluating the current address
(using the dot symbol) after a .align directive using data-based padding (e.g.
.align 6, 0) makes it non-constant, resulting in errors such as: "Error:
non-constant expression in ".if" statement" when evaluating "." inside an .if
statement. This is on aarch64.

The issue appeared when build the ARM Trusted Firmware:

The related assembly is a combination of the vector_entry/vector_base (that
does the alignment) and check_vector_size (that uses the dot symbol) macros,
defined at:
and used at

The assembly is correct and is apparently not the problem. However, switching
the ".align x, 0" directives to ".align x" solves the issue, but upstream is
not going to make that change.

The issue was discussed in depth at
and an issue was opened on the ARM Trusted Firmware tracker at

A test case was provided at

The issue was bisected down to (bad) commit

commit c1baaddf8861aea666b84baeb4746caff51a579d
Author: Renlin Li <address@hidden>
Date:   Thu Apr 2 14:59:45 2015 +0100

    [AArch64] Emit DATA_MAP in order within text section

    2015-03-27  Renlin Li  <address@hidden>

      * config/tc-aarch64.c (mapping_state): Emit MAP_DATA within text
section in order.
      (mapping_state_2): Don't emit MAP_DATA here.
      (s_aarch64_inst): Align frag during state transition.
      (md_assemble): Likewise.

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