[v2,07/15] Breakpoints, don't skip prologue of ifunc resolvers with debug info

Message ID 20180325191943.8246-8-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:

  - The minsym/symbol matching in convert_linespec_to_sals is done
    differently.  The v1 bsearch method wouldn't work for PPC64, given
    function descriptors.  convert_linespec_to_sals will be touched
    again later in the series, for PPC64.
  - Moved declarations of locals closer to uses, because at some point
    I managed to reuse 'i' in an inner loop messing the outer loop...

Without this patch, some of the tests added to gdb.base/gnu-ifunc.exp
by a following patch fail like so:

  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=0: set-break: before resolving: break gnu_ifunc
  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=0: set-break: before resolving: info breakpoints
  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=0: set-break: after resolving: break gnu_ifunc
  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=0: set-break: after resolving: info breakpoints
  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=1: set-break: before resolving: break gnu_ifunc
  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=1: set-break: before resolving: info breakpoints
  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=1: set-break: after resolving: break gnu_ifunc
  FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=1: resolved_debug=1: set-break: after resolving: info breakpoints

All of them trigger iff:

 - you have debug info for the ifunc resolver.
 - the resolver and the user-visible symbol have the same name.

If you have an ifunc that has a resolver with the same name as the
user visible symbol, debug info for the resolver masks out the ifunc
minsym.  When you set a breakpoint by name on the user visible symbol,
GDB finds the DWARF symbol for the resolver, and thinking that it's a
regular function, sets a breakpoint location past its prologue.

Like so, location 1.2, before the ifunc is resolved by the inferior:

  (gdb) break gnu_ifunc
  Breakpoint 2 at 0x7ffff7bd36ea (2 locations)
  (gdb) info breakpoints
  Num     Type           Disp Enb Address            What
  1       breakpoint     keep y   <MULTIPLE>
  1.1                         y     0x00007ffff7bd36ea <gnu_ifunc>
  1.2                         y     0x00007ffff7bd36f2 in gnu_ifunc at src/gdb/testsuite/gdb.base/gnu-ifunc-lib.c:34
  (gdb)

And like so, location 2.2, if you set the breakpoint after the ifunc
is resolved by the inferior (to "final"):

  (gdb) break gnu_ifunc
  Breakpoint 5 at 0x400757 (2 locations)
  (gdb) info breakpoints
  Num     Type           Disp Enb Address            What
  2       breakpoint     keep y   <MULTIPLE>
  2.1                         y     0x000000000040075a in final at src/gdb/testsuite/gdb.base/gnu-ifunc-resd.c:21
  2.2                         y     0x00007ffff7bd36f2 in gnu_ifunc at src/gdb/testsuite/gdb.base/gnu-ifunc-lib.c:34
  (gdb)

I don't think this is right because when users set a breakpoint at an
ifunc, they don't care about debugging the resolver.  Instead what you
should is a single location for the ifunc in the first case, and a
single location of the ifunc target in the second case.

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

	* linespec.c (struct bound_minimal_symbol_search_key): New.
	(convert_linespec_to_sals): Sort minimal symbols earlier.  Don't
	skip first line if we found a GNU ifunc minimal symbol by name.
	(compare_msymbols): Change parameters to work with a destructured
	lhs minsym.
	(compare_msymbols_for_qsort, compare_msymbols_for_bsearch): New
	functions.
---
 gdb/linespec.c | 60 +++++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 45 insertions(+), 15 deletions(-)

-- 
2.14.3

Patch

diff --git a/gdb/linespec.c b/gdb/linespec.c
index c549ba09349..70f23187e02 100644
--- a/gdb/linespec.c
+++ b/gdb/linespec.c
@@ -2308,12 +2308,6 @@  convert_linespec_to_sals (struct linespec_state *state, linespec_p ls)
   else if (ls->function_symbols != NULL || ls->minimal_symbols != NULL)
     {
       /* We have just a bunch of functions and/or methods.  */
-      int i;
-      struct symtab_and_line sal;
-      struct symbol *sym;
-      bound_minimal_symbol_d *elem;
-      struct program_space *pspace;
-
       if (ls->function_symbols != NULL)
 	{
 	  /* Sort symbols so that symbols with the same program space are next
@@ -2322,30 +2316,66 @@  convert_linespec_to_sals (struct linespec_state *state, linespec_p ls)
 		 VEC_length (symbolp, ls->function_symbols),
 		 sizeof (symbolp), compare_symbols);
 
-	  for (i = 0; VEC_iterate (symbolp, ls->function_symbols, i, sym); ++i)
+	  struct symbol *sym;
+	  for (int i = 0; VEC_iterate (symbolp, ls->function_symbols, i, sym); ++i)
 	    {
-	      pspace = SYMTAB_PSPACE (symbol_symtab (sym));
+	      program_space *pspace = SYMTAB_PSPACE (symbol_symtab (sym));
 	      set_current_program_space (pspace);
-	      if (symbol_to_sal (&sal, state->funfirstline, sym)
-		  && maybe_add_address (state->addr_set, pspace, sal.pc))
-		add_sal_to_sals (state, &sals, &sal,
-				 SYMBOL_NATURAL_NAME (sym), 0);
+
+	      /* Don't skip to the first line of the function if we
+		 had found an ifunc minimal symbol for this function,
+		 because that means that this function is an ifunc
+		 resolver with the same name as the ifunc itself.  */
+	      bool found_ifunc = false;
+
+	      if (state->funfirstline
+		   && ls->minimal_symbols != NULL
+		   && SYMBOL_CLASS (sym) == LOC_BLOCK)
+		{
+		  const CORE_ADDR addr
+		    = BLOCK_START (SYMBOL_BLOCK_VALUE (sym));
+
+		  bound_minimal_symbol_d *elem;
+		  for (int m = 0;
+		       VEC_iterate (bound_minimal_symbol_d, ls->minimal_symbols,
+				    m, elem);
+		       ++m)
+		    {
+		      if (MSYMBOL_TYPE (elem->minsym) == mst_text_gnu_ifunc
+			  && BMSYMBOL_VALUE_ADDRESS (*elem) == addr)
+			{
+			  found_ifunc = true;
+			  break;
+			}
+		    }
+		}
+
+	      if (!found_ifunc)
+		{
+		  symtab_and_line sal;
+		  if (symbol_to_sal (&sal, state->funfirstline, sym)
+		      && maybe_add_address (state->addr_set, pspace, sal.pc))
+		    add_sal_to_sals (state, &sals, &sal,
+				     SYMBOL_NATURAL_NAME (sym), 0);
+		}
 	    }
 	}
 
       if (ls->minimal_symbols != NULL)
 	{
-	  /* Sort minimal symbols by program space, too.  */
+	  /* Sort minimal symbols by program space, too  */
 	  qsort (VEC_address (bound_minimal_symbol_d, ls->minimal_symbols),
 		 VEC_length (bound_minimal_symbol_d, ls->minimal_symbols),
 		 sizeof (bound_minimal_symbol_d), compare_msymbols);
 
-	  for (i = 0;
+	  bound_minimal_symbol_d *elem;
+
+	  for (int i = 0;
 	       VEC_iterate (bound_minimal_symbol_d, ls->minimal_symbols,
 			    i, elem);
 	       ++i)
 	    {
-	      pspace = elem->objfile->pspace;
+	      program_space *pspace = elem->objfile->pspace;
 	      set_current_program_space (pspace);
 	      minsym_found (state, elem->objfile, elem->minsym, &sals);
 	    }