| Message ID | 20171106215703.GA24781@asgard.redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 -- To unsubscribe from this list: send the line "unsubscribe linux-modules" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 -- To unsubscribe from this list: send the line "unsubscribe linux-modules" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 -- To unsubscribe from this list: send the line "unsubscribe linux-modules" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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);
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(-)