[Bug ld/29820] New: ld x86: -r should not define _TLS_MODULE_BASE_

[i at maskray dot me]

https://sourceware.org/bugzilla/show_bug.cgi?id=29820

            Bug ID: 29820
           Summary: ld x86: -r should not define _TLS_MODULE_BASE_
           Product: binutils
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: i at maskray dot me
  Target Milestone: ---

cat > a.s <<eof
leaq _TLS_MODULE_BASE_@tlsdesc(%rip), %rax
call *_TLS_MODULE_BASE_@tlscall(%rax)
movl %fs:a@dtpoff(%rax), %edx
addl %fs:b@dtpoff(%rax), %edx

.section .tbss
.zero 8
a:
.zero 4
b:
.zero 4
eof
cc -c a.s
ld.bfd -r a.o a.o -o a.ro
ld.bfd a.ro

The -r link should not define _TLS_MODULE_BASE_.

% readelf -Ws a.ro
    12: 0000000000000000     0 TLS     LOCAL  DEFAULT    3 _TLS_MODULE_BASE_

Since ld currently does define _TLS_MODULE_BASE_, the final output has two
local 
_TLS_MODULE_BASE_ and the relaxation result is incorrect.

% objdump -d a.out
...
0000000000401000 <.text>:
  401000: 48 c7 c0 e0 ff ff ff          movq    $-0x20, %rax          #####
should be $0x0
  401007: 66 90                         nop
  401009: 64 8b 90 e8 ff ff ff          movl    %fs:-0x18(%rax), %edx
  401010: 64 03 90 ec ff ff ff          addl    %fs:-0x14(%rax), %edx
  401017: 48 c7 c0 e0 ff ff ff          movq    $-0x20, %rax          #####
should be $0x0
  40101e: 66 90                         nop
  401020: 64 8b 90 f8 ff ff ff          movl    %fs:-0x8(%rax), %edx
  401027: 64 03 90 fc ff ff ff          addl    %fs:-0x4(%rax), %edx

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