Handle two-linetable function in find_epilogue_using_linetable

Consider the following test-case:
...
$ cat hello.c
int main()
{
  printf("hello ");
  #include "world.inc"
$ cat world.inc
  printf("world\n");
  return 0;
}
$ gcc -g hello.c
...

The line table for the compilation unit, consisting just of
function main, is translated into these two gdb line tables, one for hello.c
and one for world.inc:
...
compunit_symtab: hello.c
symtab: hello.c
INDEX  LINE   REL-ADDRESS UNREL-ADDRESS IS-STMT PROLOGUE-END EPILOGUE-BEGIN
0      3      0x400557    0x400557      Y
1      4      0x40055b    0x40055b      Y
2      END    0x40056a    0x40056a      Y

compunit_symtab: hello.c
symtab: world.inc
INDEX  LINE   REL-ADDRESS UNREL-ADDRESS IS-STMT PROLOGUE-END EPILOGUE-BEGIN
0      1      0x40056a    0x40056a      Y
1      2      0x400574    0x400574      Y
2      3      0x400579    0x400579      Y
3      END    0x40057b    0x40057b      Y
...

The epilogue of main starts at 0x400579:
...
  400579:	5d                   	pop    %rbp
  40057a:	c3                   	ret
...

Now, say we have an epilogue_begin marker in the line table at 0x400579.

We won't find it using find_epilogue_using_linetable, because it does:
...
  const struct symtab_and_line sal = find_pc_line (start_pc, 0);
...
which gets us the line table for hello.c.

Fix this by using "find_pc_line (end_pc - 1, 0)" instead.

Tested on x86_64-linux.

Co-Authored-By: Tom de Vries <tdevries@suse.de>

PR symtab/31622
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31622

6 files changed, 284 insertions, 160 deletions

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 06b32c0..6d3732a 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -4159,8 +4159,15 @@ find_epilogue_using_linetable (CORE_ADDR func_addr)
 
   /* While the standard allows for multiple points marked with epilogue_begin
      in the same function, for performance reasons, this function will only
-     find the last address that sets this flag for a given block.  */
-  const struct symtab_and_line sal = find_pc_line (start_pc, 0);
+     find the last address that sets this flag for a given block.
+
+     The lines of a function can be described by several line tables in case
+     there are different files involved.  There's a corner case where a
+     function epilogue is in a different file than a function start, and using
+     start_pc as argument to find_pc_line will mean we won't find the
+     epilogue.  Instead, use "end_pc - 1" to maximize our chances of picking
+     the line table containing an epilogue.  */
+  const struct symtab_and_line sal = find_pc_line (end_pc - 1, 0);
   if (sal.symtab != nullptr && sal.symtab->language () != language_asm)
     {
       struct objfile *objfile = sal.symtab->compunit ()->objfile ();
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin-2.exp b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin-2.exp
new file mode 100644
index 0000000..6302ef1
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin-2.exp
@@ -0,0 +1,20 @@
+# Copyright 2022-2024 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/>.
+
+standard_testfile dw2-epilogue-begin.c dw2-epilogue-begin.S
+
+set version 2
+
+source $srcdir/$subdir/dw2-epilogue-begin.exp.tcl
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.c.inc b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.c.inc
new file mode 100644
index 0000000..4ff445c
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.c.inc
@@ -0,0 +1,51 @@
+/* Copyright 2023-2024 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/>.  */
+
+void
+__attribute__((used))
+trivial (void)
+{
+  asm ("trivial_label: .global trivial_label");		/* trivial function */
+}
+
+char global;
+
+void
+watch (void)
+{							/* watch start */
+  asm ("watch_label: .global watch_label");
+  asm ("mov $0x0, %rax");
+  int local = 0;					/* watch prologue */
+
+  asm ("watch_start: .global watch_start");
+  asm ("mov $0x1, %rax");
+  local = 1;						/* watch assign */
+  asm ("watch_reassign: .global watch_reassign");
+  asm ("mov $0x2, %rax");
+  local = 2;						/* watch reassign */
+  asm ("watch_end: .global watch_end");			/* watch end */
+}
+
+int
+main (void)
+{							/* main prologue */
+  asm ("main_label: .global main_label");
+  global = 0;
+  asm ("main_fun_call: .global main_fun_call");
+  watch ();						/* main function call */
+  asm ("main_epilogue: .global main_epilogue");
+  global = 10;
+  return 0;						/* main end */
+}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.exp b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.exp
index 7ae14fa..9b9d6c7 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.exp
@@ -13,162 +13,8 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-# Check that GDB can honor the epilogue_begin flag the compiler can place
-# in the line-table data.
-# We test 2 things: 1. that a software watchpoint triggered in an epilogue
-# is correctly ignored
-# 2. that GDB can mark the same line as both prologue and epilogue
-
-load_lib dwarf.exp
-
-# This test can only be run on targets which support DWARF-2 and use gas.
-require dwarf2_support
-# restricted to x86 to make it simpler to follow a variable
-require is_x86_64_m64_target
-
 standard_testfile .c .S
 
