Introduce OP_VAR_MSYM_VALUE

The previous patch left GDB with an inconsistency.  While with normal
expression evaluation the "unknown return type" error shows the name
of the function that misses debug info:

  (gdb) p getenv ("PATH")
  'getenv' has unknown return type; cast the call to its declared return type
   ^^^^^^

which can by handy in more complicated expressions, "ptype" does not:

  (gdb) ptype getenv ("PATH")
  function has unknown return type; cast the call to its declared return type
  ^^^^^^^^

This commit is a step toward fixing it.

The problem is that while evaluating the expression above, we have no
reference to the minimal symbol where we could extract the name from.
This is because the resulting expression tree has no reference to the
minsym at all.  During parsing, the type and address of the minsym are
extracted and an UNOP_MEMVAL / UNOP_MEMVAL_TLS operator is generated
(see write_exp_elt_msym).  With "set debug expression", here's what
you see:

            0  OP_FUNCALL            Number of args: 0
            3    UNOP_MEMVAL           Type @0x565334a51930 (<text variable, no debug info>)
            6      OP_LONG               Type @0x565334a51c60 (__CORE_ADDR), value 140737345035648 (0x7ffff7751d80)

The "print" case finds the function name, because
call_function_by_hand looks up the function by address again.
However, for "ptype", we don't reach that code, because obviously we
don't really call the function.

Unlike minsym references, references to variables with debug info have
a pointer to the variable's symbol in the expression tree, with
OP_VAR_VALUE:

  (gdb) ptype main()
  ...
            0  OP_FUNCALL            Number of args: 0
            3    OP_VAR_VALUE          Block @0x0, symbol @0x559bbbd9b358 (main(int, char**))
  ...

so I don't see why do minsyms need to be different.  So to prepare for
fixing the missing function name issue, this commit adds a new
OP_VAR_MSYM_VALUE operator that mimics OP_VAR_VALUE, except that it's
for minsyms instead of debug symbols.  For infcalls, we now get
expressions like these:

            0  OP_FUNCALL            Number of args: 0
            3    OP_VAR_MSYM_VALUE     Objfile @0x1e41bf0, msymbol @0x7fffe599b000 (getenv)

In the following patch, we'll make OP_FUNCALL extract the function
name from the symbol stored in OP_VAR_VALUE/OP_VAR_MSYM_VALUE.

OP_VAR_MSYM_VALUE will be used more in a later patch in the series
too.

gdb/ChangeLog:
2017-09-04  Pedro Alves  <palves@redhat.com>

	* ada-lang.c (resolve_subexp): Handle OP_VAR_MSYM_VALUE.
	* ax-gdb.c (gen_msym_var_ref): New function.
	(gen_expr): Handle OP_VAR_MSYM_VALUE.
	* eval.c (evaluate_var_msym_value): New function.
	* eval.c (evaluate_subexp_standard): Handle OP_VAR_MSYM_VALUE.
	<OP_FUNCALL>: Extract function name from symbol/minsym and pass it
	to call_function_by_hand.
	* expprint.c (print_subexp_standard, dump_subexp_body_standard):
	Handle OP_VAR_MSYM_VALUE.
	(union exp_element) <msymbol>: New field.
	* minsyms.h (struct type): Forward declare.
	(find_minsym_type_and_address): Declare.
	* parse.c (write_exp_elt_msym): New function.
	(write_exp_msymbol): Delete, refactored as ...
	(find_minsym_type_and_address): ... this new function.
	(write_exp_msymbol): Reimplement using OP_VAR_MSYM_VALUE.
	(operator_length_standard, operator_check_standard): Handle
	OP_VAR_MSYM_VALUE.
	* std-operator.def (OP_VAR_MSYM_VALUE): New.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 85cd3f9039966358e0815176a0070098a7243597..d34b29a5c04caaf41e3b2c123f8ca8615a055d75 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,25 @@
+2017-09-04  Pedro Alves  <palves@redhat.com>
+
+       * ada-lang.c (resolve_subexp): Handle OP_VAR_MSYM_VALUE.
+       * ax-gdb.c (gen_msym_var_ref): New function.
+       (gen_expr): Handle OP_VAR_MSYM_VALUE.
+       * eval.c (evaluate_var_msym_value): New function.
+       * eval.c (evaluate_subexp_standard): Handle OP_VAR_MSYM_VALUE.
+       <OP_FUNCALL>: Extract function name from symbol/minsym and pass it
+       to call_function_by_hand.
+       * expprint.c (print_subexp_standard, dump_subexp_body_standard):
+       Handle OP_VAR_MSYM_VALUE.
+       (union exp_element) <msymbol>: New field.
+       * minsyms.h (struct type): Forward declare.
+       (find_minsym_type_and_address): Declare.
+       * parse.c (write_exp_elt_msym): New function.
+       (write_exp_msymbol): Delete, refactored as ...
+       (find_minsym_type_and_address): ... this new function.
+       (write_exp_msymbol): Reimplement using OP_VAR_MSYM_VALUE.
+       (operator_length_standard, operator_check_standard): Handle
+       OP_VAR_MSYM_VALUE.
+       * std-operator.def (OP_VAR_MSYM_VALUE): New.
+
 2017-09-04  Pedro Alves  <palves@redhat.com>
 
