Fix crash when expanding partial symtabs with DW_TAG_imported_unitsubmit/pr-27743-psym-fix

PR gdb/27743 points out a gdb crash when expanding partial symtabs,
where one of the compilation units uses DW_TAG_imported_unit.

The bug is that partial_map_expand_apply expects only to be called for
the outermost psymtab.  However, filename searching doesn't (and
probably shouldn't) guarantee this.  The fix is to walk upward to find
the outermost CU.

A new test case is included.  It is mostly copied from other test
cases, which really sped up the effort.

This bug does not occur on trunk.  There,
psym_map_symtabs_matching_filename is gone, replaced by
psymbol_functions::expand_symtabs_matching.  When this find a match,
it calls psymtab_to_symtab, which does this same upward walk.

Tested on x86-64 Fedora 32.

I propose checking in this patch on the gdb-10 branch, and just the
new test case on trunk.

gdb/ChangeLog
2021-04-23  Tom Tromey  <tromey@adacore.com>

	PR gdb/27743:
	* psymtab.c (partial_map_expand_apply): Expand outermost psymtab.

gdb/testsuite/ChangeLog
2021-04-23  Tom Tromey  <tromey@adacore.com>

	PR gdb/27743:
	* gdb.dwarf2/imported-unit-bp.exp: New file.
	* gdb.dwarf2/imported-unit-bp-main.c: New file.
	* gdb.dwarf2/imported-unit-bp-alt.c: New file.

6 files changed, 218 insertions, 3 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9ef41bab68e..dfee3dad157 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2021-04-23  Tom Tromey  <tromey@adacore.com>
+
+	PR gdb/27743:
+	* psymtab.c (partial_map_expand_apply): Expand outermost psymtab.
+
 2021-04-25  Joel Brobecker  <brobecker@adacore.com>
 
 	* version.in: Set GDB version number to 10.2.90.DATE-git.
diff --git a/gdb/psymtab.c b/gdb/psymtab.c
index 23eed6bc1c6..71b02caae51 100644
--- a/gdb/psymtab.c
+++ b/gdb/psymtab.c
@@ -127,9 +127,10 @@ partial_map_expand_apply (struct objfile *objfile,
 {
   struct compunit_symtab *last_made = objfile->compunit_symtabs;
 
-  /* Shared psymtabs should never be seen here.  Instead they should
-     be handled properly by the caller.  */
-  gdb_assert (pst->user == NULL);
+  /* We may see a shared psymtab here, but we want to expand the
+     outermost symtab.  */
+  while (pst->user != nullptr)
+    pst = pst->user;
 
   /* Don't visit already-expanded psymtabs.  */
   if (pst->readin_p (objfile))
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 87777f30436..903871fb296 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2021-04-23  Tom Tromey  <tromey@adacore.com>
+
+	PR gdb/27743:
+	* gdb.dwarf2/imported-unit-bp.exp: New file.
+	* gdb.dwarf2/imported-unit-bp-main.c: New file.
+	* gdb.dwarf2/imported-unit-bp-alt.c: New file.
+
 2021-04-25  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.base/default.exp: Change $_gdb_minor to 3.
diff --git a/gdb/testsuite/gdb.dwarf2/imported-unit-bp-alt.c b/gdb/testsuite/gdb.dwarf2/imported-unit-bp-alt.c
new file mode 100644
index 00000000000..0785e0a344e
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/imported-unit-bp-alt.c
@@ -0,0 +1,50 @@
+/* Copyright 2020-2021 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/>.  */
+
+/* Used to insert labels with which we can build a fake line table.  */
+#define LL(N) asm ("line_label_" #N ": .globl line_label_" #N)
+
+volatile int var;
+volatile int bar;
+
+/* Generate some code to take up some space.  */
+#define FILLER do { \
+    var = 99;	    \
+} while (0)
+
+int
+func (void)
+{					/* func prologue */
+  asm ("func_label: .globl func_label");
+  LL (1);	// F1, Ln 16
+  FILLER;
+  LL (2);	// F1, Ln 17
+  FILLER;
+  LL (3);	// F2, Ln 21
+  FILLER;
+  LL (4);	// F2, Ln 22 // F1, Ln 18, !S
+  FILLER;
+  LL (5);	// F1, Ln 19 !S
+  FILLER;
+  LL (6);	// F1, Ln 20
+  FILLER;
+  LL (7);
+  FILLER;
+  return 0;				/* func end */
+}
+
+#ifdef WITHMAIN
+int main () { return 0; }
+#endif
diff --git a/gdb/testsuite/gdb.dwarf2/imported-unit-bp-main.c b/gdb/testsuite/gdb.dwarf2/imported-unit-bp-main.c
new file mode 100644
index 00000000000..e355582b358
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/imported-unit-bp-main.c
@@ -0,0 +1,24 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2004-2021 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/>.  */
+
+extern int func (void);
+
+int
+main()
+{
+  return func ();
+}
diff --git a/gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp b/gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp
new file mode 100644
index 00000000000..b6a0f25d2ce
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp
@@ -0,0 +1,128 @@
+# Copyright 2020-2021 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 that "break /absolute/file:line" works ok with imported CUs.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+# The .c files use __attribute__.
+if [get_compiler_info] {
+    return -1
+}
+if !$gcc_compiled {
+    return 0
+}
+
+standard_testfile imported-unit-bp-alt.c .S imported-unit-bp-main.c
+
+set build_options {nodebug optimize=-O1}
+
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    global srcdir subdir srcfile srcfile
+    global build_options
+    declare_labels lines_label callee_subprog_label cu_label
+
+    get_func_info func "$build_options additional_flags=-DWITHMAIN"
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name "<artificial>"}
+	} {
+	    imported_unit {
+		{import %$cu_label}
+	    }
+	}
+    }
+
+    cu {} {
+	cu_label: compile_unit {
+	    {producer "gcc"}
+	    {language @DW_LANG_C}
+	    {name ${srcfile}}
+	    {comp_dir "/tmp"}
+	    {low_pc 0 addr}
+	    {stmt_list ${lines_label} DW_FORM_sec_offset}
+	} {
+	    callee_subprog_label: subprogram {
+		{external 1 flag}
+		{name callee}
+		{inline 3 data1}
+	    }
+	    subprogram {
+		{external 1 flag}
+		{name func}
+		{low_pc $func_start addr}
+		{high_pc "$func_start + $func_len" addr}
+	    } {
+	    }
+	}
+    }
+
+    lines {version 2 default_is_stmt 1} lines_label {
+	include_dir "/tmp"
+	file_name "$srcfile" 1
+
+	program {
+	    {DW_LNE_set_address line_label_1}
+	    {DW_LNS_advance_line 15}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address line_label_2}
+	    {DW_LNS_advance_line 1}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address line_label_3}
+	    {DW_LNS_advance_line 4}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address line_label_4}
+	    {DW_LNS_advance_line 1}
+	    {DW_LNS_copy}
+
+	    {DW_LNS_advance_line -4}
+	    {DW_LNS_negate_stmt}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address line_label_5}
+	    {DW_LNS_advance_line 1}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address line_label_6}
+	    {DW_LNS_advance_line 1}
+	    {DW_LNS_negate_stmt}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address line_label_7}
+	    {DW_LNE_end_sequence}
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file $srcfile3] $build_options] } {
+    return -1
+}
+
+gdb_reinitialize_dir /tmp
+
+# Using an absolute path is important to see the bug.
+gdb_test "break /tmp/${srcfile}:19" "Breakpoint .* file $srcfile, line .*"