RFC: allow breakpoints on labels

RFC: allow breakpoints on labels

[Tom Tromey]

This patch fixes PR 8357.

The bug is that while gcc emits dwarf for labels appearing in the user's
source, there is no way to refer to these labels from gdb.  This patch
changes the dwarf reader to put labels in the symbol table, and it
changes linespecs to let the user specify a label in the current
function.

Built and regtested on x86-64 (compile farm).

I'd appreciate comments.  This also needs a doc review.

Tom

2009-08-20  Tom Tromey  <tromey@redhat.com>

	PR breakpoints/8357:
	* symtab.h (domain_enum_tag) <LABEL_DOMAIN>: Update comment.
	* linespec.c (decode_line_1): Update comment.  Call decode_label.
	(decode_label): New function.
	(symbol_found): Handle LOC_LABEL.
	* dwarf2read.c (new_symbol) <DW_TAG_label>: Set symbol's type and
	domain.  Call add_symbol_to_list.

2009-08-20  Tom Tromey  <tromey@redhat.com>

	* gdb.texinfo (Specify Location): Document labels.

2009-08-20  Tom Tromey  <tromey@redhat.com>

	* gdb.base/label.exp: New file.
	* gdb.base/label.c: New file.

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4016acc..7dcf51c 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -5783,6 +5783,13 @@ in the file @var{filename}.  You only need the file name with a
 function name to avoid ambiguity when there are identically named
 functions in different source files.
 
+@item @var{label}
+Specifies the line at which the label named @var{label} appears.
+@value{GDBN} searches for the label in the function corresponding to
+the currently selected stack frame.  If there is no current selected
+stack frame (for instance, if the inferior is not running), then
+@value{GDBN} will not search for a label.
+
 @item *@var{address}
 Specifies the program address @var{address}.  For line-oriented
 commands, such as @code{list} and @code{edit}, this specifies a source
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 445bab8..21d6f9b 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -8327,7 +8327,10 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu)
 	    {
 	      SYMBOL_VALUE_ADDRESS (sym) = DW_ADDR (attr) + baseaddr;
 	    }
+	  SYMBOL_TYPE (sym) = objfile_type (objfile)->builtin_core_addr;
+	  SYMBOL_DOMAIN (sym) = LABEL_DOMAIN;
 	  SYMBOL_CLASS (sym) = LOC_LABEL;
+	  add_symbol_to_list (sym, cu->list_in_scope);
 	  break;
 	case DW_TAG_subprogram:
 	  /* SYMBOL_BLOCK_VALUE (sym) will be filled in later by
diff --git a/gdb/linespec.c b/gdb/linespec.c
index 3e943a1..4f7e797 100644
--- a/gdb/linespec.c
+++ b/gdb/linespec.c
@@ -123,6 +123,9 @@ static struct symtabs_and_lines decode_dollar (char *copy,
 					       char ***canonical,
 					       struct symtab *file_symtab);
 
+static int decode_label (char *copy, char ***canonical,
+			 struct symtabs_and_lines *result);
+
 static struct symtabs_and_lines decode_variable (char *copy,
 						 int funfirstline,
 						 char ***canonical,
@@ -640,6 +643,7 @@ See set/show multiple-symbol."));
    FILE:LINENUM -- that line in that file.  PC returned is 0.
    FUNCTION -- line number of openbrace of that function.
    PC returned is the start of the function.
+   LABEL -- a label in the current scope
    VARIABLE -- line number of definition of that variable.
    PC returned is 0.
    FILE:FUNCTION -- likewise, but prefer functions in that file.
@@ -873,6 +877,16 @@ decode_line_1 (char **argptr, int funfirstline, struct symtab *default_symtab,
     return decode_dollar (copy, funfirstline, default_symtab,
 			  canonical, file_symtab);
 
+  /* Try the token as a label, but only if no file was specified,
+     because we can only really find labels in the current scope.  */
+
+  if (!file_symtab)
+    {
+      struct symtabs_and_lines label_result;
+      if (decode_label (copy, canonical, &label_result))
+	return label_result;
+    }
+
   /* Look up that token as a variable.
      If file specified, use that file's per-file block to start with.  */
 
