[v2,04/15] Calling ifunc functions when resolver has debug info, user symbol same name

Message ID 20180325191943.8246-5-palves@redhat.com
State New
Headers show
Series
  • Fixing GNU ifunc support
Related show

Commit Message

Pedro Alves March 25, 2018, 7:19 p.m.
In v2:

  - find_gnu_ifunc is now based on name search.  Need exposed by
    PP64 (see later patches in the series).
  - Added iterate_over_minimal_symbols function_view overload for
    that, and made it possible to stop the search if the callback says
    so.

If the GNU ifunc resolver has the same name as the user visible
symbol, and the resolver has debug info, then the DWARF info for the
resolver masks the ifunc minsym.  In that scenario, if you try calling
the ifunc from GDB, you call the resolver instead.  With the
gnu-ifunc.exp testcase added in a following patch, you'd see:

  (gdb) p gnu_ifunc (3)
  $1 = (int (*)(int)) 0x400753 <final>
  (gdb) FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=0: p gnu_ifunc (3)
                                                       ^^^^^^^^^^^^^^^^

That is, we called the ifunc resolver manually, which returned a
pointer to the ifunc target function ("final").  The "final" symbol is
the function that GDB should have called automatically,

  ~~~~~~~~~~~~
  int
  final (int arg)
  {
    return arg + 1;
  }
  ~~~~~~~~~

which is what happens if you don't have debug info for the resolver:

  (gdb) p gnu_ifunc (3)
  $1 = 4
  (gdb) PASS: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=0: resolved_debug=1: p gnu_ifunc (3)
                                                       ^^^^^^^^^^^^^^^^

or if the resolver's symbol has a different name from the ifunc (as is
the case with modern uses of ifunc via __attribute__ ifunc, such as
glibc uses):

  (gdb) p gnu_ifunc (3)
  $1 = 4
  (gdb) PASS: gdb.base/gnu-ifunc.exp: resolver_attr=1: resolver_debug=1: resolved_debug=0: p gnu_ifunc (3)
                                      ^^^^^^^^^^^^^^^

in which case after this patch, you can still call the resolver
directly if you want:

  (gdb) p gnu_ifunc_resolver (3)
  $1 = (int (*)(int)) 0x400753 <final>

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>

	* c-exp.y (variable production): Prefer ifunc minsyms over
	regular function symbols.
	* symtab.c (find_gnu_ifunc): New function.
	* minsyms.h (lookup_msym_prefer): New enum.
	(lookup_minimal_symbol_by_pc_section): Replace 'want_trampoline'
	parameter by a lookup_msym_prefer parameter.
	* symtab.h (find_gnu_ifunc): New declaration.
---
 gdb/c-exp.y    | 20 ++++++++++++++++----
 gdb/linespec.c |  7 ++++---
 gdb/minsyms.c  | 30 +++++++++++++++++++++++-------
 gdb/minsyms.h  | 13 +++++++++++--
 gdb/symtab.c   | 32 ++++++++++++++++++++++++++++++++
 gdb/symtab.h   |  3 +++
 6 files changed, 89 insertions(+), 16 deletions(-)

-- 
2.14.3

Patch

diff --git a/gdb/c-exp.y b/gdb/c-exp.y
index e2ea07cd792..723249c1f58 100644
--- a/gdb/c-exp.y
+++ b/gdb/c-exp.y
@@ -1041,10 +1041,22 @@  variable:	name_not_typename
 			      if (symbol_read_needs_frame (sym.symbol))
 				innermost_block.update (sym);
 
-			      write_exp_elt_opcode (pstate, OP_VAR_VALUE);
-			      write_exp_elt_block (pstate, sym.block);
-			      write_exp_elt_sym (pstate, sym.symbol);
-			      write_exp_elt_opcode (pstate, OP_VAR_VALUE);
+			      /* If we found a function, see if it's
+				 an ifunc resolver that has the same
+				 address as the ifunc symbol itself.
+				 If so, prefer the ifunc symbol.  */
+
+			      bound_minimal_symbol resolver
+				= find_gnu_ifunc (sym.symbol);
+			      if (resolver.minsym != NULL)
+				write_exp_msymbol (pstate, resolver);
+			      else
+				{
+				  write_exp_elt_opcode (pstate, OP_VAR_VALUE);
+				  write_exp_elt_block (pstate, sym.block);
+				  write_exp_elt_sym (pstate, sym.symbol);
+				  write_exp_elt_opcode (pstate, OP_VAR_VALUE);
+				}
 			    }
 			  else if ($1.is_a_field_of_this)
 			    {
diff --git a/gdb/linespec.c b/gdb/linespec.c
index 1236b3f4754..7ff8dcf3a5b 100644
--- a/gdb/linespec.c
+++ b/gdb/linespec.c
@@ -4431,7 +4431,7 @@  compare_msyms (const void *a, const void *b)
 /* Callback for iterate_over_minimal_symbols that adds the symbol to
    the result.  */
 
-static void
+static bool
 add_minsym (struct minimal_symbol *minsym, void *d)
 {
   struct collect_minsyms *info = (struct collect_minsyms *) d;
@@ -4446,16 +4446,17 @@  add_minsym (struct minimal_symbol *minsym, void *d)
 	  symtab_and_line sal = find_pc_sect_line (func_addr, NULL, 0);
 
 	  if (info->symtab != sal.symtab)
-	    return;
+	    return false;
 	}
     }
 
   /* Exclude data symbols when looking for breakpoint locations.  */
   if (!info->list_mode && !msymbol_is_function (info->objfile, minsym))
-    return;
+    return false;
 
   bound_minimal_symbol_d mo = {minsym, info->objfile};
   VEC_safe_push (bound_minimal_symbol_d, info->msyms, &mo);
+  return false;
 }
 
