[PATCH v2] [PR gdb/17315]: fix until behavior with trailing !is_stmt lines

[PATCH v2] [PR gdb/17315]: fix until behavior with trailing !is_stmt lines

[Bruno Larsen]

When using the command "until", it is expected that GDB will exit a
loop, if the current instruction is the last one related to that loop.
However, if there were trailing non-statement instructions, "until"
would just behave as "next".  This was most noticeable in clang-compiled
code, but might happen with gcc-compiled as well.  PR gdb/17315 relates
to this problem, as running gdb.base/watchpoint.exp with clang
would fail for this reason

The current patch fixes this by adding an extra check to the
until_next_command function, going through all the following
instructions.  If the next instruction relates to the same line and is
not marked as a statement, the end of the execution range is moved to
the end of this next instruction.

This patch also adds a test case that can be run with gcc to test that
this functionality is not silently broken in future updates.
---
Changelog:
V2:
  - Added testcase
  - Improved commit message
  - Minor cosmetic changes to the code
---
 gdb/infcmd.c                                  |  26 ++++
 gdb/testsuite/gdb.base/until-trailing-insns.c |  31 +++++
 .../gdb.base/until-trailing-insns.exp         | 118 ++++++++++++++++++
 3 files changed, 175 insertions(+)
 create mode 100644 gdb/testsuite/gdb.base/until-trailing-insns.c
 create mode 100644 gdb/testsuite/gdb.base/until-trailing-insns.exp

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 8bf58018bdd..b8e09a7962e 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1346,6 +1346,32 @@ until_next_command (int from_tty)
 
       tp->control.step_range_start = BLOCK_ENTRY_PC (SYMBOL_BLOCK_VALUE (func));
       tp->control.step_range_end = sal.end;
+
+      /* Setting the step_range_end based on the current pc, we implicitly
+	 assume that the last entry for any given line must have is_stmt set.
+	 This is not necessarily true.  Clang-13, for example, would compile
+	 the following code:
+
+for(int i=0; i<10; i++)
+  {
+    foo()
+  }
+
+	 with 2 entries after the last is_stmt linetable entry.
+	 To fix this, we iterate over the sal related to the end PC, until
+	 we find an sal related to a different line, and set that pc as the
+	 step_range_end */
+
+      struct symtab_and_line final_sal;
+      final_sal = find_pc_line (tp->control.step_range_end, 0);
+
+      while (final_sal.line == sal.line)
+        {
+	  /* if there is another stmt for the same line, we dont need this */
+	  if (final_sal.is_stmt) break;
+	  tp->control.step_range_end = final_sal.end;
+	  final_sal = find_pc_line (final_sal.end, 0);
+        }
     }
   tp->control.may_range_step = 1;
 
diff --git a/gdb/testsuite/gdb.base/until-trailing-insns.c b/gdb/testsuite/gdb.base/until-trailing-insns.c
new file mode 100644
index 00000000000..6c6990a0f02
--- /dev/null
+++ b/gdb/testsuite/gdb.base/until-trailing-insns.c
@@ -0,0 +1,31 @@
+/* Copyright 2022 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/>.  */
+int main(){/* main prologue */
+    asm("main_label: .globl main_label"); /* This is required */
+    asm("loop_start: .globl loop_start");
+    int a, i;
+    i = 0;						/* loop assignment */
+    while (1) {						/* loop line */
+	asm("loop_condition: .globl loop_condition");
+	if (i >= 10) break;				/* loop condition */
+	asm("loop_code: .globl loop_code");
+	a = i;						/* loop code */
+	asm("loop_increment: .globl loop_increment");
+	i ++;						/* loop increment */
+	asm("loop_jump: .globl loop_jump");
+    }
+    asm("main_return: .globl main_return");
+    return 0; /* main return */
+}
diff --git a/gdb/testsuite/gdb.base/until-trailing-insns.exp b/gdb/testsuite/gdb.base/until-trailing-insns.exp
new file mode 100644
index 00000000000..50cee82be5a
--- /dev/null
+++ b/gdb/testsuite/gdb.base/until-trailing-insns.exp
@@ -0,0 +1,118 @@
+# Copyright 2022 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/>.
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    unsupported "dwarf2 support required for this test"
+    return 0
+}
+if [get_compiler_info] {
+    return -1
+}
+# dwarf assembler requires gcc compiled
+if !$gcc_compiled {
+    unsupported "gcc is required for this test"
+	return 0
+}
+
+standard_testfile .c .S
+
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
+    return -1
+}
+
+
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    global srcdir subdir srcfile
+    declare_labels integer_label L
+    set int_size [get_sizeof "int" 4]
+
+    # Find start address and length for our functions.
+    lassign [function_range main [list ${srcdir}/${subdir}/$srcfile]] \
+	main_start main_len
+    set main_end "$main_start + $main_len"
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name until-trailing-isns.c}
+	    {stmt_list $L DW_FORM_sec_offset}
+	    {low_pc 0 addr}
+	} {
+	    subprogram {
+		{external 1 flag}
+		{name main}
+		{low_pc $main_start addr}
+		{high_pc $main_len DW_FORM_data4}
+	    }
+	}
+    }
+
+    lines {version 2 default_is_stmt 1} L {
+	include_dir "${srcdir}/${subdir}"
+	file_name "$srcfile" 1
+
+	# Generate a line table program.  This mimicks clang-13's behavior
+	# of adding some !is_stmt at the end of a loop line, making until
+	# not work properly
+	program {
+	    {DW_LNE_set_address $main_start}
+	    {line [gdb_get_line_number "main prologue"]}
+	    {DW_LNS_copy}
+	    {DW_LNE_set_address loop_start}
+	    {line [gdb_get_line_number "loop line"]}
+	    {DW_LNS_copy}
+	    {DW_LNE_set_address loop_condition}
+	    {line [gdb_get_line_number "loop line"]}
+	    {DW_LNS_negate_stmt}
+	    {DW_LNS_copy}
+	    {DW_LNE_set_address loop_code}
+	    {line [gdb_get_line_number "loop code"]}
+	    {DW_LNS_negate_stmt}
+	    {DW_LNS_copy}
+	    {DW_LNE_set_address loop_increment}
+	    {line [gdb_get_line_number "loop line"]}
+	    {DW_LNS_copy}
+	    {DW_LNE_set_address loop_jump}
+	    {line [gdb_get_line_number "loop line"]}
+	    {DW_LNS_negate_stmt}
+	    {DW_LNS_copy}
+	    {DW_LNE_set_address main_return}
+	    {line [gdb_get_line_number "main return"]}
+	    {DW_LNS_negate_stmt}
+	    {DW_LNS_copy}
+	    {DW_LNE_set_address $main_end}
+	    {line [expr [gdb_get_line_number "main return"] + 1]}
+	    {DW_LNS_copy}
+	    {DW_LNE_end_sequence}
+	}
+    }
+
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	[list $srcfile $asm_file] {nodebug} ] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_test "next" ".* loop code .*" "inside the loop"
+gdb_test "next" ".* loop line .*" "ending of loop"
+gdb_test "until" ".* return 0; .*" "left loop"
-- 
2.31.1