@@ -1708,6 +1722,27 @@ decode_dollar (char *copy, int funfirstline, struct symtab *default_symtab,
 
 \f
 
+/* A helper for decode_line_1 that tries to find a label.  The label
+   is searched for in the current block.
+   COPY is the name of the label to find.
+   CANONICAL is the same as the "canonical" argument to decode_line_1.
+   RESULT is a pointer to a symtabs_and_lines structure which will be
+   filled in on success.
+   This function returns 1 if a label was found, 0 otherwise.  */
+
+static int
+decode_label (char *copy, char ***canonical, struct symtabs_and_lines *result)
+{
+  struct symbol *sym;
+
+  sym = lookup_symbol (copy, get_selected_block (0), LABEL_DOMAIN, 0);
+
+  if (sym != NULL)
+    *result = symbol_found (0, canonical, copy, sym, NULL);
+
+  return sym != NULL;
+}
+
 /* Decode a linespec that's a variable.  If FILE_SYMTAB is non-NULL,
    look in that symtab's static variables first.  If NOT_FOUND_PTR is not NULL and
    the function cannot be found, store boolean true in the location pointed to
@@ -1787,7 +1822,7 @@ symbol_found (int funfirstline, char ***canonical, char *copy,
     }
   else
     {
-      if (funfirstline)
+      if (funfirstline && SYMBOL_CLASS (sym) != LOC_LABEL)
 	error (_("\"%s\" is not a function"), copy);
       else if (SYMBOL_LINE (sym) != 0)
 	{
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 740d4e0..d425d6e 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -378,8 +378,7 @@ typedef enum domain_enum_tag
 
   STRUCT_DOMAIN,
 
-  /* LABEL_DOMAIN may be used for names of labels (for gotos);
-     currently it is not used and labels are not recorded at all.  */
+  /* LABEL_DOMAIN may be used for names of labels (for gotos).  */
 
   LABEL_DOMAIN,
 
diff --git a/gdb/testsuite/gdb.base/label.c b/gdb/testsuite/gdb.base/label.c
new file mode 100644
index 0000000..f9cd8c3
--- /dev/null
+++ b/gdb/testsuite/gdb.base/label.c
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int
+main (int argc, char *argv)
+{
+  int i = 0;
+  goto there;
+
+here:
+  printf("not here\n");
+  i = 1;
+  
+there:
+  printf("but here\n");
+  if (i == 0)
+    goto here;
+
+done:
+  return 0;
+}
+
diff --git a/gdb/testsuite/gdb.base/label.exp b/gdb/testsuite/gdb.base/label.exp
new file mode 100644
index 0000000..9c4532c
--- /dev/null
+++ b/gdb/testsuite/gdb.base/label.exp
@@ -0,0 +1,66 @@
+# Copyright 2009 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if $tracelevel then {
+    strace $tracelevel
+}
+
+
+if [is_remote target] then {
+    return 0
+}
+
+
+#
+# test running programs
+#
+set prms_id 0
+set bug_id 0
+
+set testfile "label"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug nowarnings}] != "" } {
+    untested label.exp
+    return -1
+}
+
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+if {![runto_main]} {
+  fail "label tests suppressed"
+  return -1
+}
+
+gdb_test "break here" \
+  "Breakpoint.*at.*" \
+  "breakpoint here"
+
+gdb_test "break there" \
+  "Breakpoint.*at.*" \
+  "breakpoint there"
+
+gdb_test "cont" \
+  "Breakpoint 3,.*" \
+  "continue to 'there'"
+
+gdb_test "cont" \
+  "Breakpoint 2,.*" \
+  "continue to 'here'"

Re: RFC: allow breakpoints on labels

[Michael Snyder]

Tom Tromey wrote:
> This patch fixes PR 8357.
> 
> The bug is that while gcc emits dwarf for labels appearing in the user's
> source, there is no way to refer to these labels from gdb.  This patch
> changes the dwarf reader to put labels in the symbol table, and it
> changes linespecs to let the user specify a label in the current
> function.
> 
> Built and regtested on x86-64 (compile farm).
> 
> I'd appreciate comments.  This also needs a doc review.

