Add dwarf2_per_objfile to dwarf_expr_context and dwarf2_frame_cache

Evaluating DWARF expressions (such as location expressions) requires
knowing about the current objfile.  For example, it may call functions
like dwarf2_fetch_die_loc_sect_off, which currently obtain the
dwarf2_per_objfile object it needs from the dwarf2_per_cu_data object.
However, since we are going to remove this
dwarf2_per_cu_data::dwarf2_per_objfile link, these functions will need
to obtain the current dwarf2_per_objfile by parmeter.

If we go up the stack, we see that the DWARF expression contexts
(dwarf_expr_context and the classes that derive from it) need to store
the dwarf2_per_objfile, to be able to pass it to those functions that
will need it.

This patch adds a constructor to all these dwarf_expr_context variants,
accepting a dwarf2_per_objfile parameter.  This dwarf2_per_objfile
generally comes from a symbol baton created earlier.

For frame-related expressions, the dwarf2_per_objfile object must be
passed through the dwarf2_frame_cache object.  This lead to the
dwarf2_frame_find_fde function returning (by parameter) a
dwarf2_per_objfile object.  I then realized that this made the existing
"out_offset" parameter redundant.  This offset is
`objfile->text_section_offset ()`, so it can be recomputed from the
dwarf2_per_objfile object at any time.  I therefore opted to remove this
output parameter, as well as the offset field of dwarf2_frame_cache.

*Note*, there's one spot I'm particularly unsure about.  In
dwarf_evaluate_loc_desc::push_dwarf_reg_entry_value, we would save and
overwrite the offset value in the context, along with a bunch of other
state.  This is because we might be about to evaluate something in a
different CU that the current one.  If the two CUs are in the same
objfile, then the text_offset is the same, as it's a property of the
objfile.  However, if the two CUs are possibly in different objfiles,
then it means the text_offsets are different.  It would also mean we
would need to save and restore the dwarf2_per_objfile in the context.
Is that even possible?

gdb/ChangeLog:

	* dwarf2/expr.h (struct dwarf_expr_context)
	<dwarf_expr_context>: Add dwarf2_per_objfile parameter.
	<offset>: Remove.
	<per_objfile>: New member.
	* dwarf2/expr.c (dwarf_expr_context::dwarf_expr_context): Add
	dwarf2_per_objfile parameter.  Don't set offset, set
	per_objfile.
	(dwarf_expr_context::execute_stack_op): Use offset from objfile.
	* dwarf2/frame.c (dwarf2_frame_find_fde): Return (by parameter)
	a dwarf2_per_objfile object instead of an offset.
	(class dwarf_expr_executor) <dwarf_expr_executor>: Add
	constructor.
	(execute_stack_op): Add dwarf2_per_objfile parameter, pass it
	to dwarf2_expr_executor constructor.  Don't set offset.
	(dwarf2_fetch_cfa_info): Update.
	(struct dwarf2_frame_cache) <text_offset>: Remove.
	<per_objfile>: New field.
	(dwarf2_frame_cache): Update.
	(dwarf2_frame_prev_register): Update.
	* dwarf2/loc.c (class dwarf_evaluate_loc_desc)
	<dwarf_evaluate_loc_desc>: Add constructor.
	(dwarf2_evaluate_loc_desc_full): Update.
	(dwarf2_locexpr_baton_eval): Update.
	(class symbol_needs_eval_context) <symbol_needs_eval_context>:
	Add constructor.
	(dwarf2_loc_desc_get_symbol_read_needs): Update.