        * ada-lang.c (ada_evaluate_subexp) <TYPE_CODE_FUNC>: Don't handle

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 519dfb12924d12a25b3d2411ee04fa3f0ed17b62..86f09b941a39713cbb18f1c6088e9898797c6f30 100644 (file)
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -3385,6 +3385,7 @@ resolve_subexp (struct expression **expp, int *pos, int deprocedure_p,
     case OP_LONG:
     case OP_DOUBLE:
     case OP_VAR_VALUE:
+    case OP_VAR_MSYM_VALUE:
       *pos += 4;
       break;
 

diff --git a/gdb/ax-gdb.c b/gdb/ax-gdb.c
index a72a4586fd3fcd708aa638e095f8fc758c3590cf..3fdf81afee587f6bd2f1e06d38650025c23701e6 100644 (file)
--- a/gdb/ax-gdb.c
+++ b/gdb/ax-gdb.c
@@ -733,6 +733,23 @@ gen_var_ref (struct agent_expr *ax, struct axs_value *value, struct symbol *var)
       break;
     }
 }
+
+/* Generate code for a minimal symbol variable reference to AX.  The
+   variable is the symbol MINSYM, of OBJFILE.  Set VALUE to describe
+   the result.  */
+
+static void
+gen_msym_var_ref (agent_expr *ax, axs_value *value,
+                 minimal_symbol *msymbol, objfile *objf)
+{
+  CORE_ADDR address;
+  type *t = find_minsym_type_and_address (msymbol, objf, &address);
+  value->type = t;
+  value->optimized_out = false;
+  ax_const_l (ax, address);
+  value->kind = axs_lvalue_memory;
+}
+
 \f
 
 
@@ -1964,6 +1981,11 @@ gen_expr (struct expression *exp, union exp_element **pc,
       (*pc) += 4;
       break;
 
+    case OP_VAR_MSYM_VALUE:
+      gen_msym_var_ref (ax, value, (*pc)[2].msymbol, (*pc)[1].objfile);
+      (*pc) += 4;
+      break;
+
     case OP_REGISTER:
       {
        const char *name = &(*pc)[2].string;

diff --git a/gdb/eval.c b/gdb/eval.c
index 1ec67513af262d77383bc73bd9fe2c95c31b79d1..457e280f6bf994bd9a507f9c67d499afc00ee338 100644 (file)
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -676,6 +676,25 @@ make_params (int num_types, struct type **param_types)
   return type;
 }
 
+/* Helper for evaluating an OP_VAR_MSYM_VALUE.  */
+
+static value *
+evaluate_var_msym_value (enum noside noside,
+                        struct objfile *objfile, minimal_symbol *msymbol)
+{
+  if (noside == EVAL_AVOID_SIDE_EFFECTS)
+    {
+      type *the_type = find_minsym_type_and_address (msymbol, objfile, NULL);
+      return value_zero (the_type, not_lval);
+    }
+  else
+    {
+      CORE_ADDR address;
+      type *the_type = find_minsym_type_and_address (msymbol, objfile, &address);
+      return value_at_lazy (the_type, address);
+    }
+}
+
 struct value *
 evaluate_subexp_standard (struct type *expect_type,
                          struct expression *exp, int *pos,
@@ -766,6 +785,11 @@ evaluate_subexp_standard (struct type *expect_type,
 
        return ret;
       }
+    case OP_VAR_MSYM_VALUE:
+      (*pos) += 3;
+      return evaluate_var_msym_value (noside,
+                                     exp->elts[pc + 1].objfile,
+                                     exp->elts[pc + 2].msymbol);
 
     case OP_VAR_ENTRY_VALUE:
       (*pos) += 2;

diff --git a/gdb/expprint.c b/gdb/expprint.c
index 9b8ac4c070b4db0729eff48261405ab8117492ad..4939c014622d916f334069e84c22b7ca297f0efc 100644 (file)
--- a/gdb/expprint.c
+++ b/gdb/expprint.c
@@ -134,6 +134,13 @@ print_subexp_standard (struct expression *exp, int *pos,
       }
       return;
 