Questions:
1) Labels will be in a separate name-space from other symbols (functions)?
2) The search order will find functions first, and only if
there is no conflicting function, find a label?  What if
there's a function and a label of the same name, and user
wants to specify the label?
3) There's no danger of our confusing a label with a
function somewhere downstream, and doing something silly
such as applying prologue_skip or skip_trampoline to a label?


> 2009-08-20  Tom Tromey  <tromey@redhat.com>
> 
> 	PR breakpoints/8357:
> 	* symtab.h (domain_enum_tag) <LABEL_DOMAIN>: Update comment.
> 	* linespec.c (decode_line_1): Update comment.  Call decode_label.
> 	(decode_label): New function.
> 	(symbol_found): Handle LOC_LABEL.
> 	* dwarf2read.c (new_symbol) <DW_TAG_label>: Set symbol's type and
> 	domain.  Call add_symbol_to_list.
> 
> 2009-08-20  Tom Tromey  <tromey@redhat.com>
> 
> 	* gdb.texinfo (Specify Location): Document labels.
> 
> 2009-08-20  Tom Tromey  <tromey@redhat.com>
> 
> 	* gdb.base/label.exp: New file.
> 	* gdb.base/label.c: New file.
> 
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 4016acc..7dcf51c 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -5783,6 +5783,13 @@ in the file @var{filename}.  You only need the file name with a
>  function name to avoid ambiguity when there are identically named
>  functions in different source files.
>  
> +@item @var{label}
> +Specifies the line at which the label named @var{label} appears.
> +@value{GDBN} searches for the label in the function corresponding to
> +the currently selected stack frame.  If there is no current selected
> +stack frame (for instance, if the inferior is not running), then
> +@value{GDBN} will not search for a label.
> +
>  @item *@var{address}
>  Specifies the program address @var{address}.  For line-oriented
>  commands, such as @code{list} and @code{edit}, this specifies a source
> diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
> index 445bab8..21d6f9b 100644
> --- a/gdb/dwarf2read.c
> +++ b/gdb/dwarf2read.c
> @@ -8327,7 +8327,10 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu)
>  	    {
>  	      SYMBOL_VALUE_ADDRESS (sym) = DW_ADDR (attr) + baseaddr;
>  	    }
> +	  SYMBOL_TYPE (sym) = objfile_type (objfile)->builtin_core_addr;
> +	  SYMBOL_DOMAIN (sym) = LABEL_DOMAIN;
>  	  SYMBOL_CLASS (sym) = LOC_LABEL;
> +	  add_symbol_to_list (sym, cu->list_in_scope);
>  	  break;
>  	case DW_TAG_subprogram:
>  	  /* SYMBOL_BLOCK_VALUE (sym) will be filled in later by
> diff --git a/gdb/linespec.c b/gdb/linespec.c
> index 3e943a1..4f7e797 100644
> --- a/gdb/linespec.c
> +++ b/gdb/linespec.c
> @@ -123,6 +123,9 @@ static struct symtabs_and_lines decode_dollar (char *copy,
>  					       char ***canonical,
>  					       struct symtab *file_symtab);
>  
> +static int decode_label (char *copy, char ***canonical,
> +			 struct symtabs_and_lines *result);
> +
>  static struct symtabs_and_lines decode_variable (char *copy,
>  						 int funfirstline,
>  						 char ***canonical,
> @@ -640,6 +643,7 @@ See set/show multiple-symbol."));
>     FILE:LINENUM -- that line in that file.  PC returned is 0.
>     FUNCTION -- line number of openbrace of that function.
>     PC returned is the start of the function.
> +   LABEL -- a label in the current scope
>     VARIABLE -- line number of definition of that variable.
>     PC returned is 0.
>     FILE:FUNCTION -- likewise, but prefer functions in that file.
> @@ -873,6 +877,16 @@ decode_line_1 (char **argptr, int funfirstline, struct symtab *default_symtab,
>      return decode_dollar (copy, funfirstline, default_symtab,
>  			  canonical, file_symtab);
>  
> +  /* Try the token as a label, but only if no file was specified,
> +     because we can only really find labels in the current scope.  */
> +