Change-Id: I14df060669cc36ad04759f1708c6d7b1fda77727

5 files changed, 98 insertions, 53 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index e754c13..6ad1a71 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,34 @@
 2020-05-27  Simon Marchi  <simon.marchi@efficios.com>
 
+	* dwarf2/expr.h (struct dwarf_expr_context)
+	<dwarf_expr_context>: Add dwarf2_per_objfile parameter.
+	<offset>: Remove.
+	<per_objfile>: New member.
+	* dwarf2/expr.c (dwarf_expr_context::dwarf_expr_context): Add
+	dwarf2_per_objfile parameter.  Don't set offset, set
+	per_objfile.
+	(dwarf_expr_context::execute_stack_op): Use offset from objfile.
+	* dwarf2/frame.c (dwarf2_frame_find_fde): Return (by parameter)
+	a dwarf2_per_objfile object instead of an offset.
+	(class dwarf_expr_executor) <dwarf_expr_executor>: Add
+	constructor.
+	(execute_stack_op): Add dwarf2_per_objfile parameter, pass it
+	to dwarf2_expr_executor constructor.  Don't set offset.
+	(dwarf2_fetch_cfa_info): Update.
+	(struct dwarf2_frame_cache) <text_offset>: Remove.
+	<per_objfile>: New field.
+	(dwarf2_frame_cache): Update.
+	(dwarf2_frame_prev_register): Update.
+	* dwarf2/loc.c (class dwarf_evaluate_loc_desc)
+	<dwarf_evaluate_loc_desc>: Add constructor.
+	(dwarf2_evaluate_loc_desc_full): Update.
+	(dwarf2_locexpr_baton_eval): Update.
+	(class symbol_needs_eval_context) <symbol_needs_eval_context>:
+	Add constructor.
+	(dwarf2_loc_desc_get_symbol_read_needs): Update.
+
+2020-05-27  Simon Marchi  <simon.marchi@efficios.com>
+
 	* dwarf2/read.h (struct dwarf2_per_cu_data) <addr_type,
 	addr_sized_int_type>: Move to dwarf2_cu.
 	<int_type>: Move to dwarf2_per_objfile.
diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 14ffae4..91ac4c0 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -27,6 +27,7 @@
 #include "dwarf2.h"
 #include "dwarf2/expr.h"
 #include "dwarf2/loc.h"
+#include "dwarf2/read.h"
 #include "gdbsupport/underlying.h"
 #include "gdbarch.h"
 
@@ -88,17 +89,17 @@ dwarf_expr_context::address_type () const
 
 /* Create a new context for the expression evaluator.  */
 
-dwarf_expr_context::dwarf_expr_context ()
+dwarf_expr_context::dwarf_expr_context (dwarf2_per_objfile *per_objfile)
 : gdbarch (NULL),
   addr_size (0),
   ref_addr_size (0),
-  offset (0),
   recursion_depth (0),
   max_recursion_depth (0x100),
   location (DWARF_VALUE_MEMORY),
   len (0),
   data (NULL),
-  initialized (0)
+  initialized (0),
+  per_objfile (per_objfile)
 {
 }
 
@@ -631,7 +632,7 @@ dwarf_expr_context::execute_stack_op (const gdb_byte *op_ptr,
 	     index, not an address.  We don't support things like
 	     branching between the address and the TLS op.  */
 	  if (op_ptr >= op_end || *op_ptr != DW_OP_GNU_push_tls_address)
-	    result += this->offset;
+	    result += this->per_objfile->objfile->text_section_offset ();
 	  result_val = value_from_ulongest (address_type, result);
 	  break;
 
@@ -639,7 +640,7 @@ dwarf_expr_context::execute_stack_op (const gdb_byte *op_ptr,
 	case DW_OP_GNU_addr_index:
 	  op_ptr = safe_read_uleb128 (op_ptr, op_end, &uoffset);
 	  result = this->get_addr_index (uoffset);
-	  result += this->offset;
+	  result += this->per_objfile->objfile->text_section_offset ();
 	  result_val = value_from_ulongest (address_type, result);
 	  break;
 	case DW_OP_GNU_const_index:
diff --git a/gdb/dwarf2/expr.h b/gdb/dwarf2/expr.h
index 2f3d2ce..fd9c2bb 100644
--- a/gdb/dwarf2/expr.h
+++ b/gdb/dwarf2/expr.h
@@ -25,6 +25,8 @@
 #include "leb128.h"
 #include "gdbtypes.h"
 
