[Bug ld/28393] New: aarch64 ld: assertion fail at elfnn-aarch64.c:5084 with weak undef tlsdesc symbol

[acoplan at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28393

            Bug ID: 28393
           Summary: aarch64 ld: assertion fail at elfnn-aarch64.c:5084
                    with weak undef tlsdesc symbol
           Product: binutils
           Version: 2.38 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: acoplan at gcc dot gnu.org
  Target Milestone: ---

The following assembly causes the linker to hit an assertion failure and then
segfault:

$ cat t.s
.global _start
.weak   x
_start:
adrp    x0, :tlsdesc:x
$ gas/as-new t.s -o t.o
$ ld/ld-new t.o
ld/ld-new: BFD (GNU Binutils) 2.37.50.20210928 assertion fail
elfnn-aarch64.c:5084
Segmentation fault (core dumped)

The backtrace is:

(gdb) bt
#0  bfd_assert (file=0x55555584a3cb "elfnn-aarch64.c", line=5084) at
/home/alecop01/toolchain/src/binutils-gdb/bfd/bfd.c:1649
#1  0x0000555555600006 in dtpoff_base (info=0x555555aa9040 <link_info>) at
elfnn-aarch64.c:5084
#2  0x0000555555604cf6 in elf64_aarch64_relocate_section
(output_bfd=0x555555ac14b0, info=0x555555aa9040 <link_info>,
input_bfd=0x555555addd10, input_section=0x555555ae0258, contents=0x555555ad97a0
"\200", relocs=0x555555ae16e0, local_syms=0x555555ad9810,
    local_sections=0x555555adfcd0) at elfnn-aarch64.c:7064
#3  0x000055555564c5ef in elf_link_input_bfd (flinfo=0x7fffffffd700,
input_bfd=0x555555addd10) at
/home/alecop01/toolchain/src/binutils-gdb/bfd/elflink.c:11427
#4  0x000055555564f745 in bfd_elf_final_link (abfd=0x555555ac14b0,
info=0x555555aa9040 <link_info>) at
/home/alecop01/toolchain/src/binutils-gdb/bfd/elflink.c:12617
#5  0x00005555555ae503 in ldwrite () at
/home/alecop01/toolchain/src/binutils-gdb/ld/ldwrite.c:545
#6  0x00005555555aadfc in main (argc=2, argv=0x7fffffffd968) at
/home/alecop01/toolchain/src/binutils-gdb/ld/ldmain.c:513

The assembly here is motivated by GCC's output for the following C testcase:

$ cat t.c
extern __attribute((weak)) __thread int x;
void _start(void) { x = 1; }
$ ./aarch64-linux-gnu-gcc t.c -fpic -nostdlib
/home/alecop01/toolchain/build-aarch64-linux-gnu/install/bin/../lib/gcc/aarch64-linux-gnu/12.0.0/../../../../aarch64-linux-gnu/bin/ld:
BFD (7f92ed6b41c441ab2111c9f1212cbbc13222edcc) 2.37.50.20210927 assertion fail
elfnn-aarch64.c:5084
collect2: fatal error: ld terminated with signal 11 [Segmentation fault], core
dumped
compilation terminated.
$ ./aarch64-linux-gnu-gcc t.c -fpic -nostdlib -c -S -o -
        .arch armv8-a
        .file   "t.c"
        .text
        .align  2
        .global _start
        .type   _start, %function
_start:
.LFB0:
        .cfi_startproc
        stp     x29, x30, [sp, -16]!
        .cfi_def_cfa_offset 16
        .cfi_offset 29, -16
        .cfi_offset 30, -8
        mov     x29, sp
        adrp    x0, :tlsdesc:x
        ldr     x1, [x0, #:tlsdesc_lo12:x]
        add     x0, x0, :tlsdesc_lo12:x
        .tlsdesccall    x
        blr     x1
        mrs     x1, tpidr_el0
        add     x0, x1, x0
        mov     w1, 1
        str     w1, [x0]
        nop
        ldp     x29, x30, [sp], 16
        .cfi_restore 30
        .cfi_restore 29
        .cfi_def_cfa_offset 0
        ret
        .cfi_endproc
.LFE0:
        .size   _start, .-_start
        .weak   x
        .ident  "GCC: (d06dc8a2c73735e9496f434787ba4c93ceee5eea) 12.0.0
20210927 (experimental)"
        .section        .note.GNU-stack,"",@progbits

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