> +  if (!file_symtab)
> +    {
> +      struct symtabs_and_lines label_result;
> +      if (decode_label (copy, canonical, &label_result))
> +	return label_result;
> +    }
> +
>    /* Look up that token as a variable.
>       If file specified, use that file's per-file block to start with.  */
>  
> @@ -1708,6 +1722,27 @@ decode_dollar (char *copy, int funfirstline, struct symtab *default_symtab,
>  
>  \f
>  
> +/* A helper for decode_line_1 that tries to find a label.  The label
> +   is searched for in the current block.
> +   COPY is the name of the label to find.
> +   CANONICAL is the same as the "canonical" argument to decode_line_1.
> +   RESULT is a pointer to a symtabs_and_lines structure which will be
> +   filled in on success.
> +   This function returns 1 if a label was found, 0 otherwise.  */
> +
> +static int
> +decode_label (char *copy, char ***canonical, struct symtabs_and_lines *result)
> +{
> +  struct symbol *sym;
> +
> +  sym = lookup_symbol (copy, get_selected_block (0), LABEL_DOMAIN, 0);
> +
> +  if (sym != NULL)
> +    *result = symbol_found (0, canonical, copy, sym, NULL);
> +
> +  return sym != NULL;
> +}
> +
>  /* Decode a linespec that's a variable.  If FILE_SYMTAB is non-NULL,
>     look in that symtab's static variables first.  If NOT_FOUND_PTR is not NULL and
>     the function cannot be found, store boolean true in the location pointed to
> @@ -1787,7 +1822,7 @@ symbol_found (int funfirstline, char ***canonical, char *copy,
>      }
>    else
>      {
> -      if (funfirstline)
> +      if (funfirstline && SYMBOL_CLASS (sym) != LOC_LABEL)
>  	error (_("\"%s\" is not a function"), copy);
>        else if (SYMBOL_LINE (sym) != 0)
>  	{
> diff --git a/gdb/symtab.h b/gdb/symtab.h
> index 740d4e0..d425d6e 100644
> --- a/gdb/symtab.h
> +++ b/gdb/symtab.h
> @@ -378,8 +378,7 @@ typedef enum domain_enum_tag
>  
>    STRUCT_DOMAIN,
>  
> -  /* LABEL_DOMAIN may be used for names of labels (for gotos);
> -     currently it is not used and labels are not recorded at all.  */
> +  /* LABEL_DOMAIN may be used for names of labels (for gotos).  */
>  
>    LABEL_DOMAIN,
>  
> diff --git a/gdb/testsuite/gdb.base/label.c b/gdb/testsuite/gdb.base/label.c
> new file mode 100644
> index 0000000..f9cd8c3
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/label.c
> @@ -0,0 +1,21 @@
> +#include <stdio.h>
> +
> +int
> +main (int argc, char *argv)
> +{
> +  int i = 0;
> +  goto there;
> +
> +here:
> +  printf("not here\n");
> +  i = 1;
> +  
> +there:
> +  printf("but here\n");
> +  if (i == 0)
> +    goto here;
> +
> +done:
> +  return 0;
> +}
> +
> diff --git a/gdb/testsuite/gdb.base/label.exp b/gdb/testsuite/gdb.base/label.exp
> new file mode 100644
> index 0000000..9c4532c
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/label.exp
> @@ -0,0 +1,66 @@
> +# Copyright 2009 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +if $tracelevel then {
> +    strace $tracelevel
> +}
> +
> +
> +if [is_remote target] then {
> +    return 0
> +}
> +
> +
> +#
> +# test running programs
> +#
> +set prms_id 0
> +set bug_id 0
> +
> +set testfile "label"
> +set srcfile ${testfile}.c
> +set binfile ${objdir}/${subdir}/${testfile}
> +
> +if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug nowarnings}] != "" } {
> +    untested label.exp
> +    return -1
> +}
> +
> +
> +gdb_exit
> +gdb_start
> +gdb_reinitialize_dir $srcdir/$subdir
> +gdb_load ${binfile}
> +
> +if {![runto_main]} {
> +  fail "label tests suppressed"
> +  return -1
> +}
> +
> +gdb_test "break here" \
> +  "Breakpoint.*at.*" \
> +  "breakpoint here"
> +
> +gdb_test "break there" \
> +  "Breakpoint.*at.*" \
> +  "breakpoint there"
> +
> +gdb_test "cont" \
> +  "Breakpoint 3,.*" \
> +  "continue to 'there'"
> +
> +gdb_test "cont" \
> +  "Breakpoint 2,.*" \
> +  "continue to 'here'"