+struct dwarf2_per_objfile;
+
 /* The location of a value.  */
 enum dwarf_value_location
 {
@@ -117,7 +119,7 @@ struct dwarf_stack_value
    its current state and its callbacks.  */
 struct dwarf_expr_context
 {
-  dwarf_expr_context ();
+  dwarf_expr_context (dwarf2_per_objfile *per_objfile);
   virtual ~dwarf_expr_context () = default;
 
   void push_address (CORE_ADDR value, bool in_stack_memory);
@@ -139,10 +141,6 @@ struct dwarf_expr_context
      context and operations depending on DW_FORM_ref_addr are not allowed.  */
   int ref_addr_size;
 
-  /* Offset used to relocate DW_OP_addr, DW_OP_addrx, and
-     DW_OP_GNU_addr_index arguments.  */
-  CORE_ADDR offset;
-
   /* The current depth of dwarf expression recursion, via DW_OP_call*,
      DW_OP_fbreg, DW_OP_push_object_address, etc., and the maximum
      depth we'll tolerate before raising an error.  */
@@ -185,6 +183,9 @@ struct dwarf_expr_context
      two cases need to be handled separately.)  */
   std::vector<dwarf_expr_piece> pieces;
 
+  /* We evaluate the expression in the context of this objfile.  */
+  dwarf2_per_objfile *per_objfile;
+
   /* Return the value of register number REGNUM (a DWARF register number),
      read as an address.  */
   virtual CORE_ADDR read_addr_from_reg (int regnum) = 0;
diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
index a05f841..a8748e4 100644
--- a/gdb/dwarf2/frame.c
+++ b/gdb/dwarf2/frame.c
@@ -166,8 +166,8 @@ struct comp_unit
   auto_obstack obstack;
 };
 
-static struct dwarf2_fde *dwarf2_frame_find_fde (CORE_ADDR *pc,
-						 CORE_ADDR *out_offset);
+static struct dwarf2_fde *dwarf2_frame_find_fde
+  (CORE_ADDR *pc, dwarf2_per_objfile **out_per_objfile);
 
 static int dwarf2_frame_adjust_regnum (struct gdbarch *gdbarch, int regnum,
 				       int eh_frame_p);
@@ -237,7 +237,11 @@ register %s (#%d) at %s"),
 
 class dwarf_expr_executor : public dwarf_expr_context
 {
- public:
+public:
+
+  dwarf_expr_executor (dwarf2_per_objfile *per_objfile)
+    : dwarf_expr_context (per_objfile)
+  {}
 
   struct frame_info *this_frame;
 
@@ -311,19 +315,18 @@ class dwarf_expr_executor : public dwarf_expr_context
 
 static CORE_ADDR
 execute_stack_op (const gdb_byte *exp, ULONGEST len, int addr_size,
-		  CORE_ADDR offset, struct frame_info *this_frame,
-		  CORE_ADDR initial, int initial_in_stack_memory)
+		  struct frame_info *this_frame, CORE_ADDR initial,
+		  int initial_in_stack_memory, dwarf2_per_objfile *per_objfile)
 {
   CORE_ADDR result;
 
-  dwarf_expr_executor ctx;
+  dwarf_expr_executor ctx (per_objfile);
   scoped_value_mark free_values;
 
   ctx.this_frame = this_frame;
   ctx.gdbarch = get_frame_arch (this_frame);
   ctx.addr_size = addr_size;
   ctx.ref_addr_size = -1;
-  ctx.offset = offset;
 
   ctx.push_address (initial, initial_in_stack_memory);
   ctx.eval (exp, len);
@@ -883,14 +886,16 @@ dwarf2_fetch_cfa_info (struct gdbarch *gdbarch, CORE_ADDR pc,
 		       const gdb_byte **cfa_end_out)
 {
   struct dwarf2_fde *fde;
-  CORE_ADDR text_offset;
+  dwarf2_per_objfile *per_objfile;
   CORE_ADDR pc1 = pc;
 
