libdw: Handle split DWARF in dwarf_macro_getsrcfiles

Macro information references file names from the line number information
table, which is tricky in split DWARF for a couple of reasons.

First, the line number information for a macro unit comes from the
.debug_line.dwo section in the split file, not the .debug_line section
in the skeleton file.  This was not specified in the GNU DebugFission
design document [1] or the DWARF 5 standard, but it is how GCC and Clang
behave in practice and was clarified in DWARF standard issue
200602.1 [2] for the upcoming DWARF 6 standard.

dwarf_macro_getsrcfiles uses the line number information from whichever
Dwarf handle it was passed.  This is error-prone, since the most natural
thing to do is to pass the skeleton Dwarf handle.  Fix this by storing
the appropriate Dwarf handle in Dwarf_Macro_Op_Table and using that one.

Second, for .debug_macinfo.dwo in GNU DebugFission (generated by gcc
-gdwarf-4 -gstrict-dwarf -gsplit-dwarf), the offset into .debug_line.dwo
is implicitly 0.  Again, this isn't in any specification, but it's how
GCC behaves in practice (Clang never generates macro information for
DWARF 4 split DWARF).  Make get_macinfo_table default to 0 for split
DWARF when it can't find DW_AT_stmt_list.

1: https://gcc.gnu.org/wiki/DebugFission
2: https://dwarfstd.org/issues/200602.1.html

Signed-off-by: Omar Sandoval <[email protected]>

1 files changed, 4 insertions, 1 deletions

diff --git a/libdw/dwarf_macro_getsrcfiles.c b/libdw/dwarf_macro_getsrcfiles.c
index 4e8deeeb..11c587af 100644
--- a/libdw/dwarf_macro_getsrcfiles.c
+++ b/libdw/dwarf_macro_getsrcfiles.c
@@ -36,6 +36,9 @@ int
 dwarf_macro_getsrcfiles (Dwarf *dbg, Dwarf_Macro *macro,
 			 Dwarf_Files **files, size_t *nfiles)
 {
+  /* This was needed before Dwarf_Macro_Op_Table stored the Dwarf handle.  */
+  (void)dbg;
+
   /* macro is declared NN */
   Dwarf_Macro_Op_Table *const table = macro->table;
   if (table->files == NULL)
@@ -71,7 +74,7 @@ dwarf_macro_getsrcfiles (Dwarf *dbg, Dwarf_Macro *macro,
 	 the same unit through dwarf_getsrcfiles, and the file names
 	 will be broken.  */
 
-      if (__libdw_getsrclines (dbg, line_offset, table->comp_dir,
+      if (__libdw_getsrclines (table->dbg, line_offset, table->comp_dir,
 			       table->address_size, NULL, &table->files) < 0)
 	table->files = (void *) -1;
     }