1 files changed, 183 insertions, 60 deletions

diff --git a/gdb/tui/tui-disasm.c b/gdb/tui/tui-disasm.c
index 98c691f..726b7c2 100644
--- a/gdb/tui/tui-disasm.c
+++ b/gdb/tui/tui-disasm.c
@@ -81,25 +81,58 @@ len_without_escapes (const std::string &str)
   return len;
 }
 
-/* Function to set the disassembly window's content.
-   Disassemble count lines starting at pc.
-   Return address of the count'th instruction after pc.  */
+/* Function to disassemble up to COUNT instructions starting from address
+   PC into the ASM_LINES vector (which will be emptied of any previous
+   contents).  Return the address of the COUNT'th instruction after pc.
+   When ADDR_SIZE is non-null then place the maximum size of an address and
+   label into the value pointed to by ADDR_SIZE, and set the addr_size
+   field on each item in ASM_LINES, otherwise the addr_size fields within
+   ASM_LINES are undefined.
+
+   It is worth noting that ASM_LINES might not have COUNT entries when this
+   function returns.  If the disassembly is truncated for some other
+   reason, for example, we hit invalid memory, then ASM_LINES can have
+   fewer entries than requested.  */
 static CORE_ADDR
 tui_disassemble (struct gdbarch *gdbarch,
 		 std::vector<tui_asm_line> &asm_lines,
-		 CORE_ADDR pc, int pos, int count,
+		 CORE_ADDR pc, int count,
 		 size_t *addr_size = nullptr)
 {
   bool term_out = source_styling && gdb_stdout->can_emit_style_escape ();
   string_file gdb_dis_out (term_out);
 
+  /* Must start with an empty list.  */
+  asm_lines.clear ();
+
   /* Now construct each line.  */
   for (int i = 0; i < count; ++i)
     {
-      print_address (gdbarch, pc, &gdb_dis_out);
-      asm_lines[pos + i].addr = pc;
-      asm_lines[pos + i].addr_string = std::move (gdb_dis_out.string ());
+      tui_asm_line tal;
+      CORE_ADDR orig_pc = pc;
 
+      try
+	{
+	  pc = pc + gdb_print_insn (gdbarch, pc, &gdb_dis_out, NULL);
+	}
+      catch (const gdb_exception_error &except)
+	{
+	  /* If PC points to an invalid address then we'll catch a
+	     MEMORY_ERROR here, this should stop the disassembly, but
+	     otherwise is fine.  */
+	  if (except.error != MEMORY_ERROR)
+	    throw;
+	  return pc;
+	}
+
+      /* Capture the disassembled instruction.  */
+      tal.insn = std::move (gdb_dis_out.string ());
+      gdb_dis_out.clear ();
+
+      /* And capture the address the instruction is at.  */
+      tal.addr = orig_pc;
+      print_address (gdbarch, orig_pc, &gdb_dis_out);
+      tal.addr_string = std::move (gdb_dis_out.string ());
       gdb_dis_out.clear ();
 
       if (addr_size != nullptr)
@@ -107,23 +140,45 @@ tui_disassemble (struct gdbarch *gdbarch,
 	  size_t new_size;
 
 	  if (term_out)
-	    new_size = len_without_escapes (asm_lines[pos + i].addr_string);
+	    new_size = len_without_escapes (tal.addr_string);
 	  else
-	    new_size = asm_lines[pos + i].addr_string.size ();
+	    new_size = tal.addr_string.size ();
 	  *addr_size = std::max (*addr_size, new_size);
-	  asm_lines[pos + i].addr_size = new_size;
+	  tal.addr_size = new_size;
 	}
 
-      pc = pc + gdb_print_insn (gdbarch, pc, &gdb_dis_out, NULL);
-
-      asm_lines[pos + i].insn = std::move (gdb_dis_out.string ());
-
-      /* Reset the buffer to empty.  */
-      gdb_dis_out.clear ();
+      asm_lines.push_back (std::move (tal));
     }
   return pc;
 }
 
