[ia64-hpux] unwinding bsp value from system call

This fixes unwinding from a thread that is stopped inside a system call.
This can be seen when switching to a thread that is stopped doing a
pthread_cond_wait, for instance...

The comments inside the code should explain what is happening in our
case (the HP-UX exception in the case of system calls): Under certain
circumstances (program stopped inside syscall), the offset to apply to
the current BSP in order to compute the previous BSP is not the usual
CFM & 0x7f.

We parts in this patch:

  1. Figuring out that we are stopped inside a syscal: This requires
     a TT_LWP_RUREGS ttrace call, which is not directly possible from
     ia64-tdep.c.  So use defined a new TARGET_OBJECT_HPUX_UREGS object
     to request it from the -nat side.

  2. Add a gdbarch_tdep method that allows us to change the default
     behavior on ia64-hpux, permitting us to have a different "size of
     register frame" in that one particular case.

gdb/ChangeLog:

        * target.h (enum target_object): Add TARGET_OBJECT_HPUX_UREGS.
        * ia64-tdep.h (struct frame_info): forward declaration.
        (struct gdbarch_tdep): Add field size_of_register_frame.
        * ia64-tdep.c (ia64_access_reg): Use tdep->size_of_register_frame
        to determine the size of the register frame.
        (ia64_size_of_register_frame): New function.
        (ia64_gdbarch_init): Set tdep->size_of_register_frame.
        * ia64-hpux-tdep.c: Include "target.h" and "frame.h".
        (IA64_HPUX_UREG_REASON): New macro.
        (ia64_hpux_stopped_in_syscall, ia64_hpux_size_of_register_frame):
        New functions.
        (ia64_hpux_init_abi): Set tdep->size_of_register_frame.
        * ia64-hpux-nat.c (ia64_hpux_xfer_uregs): New function.
        (ia64_hpux_xfer_partial): Add handling of TARGET_OBJECT_HPUX_UREGS
        objects.

1 files changed, 9 insertions, 0 deletions

diff --git a/gdb/ia64-tdep.h b/gdb/ia64-tdep.h
index 7e53cb6f655..384cb14bd8a 100644
--- a/gdb/ia64-tdep.h
+++ b/gdb/ia64-tdep.h
@@ -195,11 +195,20 @@
 #define IA64_NAT32_REGNUM	(IA64_NAT0_REGNUM + 32)
 #define IA64_NAT127_REGNUM	(IA64_NAT0_REGNUM + 127)
 
+struct frame_info;
+
 struct gdbarch_tdep
 {
   CORE_ADDR (*sigcontext_register_address) (struct gdbarch *, CORE_ADDR, int);
   int (*pc_in_sigtramp) (CORE_ADDR);
 
+  /* Return the total size of THIS_FRAME's register frame.
+     CFM is THIS_FRAME's cfm register value.
+
+     Normally, the size of the register frame is always obtained by
+     extracting the lowest 7 bits ("cfm & 0x7f").  */
+  int (*size_of_register_frame) (struct frame_info *this_frame, ULONGEST cfm);
+
   /* ISA-specific data types.  */
   struct type *ia64_ext_type;
 };