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

1 files changed, 9 insertions, 2 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 ();