+/* Look backward from ADDR for an address from which we can start
+   disassembling, this needs to be something we can be reasonably
+   confident will fall on an instruction boundary.  We use msymbol
+   addresses, or the start of a section.  */
+
+static CORE_ADDR
+tui_find_backward_disassembly_start_address (CORE_ADDR addr)
+{
+  struct bound_minimal_symbol msym, msym_prev;
+
+  msym = lookup_minimal_symbol_by_pc_section (addr - 1, nullptr,
+					      lookup_msym_prefer::TEXT,
+					      &msym_prev);
+  if (msym.minsym != nullptr)
+    return BMSYMBOL_VALUE_ADDRESS (msym);
+  else if (msym_prev.minsym != nullptr)
+    return BMSYMBOL_VALUE_ADDRESS (msym_prev);
+
+  /* Find the section that ADDR is in, and look for the start of the
+     section.  */
+  struct obj_section *section = find_pc_section (addr);
+  if (section != NULL)
+    return obj_section_addr (section);
+
+  return addr;
+}
+
 /* Find the disassembly address that corresponds to FROM lines above
    or below the PC.  Variable sized instructions are taken into
    account by the algorithm.  */
@@ -134,65 +189,125 @@ tui_find_disassembly_address (struct gdbarch *gdbarch, CORE_ADDR pc, int from)
   int max_lines;
 
   max_lines = (from > 0) ? from : - from;
-  if (max_lines <= 1)
+  if (max_lines == 0)
     return pc;
 
-  std::vector<tui_asm_line> asm_lines (max_lines);
+  std::vector<tui_asm_line> asm_lines;
 
   new_low = pc;
   if (from > 0)
     {
-      tui_disassemble (gdbarch, asm_lines, pc, 0, max_lines);
-      new_low = asm_lines[max_lines - 1].addr;
+      /* Always disassemble 1 extra instruction here, then if the last
+	 instruction fails to disassemble we will take the address of the
+	 previous instruction that did disassemble as the result.  */
+      tui_disassemble (gdbarch, asm_lines, pc, max_lines + 1);
+      new_low = asm_lines.back ().addr;
     }
   else
     {
+      /* In order to disassemble backwards we need to find a suitable
+	 address to start disassembling from and then work forward until we
+	 re-find the address we're currently at.  We can then figure out
+	 which address will be at the top of the TUI window after our
+	 backward scroll.  During our backward disassemble we need to be
+	 able to distinguish between the case where the last address we
+	 _can_ disassemble is ADDR, and the case where the disassembly
+	 just happens to stop at ADDR, for this reason we increase
+	 MAX_LINES by one.  */
+      max_lines++;
+
+      /* When we disassemble a series of instructions this will hold the
+	 address of the last instruction disassembled.  */
       CORE_ADDR last_addr;
-      int pos;
-      struct bound_minimal_symbol msymbol;
-
-      /* Find backward an address which is a symbol and for which
-         disassembling from that address will fill completely the
-         window.  */
-      pos = max_lines - 1;
-      do {
-         new_low -= 1 * max_lines;
-         msymbol = lookup_minimal_symbol_by_pc_section (new_low, 0);
-
-         if (msymbol.minsym)
-            new_low = BMSYMBOL_VALUE_ADDRESS (msymbol);
-         else
-            new_low += 1 * max_lines;
-
-         tui_disassemble (gdbarch, asm_lines, new_low, 0, max_lines);
-         last_addr = asm_lines[pos].addr;
-      } while (last_addr > pc && msymbol.minsym);
+
+      /* And this will hold the address of the next instruction that would
+	 have been disassembled.  */
+      CORE_ADDR next_addr;
+
+      /* As we search backward if we find an address that looks like a
+	 promising starting point then we record it in this structure.  If
+	 the next address we try is not a suitable starting point then we
+	 will fall back to the address held here.  */
+      gdb::optional<CORE_ADDR> possible_new_low;
+
+      /* The previous value of NEW_LOW so we know if the new value is
+	 different or not.  */
+      CORE_ADDR prev_low;
+
+      do
+	{
+	  /* Find an address from which we can start disassembling.  */
+	  prev_low = new_low;
+	  new_low = tui_find_backward_disassembly_start_address (new_low);
+
+	  /* Disassemble forward.  */
+	  next_addr = tui_disassemble (gdbarch, asm_lines, new_low, max_lines);
+	  last_addr = asm_lines.back ().addr;
+
+	  /* If disassembling from the current value of NEW_LOW reached PC
+	     (or went past it) then this would do as a starting point if we
+	     can't find anything better, so remember it.  */
+	  if (last_addr >= pc && new_low != prev_low
+	      && asm_lines.size () >= max_lines)
+	    possible_new_low.emplace (new_low);
+
+	  /* Continue searching until we find a value of NEW_LOW from which
+	     disassembling MAX_LINES instructions doesn't reach PC.  We
+	     know this means we can find the required number of previous
+	     instructions then.  */
+	}
+      while ((last_addr > pc
+	      || (last_addr == pc && asm_lines.size () < max_lines))
+	     && new_low != prev_low);
+
+      /* If we failed to disassemble the required number of lines then the
+	 following walk forward is not going to work, it assumes that
+	 ASM_LINES contains exactly MAX_LINES entries.  Instead we should
+	 consider falling back to a previous possible start address in
+	 POSSIBLE_NEW_LOW.  */
+      if (asm_lines.size () < max_lines)
+	{
+	  if (!possible_new_low.has_value ())
+	    return pc;
+
+	  /* Take the best possible match we have.  */
+	  new_low = *possible_new_low;
+	  next_addr = tui_disassemble (gdbarch, asm_lines, new_low, max_lines);
+	  last_addr = asm_lines.back ().addr;
+	  gdb_assert (asm_lines.size () >= max_lines);
+	}
 
