On Mon, Nov 06, 2017 at 07:24:55PM -0800, Lucas De Marchi wrote:

On Mon, Nov 6, 2017 at 1:57 PM, Eugene Syromiatnikov [off-list ref] wrote:

quoted

There are two places where _cleanup_free_ variables are not initialised
by the time function exits that have been caught by gcc:

        In file included from libkmod/libkmod.c:35:0:
        libkmod/libkmod.c: In function 'kmod_lookup_alias_is_builtin':
        ./shared/util.h:73:13: warning: 'line' may be used uninitialized in this function [-Wmaybe-uninitialized]
                 free(*(void**) p);
                     ^
        libkmod/libkmod.c:551:23: note: 'line' was declared here
          _cleanup_free_ char *line;
                               ^
        In file included from libkmod/libkmod-module.c:42:0:
        libkmod/libkmod-module.c: In function 'kmod_module_probe_insert_module':
        ./shared/util.h:73:13: warning: 'cmd' may be used uninitialized in this function [-Wmaybe-uninitialized]
                 free(*(void**) p);
                     ^
        libkmod/libkmod-module.c:996:23: note: 'cmd' was declared here
          _cleanup_free_ char *cmd;
                       ^

This patch initializes them to NULL so free become no-op in these cases.
---
 libkmod/libkmod-module.c | 2 +-
 libkmod/libkmod.c        | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libkmod/libkmod-module.c b/libkmod/libkmod-module.c
index 0a3ef11..6f23c1a 100644
--- a/libkmod/libkmod-module.c
+++ b/libkmod/libkmod-module.c

@@ -995,7 +995,7 @@ static int module_do_install_commands(struct kmod_module *mod,
 {
        const char *command = kmod_module_get_install_commands(mod);
        char *p;
-       _cleanup_free_ char *cmd;
+       _cleanup_free_ char *cmd = NULL;
        int err;
        size_t cmdlen, options_len, varlen;

diff --git a/libkmod/libkmod.c b/libkmod/libkmod.c
index 69fe431..964772d 100644
--- a/libkmod/libkmod.c
+++ b/libkmod/libkmod.c

@@ -556,7 +556,7 @@ finish:

 bool kmod_lookup_alias_is_builtin(struct kmod_ctx *ctx, const char *name)
 {
-       _cleanup_free_ char *line;
+       _cleanup_free_ char *line = NULL;

This seems to be a bogus warning. See the line just below... there's
no way to exit this function without first  assigning 'line'.

In this instance, I initially thought that gcc is smart and derives
"uninitialised variable" from the lookup_builtin_file call, but nope, it
was happy only after line was initialised on declaration. On the other
hand, documentation[1] mentions that cleanup function is also called
during stack unwinding in case -fexceptions is enabled, and RHEL's RPM
package indeed has this flag, at least, so this GCC's complaint still
seems relevant.

[1] https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html

Lucas De Marchi