* [PATCH] libkmod: fix uninitialized variable usage warnings
@ 2017-11-06 21:57 Eugene Syromiatnikov
2017-11-07 3:24 ` Lucas De Marchi
0 siblings, 1 reply; 4+ messages in thread
From: Eugene Syromiatnikov @ 2017-11-06 21:57 UTC (permalink / raw)
To: linux-modules; +Cc: Yauheni Kaliuta
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;
line = lookup_builtin_file(ctx, name);
--
2.1.4
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] libkmod: fix uninitialized variable usage warnings 2017-11-06 21:57 [PATCH] libkmod: fix uninitialized variable usage warnings Eugene Syromiatnikov @ 2017-11-07 3:24 ` Lucas De Marchi 2017-11-07 11:59 ` Eugene Syromiatnikov 0 siblings, 1 reply; 4+ messages in thread From: Lucas De Marchi @ 2017-11-07 3:24 UTC (permalink / raw) To: Eugene Syromiatnikov; +Cc: linux-modules, Yauheni Kaliuta On Mon, Nov 6, 2017 at 1:57 PM, Eugene Syromiatnikov <esyr@redhat.com> wrote: > 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'. Lucas De Marchi ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] libkmod: fix uninitialized variable usage warnings 2017-11-07 3:24 ` Lucas De Marchi @ 2017-11-07 11:59 ` Eugene Syromiatnikov 2017-11-07 16:45 ` Lucas De Marchi 0 siblings, 1 reply; 4+ messages in thread From: Eugene Syromiatnikov @ 2017-11-07 11:59 UTC (permalink / raw) To: Lucas De Marchi; +Cc: linux-modules, Yauheni Kaliuta 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 <esyr@redhat.com> wrote: > > 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] libkmod: fix uninitialized variable usage warnings 2017-11-07 11:59 ` Eugene Syromiatnikov @ 2017-11-07 16:45 ` Lucas De Marchi 0 siblings, 0 replies; 4+ messages in thread From: Lucas De Marchi @ 2017-11-07 16:45 UTC (permalink / raw) To: Eugene Syromiatnikov; +Cc: linux-modules, Yauheni Kaliuta On Tue, Nov 7, 2017 at 3:59 AM, Eugene Syromiatnikov <esyr@redhat.com> wrote: > 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 <esyr@redhat.com> wrote: >> > 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. This is likely to trigger "double assignment" warnings on other compilers. A good question would be.... why is -fexceptions being used in a C-only library? If it was a binary or a library that links to a C++-library, I would understand, but in this case it seems nonsense. /me lost An acceptable solution would be to just merge the 2 lines so we initialize line on declaration. I added -fexceptions here to reproduce the issue, but it didn't reproduce using gcc 7.2.1 on Fedora 27. I also remember not having the issue with gcc 6. So I still think it's a compiler bug, although I don't mind if the solution proposed above is applied (but mention on commit message the exact compiler version). Lucas De Marchi ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2017-11-07 16:45 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2017-11-06 21:57 [PATCH] libkmod: fix uninitialized variable usage warnings Eugene Syromiatnikov 2017-11-07 3:24 ` Lucas De Marchi 2017-11-07 11:59 ` Eugene Syromiatnikov 2017-11-07 16:45 ` Lucas De Marchi
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