       /* Scan forward disassembling one instruction at a time until
          the last visible instruction of the window matches the pc.
          We keep the disassembled instructions in the 'lines' window
          and shift it downward (increasing its addresses).  */
+      int pos = max_lines - 1;
       if (last_addr < pc)
         do
           {
-            CORE_ADDR next_addr;
-
             pos++;
             if (pos >= max_lines)
               pos = 0;
 
-            next_addr = tui_disassemble (gdbarch, asm_lines,
-					 last_addr, pos, 1);
-
+	    CORE_ADDR old_next_addr = next_addr;
+	    std::vector<tui_asm_line> single_asm_line;
+	    next_addr = tui_disassemble (gdbarch, single_asm_line,
+					 next_addr, 1);
             /* If there are some problems while disassembling exit.  */
-            if (next_addr <= last_addr)
-              break;
-            last_addr = next_addr;
-          } while (last_addr <= pc);
+	    if (next_addr <= old_next_addr)
+	      return pc;
+	    gdb_assert (single_asm_line.size () == 1);
+	    asm_lines[pos] = single_asm_line[0];
+	  } while (next_addr <= pc);
       pos++;
       if (pos >= max_lines)
          pos = 0;
       new_low = asm_lines[pos].addr;
+
+      /* When scrolling backward the addresses should move backward, or at
+	 the very least stay the same if we are at the first address that
+	 can be disassembled.  */
+      gdb_assert (new_low <= pc);
     }
   return new_low;
 }
@@ -224,9 +339,9 @@ tui_disasm_window::set_contents (struct gdbarch *arch,
   line_width = width - TUI_EXECINFO_SIZE - 2;
 
   /* Get temporary table that will hold all strings (addr & insn).  */
-  std::vector<tui_asm_line> asm_lines (max_lines);
+  std::vector<tui_asm_line> asm_lines;
   size_t addr_size = 0;
-  tui_disassemble (gdbarch, asm_lines, pc, 0, max_lines, &addr_size);
+  tui_disassemble (gdbarch, asm_lines, pc, max_lines, &addr_size);
 
   /* Align instructions to the same column.  */
   insn_pos = (1 + (addr_size / tab_len)) * tab_len;
@@ -237,17 +352,29 @@ tui_disasm_window::set_contents (struct gdbarch *arch,
     {
       tui_source_element *src = &content[i];
 
-      std::string line
-	= (asm_lines[i].addr_string
-	   + n_spaces (insn_pos - asm_lines[i].addr_size)
-	   + asm_lines[i].insn);
+      std::string line;
+      CORE_ADDR addr;
+
+      if (i < asm_lines.size ())
+	{
+	  line
+	    = (asm_lines[i].addr_string
+	       + n_spaces (insn_pos - asm_lines[i].addr_size)
+	       + asm_lines[i].insn);
+	  addr = asm_lines[i].addr;
+	}
+      else
+	{
+	  line = "";
+	  addr = 0;
+	}
 
       const char *ptr = line.c_str ();
       src->line = tui_copy_source_line (&ptr, -1, offset, line_width, 0);
 
       src->line_or_addr.loa = LOA_ADDRESS;
-      src->line_or_addr.u.addr = asm_lines[i].addr;
-      src->is_exec_point = asm_lines[i].addr == cur_pc;
+      src->line_or_addr.u.addr = addr;
+      src->is_exec_point = (addr == cur_pc && line.size () > 0);
     }
   return true;
 }
@@ -326,10 +453,6 @@ tui_disasm_window::do_scroll_vertical (int num_to_scroll)
       CORE_ADDR pc;
 
       pc = start_line_or_addr.u.addr;
-      if (num_to_scroll >= 0)
-	num_to_scroll++;
-      else
-	--num_to_scroll;
 
       symtab_and_line sal {};
       sal.pspace = current_program_space;