[PATCH] Fix symtab/23853: symlinked default symtab

[Keith Seitz]

This patch attempts to fix a bug dealing with setting breakpoints
in default symtabs that are symlinks. For example:

(gdb) list
11 GNU General Public License for more details.
12
13 You should have received a copy of the GNU General Public License
14 along with this program. If not, see <http://www.gnu.org/licenses/>. */
15
16 static int
17 foo (void)
18 {
19 return 0; /* break here */
20 }
(gdb)
21
22 int
23 main (void)
24 {
25 return foo ();
26 }
(gdb) b 19
No line 19 in the current file.
Make breakpoint pending on future shared library load? (y or [n])

The problem here is that when convert_sals_line_offset sets the default
symtab, it immediately calls symtab_to_fullname, passing that fullname
to collect_symtabs_from_filename.

When we iterate over the compunit_symtabs in iterate_over_some_symtabs,
NAME is this the fullname from symtab_to_fullname while the symtab
filename is the symlink name (gotten from debuginfo).
compare_filenames_for_search is then called to ascertain a match between,
e.g., "symlink.c" and "/path/to/realsource.c".
The first comparison fails (compare_filenames_for_search returns early
with a simple strlen comparison).

Later in iterate_over_some_symtabs, symtab_to_fullname would be called
with the result of symtab_to_fullname, but only if the user has set
"basenames-may-differ." This flag defaults to "off" because, as
iterate_over_some_symtabs says, realpath is very expensive to use.

However, there seems little reason not to check the fullname if it is
already known (non-NULL). That's what this patch does.

gdb/ChangeLog

PR symtab/23853
* symtab.c (iterate_over_some_symtabs): If the symtab has a
fullname, check whether it is a filename match, too.

gdb/testsuite/ChangeLog

PR symtab/23853
* gdb.base/symlink-sourcefile.c: New file.
* gdb.base/symlink-sourcefile.exp: New file.
---
gdb/ChangeLog | 6 +++
gdb/symtab.c | 4 +-
gdb/testsuite/ChangeLog | 6 +++
gdb/testsuite/gdb.base/symlink-sourcefile.c | 26 +++++++++++
gdb/testsuite/gdb.base/symlink-sourcefile.exp | 44 +++++++++++++++++++
5 files changed, 85 insertions(+), 1 deletion(-)
create mode 100644 gdb/testsuite/gdb.base/symlink-sourcefile.c
create mode 100644 gdb/testsuite/gdb.base/symlink-sourcefile.exp

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index bc77fe85c7..557c72b203 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+YYYY-MM-DD Keith Seitz <***@redhat.com>
+
+ PR symtab/23853
+ * symtab.c (iterate_over_some_symtabs): If the symtab has a
+ fullname, check whether it is a filename match, too.
+
2018-11-04 Tom Tromey <***@tromey.com>

* varobj.c (install_default_visualizer): Update.
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 7649908d9c..5b39db6d33 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -412,7 +412,9 @@ iterate_over_some_symtabs (const char *name,
{
ALL_COMPUNIT_FILETABS (cust, s)
{
- if (compare_filenames_for_search (s->filename, name))
+ if (compare_filenames_for_search (s->filename, name)
+ || (s->fullname != nullptr
+ && compare_filenames_for_search (s->fullname, name)))
{
if (callback (s))
return true;
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 0df75aa54f..4befa4f4c9 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+YYYY-MM-DD Keith Seitz <***@redhat.com>
+
+ PR symtab/23853
+ * gdb.base/symlink-sourcefile.c: New file.
+ * gdb.base/symlink-sourcefile.exp: New file.
+
2018-11-01 Joel Brobecker <***@adacore.com>

* gdb.ada/watch_minus_l: New testcase.
diff --git a/gdb/testsuite/gdb.base/symlink-sourcefile.c b/gdb/testsuite/gdb.base/symlink-sourcefile.c
new file mode 100644
index 0000000000..2cf0d0e2fe
--- /dev/null
+++ b/gdb/testsuite/gdb.base/symlink-sourcefile.c
@@ -0,0 +1,26 @@
+/* Copyright 2018 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/>. */
+
+static int
+foo (void)
+{
+ return 0; /* break here */
+}
+
+int
+main (void)
+{
+ return foo ();
+}
diff --git a/gdb/testsuite/gdb.base/symlink-sourcefile.exp b/gdb/testsuite/gdb.base/symlink-sourcefile.exp
new file mode 100644
index 0000000000..084be07151
--- /dev/null
+++ b/gdb/testsuite/gdb.base/symlink-sourcefile.exp
@@ -0,0 +1,44 @@
+# Copyright 2018 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/>.
+
+# Test GDB when source files are symlinks.
+standard_testfile
+
+set test "file symbolic link name"
+set linksrc "link-${srcfile}"
+set srcfilelink [standard_output_file $linksrc]
+
+
+# Remove any existing symlink and build executable using the
+# symlink.
+remote_file host delete $srcfilelink
+set status [remote_exec host \
+ "ln -sf $srcdir/$subdir/$srcfile $srcfilelink"]
+if {[lindex $status 0] != 0} {
+ unsupported "$test (host does not support symbolic links)"
+ return 0
+}
+
+if {[prepare_for_testing $testfile $testfile $srcfilelink]} {
+ return -1
+}
+
+if {![runto_main]} {
+ untested "could not run to main"
+ return -1
+}
+
+gdb_breakpoint [gdb_get_line_number "break here" $srcfile] message
+gdb_continue_to_breakpoint "run to breakpoint marker"

[Pedro Alves]

