[Bug tree-optimization/65953] New: [5/6 Regression] undefined reference to static __thread variable

[Bug tree-optimization/65953] New: [5/6 Regression] undefined reference to static __thread variable

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65953

            Bug ID: 65953
           Summary: [5/6 Regression] undefined reference to static
                    __thread variable
           Product: gcc
           Version: 5.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: trippels at gcc dot gnu.org
  Target Milestone: ---

A Gentoo user pointed me to a Mono build failure with gcc-5:

markus@x4 /tmp % cat mini.i
static __thread int *mono_jit_tls;
long mono_get_jit_tls_offset_foo;
int* mono_set_jit_tls_jit_tls;
void
fn1 ()
{
  __asm("movq $mono_jit_tls@TPOFF, %0" : "=r"(mono_get_jit_tls_offset_foo));
}

void
fn2 () { mono_jit_tls = mono_set_jit_tls_jit_tls; }

markus@x4 /tmp % gcc -nostdlib -O2 mini.i
/tmp/ccuc43K9.o:mini.i:function fn1: error: undefined reference to
'mono_jit_tls'
collect2: error: ld returned 1 exit status
markus@x4 /tmp % /usr/x86_64-pc-linux-gnu/gcc-bin/4.8.4/gcc -nostdlib -O2
mini.i
markus@x4 /tmp % /usr/x86_64-pc-linux-gnu/gcc-bin/4.9.2/gcc -nostdlib -O2
mini.i
markus@x4 /tmp % clang -nostdlib -O2 mini.i
markus@x4 /tmp % icc -nostdlib -O2 mini.i
markus@x4 /tmp %

[Bug tree-optimization/65953] [5/6 Regression] undefined reference to static __thread variable

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65953

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |jakub at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Looks like a Mono bug to me.  mono_jit_tls isn't __attribute__((used)), and the
compiler determines it is a write-only variable (doesn't know the asm uses it).
Wonder why they use asm at all for this...

[Bug tree-optimization/65953] [5/6 Regression] undefined reference to static __thread variable

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65953

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> Looks like a Mono bug to me.  mono_jit_tls isn't __attribute__((used)), and
> the compiler determines it is a write-only variable (doesn't know the asm
> uses it).

I can think of one reason, the whole Coroutines and switching of the thread
behind the compiler with getcontext/setcontext.