   /* Find the correct FDE.  */
-  fde = dwarf2_frame_find_fde (&pc1, &text_offset);
+  fde = dwarf2_frame_find_fde (&pc1, &per_objfile);
   if (fde == NULL)
     error (_("Could not compute CFA; needed to translate this expression"));
 
+  gdb_assert (per_objfile != nullptr);
+
   dwarf2_frame_state fs (pc1, fde->cie);
 
   /* Check for "quirks" - known bugs in producers.  */
@@ -898,14 +903,15 @@ dwarf2_fetch_cfa_info (struct gdbarch *gdbarch, CORE_ADDR pc,
 
   /* First decode all the insns in the CIE.  */
   execute_cfa_program (fde, fde->cie->initial_instructions,
-		       fde->cie->end, gdbarch, pc, &fs, text_offset);
+		       fde->cie->end, gdbarch, pc, &fs,
+		       per_objfile->objfile->text_section_offset ());
 
   /* Save the initialized register set.  */
   fs.initial = fs.regs;
 
   /* Then decode the insns in the FDE up to our target PC.  */
   execute_cfa_program (fde, fde->instructions, fde->end, gdbarch, pc, &fs,
-		       text_offset);
+		       per_objfile->objfile->text_section_offset ());
 
   /* Calculate the CFA.  */
   switch (fs.regs.cfa_how)
@@ -923,7 +929,7 @@ dwarf2_fetch_cfa_info (struct gdbarch *gdbarch, CORE_ADDR pc,
       }
 
     case CFA_EXP:
-      *text_offset_out = text_offset;
+      *text_offset_out = per_objfile->objfile->text_section_offset ();
       *cfa_start_out = fs.regs.cfa_exp;
       *cfa_end_out = fs.regs.cfa_exp + fs.regs.cfa_exp_len;
       return 0;
@@ -956,8 +962,8 @@ struct dwarf2_frame_cache
   /* Target address size in bytes.  */
   int addr_size;
 
-  /* The .text offset.  */
-  CORE_ADDR text_offset;
+  /* The dwarf2_per_objfile from which this frame description came.  */
+  dwarf2_per_objfile *per_objfile;
 
   /* If not NULL then this frame is the bottom frame of a TAILCALL_FRAME
      sequence.  If NULL then it is a normal case with no TAILCALL_FRAME
@@ -1003,8 +1009,9 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   CORE_ADDR pc1 = get_frame_address_in_block (this_frame);
 
   /* Find the correct FDE.  */
-  fde = dwarf2_frame_find_fde (&pc1, &cache->text_offset);
+  fde = dwarf2_frame_find_fde (&pc1, &cache->per_objfile);
   gdb_assert (fde != NULL);
+  gdb_assert (cache->per_objfile != nullptr);
 
   /* Allocate and initialize the frame state.  */
   struct dwarf2_frame_state fs (pc1, fde->cie);
@@ -1018,7 +1025,7 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   execute_cfa_program (fde, fde->cie->initial_instructions,
 		       fde->cie->end, gdbarch,
 		       get_frame_address_in_block (this_frame), &fs,
-		       cache->text_offset);
+		       cache->per_objfile->objfile->text_section_offset ());
 
