Synthetic symbol leak in in elf_x86_64_get_synthetic_symtab and elf_read_minimal_symbols

Alex Lindsay
2017-08-07T15:19:24Z

Detected this leak with valgrind memcheck:

==21225== 463 (336 direct, 127 indirect) bytes in 1 blocks are
definitely lost in loss record 10,770 of 10,949^M
==21225== at 0x4C2DB8F: malloc (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)^M
==21225== by 0x6C6DA2: bfd_malloc (libbfd.c:193)^M
==21225== by 0x6C6F4D: bfd_zmalloc (libbfd.c:278)^M
==21225== by 0x6D252E: elf_x86_64_get_synthetic_symtab
(elf64-x86-64.c:6846)^M
==21225== by 0x4B397A: elf_read_minimal_symbols (elfread.c:1124)^M
==21225== by 0x4B397A: elf_symfile_read(objfile*,
enum_flags<symfile_add_flag>) (elfread.c:1182)^M
==21225== by 0x63AC94: read_symbols(objfile*,
enum_flags<symfile_add_flag>) (symfile.c:861)^M
==21225== by 0x63A773: syms_from_objfile_1 (symfile.c:1062)

We perform a couple of dynamic allocations in
elf_x86_64_get_synthetic_symtab (elf64-x86-64.c):

s = *ret = (asymbol *) bfd_zmalloc (size);

names = (char *) bfd_malloc (size);

that appear to never get freed. My patch for this:

diff --git a/gdb/elfread.c b/gdb/elfread.c
index ece704ca7c..5ed8a6f957 100644
--- a/gdb/elfread.c
+++ b/gdb/elfread.c
@@ -1144,6 +1144,9 @@ elf_read_minimal_symbols (struct objfile *objfile,
int symfile_flags,

if (symtab_create_debug)
fprintf_unfiltered (gdb_stdlog, "Done reading minimal symbols.\n");
+ if (synthcount > 0)
+ xfree ((char *) synthsyms->name);
+ xfree (synthsyms);
}

/* Scan and build partial symbols for a symbol file.