[PATCH] Fix PR 8841 for nios2-linux

[Yao Qi <qiyaoltc@gmail.com>]

This patch is to use gdbarch method code_of_frame_writable, to skip
signal trampoline frame for breakpoint setting on nios2-linux.  The patch
was written last year, but forgot to upstream it.

I don't have the env to test this patch, so Sandra could you try this
patch?

gdb:

2017-10-16  Yao Qi  <yao.qi@linaro.org>

	PR gdb/8841
	* nios2-linux-tdep.c (nios2_linux_code_of_frame_writable): New
	function.
	(nios2_linux_init_abi): Install gdbarch code_of_frame_writable.
---
 gdb/nios2-linux-tdep.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/gdb/nios2-linux-tdep.c b/gdb/nios2-linux-tdep.c
index 8cada54..788d711 100644
--- a/gdb/nios2-linux-tdep.c
+++ b/gdb/nios2-linux-tdep.c
@@ -185,6 +185,22 @@ static struct tramp_frame nios2_r2_linux_rt_sigreturn_tramp_frame =
   nios2_linux_rt_sigreturn_init
 };
 
+/* Implement the code_of_frame_writable gdbarch method.  */
+
+static int
+nios2_linux_code_of_frame_writable (struct gdbarch *gdbarch,
+				    struct frame_info *frame)
+{
+  if (get_frame_type (frame) == SIGTRAMP_FRAME)
+    {
+      /* The kernel creates a signal trampoline at address 0x1044
+	 that GDB cannot write to to set a software breakpoint.  */
+      return 0;
+    }
+  else
+    return 1;
+}
+
 /* When FRAME is at a syscall instruction, return the PC of the next
    instruction to be executed.  */
 
@@ -234,6 +250,9 @@ nios2_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 
   tdep->syscall_next_pc = nios2_linux_syscall_next_pc;
 
+  set_gdbarch_code_of_frame_writable (gdbarch,
+				      nios2_linux_code_of_frame_writable);
+
   /* Index of target address word in glibc jmp_buf.  */
   tdep->jb_pc = 10;
 }
-- 
1.9.1