   /* Save the initialized register set.  */
   fs.initial = fs.regs;
@@ -1034,8 +1041,9 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
       && entry_pc < fde->initial_location + fde->address_range)
     {
       /* Decode the insns in the FDE up to the entry PC.  */
-      instr = execute_cfa_program (fde, fde->instructions, fde->end, gdbarch,
-				   entry_pc, &fs, cache->text_offset);
+      instr = execute_cfa_program
+	(fde, fde->instructions, fde->end, gdbarch, entry_pc, &fs,
+	 cache->per_objfile->objfile->text_section_offset ());
 
       if (fs.regs.cfa_how == CFA_REG_OFFSET
 	  && (dwarf_reg_to_regnum (gdbarch, fs.regs.cfa_reg)
@@ -1051,7 +1059,7 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   /* Then decode the insns in the FDE up to our target PC.  */
   execute_cfa_program (fde, instr, fde->end, gdbarch,
 		       get_frame_address_in_block (this_frame), &fs,
-		       cache->text_offset);
+		       cache->per_objfile->objfile->text_section_offset ());
 
   try
     {
@@ -1069,8 +1077,8 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
 	case CFA_EXP:
 	  cache->cfa =
 	    execute_stack_op (fs.regs.cfa_exp, fs.regs.cfa_exp_len,
-			      cache->addr_size, cache->text_offset,
-			      this_frame, 0, 0);
+			      cache->addr_size, this_frame, 0, 0,
+			      cache->per_objfile);
 	  break;
 
 	default:
@@ -1270,8 +1278,9 @@ dwarf2_frame_prev_register (struct frame_info *this_frame, void **this_cache,
     case DWARF2_FRAME_REG_SAVED_EXP:
       addr = execute_stack_op (cache->reg[regnum].loc.exp.start,
 			       cache->reg[regnum].loc.exp.len,
-			       cache->addr_size, cache->text_offset,
-			       this_frame, cache->cfa, 1);
+			       cache->addr_size,
+			       this_frame, cache->cfa, 1,
+			       cache->per_objfile);
       return frame_unwind_got_memory (this_frame, regnum, addr);
 
     case DWARF2_FRAME_REG_SAVED_VAL_OFFSET:
@@ -1281,8 +1290,9 @@ dwarf2_frame_prev_register (struct frame_info *this_frame, void **this_cache,
     case DWARF2_FRAME_REG_SAVED_VAL_EXP:
       addr = execute_stack_op (cache->reg[regnum].loc.exp.start,
 			       cache->reg[regnum].loc.exp.len,
-			       cache->addr_size, cache->text_offset,
-			       this_frame, cache->cfa, 1);
+			       cache->addr_size,
+			       this_frame, cache->cfa, 1,
+			       cache->per_objfile);
       return frame_unwind_got_constant (this_frame, regnum, addr);
 
     case DWARF2_FRAME_REG_UNSPECIFIED:
@@ -1650,7 +1660,7 @@ set_comp_unit (struct objfile *objfile, struct comp_unit *unit)
    initial location associated with it into *PC.  */
 
 static struct dwarf2_fde *
-dwarf2_frame_find_fde (CORE_ADDR *pc, CORE_ADDR *out_offset)
+dwarf2_frame_find_fde (CORE_ADDR *pc, dwarf2_per_objfile **out_per_objfile)
 {
   for (objfile *objfile : current_program_space->objfiles ())
     {
@@ -1682,8 +1692,9 @@ dwarf2_frame_find_fde (CORE_ADDR *pc, CORE_ADDR *out_offset)
       if (it != fde_table->end ())
         {
           *pc = (*it)->initial_location + offset;
-	  if (out_offset)
-	    *out_offset = offset;
+	  if (out_per_objfile != nullptr)
+	    *out_per_objfile = get_dwarf2_per_objfile (objfile);
+
           return *it;
         }
     }
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index 414f9bc..964726e 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -617,7 +617,10 @@ sect_variable_value (struct dwarf_expr_context *ctx, sect_offset sect_off,
 
 class dwarf_evaluate_loc_desc : public dwarf_expr_context
 {
- public:
+public:
+  dwarf_evaluate_loc_desc (dwarf2_per_objfile *per_objfile)
+    : dwarf_expr_context (per_objfile)
+  {}
 
   struct frame_info *frame;
   struct dwarf2_per_cu_data *per_cu;
@@ -733,8 +736,6 @@ class dwarf_evaluate_loc_desc : public dwarf_expr_context
     this->gdbarch = per_cu->objfile ()->arch ();
     scoped_restore save_addr_size = make_scoped_restore (&this->addr_size);
     this->addr_size = per_cu->addr_size ();
-    scoped_restore save_offset = make_scoped_restore (&this->offset);
-    this->offset = per_cu->text_offset ();
 
     this->eval (data_src, size);
   }
@@ -2191,7 +2192,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
   if (size == 0)
     return allocate_optimized_out_value (subobj_type);
 
