[Bug ld/16017] LD creates invalid PLT instructions on CORTEX-M3

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16017

--- Comment #31 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot 
gnu.org> ---
The binutils-2_34-branch branch has been updated by Tamar Christina
<address@hidden>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=aaf3f0599a210699a76767c07a7d7f62d7633d71

commit aaf3f0599a210699a76767c07a7d7f62d7633d71
Author: Tamar Christina <address@hidden>
Date:   Wed Apr 1 10:47:18 2020 +0100

    Arm: Fix LSB of GOT for Thumb2 only PLT.

    When you have a Thumb only PLT then the address in the GOT for PLT0 needs
to
    have the Thumb bit set since the instruction used in PLTn to get there is
    `ldr.w  pc` which is an inter-working instruction:

    the PLT sequence in question is

    00000120 <foo@plt>:
     120:   f240 0c98       movw    ip, #152        ; 0x98
     124:   f2c0 0c01       movt    ip, #1
     128:   44fc            add     ip, pc
     12a:   f8dc f000       ldr.w   pc, [ip]
     12e:   e7fc            b.n     12a <foo@plt+0xa>

    Disassembly of section .text:

    00000130 <bar>:
     130:   b580            push    {r7, lr}
     132:   af00            add     r7, sp, #0
     134:   f7ff fff4       bl      120 <foo@plt>

    and previously the linker would generate

    Hex dump of section '.got':
     ...
      0x000101b8 40010100 00000000 00000000 10010000 @...............

    Which would make it jump and transition out of thumb mode and crash since
you
    only have thumb mode on such cores.

    Now it correctly generates

    Hex dump of section '.got':
     ...
      0x000101b8 40010100 00000000 00000000 11010000 @...............

    Thanks to Amol for testing patch and to rgujju for reporting it.

    bfd/ChangeLog:

            PR ld/16017
            * elf32-arm.c (elf32_arm_populate_plt_entry): Set LSB of the PLT0
            address in the GOT if in thumb only mode.

    ld/ChangeLog:

            PR ld/16017
            * testsuite/ld-arm/arm-elf.exp (thumb-plt-got): New.
            * testsuite/ld-arm/thumb-plt-got.d: New test.

    (cherry picked from commit a7618269b727da9cf56727c22cb538ff5f0e4d25)
    (cherry picked from commit 3ce23ca1de4c769c4b7247f0724a10ef5fb24a11)

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