expressions with C preprocessor macro info

[Pedro Alves <pedro@codesourcery.com>]

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Hi,

I noticed while doing something else in parse.c, something suspicous.
It happens that after preprocessor macros support went
in, parse.c:parse_exp_in_context got changed in a form that
introduced a bug here:

static struct expression *
parse_exp_in_context (char **stringptr, struct block *block, int comma, 
		      int void_context_p)
{
...
  if (!block)
    block = get_selected_block (&expression_context_pc);

   ^^^ if this returns a block, expression_context_pc contains
       an accurate pc.

  /* Fall back to using the current source static context, if any. */

  if (!block)
    {
      struct symtab_and_line cursal = get_current_source_symtab_and_line ();
      if (cursal.symtab)
	block = BLOCKVECTOR_BLOCK (BLOCKVECTOR (cursal.symtab), STATIC_BLOCK);
    }

  /* Save the context, if specified by caller, or found above. */

  if (block)
    {
      expression_context_block = block;
      expression_context_pc = BLOCK_START (block);

      ^^^ but here we're always overriding it with BLOCK_START.

    }

Talking about this with Jim Blandy, he explained it like so:

 "We want the exact PC because macros are scoped from one line to the
 next, not by block.  For example, we could have:

    {
      int foo;

      f ();
#define M slurgh;
      g ();
#undef M
      h ();
    }

 In this case, there will be only one lexical block covering the
 declaration of foo and all three statements, but we'd like to see the
 definition of M when we're stopped at the call to g, and not when
 we're stopped at the calls to f or h.  So we need to take a PC, find
 the source line and file, and then use that to decide whether any
 given macro is in scope."

Currently, "print M" when stopped at the g (); call above prints:
(gdb) print M
No symbol "M" in current context.

The attached patch fixes the issue, and adds a test to ensure
we don't regress again.

Tested on x86_64-unknown-linux-pc.

OK?

-- 
Pedro Alves

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2008-05-03  Pedro Alves  <pedro@codesourcery.com>

	gdb/
	* parse.c (parse_exp_in_context): Don't override
	expression_context_pc if get_selected_block returned a valid block.

	gdb/testsuite/
	* gdb.base/macscp.exp, gdb.base/macscp1.c: Add test for printing
	expressions with macros.

---
 gdb/parse.c                       |   26 ++++++++++++--------------
 gdb/testsuite/gdb.base/macscp.exp |   23 +++++++++++++++++++++++
 gdb/testsuite/gdb.base/macscp1.c  |   13 +++++++++++++
 3 files changed, 48 insertions(+), 14 deletions(-)

Index: src/gdb/parse.c
===================================================================
--- src.orig/gdb/parse.c	2008-05-03 20:32:38.000000000 +0100
+++ src/gdb/parse.c	2008-05-03 20:43:01.000000000 +0100
@@ -961,26 +961,24 @@ parse_exp_in_context (char **stringptr, 
   old_chain = make_cleanup (free_funcalls, 0 /*ignore*/);
   funcall_chain = 0;
 
-  /* If no context specified, try using the current frame, if any. */
+  expression_context_block = block;
 
-  if (!block)
-    block = get_selected_block (&expression_context_pc);
+  /* If no context specified, try using the current frame, if any.  */
+  if (!expression_context_block)
+    expression_context_block = get_selected_block (&expression_context_pc);
+  else
+    expression_context_pc = BLOCK_START (expression_context_block);
 
-  /* Fall back to using the current source static context, if any. */
+  /* Fall back to using the current source static context, if any.  */
 
-  if (!block)
+  if (!expression_context_block)
     {
       struct symtab_and_line cursal = get_current_source_symtab_and_line ();
       if (cursal.symtab)
-	block = BLOCKVECTOR_BLOCK (BLOCKVECTOR (cursal.symtab), STATIC_BLOCK);
-    }
-
-  /* Save the context, if specified by caller, or found above. */
-
-  if (block)
-    {
-      expression_context_block = block;
-      expression_context_pc = BLOCK_START (block);
+	expression_context_block
+	  = BLOCKVECTOR_BLOCK (BLOCKVECTOR (cursal.symtab), STATIC_BLOCK);
+      if (expression_context_block)
+	expression_context_pc = BLOCK_START (expression_context_block);
     }
 
   expout_size = 10;
Index: src/gdb/testsuite/gdb.base/macscp.exp
===================================================================
--- src.orig/gdb/testsuite/gdb.base/macscp.exp	2008-05-03 20:32:39.000000000 +0100
+++ src/gdb/testsuite/gdb.base/macscp.exp	2008-05-03 20:37:56.000000000 +0100
@@ -24,6 +24,7 @@ if $tracelevel then {
 set prms_id 0
 set bug_id 0
 
+set srcfile macscp1.c
 set testfile "macscp"
 set binfile ${objdir}/${subdir}/${testfile}
 
@@ -405,3 +406,25 @@ for {set i 0} {$i < [llength $funcs]} {i
         }
     }
 }
+
+gdb_test "break [gdb_get_line_number "set breakpoint here"]" \
+    "Breakpoint.*at.* file .*, line.*" \
+    "breakpoint macscp_expr"
+
+gdb_test "continue" "foo = 0;.*" "continue to macsp_expr"
+
+gdb_test "print M" \
+    "No symbol \"M\" in current context\." \
+    "print expression with macro before define."
+
+gdb_test "next" "foo = 1;" "next to definition"
+
+gdb_test "print M" \
+    " = 0" \
+    "print expression with macro in scope."
+
+gdb_test "next" "foo = 2;" "next to definition"
+
+gdb_test "print M" \
+    "No symbol \"M\" in current context\." \
+    "print expression with macro after undef."
Index: src/gdb/testsuite/gdb.base/macscp1.c
===================================================================
--- src.orig/gdb/testsuite/gdb.base/macscp1.c	2008-05-03 20:32:39.000000000 +0100
+++ src/gdb/testsuite/gdb.base/macscp1.c	2008-05-03 20:37:56.000000000 +0100
@@ -63,6 +63,18 @@ macscp1_3 ()
   puts ("macscp1_3");
 }
 
+void
+macscp_expr (void)
+{
+  int foo = -1;
+
+  foo = 0;  /* set breakpoint here */
+#define M foo
+  foo = 1;
+#undef M
+  foo = 2;
+}
+
 int
 main (int argc, char **argv)
 {
@@ -77,4 +89,5 @@ main (int argc, char **argv)
   macscp4_2_from_macscp3 ();
   macscp3_2 ();
   macscp1_3 ();
+  macscp_expr ();
 }