Patchwork [06/11] Fix setting breakpoints on ifunc functions after they're already resolved

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Submitter Pedro Alves
Date March 9, 2018, 9:16 p.m.
Message ID <20180309211612.12941-7-palves@redhat.com>
Download mbox | patch
Permalink /patch/26270/
State New
Headers show

Comments

Pedro Alves - March 9, 2018, 9:16 p.m.
This fixes setting breakpoints on ifunc functions by name after the
ifunc has already been resolved.

In that case, if you have debug info for the ifunc resolver, without
the fix, then gdb puts a breakpoint past the prologue of the resolver,
instead of setting a breakpoint at the ifunc target:

  break gnu_ifunc
  Breakpoint 4 at 0x7ffff7bd36f2: file src/gdb/testsuite/gdb.base/gnu-ifunc-lib.c, line 34.
  (gdb) continue
  Continuing.
  [Inferior 1 (process 13300) exited normally]
  (gdb)

above we should have stopped at "final", but didn't because we never
resolved the ifunc to the final location.

If you don't have debug info for the resolver, GDB manages to resolve
the ifunc target, but, it should be setting a breakpoint after the
prologue of the final function, and instead what you get is that GDB
sets a breakpoint on the first address of the target function.  With
the gnu-ifunc.exp tests added by a later patch, we get, without the
fix:

  (gdb) break gnu_ifunc
  Breakpoint 4 at 0x400753
  (gdb) continue
  Continuing.

  Breakpoint 4, final (arg=1) at src/gdb/testsuite/gdb.base/gnu-ifunc-resd.c:20
  20	{

vs, fixed:

  (gdb) break gnu_ifunc
  Breakpoint 4 at 0x40075a: file src/gdb/testsuite/gdb.base/gnu-ifunc-resd.c, line 21.
  (gdb) continue
  Continuing.

  Breakpoint 4, final (arg=2) at src/gdb/testsuite/gdb.base/gnu-ifunc-resd.c:21
  21	  return arg + 1;
  (gdb)

Fix the problems above by moving the ifunc target resolving to
linespec.c, before we skip a function's prologue.  We need to save
something in the sal, so that set_breakpoint_location_function knows
that it needs to create a bp_gnu_ifunc_resolver bp_location.  Might as
well just save a pointer to the minsym.

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

	* breakpoint.c (set_breakpoint_location_function): Don't resolve
	ifunc targets here.  Instead, if we have an ifunc minsym, use its
	address/name.
	(add_location_to_breakpoint): Store the minsym and the objfile in
	the breakpoint location.
	* breakpoint.h (bp_location) <msymbol, objfile>: New fields.
	* linespec.c (minsym_found): Resolve GNU ifunc targets here.
	Record the minsym in the sal.
	* symtab.h (symtab_and_line) <msymbol>: New field.
---
 gdb/breakpoint.c | 31 +++++++++++++------------------
 gdb/breakpoint.h |  8 ++++++++
 gdb/linespec.c   | 14 +++++++++++---
 gdb/symtab.h     |  1 +
 4 files changed, 33 insertions(+), 21 deletions(-)

Patch

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 454fda7684a..928411149e4 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -7180,37 +7180,30 @@  set_breakpoint_location_function (struct bp_location *loc, int explicit_loc)
       || loc->owner->type == bp_hardware_breakpoint
       || is_tracepoint (loc->owner))
     {
-      int is_gnu_ifunc;
       const char *function_name;
-      CORE_ADDR func_addr;
 
-      find_pc_partial_function_gnu_ifunc (loc->address, &function_name,
-					  &func_addr, NULL, &is_gnu_ifunc);
-
-      if (is_gnu_ifunc && !explicit_loc)
+      if (loc->msymbol != NULL
+	  && MSYMBOL_TYPE (loc->msymbol) == mst_text_gnu_ifunc
+	  && !explicit_loc)
 	{
 	  struct breakpoint *b = loc->owner;
 
