[Bug binutils/26907] New: objcopy gives memsiz to segment containing empty SHT_NOBITS section

[jozef.l at mittosystems dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=26907

            Bug ID: 26907
           Summary: objcopy gives memsiz to segment containing empty
                    SHT_NOBITS section
           Product: binutils
           Version: 2.36 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: jozef.l at mittosystems dot com
  Target Milestone: ---

Created attachment 12971
  --> https://sourceware.org/bugzilla/attachment.cgi?id=12971&action=edit
bss_lma_adjust.s

Consider a linker script that allows .text, .data and .bss to reside in the
same segment.

When an empty .bss section resides between non-empty .text and .data sections
in the linked output file, an objcopy of this output file adjusts the sh_offset
of the .bss section, and gives the segment containing it positive size.

The segment layout of the linked output file is:

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000001000 0x0000000000000000 0x0000000000000000
                 0x000000000000003a 0x000000000000003a  RWE    0x1000
  LOAD           0x0000000000000038 0x0000000000000038 0x0000000000000038
                 0x0000000000000000 0x0000000000000000  RW     0x1000

 Section to Segment mapping:
  Segment Sections...
   00     .text .note.gnu.property .bss .data
   01     .bss

The two instances of the empty .bss is potentially a red flag itself.

After running objcopy, memsiz of the second segment increase from 0 to 2 bytes,
along with the aforementioned change in sh_offset.

I've attached a linker script and assembly file that reproduces the bug.

$(AS) bss_lma_adjust.s
$(LD) a.out -o before.out -T bss_lma_adjust.ld
$(OBJCOPY) before.out after.out

> objcopy: after.out: section .bss lma 0x38 adjusted to 0x3a

Note that the assignment to '.' in .bss is required to reproduce the issue (any
assignment to '.' will do).

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