Post by Keith Seitz
This patch attempts to fix a bug dealing with setting breakpoints
(gdb) list
11 GNU General Public License for more details.
12
13 You should have received a copy of the GNU General Public License
14 along with this program. If not, see <http://www.gnu.org/licenses/>. */
15
16 static int
17 foo (void)
18 {
19 return 0; /* break here */
20 }
(gdb)
21
22 int
23 main (void)
24 {
25 return foo ();
26 }
(gdb) b 19
No line 19 in the current file.
Make breakpoint pending on future shared library load? (y or [n])
The problem here is that when convert_sals_line_offset sets the default

s/convert_sals_line_offset/create_sals_line_offset/

Post by Keith Seitz
symtab, it immediately calls symtab_to_fullname, passing that fullname
to collect_symtabs_from_filename.
When we iterate over the compunit_symtabs in iterate_over_some_symtabs,
NAME is this the fullname from symtab_to_fullname while the symtab
filename is the symlink name (gotten from debuginfo).
compare_filenames_for_search is then called to ascertain a match between,
e.g., "symlink.c" and "/path/to/realsource.c".
The first comparison fails (compare_filenames_for_search returns early
with a simple strlen comparison).
Later in iterate_over_some_symtabs, symtab_to_fullname would be called
with the result of symtab_to_fullname, but only if the user has set

This sentence doesn't seem to make sense (symtab_to_fullname twice)?

I think you meant something like this:

Later in iterate_over_some_symtabs, the passed-in fullname would be compared
with the symtab's fullname but only if the user has set

Post by Keith Seitz
"basenames-may-differ." This flag defaults to "off" because, as
iterate_over_some_symtabs says, realpath is very expensive to use.
However, there seems little reason not to check the fullname if it is
already known (non-NULL). That's what this patch does.

My first reaction was, why are we doing that, passing down the
fullname instead of the symtab's filename, especially considering
basenames_may_differ. Pedantically looks odd at first sight.

I suppose I don't see a great reason to not chech fullname either,
so I guess that's fine.

Actually, if create_sals_line_offset has a default symtab handy, why
does it need to iterate over symtabs? Couldn't it just use the
default directly?

Post by Keith Seitz
gdb/ChangeLog
PR symtab/23853
* symtab.c (iterate_over_some_symtabs): If the symtab has a
fullname, check whether it is a filename match, too.
gdb/testsuite/ChangeLog
PR symtab/23853
* gdb.base/symlink-sourcefile.c: New file.
* gdb.base/symlink-sourcefile.exp: New file.
---
gdb/ChangeLog | 6 +++
gdb/symtab.c | 4 +-
gdb/testsuite/ChangeLog | 6 +++
gdb/testsuite/gdb.base/symlink-sourcefile.c | 26 +++++++++++
gdb/testsuite/gdb.base/symlink-sourcefile.exp | 44 +++++++++++++++++++
5 files changed, 85 insertions(+), 1 deletion(-)
create mode 100644 gdb/testsuite/gdb.base/symlink-sourcefile.c
create mode 100644 gdb/testsuite/gdb.base/symlink-sourcefile.exp
diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index bc77fe85c7..557c72b203 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+
+ PR symtab/23853
+ * symtab.c (iterate_over_some_symtabs): If the symtab has a
+ fullname, check whether it is a filename match, too.
+
* varobj.c (install_default_visualizer): Update.
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 7649908d9c..5b39db6d33 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -412,7 +412,9 @@ iterate_over_some_symtabs (const char *name,
{
ALL_COMPUNIT_FILETABS (cust, s)
{
- if (compare_filenames_for_search (s->filename, name))
+ if (compare_filenames_for_search (s->filename, name)
+ || (s->fullname != nullptr
+ && compare_filenames_for_search (s->fullname, name)))

This may use a comment. Otherwise a reader is wondering why we're comparing
the fullname, when basenames_may_differ is false, which pedantically looks
odd at first sight.

Also, I'm looking at this wondering about redundant checks and
efficiency.

I.e., if s->fullname is not NULL and the new check fails above, then
this one below:

if (compare_filenames_for_search (symtab_to_fullname (s), name))
{

... is guaranteed to fail too, AFAICS. That would suggest tweaking
that one to:

if (s->fullname == nullptr
|| compare_filenames_for_search (symtab_to_fullname (s), name))
{

then. Right?

I noticed that psym_map_symtabs_matching_filename uses the same
search algorithm, which looks like should be changed to match.
Maybe dw2_map_symtabs_matching_filename and
skiplist_entry::do_skip_file_p too. And others. Not sure.
I just grepped for basenames_may_differ and found these.

Post by Keith Seitz
+
+# Test GDB when source files are symlinks.

Please mention the specific case of the default symtab somewhere.
Either here, or at the gdb_breakpoint line below. That's important
for the test, right?

Post by Keith Seitz
+standard_testfile
+
+set test "file symbolic link name"
+set linksrc "link-${srcfile}"
+set srcfilelink [standard_output_file $linksrc]
+
+
+# Remove any existing symlink and build executable using the
+# symlink.
+remote_file host delete $srcfilelink
+set status [remote_exec host \
+ "ln -sf $srcdir/$subdir/$srcfile $srcfilelink"]
+if {[lindex $status 0] != 0} {
+ unsupported "$test (host does not support symbolic links)"
+ return 0
+}
+
+if {[prepare_for_testing $testfile $testfile $srcfilelink]} {
+ return -1
+}
+
+if {![runto_main]} {
+ untested "could not run to main"
+ return -1
+}
+
+gdb_breakpoint [gdb_get_line_number "break here" $srcfile] message
+gdb_continue_to_breakpoint "run to breakpoint marker"

Thanks,
Pedro Alves