-	  gdb_assert (loc->pspace == current_program_space);
-	  if (gnu_ifunc_resolve_name (function_name,
-				      &loc->requested_address))
-	    {
-	      /* Recalculate ADDRESS based on new REQUESTED_ADDRESS.  */
-	      loc->address = adjust_breakpoint_address (loc->gdbarch,
-							loc->requested_address,
-							b->type);
-	    }
-	  else if (b->type == bp_breakpoint && b->loc == loc
-	           && loc->next == NULL && b->related_breakpoint == b)
+	  function_name = MSYMBOL_LINKAGE_NAME (loc->msymbol);
+
+	  if (b->type == bp_breakpoint && b->loc == loc
+	      && loc->next == NULL && b->related_breakpoint == b)
 	    {
 	      /* Create only the whole new breakpoint of this type but do not
 		 mess more complicated breakpoints with multiple locations.  */
 	      b->type = bp_gnu_ifunc_resolver;
 	      /* Remember the resolver's address for use by the return
 	         breakpoint.  */
-	      loc->related_address = func_addr;
+	      loc->related_address
+		= MSYMBOL_VALUE_ADDRESS (loc->objfile, loc->msymbol);
 	    }
 	}
+      else
+	find_pc_partial_function (loc->address, &function_name, NULL, NULL);
 
       if (function_name)
 	loc->function_name = xstrdup (function_name);
@@ -8674,6 +8667,8 @@  add_location_to_breakpoint (struct breakpoint *b,
   loc->line_number = sal->line;
   loc->symtab = sal->symtab;
   loc->symbol = sal->symbol;
+  loc->msymbol = sal->msymbol;
+  loc->objfile = sal->objfile;
 
   set_breakpoint_location_function (loc,
 				    sal->explicit_pc || sal->explicit_line);
diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index 8bb81d8d17e..0aeca3b7f95 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -491,6 +491,14 @@  public:
      ascertain when an event location was set at a different location than
      the one originally selected by parsing, e.g., inlined symbols.  */
   const struct symbol *symbol = NULL;
+
+  /* Similarly, the minimal symbol found by the location parser, if
+     any.  This may be used to ascertain if the location was
+     originally set on a GNU ifunc symbol.  */
+  const minimal_symbol *msymbol = NULL;
+
+  /* The objfile the symbol or minimal symbol were found in.  */
+  const struct objfile *objfile = NULL;
 };
 
 /* The possible return values for print_bpstat, print_it_normal,
diff --git a/gdb/linespec.c b/gdb/linespec.c
index 1236b3f4754..1f1fb695c14 100644
--- a/gdb/linespec.c
+++ b/gdb/linespec.c
@@ -4334,10 +4334,17 @@  minsym_found (struct linespec_state *self, struct objfile *objfile,
 	      struct minimal_symbol *msymbol,
 	      std::vector<symtab_and_line> *result)
 {
-  struct symtab_and_line sal;
-
+  symtab_and_line sal;
   CORE_ADDR func_addr;
-  if (msymbol_is_function (objfile, msymbol, &func_addr))
+  bool is_function;
+
+  if (MSYMBOL_TYPE (msymbol) == mst_text_gnu_ifunc)
+    is_function = gnu_ifunc_resolve_name (MSYMBOL_LINKAGE_NAME (msymbol),
+					  &func_addr);
+  else
+    is_function = msymbol_is_function (objfile, msymbol, &func_addr);
+
+  if (is_function)
     {
       sal = find_pc_sect_line (func_addr, NULL, 0);
 
@@ -4360,6 +4367,7 @@  minsym_found (struct linespec_state *self, struct objfile *objfile,
   else
     {
       sal.objfile = objfile;
+      sal.msymbol = msymbol;
       sal.pc = MSYMBOL_VALUE_ADDRESS (objfile, msymbol);
       sal.pspace = current_program_space;
     }
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 5dc52c58e0e..52ab1357300 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1761,6 +1761,7 @@  struct symtab_and_line
   struct symtab *symtab = NULL;
   struct symbol *symbol = NULL;
   struct obj_section *section = NULL;
+  struct minimal_symbol *msymbol = NULL;
   /* Line number.  Line numbers start at 1 and proceed through symtab->nlines.
      0 is never a valid line number; it is used to indicate that line number
      information is not available.  */