Re: RFC: allow breakpoints on labels

[Eli Zaretskii]

> From: Tom Tromey <tromey@redhat.com>
> Date: Thu, 20 Aug 2009 11:15:46 -0600
> 
> I'd appreciate comments.  This also needs a doc review.

The patch for the manual is fine.

As for the feature itself: I wonder if it would be possible to support
FILE:LABEL and/or FUNCTION:LABEL as well.  Since labels are local to
the function in which they are used, just LABEL sounds too
restrictive.

Thanks.

Re: RFC: allow breakpoints on labels

[Tom Tromey]

>>>>> "Michael" == Michael Snyder <msnyder@vmware.com> writes:

Michael> 1) Labels will be in a separate name-space from other symbols
Michael> (functions)?

Yes.  Here I just reused some existing gdb infrastructure, which appears
to mostly be unused.

You can't even "print label" at the moment, due to this.
It might be nice to implement the GCC address-of-label extension, though
this doesn't seem to be extremely useful.

Michael> 2) The search order will find functions first, and only if
Michael> there is no conflicting function, find a label?  What if
Michael> there's a function and a label of the same name, and user
Michael> wants to specify the label?

Yes, functions are searched first.  There's no way to pick the label in
this case.

Michael> 3) There's no danger of our confusing a label with a
Michael> function somewhere downstream, and doing something silly
Michael> such as applying prologue_skip or skip_trampoline to a label?

I don't think so, but I'm really not sure how I would be sure.

Tom

Re: RFC: allow breakpoints on labels

[Tom Tromey]

>>>>> "Eli" == Eli Zaretskii <eliz@gnu.org> writes:

Eli> The patch for the manual is fine.

Thanks.

Eli> As for the feature itself: I wonder if it would be possible to support
Eli> FILE:LABEL and/or FUNCTION:LABEL as well.  Since labels are local to
Eli> the function in which they are used, just LABEL sounds too
Eli> restrictive.

I will look into it.  FUNCTION:LABEL does seem natural to me, but
linespec seems quite difficult to modify correctly, and from what I can
see this would be a new syntax there.

Tom

Re: RFC: allow breakpoints on labels

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tromey@redhat.com> writes:

Tom> This patch fixes PR 8357.

This has been sitting around for almost a year:

http://sourceware.org/ml/gdb-patches/2009-08/msg00322.html

I am going to file a bug report for the suggested follow-up feature:

http://sourceware.org/ml/gdb-patches/2009-08/msg00327.html

... and check this in on the trunk.

Tom

Re: RFC: allow breakpoints on labels

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tromey@redhat.com> writes:

Tom> This has been sitting around for almost a year:
Tom> http://sourceware.org/ml/gdb-patches/2009-08/msg00322.html

I needed to set the pspace on the new sal, and I took the opportunity to
update the .exp file as well.  Here is the patch I am committing.