+    case OP_VAR_MSYM_VALUE:
+      {
+       (*pos) += 3;
+       fputs_filtered (MSYMBOL_PRINT_NAME (exp->elts[pc + 2].msymbol), stream);
+      }
+      return;
+
     case OP_VAR_ENTRY_VALUE:
       {
        (*pos) += 2;
@@ -876,6 +883,15 @@ dump_subexp_body_standard (struct expression *exp,
                        SYMBOL_PRINT_NAME (exp->elts[elt + 1].symbol));
       elt += 3;
       break;
+    case OP_VAR_MSYM_VALUE:
+      fprintf_filtered (stream, "Objfile @");
+      gdb_print_host_address (exp->elts[elt].objfile, stream);
+      fprintf_filtered (stream, ", msymbol @");
+      gdb_print_host_address (exp->elts[elt + 1].msymbol, stream);
+      fprintf_filtered (stream, " (%s)",
+                       MSYMBOL_PRINT_NAME (exp->elts[elt + 1].msymbol));
+      elt += 3;
+      break;
     case OP_VAR_ENTRY_VALUE:
       fprintf_filtered (stream, "Entry value of symbol @");
       gdb_print_host_address (exp->elts[elt].symbol, stream);

diff --git a/gdb/expression.h b/gdb/expression.h
index 8fe6b070445492243f4162a591a5e453b3c198e8..9e4ddf5ded2472a6a1224c5373e089dad0e1d9d6 100644 (file)
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -64,6 +64,7 @@ union exp_element
   {
     enum exp_opcode opcode;
     struct symbol *symbol;
+    struct minimal_symbol *msymbol;
     LONGEST longconst;
     DOUBLEST doubleconst;
     gdb_byte decfloatconst[16];

diff --git a/gdb/minsyms.h b/gdb/minsyms.h
index e763f62aa36b7c5934bd86f2997a1787968dada9..dc517254e9e8eb406b0fc57ffe8c8e740c5c4f1f 100644 (file)
--- a/gdb/minsyms.h
+++ b/gdb/minsyms.h
@@ -20,6 +20,8 @@
 #ifndef MINSYMS_H
 #define MINSYMS_H
 
+struct type;
+
 /* Several lookup functions return both a minimal symbol and the
    objfile in which it is found.  This structure is used in these
    cases.  */
@@ -275,4 +277,11 @@ void iterate_over_minimal_symbols (struct objfile *objf,
 
 CORE_ADDR minimal_symbol_upper_bound (struct bound_minimal_symbol minsym);
 
+/* Return the type of MSYMBOL, a minimal symbol of OBJFILE.  If
+   ADDRESS_P is not NULL, set it to the MSYMBOL's resolved
+   address.  */
+
+type *find_minsym_type_and_address (minimal_symbol *msymbol, objfile *objf,
+                                   CORE_ADDR *address_p);
+
 #endif /* MINSYMS_H */

diff --git a/gdb/parse.c b/gdb/parse.c
index abf59d77e828e2ae236a044b22b5ba41de8bf5ff..83bfa4b24138ca3533c7e9934014ae7aa50e10b5 100644 (file)
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -255,6 +255,16 @@ write_exp_elt_sym (struct parser_state *ps, struct symbol *expelt)
   write_exp_elt (ps, &tmp);
 }
 
+void
+write_exp_elt_msym (struct parser_state *ps, minimal_symbol *expelt)
+{
+  union exp_element tmp;
+
+  memset (&tmp, 0, sizeof (union exp_element));
+  tmp.msymbol = expelt;
+  write_exp_elt (ps, &tmp);
+}
+
 void
 write_exp_elt_block (struct parser_state *ps, const struct block *b)
 {
@@ -470,17 +480,17 @@ write_exp_bitstring (struct parser_state *ps, struct stoken str)
   write_exp_elt_longcst (ps, (LONGEST) bits);
 }
 
-/* Add the appropriate elements for a minimal symbol to the end of
-   the expression.  */
+/* Return the type of MSYMBOL, a minimal symbol of OBJFILE.  If
+   ADDRESS_P is not NULL, set it to the MSYMBOL's resolved
+   address.  */
 
-void
-write_exp_msymbol (struct parser_state *ps,
-                  struct bound_minimal_symbol bound_msym)
+type *
+find_minsym_type_and_address (minimal_symbol *msymbol,
+                             struct objfile *objfile,
+                             CORE_ADDR *address_p)
 {
-  struct minimal_symbol *msymbol = bound_msym.minsym;
-  struct objfile *objfile = bound_msym.objfile;
+  bound_minimal_symbol bound_msym = {msymbol, objfile};
   struct gdbarch *gdbarch = get_objfile_arch (objfile);
-
   CORE_ADDR addr = BMSYMBOL_VALUE_ADDRESS (bound_msym);
   struct obj_section *section = MSYMBOL_OBJ_SECTION (objfile, msymbol);
   enum minimal_symbol_type type = MSYMBOL_TYPE (msymbol);
@@ -515,51 +525,54 @@ write_exp_msymbol (struct parser_state *ps,
   if (overlay_debugging)
     addr = symbol_overlayed_address (addr, section);
 
