[RFC PATCH] scripts/lsan-suppressions: Add a LeakSanitizer suppressions file

[Peter Maydell <peter.maydell@linaro.org>]

Add a LeakSanitizer suppressions file that documents and suppresses
known false-positive leaks in either QEMU or its dependencies.
To use it you'll need to set
  LSAN_OPTIONS="suppressions=/path/to/scripts/lsan-suppressions.txt"
when running a QEMU built with the leak-sanitizer.

The first and currently only entry is for a deliberate leak in glib's
g_set_user_dirs() that otherwise causes false positive leak reports
in the qga-ssh-test because of its use of G_TEST_OPTION_ISOLATE_DIRS:

Direct leak of 321 byte(s) in 5 object(s) allocated from:
    #0 0x5555dd8abd1e in __interceptor_malloc (/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/asan/qga/qga-ssh-test+0x19cd1e) (BuildId: 7991a166007e8206c51bee401722a8335e7990bb)
    #1 0x7fb5bc724738 in g_malloc debian/build/deb/../../../glib/gmem.c:128:13
    #2 0x7fb5bc739583 in g_strdup debian/build/deb/../../../glib/gstrfuncs.c:361:17
    #3 0x7fb5bc757a29 in set_str_if_different debian/build/deb/../../../glib/gutils.c:1659:21
    #4 0x7fb5bc757a29 in set_str_if_different debian/build/deb/../../../glib/gutils.c:1647:1
    #5 0x7fb5bc757a29 in g_set_user_dirs debian/build/deb/../../../glib/gutils.c:1743:9
    #6 0x7fb5bc743d78 in test_do_isolate_dirs debian/build/deb/../../../glib/gtestutils.c:1486:3
    #7 0x7fb5bc743d78 in test_case_run debian/build/deb/../../../glib/gtestutils.c:2917:16
    #8 0x7fb5bc743d78 in g_test_run_suite_internal debian/build/deb/../../../glib/gtestutils.c:3018:16
    #9 0x7fb5bc74380a in g_test_run_suite_internal debian/build/deb/../../../glib/gtestutils.c:3035:18
    #10 0x7fb5bc74380a in g_test_run_suite_internal debian/build/deb/../../../glib/gtestutils.c:3035:18
    #11 0x7fb5bc743fe9 in g_test_run_suite debian/build/deb/../../../glib/gtestutils.c:3112:13
    #12 0x7fb5bc744055 in g_test_run debian/build/deb/../../../glib/gtestutils.c:2231:7
    #13 0x7fb5bc744055 in g_test_run debian/build/deb/../../../glib/gtestutils.c:2218:1
    #14 0x5555dd9293b1 in main qga/commands-posix-ssh.c:439:12
    #15 0x7fb5bc3dfd8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #16 0x7fb5bc3dfe3f in __libc_start_main csu/../csu/libc-start.c:392:3
    #17 0x5555dd828ed4 in _start (/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/asan/qga/qga-ssh-test+0x119ed4) (BuildId: 7991a166007e8206c51bee401722a8335e7990bb)

(Strictly speaking, this is a genuine leak, it's just a deliberate
one by glib; they document it in their valgrind-format suppression
file upstream.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Does this seem like a good idea?  It gives us a place to document
things like this and to suppress them so we could in theory get a
complete clean 'make check' run with the leak sanitizer on.  It might
be nice if there was an easy way to enable all our "recommended
sanitizer settings" (ASAN_OPTIONS="fast_unwind_on_malloc=0 is
pretty much required to get useful backtraces, for instance), but
I'm not sure there's a neat way to do that.

 scripts/lsan-suppressions.txt | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 scripts/lsan-suppressions.txt

diff --git a/scripts/lsan-suppressions.txt b/scripts/lsan-suppressions.txt
new file mode 100644
index 00000000000..5c3cffaa5a0
--- /dev/null
+++ b/scripts/lsan-suppressions.txt
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2024 Linaro Limited
+
+# This is a set of suppressions for LeakSanitizer; you can use it
+# by setting
+#   LSAN_OPTIONS="suppressions=/path/to/scripts/lsan-suppressions.txt"
+# when running a QEMU built with the leak-sanitizer.
+
+# g_set_user_dirs() deliberately leaks the previous cached g_get_user_*
+# values. This is documented in upstream glib's valgrind-format
+# suppression file:
+# https://github.com/GNOME/glib/blob/main/tools/glib.supp
+# This avoids false positive leak reports for the qga-ssh-test.
+leak:g_set_user_dirs
-- 
2.34.1