-  dwarf_evaluate_loc_desc ctx;
+  dwarf2_per_objfile *per_objfile = get_dwarf2_per_objfile (objfile);
+  dwarf_evaluate_loc_desc ctx (per_objfile);
   ctx.frame = frame;
   ctx.per_cu = per_cu;
   ctx.obj_address = 0;
@@ -2201,7 +2203,6 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
   ctx.gdbarch = objfile->arch ();
   ctx.addr_size = per_cu->addr_size ();
   ctx.ref_addr_size = per_cu->ref_addr_size ();
-  ctx.offset = per_cu->text_offset ();
 
   try
     {
@@ -2398,6 +2399,10 @@ dwarf2_evaluate_loc_desc (struct type *type, struct frame_info *frame,
 
 struct evaluate_for_locexpr_baton : public dwarf_evaluate_loc_desc
 {
+  evaluate_for_locexpr_baton (dwarf2_per_objfile *per_objfile)
+    : dwarf_evaluate_loc_desc (per_objfile)
+  {}
+
   /* The data that was passed in.  */
   gdb::array_view<const gdb_byte> data_view;
 
@@ -2443,12 +2448,11 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
 			   CORE_ADDR *valp,
 			   bool push_initial_value)
 {
-  struct objfile *objfile;
-
   if (dlbaton == NULL || dlbaton->size == 0)
     return 0;
 
-  evaluate_for_locexpr_baton ctx;
+  dwarf2_per_objfile *per_objfile = dlbaton->per_objfile;
+  evaluate_for_locexpr_baton ctx (per_objfile);
 
   ctx.frame = frame;
   ctx.per_cu = dlbaton->per_cu;
@@ -2460,12 +2464,9 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
       ctx.data_view = addr_stack->valaddr;
     }
 
-  objfile = dlbaton->per_objfile->objfile;
-
-  ctx.gdbarch = objfile->arch ();
+  ctx.gdbarch = per_objfile->objfile->arch ();
   ctx.addr_size = dlbaton->per_cu->addr_size ();
   ctx.ref_addr_size = dlbaton->per_cu->ref_addr_size ();
-  ctx.offset = dlbaton->per_cu->text_offset ();
 
   if (push_initial_value)
     ctx.push_address (ctx.obj_address, false);
@@ -2675,7 +2676,10 @@ dwarf2_compile_property_to_c (string_file *stream,
 
 class symbol_needs_eval_context : public dwarf_expr_context
 {
- public:
+public:
+  symbol_needs_eval_context (dwarf2_per_objfile *per_objfile)
+    : dwarf_expr_context (per_objfile)
+  {}
 
   enum symbol_needs_kind needs;
   struct dwarf2_per_cu_data *per_cu;
@@ -2792,14 +2796,13 @@ dwarf2_loc_desc_get_symbol_read_needs (const gdb_byte *data, size_t size,
 
   scoped_value_mark free_values;
 
-  symbol_needs_eval_context ctx;
+  symbol_needs_eval_context ctx (get_dwarf2_per_objfile (objfile));
 
   ctx.needs = SYMBOL_NEEDS_NONE;
   ctx.per_cu = per_cu;
   ctx.gdbarch = objfile->arch ();
   ctx.addr_size = per_cu->addr_size ();
   ctx.ref_addr_size = per_cu->ref_addr_size ();
-  ctx.offset = per_cu->text_offset ();
 
   ctx.eval (data, size);