-  write_exp_elt_opcode (ps, OP_LONG);
-  /* Let's make the type big enough to hold a 64-bit address.  */
-  write_exp_elt_type (ps, objfile_type (objfile)->builtin_core_addr);
-  write_exp_elt_longcst (ps, (LONGEST) addr);
-  write_exp_elt_opcode (ps, OP_LONG);
-
   if (section && section->the_bfd_section->flags & SEC_THREAD_LOCAL)
     {
-      write_exp_elt_opcode (ps, UNOP_MEMVAL_TLS);
-      write_exp_elt_objfile (ps, objfile);
-      write_exp_elt_type (ps, objfile_type (objfile)->nodebug_tls_symbol);
-      write_exp_elt_opcode (ps, UNOP_MEMVAL_TLS);
-      return;
+      /* Skip translation if caller does not need the address.  */
+      if (address_p != NULL)
+       *address_p = target_translate_tls_address (objfile, addr);
+      return objfile_type (objfile)->nodebug_tls_symbol;
     }
 
-  write_exp_elt_opcode (ps, UNOP_MEMVAL);
+  if (address_p != NULL)
+    *address_p = addr;
+
+  struct type *the_type;
+
   switch (type)
     {
     case mst_text:
     case mst_file_text:
     case mst_solib_trampoline:
-      write_exp_elt_type (ps, objfile_type (objfile)->nodebug_text_symbol);
-      break;
+      return objfile_type (objfile)->nodebug_text_symbol;
 
     case mst_text_gnu_ifunc:
-      write_exp_elt_type (ps, objfile_type (objfile)
-                         ->nodebug_text_gnu_ifunc_symbol);
-      break;
+      return objfile_type (objfile)->nodebug_text_gnu_ifunc_symbol;
 
     case mst_data:
     case mst_file_data:
     case mst_bss:
     case mst_file_bss:
-      write_exp_elt_type (ps, objfile_type (objfile)->nodebug_data_symbol);
-      break;
+      return objfile_type (objfile)->nodebug_data_symbol;
 
     case mst_slot_got_plt:
-      write_exp_elt_type (ps, objfile_type (objfile)->nodebug_got_plt_symbol);
-      break;
+      return objfile_type (objfile)->nodebug_got_plt_symbol;
 
     default:
-      write_exp_elt_type (ps, objfile_type (objfile)->nodebug_unknown_symbol);
-      break;
+      return objfile_type (objfile)->nodebug_unknown_symbol;
     }
-  write_exp_elt_opcode (ps, UNOP_MEMVAL);
+}
+
+/* Add the appropriate elements for a minimal symbol to the end of
+   the expression.  */
+
+void
+write_exp_msymbol (struct parser_state *ps,
+                  struct bound_minimal_symbol bound_msym)
+{
+  write_exp_elt_opcode (ps, OP_VAR_MSYM_VALUE);
+  write_exp_elt_objfile (ps, bound_msym.objfile);
+  write_exp_elt_msym (ps, bound_msym.minsym);
+  write_exp_elt_opcode (ps, OP_VAR_MSYM_VALUE);
 }
 
 /* Mark the current index as the starting location of a structure
@@ -884,6 +897,7 @@ operator_length_standard (const struct expression *expr, int endpos,
     case OP_DOUBLE:
     case OP_DECFLOAT:
     case OP_VAR_VALUE:
+    case OP_VAR_MSYM_VALUE:
       oplen = 4;
       break;
 
@@ -1840,6 +1854,9 @@ operator_check_standard (struct expression *exp, int pos,
        type = SYMBOL_TYPE (symbol);
       }
       break;
+    case OP_VAR_MSYM_VALUE:
+      objfile = elts[pos + 1].objfile;
+      break;
     }
 
   /* Invoke callbacks for TYPE and OBJFILE if they were set as non-NULL.  */

diff --git a/gdb/std-operator.def b/gdb/std-operator.def
index 465072616f352e37dd5200b399b315e29c9dae34..9007dd48489419a8fe9509e6aef2ad2cc9fde8cd 100644 (file)
--- a/gdb/std-operator.def
+++ b/gdb/std-operator.def
@@ -132,6 +132,12 @@ OP (OP_VAR_VALUE)
    current function.  Implemented via DW_OP_entry_value.  */
 OP (OP_VAR_ENTRY_VALUE)
 
+/* OP_VAR_MSYM_VALUE takes one struct objfile * in the following
+   element, and one struct minimal_symbol * in the following
+   exp_element, followed by another OP_VAR_MSYM_VALUE, making four
+   exp_elements.  */
+OP (OP_VAR_MSYM_VALUE)
+
 /* OP_LAST is followed by an integer in the next exp_element.
    The integer is zero for the last value printed,
    or it is the absolute number of a history element.