[Bug binutils/16177] New: R_ARM_COPY reloc generated for reference in writable section

[roland at gnu dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16177

            Bug ID: 16177
           Summary: R_ARM_COPY reloc generated for reference in writable
                    section
           Product: binutils
           Version: 2.25 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: roland at gnu dot org

When a writable input section (i.e. data) refers to a symbol defined in an
ET_DYN object, BFD ld for ARM targets generates a COPY dynamic reloc.  For
other targets like x86, this situation generates a plain data dynamic
reloc.  Gold for ARM also generates the plain data dynamic reloc.

I can't understand any rationale for generating a synthetic data object and
copy reloc for it in this situation.  A copy reloc is only appropriate when
the reference is from a read-only input section (e.g. from an instruction).

    $ cat data-ref.s
    .globl _start
        .p2align 4
    _start:
        bkpt

    .data
        .globl data_object
    object_reference:
        .long data_object
        .size object_reference,4
    $ cat libdata.s
        .data
        .globl data_object
        .type data_object, %object
        .size data_object, 4
    data_object:
          .long 123
    $ ./gas/as-new -o data-ref.o data-ref.s 
    $ ./gas/as-new -o libdata.o libdata.s
    $ ./ld/ld-new -shared -o libdata.so libdata.o
    $ ./ld/ld-new -o data-ref data-ref.o libdata.so
    $ readelf -r data-ref

    Relocation section '.rel.dyn' at offset 0x224 contains 1 entries:
     Offset     Info    Type            Sym.Value  Sym. Name
    100302bc  00000314 R_ARM_COPY        100302bc   data_object
    $ ./gold/ld-new -o data-ref-gold data-ref.o libdata.so
    $ readelf -r data-ref-gold

    Relocation section '.rel.dyn' at offset 0x190 contains 1 entries:
     Offset     Info    Type            Sym.Value  Sym. Name
    00009230  00000102 R_ARM_ABS32       00000000   data_object
    $

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