Tom

2010-07-13  Tom Tromey  <tromey@redhat.com>

	PR breakpoints/8357:
	* symtab.h (domain_enum_tag) <LABEL_DOMAIN>: Update comment.
	* linespec.c (decode_line_1): Update comment.  Call decode_label.
	(decode_label): New function.
	(symbol_found): Handle LOC_LABEL.
	* dwarf2read.c (new_symbol) <DW_TAG_label>: Set symbol's type and
	domain.  Call add_symbol_to_list.

2010-07-13  Tom Tromey  <tromey@redhat.com>

	* gdb.texinfo (Specify Location): Document labels.

2010-07-13  Tom Tromey  <tromey@redhat.com>

	* gdb.base/label.exp: New file.
	* gdb.base/label.c: New file.

Index: dwarf2read.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2read.c,v
retrieving revision 1.412
diff -u -r1.412 dwarf2read.c
--- dwarf2read.c	13 Jul 2010 15:09:03 -0000	1.412
+++ dwarf2read.c	13 Jul 2010 20:04:43 -0000
@@ -8807,7 +8807,10 @@
 	    {
 	      SYMBOL_VALUE_ADDRESS (sym) = DW_ADDR (attr) + baseaddr;
 	    }
+	  SYMBOL_TYPE (sym) = objfile_type (objfile)->builtin_core_addr;
+	  SYMBOL_DOMAIN (sym) = LABEL_DOMAIN;
 	  SYMBOL_CLASS (sym) = LOC_LABEL;
+	  add_symbol_to_list (sym, cu->list_in_scope);
 	  break;
 	case DW_TAG_subprogram:
 	  /* SYMBOL_BLOCK_VALUE (sym) will be filled in later by
Index: linespec.c
===================================================================
RCS file: /cvs/src/src/gdb/linespec.c,v
retrieving revision 1.103
diff -u -r1.103 linespec.c
--- linespec.c	14 May 2010 23:41:04 -0000	1.103
+++ linespec.c	13 Jul 2010 20:04:43 -0000
@@ -122,6 +122,9 @@
 					       char ***canonical,
 					       struct symtab *file_symtab);
 
+static int decode_label (char *copy, char ***canonical,
+			 struct symtabs_and_lines *result);
+
 static struct symtabs_and_lines decode_variable (char *copy,
 						 int funfirstline,
 						 char ***canonical,
@@ -672,6 +675,7 @@
    FILE:LINENUM -- that line in that file.  PC returned is 0.
    FUNCTION -- line number of openbrace of that function.
    PC returned is the start of the function.
+   LABEL -- a label in the current scope
    VARIABLE -- line number of definition of that variable.
    PC returned is 0.
    FILE:FUNCTION -- likewise, but prefer functions in that file.
@@ -903,6 +907,16 @@
     return decode_dollar (copy, funfirstline, default_symtab,
 			  canonical, file_symtab);
 
+  /* Try the token as a label, but only if no file was specified,
+     because we can only really find labels in the current scope.  */
+
+  if (!file_symtab)
+    {
+      struct symtabs_and_lines label_result;
+      if (decode_label (copy, canonical, &label_result))
+	return label_result;
+    }
+
   /* Look up that token as a variable.
      If file specified, use that file's per-file block to start with.  */
 
