https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64697
jon.turney at dronecode dot org.uk changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jon.turney at dronecode dot
org.uk
--- Comment #21 from jon.turney at dronecode dot org.uk ---
I looked into this a bit, as gdb 9.0 now uses thread_local in a way which trips
over this.
I came up with a slightly simpler reproduction:
$ cat def.h
extern thread_local int tlv;
$ cat def.cc
#include "def.h"
thread_local int tlv;
$ cat use.cc
#include "def.h"
int main()
{
tlv = 1;
}
$ x86_64-pc-cygwin-gcc def.cc use.cc --save-temps
/tmp/ccMAKHhL.o:use.cc:(.text$_ZTW3tlv[_ZTW3tlv]+0x15): relocation truncated to
fit: R_X86_64_PC32 against undefined symbol `TLS init function for tlv'
collect2: error: ld returned 1 exit status
This compiles without error with x86_64-w64-mingw32-gcc.
Looking at use.s:
.file "use.cc"
.text
.section .text$_ZTW3tlv,"x"
.linkonce discard
.globl _ZTW3tlv
.def _ZTW3tlv; .scl 2; .type 32; .endef
.seh_proc _ZTW3tlv
_ZTW3tlv:
.LFB1:
pushq %rbp
.seh_pushreg %rbp
movq %rsp, %rbp
.seh_setframe %rbp, 0
subq $32, %rsp
.seh_stackalloc 32
.seh_endprologue
movq .refptr._ZTH3tlv(%rip), %rax
testq %rax, %rax
je .L2
call _ZTH3tlv
.L2:
movq .refptr.__emutls_v.tlv(%rip), %rcx
call __emutls_get_address
addq $32, %rsp
popq %rbp
ret
.seh_endproc
.def __main; .scl 2; .type 32; .endef
.text
.globl main
.def main; .scl 2; .type 32; .endef
.seh_proc main
main:
.LFB0:
pushq %rbp
.seh_pushreg %rbp
movq %rsp, %rbp
.seh_setframe %rbp, 0
subq $32, %rsp
.seh_stackalloc 32
.seh_endprologue
call __main
call _ZTW3tlv
movl $1, (%rax)
movl $0, %eax
addq $32, %rsp
popq %rbp
ret
.seh_endproc
.weak _ZTH3tlv
.ident "GCC: (GNU) 7.4.0"
.def _ZTH3tlv; .scl 2; .type 32; .endef
.def __emutls_get_address; .scl 2; .type 32; .endef
.section .rdata$.refptr.__emutls_v.tlv, "dr"
.globl .refptr.__emutls_v.tlv
.linkonce discard
.refptr.__emutls_v.tlv:
.quad __emutls_v.tlv
.section .rdata$.refptr._ZTH3tlv, "dr"
.globl .refptr._ZTH3tlv
.linkonce discard
.refptr._ZTH3tlv:
.quad _ZTH3tlv
The problem seems to be in the TLS wrapper function (_ZTW3tlv):
[...]
movq .refptr._ZTH3tlv(%rip), %rax
testq %rax, %rax
je .L2
call _ZTH3tlv
[...]
.weak _ZTH3tlv
[...]
.refptr._ZTH3tlv:
.quad _ZTH3tlv
The call here is to absolute address 0 (since the weak symbol has no other
defintion), which is encoded relative to %rip. This requires a relocation, and
the relative offset can't be contained in 32 signed bits, if the ImageBase is
>2GB.
As some confirmation of this analysis, this problem can be shown with
x86_64-w64-mingw32-gcc, if the ImageBase is altered from 0x40 0000 (the default
for that) to 0x1 0040 00000 (the default for x86_64 Cygwin)
$ x86_64-w64-mingw32-gcc def.cc use.cc -Wl,--image-base,0x100400000
/tmp/cc3XRN6L.o:use.cc:(.text$_ZTW3tlv[_ZTW3tlv]+0x15): relocation truncated to
fit: R_X86_64_PC32 against undefined symbol `TLS init function for tlv'
collect2: error: ld returned 1 exit status
Naively, I think this could be fixed by generating code which indirects the
call through the pseudo-reloc, but I'm not sure that makes sense.
