another armv7-m exception handling problem

[Patrick Oppenlander <patrick.oppenlander@gmail.com>]

Not sure if this is a musl, gcc or ld bug.

Running gcc-8.3.0 musl 1.1.24 static pie.

Simple test case:

int main()
{
        try {
                throw 1;
        } catch (int d) {
                return d;
        }
        return 0;
}

Expected:
% ./a.out
% echo $?
1

Actual:
% ./a.out
terminate called after throwing an instance of 'int'
terminate called recursively
Aborted (core dumped)

The problem is that get_eit_entry is returning _URC_FAILURE here:

  if (__gnu_Unwind_Find_exidx)
    {
      eitp = (const __EIT_entry *) __gnu_Unwind_Find_exidx (return_address,
                                                            &nrec);
      if (!eitp)
        {
          UCB_PR_ADDR (ucbp) = 0;
          return _URC_FAILURE;        <----- !!!!
        }
    }

Looks like a linker or program load problem to me -- the GOT entry for
__gnu_Unwind_Find_exidx is correctly set to 0, but after program load
it's been offset to some non-zero value. There's an R_ARM_RELATIVE
relocation on the GOT entry.

Not sure where this is going wrong.

Kind regards,

Patrick