@@ -1838,6 +1852,27 @@
 
 \f
 
+/* A helper for decode_line_1 that tries to find a label.  The label
+   is searched for in the current block.
+   COPY is the name of the label to find.
+   CANONICAL is the same as the "canonical" argument to decode_line_1.
+   RESULT is a pointer to a symtabs_and_lines structure which will be
+   filled in on success.
+   This function returns 1 if a label was found, 0 otherwise.  */
+
+static int
+decode_label (char *copy, char ***canonical, struct symtabs_and_lines *result)
+{
+  struct symbol *sym;
+
+  sym = lookup_symbol (copy, get_selected_block (0), LABEL_DOMAIN, 0);
+
+  if (sym != NULL)
+    *result = symbol_found (0, canonical, copy, sym, NULL);
+
+  return sym != NULL;
+}
+
 /* Decode a linespec that's a variable.  If FILE_SYMTAB is non-NULL,
    look in that symtab's static variables first.  If NOT_FOUND_PTR is not NULL and
    the function cannot be found, store boolean true in the location pointed to
@@ -1917,7 +1952,7 @@
     }
   else
     {
-      if (funfirstline)
+      if (funfirstline && SYMBOL_CLASS (sym) != LOC_LABEL)
 	error (_("\"%s\" is not a function"), copy);
       else if (SYMBOL_LINE (sym) != 0)
 	{
@@ -1928,6 +1963,7 @@
 	  memset (&values.sals[0], 0, sizeof (values.sals[0]));
 	  values.sals[0].symtab = SYMBOL_SYMTAB (sym);
 	  values.sals[0].line = SYMBOL_LINE (sym);
+	  values.sals[0].pspace = SYMTAB_PSPACE (SYMBOL_SYMTAB (sym));
 	  return values;
 	}
       else
Index: symtab.h
===================================================================
RCS file: /cvs/src/src/gdb/symtab.h,v
retrieving revision 1.154
diff -u -r1.154 symtab.h
--- symtab.h	28 Jun 2010 20:35:52 -0000	1.154
+++ symtab.h	13 Jul 2010 20:04:44 -0000
@@ -377,8 +377,7 @@
 
   STRUCT_DOMAIN,
 
-  /* LABEL_DOMAIN may be used for names of labels (for gotos);
-     currently it is not used and labels are not recorded at all.  */
+  /* LABEL_DOMAIN may be used for names of labels (for gotos).  */
 
   LABEL_DOMAIN,
 
Index: doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.737
diff -u -r1.737 gdb.texinfo
--- doc/gdb.texinfo	1 Jul 2010 17:40:04 -0000	1.737
+++ doc/gdb.texinfo	13 Jul 2010 20:04:47 -0000
@@ -6330,6 +6330,13 @@
 function name to avoid ambiguity when there are identically named
 functions in different source files.
 
+@item @var{label}
+Specifies the line at which the label named @var{label} appears.
+@value{GDBN} searches for the label in the function corresponding to
+the currently selected stack frame.  If there is no current selected
+stack frame (for instance, if the inferior is not running), then
+@value{GDBN} will not search for a label.
+
 @item *@var{address}
 Specifies the program address @var{address}.  For line-oriented
 commands, such as @code{list} and @code{edit}, this specifies a source
Index: testsuite/gdb.base/label.c
===================================================================
RCS file: testsuite/gdb.base/label.c
diff -N testsuite/gdb.base/label.c
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/label.c	13 Jul 2010 20:04:49 -0000
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int
+main (int argc, char *argv)
+{
+  int i = 0;
+  goto there;
+
+here:
+  printf("not here\n");
+  i = 1;
+  
+there:
+  printf("but here\n");
+  if (i == 0)
+    goto here;
+
+done:
+  return 0;
+}
+
Index: testsuite/gdb.base/label.exp
===================================================================
RCS file: testsuite/gdb.base/label.exp
diff -N testsuite/gdb.base/label.exp
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/label.exp	13 Jul 2010 20:04:49 -0000
@@ -0,0 +1,59 @@
+# Copyright 2010 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if $tracelevel then {
+    strace $tracelevel
+}
+
+
+if [is_remote target] then {
+    return 0
+}
+
+
+#
+# test running programs
+#
+
+set testfile "label"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+
+if { [prepare_for_testing ${testfile}.exp $testfile ${testfile}.c debug] } {
+    untested label.exp
+    return -1
+}
+
+
+if {![runto_main]} {
+  fail "label tests suppressed"
+  return -1
+}
+
+gdb_test "break here" \
+  "Breakpoint.*at.*" \
+  "breakpoint here"
+
+gdb_test "break there" \
+  "Breakpoint.*at.*" \
+  "breakpoint there"
+
+gdb_test "cont" \
+  "Breakpoint 3,.*" \
+  "continue to 'there'"
+
+gdb_test "cont" \
+  "Breakpoint 2,.*" \
+  "continue to 'here'"