-set trivial_line [gdb_get_line_number "trivial function"]
-set main_prologue [gdb_get_line_number "main prologue"]
-set main_epilogue [gdb_get_line_number "main end"]
-set watch_start_line [gdb_get_line_number "watch start"]
-
-set asm_file [standard_output_file $srcfile2]
-
-# The producer will be set to clang because at the time of writing
-# we only care about epilogues if the producer is clang.  When the
-# producer is GCC, variables use CFA locations, so watchpoints can
-# continue working even on epilogues.
-Dwarf::assemble $asm_file {
-    global srcdir subdir srcfile srcfile2
-    global trivial_line main_prologue main_epilogue watch_start_line
-    declare_labels lines_label
-
-    get_func_info main
-    get_func_info trivial
-    get_func_info watch
-
-    cu {} {
-	compile_unit {
-	    {language @DW_LANG_C}
-	    {name dw2-prologue-end.c}
-	    {stmt_list ${lines_label} DW_FORM_sec_offset}
-	    {producer "clang version 17.0.1"}
-	} {
-	    declare_labels char_label
-
-	    char_label: base_type {
-		{name char}
-		{encoding @DW_ATE_signed}
-		{byte_size 1 DW_FORM_sdata}
-	    }
-
-	    subprogram {
-		{external 1 flag}
-		{name trivial}
-		{low_pc $trivial_start addr}
-		{high_pc "$trivial_start + $trivial_len" addr}
-	    }
-	    subprogram {
-		{external 1 flag}
-		{name watch}
-		{low_pc $watch_start addr}
-		{high_pc "$watch_start + $watch_len" addr}
-	    } {
-		DW_TAG_variable {
-		    {name local}
-		    {type :$char_label}
-		    {DW_AT_location {DW_OP_reg0} SPECIAL_expr}
-		}
-	    }
-	    subprogram {
-		{external 1 flag}
-		{name main}
-		{low_pc $main_start addr}
-		{high_pc "$main_start + $main_len" addr}
-	    }
-	}
-    }
-
-    lines {version 5} lines_label {
-	set diridx [include_dir "${srcdir}/${subdir}"]
-	file_name "$srcfile" $diridx
-
-	program {
-	    DW_LNS_set_file $diridx
-	    DW_LNE_set_address $trivial_start
-	    line $trivial_line
-	    DW_LNS_set_prologue_end
-	    DW_LNS_set_epilogue_begin
-	    DW_LNS_copy
-
-	    DW_LNE_set_address watch
-	    line $watch_start_line
-	    DW_LNS_copy
-
-	    DW_LNE_set_address watch_start
-	    line [gdb_get_line_number "watch assign"]
-	    DW_LNS_set_prologue_end
-	    DW_LNS_copy
-
-	    DW_LNE_set_address watch_reassign
-	    line [gdb_get_line_number "watch reassign"]
-	    DW_LNS_set_epilogue_begin
-	    DW_LNS_copy
-
-	    DW_LNE_set_address watch_end
-	    line [gdb_get_line_number "watch end"]
-	    DW_LNS_copy
-
-	    DW_LNE_set_address $main_start
-	    line $main_prologue
-	    DW_LNS_set_prologue_end
-	    DW_LNS_copy
-
-	    DW_LNE_set_address main_fun_call
-	    line [gdb_get_line_number "main function call"]
-	    DW_LNS_copy
-
-	    DW_LNE_set_address main_epilogue
-	    line $main_epilogue
-	    DW_LNS_set_epilogue_begin
-	    DW_LNS_copy
-
-	    DW_LNE_set_address "$main_start + $main_len"
-	    DW_LNE_end_sequence
-	}
-    }
-}
-
-if { [prepare_for_testing "failed to prepare" ${testfile} \
-	  [list $srcfile $asm_file] {nodebug}] } {
-    return -1
-}
-
-if ![runto_main] {
-    return -1
-}
-
-# Moving to the scope with a local variable.
-gdb_breakpoint $watch_start_line
-gdb_continue_to_breakpoint "continuing to function" ".*"
-gdb_test "next" "local = 2.*" "stepping to epilogue"
-
-# Forcing software watchpoints because hardware ones don't care if we
-# are in the epilogue or not.
-gdb_test_no_output "set can-use-hw-watchpoints 0"
-
-# Test that the software watchpoint will not trigger in this case
-gdb_test "watch local" "\[W|w\]atchpoint .: local" "set watchpoint"
-gdb_test "continue" ".*\[W|w\]atchpoint . deleted.*" \
-    "confirm watchpoint doesn't trigger"
+set version 1
 
