http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50678
--- Comment #50 from Iain Sandoe <iains at gcc dot gnu.org> 2011-10-18 19:18:38
UTC ---
well I've hit a few issues.
1. _Unwind_Find_FDE is not part of the public interface (nor are the types it
needs).
2. if the vendor decides to 'fix' libunwind .. we won't detect this ...
(although I still think this idea is worth pursuing, on the grounds that 'no
fix' or a fix to Libc are more likely).
3. _Unwind_Find_FDE is returning NULL in the following proof-of-concept hack..
.. not having any joy debugging this from the c++ case (maybe have to try a
newer debugger)..
(have to do some other things for a while - but if you can spot my obvious
mistake .. then let me know).
#if defined (__x86_64__)
/* Work around radar #10302855/pr50678, where the unwinders (libunwind or
libgcc_s depending on the system revision) and the DWARF unwind data for
the sigtramp have different ideas about register numbering (causing rbx
and rdx to be transposed). */
#define DX86FIX_CHECKED 0x01
#define DX86FIX_DOFIXUP 0x02
struct dwarf_eh_bases
{
void *tbase;
void *dbase;
void *func;
};
typedef int sword __attribute__ ((mode (SI)));
typedef unsigned int uword __attribute__ ((mode (SI)));
struct dwarf_fde
{
uword length;
sword CIE_delta;
unsigned char pc_begin[];
} __attribute__ ((packed, aligned (__alignof__ (void *))));
extern struct dwarf_fde * _Unwind_Find_FDE (void *, struct dwarf_eh_bases *);
static void
__gnat_darwin_maybe_fixup_unwind_context (ucontext_t *uc, void *ad)
{
static unsigned need_fixup = 0;
/* Look for the FDE for the sig tramp. */
if ((need_fixup & DX86FIX_CHECKED) == 0)
{
struct dwarf_eh_bases bases;
const struct dwarf_fde *myfde = _Unwind_Find_FDE (ad, &bases);
if (myfde == NULL)
need_fixup |= DX86FIX_DOFIXUP; /* We're likely broken. */
else
{
unsigned MCONTEXT_SS_RBX, MCONTEXT_SS_RDX, ts;
/* These are the offsets for the registers. */
ts = __builtin_offsetof (_STRUCT_MCONTEXT,__ss);
MCONTEXT_SS_RBX = __builtin_offsetof (_STRUCT_X86_THREAD_STATE64,__rbx);
MCONTEXT_SS_RBX += ts;
MCONTEXT_SS_RDX = __builtin_offsetof (_STRUCT_X86_THREAD_STATE64,__rdx);
MCONTEXT_SS_RDX += ts;
// UNFINISHED
}
need_fixup |= DX86FIX_CHECKED;
}
if (need_fixup & DX86FIX_DOFIXUP)
{
unsigned long t = uc->uc_mcontext->__ss.__rbx;
uc->uc_mcontext->__ss.__rbx = uc->uc_mcontext->__ss.__rdx;
uc->uc_mcontext->__ss.__rdx = t;
}
}
#endif
static void
__gnat_error_handler (int sig, siginfo_t *si, void *ucontext)
{
struct Exception_Data *exception;
const char *msg;
#if defined (__x86_64__)
/* We pass the address from here so that we don't need to worry about
inlining. */
__gnat_darwin_maybe_fixup_unwind_context ((ucontext_t *)ucontext,
__builtin_return_address (0));
#endif
