[PATCH] gdb/csky add unwinder for long branch cases

[PATCH] gdb/csky add unwinder for long branch cases

[Jiangshuai Li via Gdb-patches]

There are two sequences of instructions for long branch:
1. jmpi [pc+4]    //insn code: 0xeac00001
   .long addr

2. lrw t1, [pc+8] //insn code: 0xea8d0002
   jmp t1         //insn code: 0x7834
   nop            //insn code: 0x6c03
   .long addr
---
 gdb/csky-tdep.c | 60 ++++++++++++++++++++++++++++++++++++++++++++-----
 gdb/csky-tdep.h |  5 +++++
 2 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/gdb/csky-tdep.c b/gdb/csky-tdep.c
index ba53c1b10ca..3cd7a775f8d 100644
--- a/gdb/csky-tdep.c
+++ b/gdb/csky-tdep.c
@@ -2358,21 +2358,71 @@ static const struct frame_unwind csky_unwind_cache = {
   NULL
 };
 
+static CORE_ADDR
+csky_check_long_branch (struct frame_info *frame, CORE_ADDR pc)
+{
+  gdb_byte buf[8];
+  struct gdbarch *gdbarch = get_frame_arch (frame);
+  enum bfd_endian byte_order_for_code
+	= gdbarch_byte_order_for_code (gdbarch);
+
+  if (target_read_memory (pc, buf, 8) == 0)
+    {
+      unsigned int data0
+	= extract_unsigned_integer (buf, 4, byte_order_for_code);
+      unsigned int data1
+	= extract_unsigned_integer (buf + 4, 4, byte_order_for_code);
+
+      /* Case: jmpi [pc+4] : 0xeac00001
+	 .long addr   */
+      if (data0 == CSKY_JMPI_PC_4)
+	return data1;
+
+      /* Case: lrw t1, [pc+8] : 0xea8d0002
+	       jmp t1         : 0x7834
+	       nop            : 0x6c03
+	       .long addr  */
+      if ((data0 == CSKY_LRW_T1_PC_8) && (data1 == CSKY_JMP_T1_VS_NOP))
+	{
+	  if (target_read_memory (pc + 8, buf, 4) == 0)
+	    return  extract_unsigned_integer (buf, 4, byte_order_for_code);
+	}
 
+      return 0;
+    }
+
+  return 0;
+}
 
 static int
 csky_stub_unwind_sniffer (const struct frame_unwind *self,
-			 struct frame_info *this_frame,
-			 void **this_prologue_cache)
+			  struct frame_info *this_frame,
+			  void **this_prologue_cache)
 {
-  CORE_ADDR addr_in_block;
+  CORE_ADDR addr_in_block, pc;
+  gdb_byte dummy[4];
+  const char *name;
+  CORE_ADDR start_addr;
 
+  /* Get pc */
   addr_in_block = get_frame_address_in_block (this_frame);
+  pc = get_frame_pc (this_frame);
 
-  if (find_pc_partial_function (addr_in_block, NULL, NULL, NULL) == 0
-      || in_plt_section (addr_in_block))
+  if (in_plt_section (addr_in_block)
+      || target_read_memory (pc, dummy, 4) != 0)
     return 1;
 
+  /* Find the starting address and name of the function containing the PC.  */
+  if (find_pc_partial_function (pc, &name, &start_addr, NULL) == 0)
+    {
+      start_addr = csky_check_long_branch (this_frame, pc);
+      /* if not long branch, return 0.  */
+      if (start_addr != 0)
+	return 1;
+
+      return 0;
+    }
+
   return 0;
 }
 
diff --git a/gdb/csky-tdep.h b/gdb/csky-tdep.h
index f845b9ab744..dbdcd15b3a7 100644
--- a/gdb/csky-tdep.h
+++ b/gdb/csky-tdep.h
@@ -385,4 +385,9 @@ enum csky_regnum
 /* Macro for kernel 4.x  */
 #define CSKY_MOVI_R7_139 0x008bea07
 
+/* Macro for check long branch.  */
+#define CSKY_JMPI_PC_4      0x1eac0
+#define CSKY_LRW_T1_PC_8    0x2ea8d
+#define CSKY_JMP_T1_VS_NOP  0x6c037834
+
 #endif
-- 
2.25.1