-# First we test that the trivial function has a line with both a prologue
-# and an epilogue. Do this by finding a line that has 3 Y columns
-set sep "\[ \t\]"
-set hex_number "0x\[0-9a-f\]+"
-gdb_test_multiple "maint info line-table" "test epilogue in linetable" -lbl {
-    -re "\[0-9\]$sep+$trivial_line$sep+$hex_number$sep+$hex_number$sep+Y$sep+Y$sep+Y" {
-	pass $gdb_test_name
-    }
-}
+source $srcdir/$subdir/dw2-epilogue-begin.exp.tcl
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.exp.tcl b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.exp.tcl
new file mode 100644
index 0000000..155916b
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-epilogue-begin.exp.tcl
@@ -0,0 +1,199 @@
+# Copyright 2022-2024 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/>.
+
+# Check that GDB can honor the epilogue_begin flag the compiler can place
+# in the line-table data.
+# We test 2 things: 1. that a software watchpoint triggered in an epilogue
+# is correctly ignored
+# 2. that GDB can mark the same line as both prologue and epilogue
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+require dwarf2_support
+# restricted to x86 to make it simpler to follow a variable
+require is_x86_64_m64_target
+
+set trivial_line [gdb_get_line_number "trivial function"]
+set main_prologue [gdb_get_line_number "main prologue"]
+set main_epilogue [gdb_get_line_number "main end"]
+set watch_start_line [gdb_get_line_number "watch start"]
+
+set asm_file [standard_output_file $srcfile2]
+
+# The producer will be set to clang because at the time of writing
+# we only care about epilogues if the producer is clang.  When the
+# producer is GCC, variables use CFA locations, so watchpoints can
+# continue working even on epilogues.
+Dwarf::assemble $asm_file {
+    global srcdir subdir srcfile srcfile2
+    global trivial_line main_prologue main_epilogue watch_start_line
+    declare_labels lines_label
+
+    get_func_info main
+    get_func_info trivial
+    get_func_info watch
+
+    if { $::version == 1 } {
+	set switch_file {}
+    } elseif { $::version == 2 } {
+	set switch_file { set f $f2 }
+    } else {
+	error "Unhandled version: $::version"
+    }
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name dw2-prologue-end.c}
+	    {stmt_list ${lines_label} DW_FORM_sec_offset}
+	    {producer "clang version 17.0.1"}
+	} {
+	    declare_labels char_label
+
+	    char_label: base_type {
+		{name char}
+		{encoding @DW_ATE_signed}
+		{byte_size 1 DW_FORM_sdata}
+	    }
+
+	    subprogram {
+		{external 1 flag}
+		{name trivial}
+		{low_pc $trivial_start addr}
+		{high_pc "$trivial_start + $trivial_len" addr}
+	    }
+	    subprogram {
+		{external 1 flag}
+		{name watch}
+		{low_pc $watch_start addr}
+		{high_pc "$watch_start + $watch_len" addr}
+	    } {
+		DW_TAG_variable {
+		    {name local}
+		    {type :$char_label}
+		    {DW_AT_location {DW_OP_reg0} SPECIAL_expr}
+		}
+	    }
+	    subprogram {
+		{external 1 flag}
+		{name main}
+		{low_pc $main_start addr}
+		{high_pc "$main_start + $main_len" addr}
+	    }
