[PATCH] [SPARC64] Figure out where a longjmp will land

[jose.marchesi@oracle.com (Jose E. Marchesi)]

This is related to PR gdb/14971.  All tests in gdb.base/longjmp.exp pass
after applying this patch.

Note that in sparc64 glibc does not install probes in setjmp, nor it
mangles pointers.

Tested on sparc64-*-linux-gnu.

2013-10-08  Jose E. Marchesi  <jose.marchesi@oracle.com>

	PR gdb/14971
	* sparc-tdep.c (sparc_is_annulled_branch_insn): New function.
	* sparc-tdep.h: And its prototype.

	* sparc64-linux-tdep.c (sparc64_linux_get_longjmp_target): New
	function.
	(sparc64_linux_init_abi): Register the get_longjmp_target hook.


Index: sparc-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/sparc-tdep.c,v
retrieving revision 1.233
diff -u -r1.233 sparc-tdep.c
--- sparc-tdep.c	24 Jun 2013 22:18:32 -0000	1.233
+++ sparc-tdep.c	8 Oct 2013 17:13:35 -0000
@@ -121,6 +121,17 @@
   return ((insn & 0xc1c00000) == 0);
 }
 
+/* Return non-zero if the instruction corresponding to PC is an
+   "annulled" branch, i.e. the annul bit is set.  */
+
+int
+sparc_is_annulled_branch_insn (CORE_ADDR pc)
+{
+  const unsigned long insn = sparc_fetch_instruction (pc);
+
+  return X_A(insn);
+}
+
 /* OpenBSD/sparc includes StackGhost, which according to the author's
    website http://stackghost.cerias.purdue.edu "... transparently and
    automatically protects applications' stack frames; more
Index: sparc-tdep.h
===================================================================
RCS file: /cvs/src/src/gdb/sparc-tdep.h,v
retrieving revision 1.33
diff -u -r1.33 sparc-tdep.h
--- sparc-tdep.h	1 Jan 2013 06:32:51 -0000	1.33
+++ sparc-tdep.h	8 Oct 2013 17:13:35 -0000
@@ -202,6 +202,12 @@
 extern void sparc_collect_rwindow (const struct regcache *regcache,
 				   CORE_ADDR sp, int regnum);
 
+\f
+
+extern int sparc_is_annulled_branch_insn (CORE_ADDR pc);
+
+\f
+
 /* Register offsets for SunOS 4.  */
 extern const struct sparc_gregset sparc32_sunos4_gregset;
 extern const struct sparc_fpregset sparc32_sunos4_fpregset;
Index: sparc64-linux-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/sparc64-linux-tdep.c,v
retrieving revision 1.31
diff -u -r1.31 sparc64-linux-tdep.c
--- sparc64-linux-tdep.c	1 Jan 2013 06:32:51 -0000	1.31
+++ sparc64-linux-tdep.c	8 Oct 2013 17:13:35 -0000
@@ -233,6 +233,54 @@
 }
 
 \f
+/* Figure out where a longjmp will land.  Get the args out of the
+   output registers.  We expect the first arg to be a pointer to the
+   jmp_buf structure from which we extract the address that we will
+   land at.  This address is copied into PC.  This routine returns
+   non-zero on success.  */
+
+static int
+sparc64_linux_get_longjmp_target (struct frame_info *frame, CORE_ADDR *pc)
+{
+  struct gdbarch *gdbarch = get_frame_arch (frame);
+  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+  CORE_ADDR jb_addr;
+  gdb_byte buf[8];
+
+  jb_addr = get_frame_register_unsigned (frame, SPARC_O0_REGNUM);
+
+  /* setjmp and longjmp in SPARC64 are implemented in glibc using the
+     setcontext and getcontext system calls respectively.  These
+     system calls operate on ucontext_t structures, which happen to
+     partially have the same structure than jmp_buf.  However the
+     ucontext returned by getcontext, and thus the jmp_buf structure
+     returned by setjmp, contains the context of the trap instruction
+     in the glibc __[sig]setjmp wrapper, not the context of the user
+     code calling setjmp.
+
+     %o7 in the jmp_buf structure is stored at offset 18*8 in the
+     mc_gregs array, which is itself located at offset 32 into
+     jmp_buf.  See bits/setjmp.h.  This register contains the address
+     of the 'call setjmp' instruction in user code.
+
+     In order to determine the longjmp target address in the
+     initiating frame we need to examine the call instruction itself,
+     in particular whether the annul bit is set.  If it is not set
+     then we need to jump over the instruction at the delay slot.  */
+
+  if (target_read_memory (jb_addr + 32 + (18 * 8), buf, 8))
+    return 0;
+
+  *pc = extract_unsigned_integer (buf, 8, gdbarch_byte_order (gdbarch));
+
+  if (!sparc_is_annulled_branch_insn (*pc))
+      *pc += 4; /* delay slot insn  */
+  *pc += 4; /* call insn  */
+
+  return 1;
+}
+
+\f
 
 static void
 sparc64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
@@ -272,6 +320,9 @@
   /* Make sure we can single-step over signal return system calls.  */
   tdep->step_trap = sparc64_linux_step_trap;
 
+  /* Make sure we can single-step over longjmp calls.  */
+  set_gdbarch_get_longjmp_target (gdbarch, sparc64_linux_get_longjmp_target);
+
   set_gdbarch_write_pc (gdbarch, sparc64_linux_write_pc);
 
   /* Functions for 'catch syscall'.  */