 /* Search for minimal symbols called NAME.  If SEARCH_PSPACE
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index 72969b77787..c75c316c08d 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -469,11 +469,10 @@  linkage_name_str (const lookup_name_info &lookup_name)
 /* See minsyms.h.  */
 
 void
-iterate_over_minimal_symbols (struct objfile *objf,
-			      const lookup_name_info &lookup_name,
-			      void (*callback) (struct minimal_symbol *,
-						void *),
-			      void *user_data)
+iterate_over_minimal_symbols
+  (struct objfile *objf,
+   const lookup_name_info &lookup_name,
+   gdb::function_view<bool (minimal_symbol *)> callback)
 {
 
   /* The first pass is over the ordinary hash table.  */
@@ -490,7 +489,8 @@  iterate_over_minimal_symbols (struct objfile *objf,
 	   iter = iter->hash_next)
 	{
 	  if (mangled_cmp (MSYMBOL_LINKAGE_NAME (iter), name) == 0)
-	    (*callback) (iter, user_data);
+	    if (callback (iter))
+	      return;
 	}
     }
 
@@ -509,12 +509,28 @@  iterate_over_minimal_symbols (struct objfile *objf,
 	   iter != NULL;
 	   iter = iter->demangled_hash_next)
 	if (name_match (MSYMBOL_SEARCH_NAME (iter), lookup_name, NULL))
-	  (*callback) (iter, user_data);
+	  if (callback (iter))
+	    return;
     }
 }
 
 /* See minsyms.h.  */
 
+void
+iterate_over_minimal_symbols (struct objfile *objf,
+			      const lookup_name_info &lookup_name,
+			      bool (*callback) (struct minimal_symbol *,
+						void *),
+			      void *user_data)
+{
+  iterate_over_minimal_symbols (objf, lookup_name, [&] (minimal_symbol *iter)
+    {
+      return callback (iter, user_data);
+    });
+}
+
+/* See minsyms.h.  */
+
 struct bound_minimal_symbol
 lookup_minimal_symbol_text (const char *name, struct objfile *objf)
 {
diff --git a/gdb/minsyms.h b/gdb/minsyms.h
index 11a202025d3..6bd34a58058 100644
--- a/gdb/minsyms.h
+++ b/gdb/minsyms.h
@@ -20,6 +20,8 @@ 
 #ifndef MINSYMS_H
 #define MINSYMS_H
 
+#include "common/function-view.h"
+
 struct type;
 
 /* Several lookup functions return both a minimal symbol and the
@@ -266,14 +268,21 @@  struct bound_minimal_symbol lookup_minimal_symbol_by_pc (CORE_ADDR);
    should that need to be done.
 
    For each matching symbol, CALLBACK is called with the symbol and
-   USER_DATA as arguments.  */
+   USER_DATA as arguments.  If CALLBACK returns true, the search
+   stops.  */
 
 void iterate_over_minimal_symbols (struct objfile *objf,
 				   const lookup_name_info &name,
-				   void (*callback) (struct minimal_symbol *,
+				   bool (*callback) (struct minimal_symbol *,
 						     void *),
 				   void *user_data);
 
+/* Same, but use a gdb::function_view as callback type.  */
+void iterate_over_minimal_symbols
+  (struct objfile *objf,
+   const lookup_name_info &name,
+   gdb::function_view<bool (minimal_symbol *)> callback);
+
 /* Compute the upper bound of MINSYM.  The upper bound is the last
    address thought to be part of the symbol.  If the symbol has a
    size, it is used.  Otherwise use the lesser of the next minimal
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 2b1f9558abe..9d9d447776e 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -4945,6 +4945,38 @@  symbol_is_function_or_method (minimal_symbol *msymbol)
     }
 }
 
+/* See symtab.h.  */
+
+bound_minimal_symbol
+find_gnu_ifunc (const symbol *sym)
+{
+  if (SYMBOL_CLASS (sym) != LOC_BLOCK)
+    return {};
+
+  lookup_name_info lookup_name (SYMBOL_SEARCH_NAME (sym),
+				symbol_name_match_type::SEARCH_NAME);
+  struct objfile *objfile = symbol_objfile (sym);
+
+  CORE_ADDR address = BLOCK_START (SYMBOL_BLOCK_VALUE (sym));
+  minimal_symbol *ifunc = NULL;
+
+  iterate_over_minimal_symbols (objfile, lookup_name,
+				[&] (minimal_symbol *minsym)
+    {
+      if (MSYMBOL_TYPE (minsym) == mst_text_gnu_ifunc
+	  && MSYMBOL_VALUE_ADDRESS (objfile, minsym) == address)
+	{
+	  ifunc = minsym;
+	  return true;
+	}
+      return false;
+    });
+
+  if (ifunc != NULL)
+    return {ifunc, objfile};
+  return {};
+}
+
 /* Add matching symbols from SYMTAB to the current completion list.  */
 
 static void
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 22b52019ee3..ddf4cb2e310 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1681,6 +1681,9 @@  extern int find_pc_partial_function (CORE_ADDR, const char **, CORE_ADDR *,
 
 extern struct type *find_gnu_ifunc_target_type (CORE_ADDR resolver_funaddr);
 
+/* Find the GNU ifunc minimal symbol that matches SYM.  */
+extern bound_minimal_symbol find_gnu_ifunc (const symbol *sym);
+
 extern void clear_pc_function_cache (void);
 
 /* Expand symtab containing PC, SECTION if not already expanded.  */