[PATCH] GDB: Treat memory exception from tui_disassemble() gracefully

[Shahab Vahedi]

From: Shahab Vahedi <shahab@synopsys.com>

In TUI mode, when the assembly layout reaches the end of a binary,
GDB wants to disassemle the addresses beyond the last valid ones.
This results in a "MEMORY_ERROR" exception to be thrown when
tui_disasm_window::set_contents() invokes tui_disassemble(). When
that happens set_contents() bails out prematurely without filling
the "content" for the valid addresses. This eventually leads to
no assembly lines or termination of GDB when you scroll down to
the last lines of the program.

With this change, tui_disassemble() is surrounded with try/catch.
If a MEMORY_ERROR exception is caught, it is ignored.

The issue has been discussed at length in bug 25345:
  https://sourceware.org/bugzilla/show_bug.cgi?id=25345

gdb/ChangeLog:
2020-01-08  Shahab Vahedi  <shahab@synopsys.com>
        * tui/tui-disasm.c (tui_disasm_window::set_contents):
        Handle MEMORY_ERROR exception gracefully.
---
 gdb/tui/tui-disasm.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/gdb/tui/tui-disasm.c b/gdb/tui/tui-disasm.c
index 98c691f3387..7faaa45f039 100644
--- a/gdb/tui/tui-disasm.c
+++ b/gdb/tui/tui-disasm.c
@@ -226,7 +226,18 @@ tui_disasm_window::set_contents (struct gdbarch *arch,
   /* Get temporary table that will hold all strings (addr & insn).  */
   std::vector<tui_asm_line> asm_lines (max_lines);
   size_t addr_size = 0;
-  tui_disassemble (gdbarch, asm_lines, pc, 0, max_lines, &addr_size);
+  try
+    {
+      tui_disassemble (gdbarch, asm_lines, pc, 0, max_lines, &addr_size);
+    }
+  catch (const gdb_exception &except)
+    {
+      /* In cases where max_lines is asking tui_disassemble() to fetch
+	 too much, like when PC goes past the valid address range, a
+	 MEMORY_ERROR is thrown, but it is alright.  */
+      if (except.error != MEMORY_ERROR)
+	  throw;
+    }
 
   /* Align instructions to the same column.  */
   insn_pos = (1 + (addr_size / tab_len)) * tab_len;
-- 
2.24.1