+	}
+    }
+
+    lines {version 5} lines_label {
+	set diridx [include_dir "${srcdir}/${subdir}"]
+	set f1 [file_name "$srcfile" $diridx]
+	set f2 [file_name "$srcfile.inc" $diridx]
+
+	set f $f1
+	program {
+	    DW_LNS_set_file $f
+
+	    DW_LNE_set_address $trivial_start
+	    line $trivial_line
+	    DW_LNS_set_prologue_end
+	    DW_LNS_set_epilogue_begin
+	    DW_LNS_copy
+
+	    DW_LNE_set_address $trivial_end
+	    DW_LNE_end_sequence
+
+
+	    DW_LNS_set_file $f
+
+	    DW_LNE_set_address $watch_start
+	    line $watch_start_line
+	    DW_LNS_copy
+
+	    DW_LNE_set_address watch_start
+	    line [gdb_get_line_number "watch assign"]
+	    DW_LNS_set_prologue_end
+	    DW_LNS_copy
+
+	    eval $switch_file
+	    DW_LNS_set_file $f
+
+	    DW_LNE_set_address watch_reassign
+	    line [gdb_get_line_number "watch reassign"]
+	    DW_LNS_set_epilogue_begin
+	    DW_LNS_copy
+
+	    DW_LNE_set_address watch_end
+	    line [gdb_get_line_number "watch end"]
+	    DW_LNS_copy
+
+	    DW_LNE_set_address $watch_end
+	    DW_LNE_end_sequence
+
+
+	    DW_LNS_set_file $f
+
+	    DW_LNE_set_address $main_start
+	    line $main_prologue
+	    DW_LNS_set_prologue_end
+	    DW_LNS_copy
+
+	    DW_LNE_set_address main_fun_call
+	    line [gdb_get_line_number "main function call"]
+	    DW_LNS_copy
+
+	    DW_LNE_set_address main_epilogue
+	    line $main_epilogue
+	    DW_LNS_set_epilogue_begin
+	    DW_LNS_copy
+
+	    DW_LNE_set_address $main_end
+	    DW_LNE_end_sequence
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# Moving to the scope with a local variable.
+
+gdb_breakpoint $srcfile:$watch_start_line
+gdb_continue_to_breakpoint "continuing to function" ".*"
+gdb_test "next" "local = 2.*" "stepping to epilogue"
+
+# Forcing software watchpoints because hardware ones don't care if we
+# are in the epilogue or not.
+gdb_test_no_output "set can-use-hw-watchpoints 0"
+
+# Test that the software watchpoint will not trigger in this case
+gdb_test "watch local" "\[W|w\]atchpoint .: local" "set watchpoint"
+gdb_test "continue" ".*\[W|w\]atchpoint . deleted.*" \
+    "confirm watchpoint doesn't trigger"
+
+# First we test that the trivial function has a line with both a prologue
+# and an epilogue. Do this by finding a line that has 3 Y columns
+set sep "\[ \t\]"
+set hex_number "0x\[0-9a-f\]+"
+gdb_test_multiple "maint info line-table" "test epilogue in linetable" -lbl {
+    -re "\[0-9\]$sep+$trivial_line$sep+$hex_number$sep+$hex_number$sep+Y$sep+Y$sep+Y" {
+	pass $gdb_test_name
+    }
+}
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 1a97f83..44862db 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -2427,10 +2427,11 @@ namespace eval Dwarf {
 	    variable _line_file_names
 	    lappend _line_file_names $filename $diridx
 
+	    set nr_filenames [expr [llength $_line_file_names] / 2]
 	    if { $Dwarf::_line_unit_version >= 5 } {
-		return [expr [llength $_line_file_names] - 1]
+		return [expr $nr_filenames - 1]
 	    } else {
-		return [llength $_line_file_names]
+		return $nr_filenames
 	    }
 	}