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

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

    > Shall I address him directly?
    
    So yes, that might be a good idea.
    
    Your last diff is fine with me, so if Dave doesn't respond within a
    couple of days after you ping him, feel free to move ahead with this.

I just committed the attached amended patch, reviewed by Mark and Dave
off-list and authorized by Mark.

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

	* 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.

diff --git a/gdb/sparc-tdep.c b/gdb/sparc-tdep.c
index 880d276..4057d0d 100644
--- a/gdb/sparc-tdep.c
+++ b/gdb/sparc-tdep.c
@@ -121,6 +121,37 @@ sparc_is_unimp_insn (CORE_ADDR pc)
   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)
+{
+  /* The branch instructions featuring an annul bit can be identified
+     by the following bit patterns:
+
+     OP=0
+      OP2=1: Branch on Integer Condition Codes with Prediction (BPcc).
+      OP2=2: Branch on Integer Condition Codes (Bcc).
+      OP2=5: Branch on FP Condition Codes with Prediction (FBfcc).
+      OP2=6: Branch on FP Condition Codes (FBcc).
+      OP2=3 && Bit28=0:
+             Branch on Integer Register with Prediction (BPr).
+
+     This leaves out ILLTRAP (OP2=0), SETHI/NOP (OP2=4) and the V8
+     coprocessor branch instructions (Op2=7).  */
+
+  const unsigned long insn = sparc_fetch_instruction (pc);
+  const unsigned op2 = X_OP2 (insn);
+
+  if ((X_OP (insn) == 0)
+      && ((op2 == 1) || (op2 == 2) || (op2 == 5) || (op2 == 6)
+	  || ((op2 == 3) && ((insn & 0x10000000) == 0))))
+    return X_A (insn);
+  else
+    return 0;
+}
+
 /* OpenBSD/sparc includes StackGhost, which according to the author's
    website http://stackghost.cerias.purdue.edu "... transparently and
    automatically protects applications' stack frames; more
diff --git a/gdb/sparc-tdep.h b/gdb/sparc-tdep.h
index cafc627..6fd7641 100644
--- a/gdb/sparc-tdep.h
+++ b/gdb/sparc-tdep.h
@@ -220,6 +220,8 @@ extern void sparc32_collect_fpregset (const struct sparc_fpregset *fpregset,
 				      const struct regcache *regcache,
 				      int regnum, void *fpregs);
 
+extern int sparc_is_annulled_branch_insn (CORE_ADDR pc);
+
 /* Functions and variables exported from sparc-sol2-tdep.c.  */
 
 /* Register offsets for Solaris 2.  */
diff --git a/gdb/sparc64-linux-tdep.c b/gdb/sparc64-linux-tdep.c
index 3f53f6c..f6ddff0 100644
--- a/gdb/sparc64-linux-tdep.c
+++ b/gdb/sparc64-linux-tdep.c
@@ -233,6 +233,50 @@ sparc64_linux_get_syscall_number (struct gdbarch *gdbarch,
 }
 
 
+/* Implement the "get_longjmp_target" gdbarch method.  */
+
+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;
+}
+
+
 
 static void
 sparc64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
@@ -272,6 +316,9 @@ sparc64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
   /* 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'.  */