Re: Synthetic symbol leak in in elf_x86_64_get_synthetic_symtab and elf_read_minimal_symbols

Yao Qi
2017-08-17T11:00:58Z

Alex Lindsay <alexlindsay239@gmail.com> writes:

> I can verify that the objdump example is fixed in HEAD, but I still
> get this leak with `valgrind --leak-check=full
> --show-leak-kinds=definite gdb ./hello`:

Yes, because your patch is not pushed in yet :) I tweaked your patch a
little bit, and pushed it in. Again, thanks for your contribution. Do
you still see other memory leak issues after this fix?

--
Yao (齐尧)

From ba7139188c75a9c620cadea59158c5ffcab28acf Mon Sep 17 00:00:00 2001
From: Alex Lindsay <alexlindsay239@gmail.com>
Date: Thu, 17 Aug 2017 11:53:53 +0100
Subject: [PATCH] Synthetic symbol leak in elf_read_minimal_symbols

Detected this leak with valgrind memcheck:

==30840== 194 bytes in 1 blocks are definitely lost in loss record 9,138 of 10,922
==30840== at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==30840== by 0x80DF82: bfd_malloc (libbfd.c:193)
==30840== by 0x80E12D: bfd_zmalloc (libbfd.c:278)
==30840== by 0x819E80: elf_x86_64_get_synthetic_symtab (elf64-x86-64.c:6835)
==30840== by 0x4F7B01: elf_read_minimal_symbols(objfile*, int, elfinfo const*) (elfread.c:1124)
==30840== by 0x4F7CE7: elf_symfile_read(objfile*, enum_flags<symfile_add_flag>) (elfread.c:1182)
==30840== by 0x7557FC: read_symbols(objfile*, enum_flags<symfile_add_flag>) (symfile.c:861)
==30840== by 0x755EE1: syms_from_objfile_1(objfile*, section_addr_info*, enum_flags<symfile_add_flag>) (symfile.c:1062)

We perform a dynamic allocation in
elf64-x86-64.c:elf_x86_64_get_synthetic_symtab

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

that appear to never get freed.

gdb:

2017-08-17 Alex Lindsay <alexlindsay239@gmail.com>

* elfread.c (elf_read_minimal_symbols): xfree synthsyms.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 10d63b0..d2c194e 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2017-08-17 Alex Lindsay <alexlindsay239@gmail.com> (tiny change)
+
+ * elfread.c (elf_read_minimal_symbols): xfree synthsyms.
+
2017-08-17 Ruslan Kabatsayev <b7.10110111@gmail.com>

* NEWS: Mention new shortcuts for nexti and stepi in TUI
diff --git a/gdb/elfread.c b/gdb/elfread.c
index ece704c..a654661 100644
--- a/gdb/elfread.c
+++ b/gdb/elfread.c
@@ -1132,6 +1132,9 @@ elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags,
synth_symbol_table[i] = synthsyms + i;
elf_symtab_read (reader, objfile, ST_SYNTHETIC, synthcount,
synth_symbol_table.get (), true);
+
+ xfree (synthsyms);
+ synthsyms = NULL;
}

/* Install any minimal symbols that have been collected as the current