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Re: [libvirt] [PATCH 2/2] tests: Avoid "jump skips variable initialization" with GCC 9.



On Fri, Jan 25, 2019 at 12:54:13PM +0000, Daniel P. Berrangé wrote:
> On Mon, Jan 21, 2019 at 04:38:25PM +0100, Peter Krempa wrote:
> > On Mon, Jan 21, 2019 at 15:13:21 +0000, Richard W.M. Jones wrote:
> > > GCC 9 gives pages of errors like:
> > > 
> > > qemumonitorjsontest.c: In function 'mymain':
> > > qemumonitorjsontest.c:2904:9: error: jump skips variable initialization [-Werror=jump-misses-init]
> > >  2904 |         goto cleanup;
> > >       |         ^~~~
> > > qemumonitorjsontest.c:3111:2: note: label 'cleanup' defined here
> > >  3111 |  cleanup:
> > >       |  ^~~~~~~
> > > qemumonitorjsontest.c:2920:54: note: '({anonymous})' declared here
> > >  2920 |     simpleFunc = (testQemuMonitorJSONSimpleFuncData) {.xmlopt = driver.xmlopt, \
> > >       |                                                      ^
> > > qemumonitorjsontest.c:3008:5: note: in expansion of macro 'DO_TEST_GEN'
> > >  3008 |     DO_TEST_GEN(qemuMonitorJSONBlockdevMediumInsert);
> > >       |     ^~~~~~~~~~~
> > > 
> > > By moving the cleanup section up near the top of the function we can
> > > avoid this.  I think a better way might be to disable the warning.
> > > ---
> > >  tests/qemumonitorjsontest.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/tests/qemumonitorjsontest.c b/tests/qemumonitorjsontest.c
> > > index 1a8a31717f..299c5f0cbe 100644
> > > --- a/tests/qemumonitorjsontest.c
> > > +++ b/tests/qemumonitorjsontest.c
> > > @@ -2900,8 +2900,12 @@ mymain(void)
> > >  
> > >      if (!(qapiData.schema = testQEMUSchemaLoad())) {
> > >          VIR_TEST_VERBOSE("failed to load qapi schema\n");
> > > -        ret = -1;
> > > -        goto cleanup;
> > > +    cleanup:
> > > +        VIR_FREE(metaschemastr);
> > > +        virJSONValueFree(metaschema);
> > > +        virHashFree(qapiData.schema);
> > > +        qemuTestDriverFree(&driver);
> > > +        return -1;
> > >      }
> > >  
> > >  #define DO_TEST(name) \
> > > @@ -3098,7 +3102,6 @@ mymain(void)
> > >      if (!(metaschema = testQEMUSchemaGetLatest()) ||
> > >          !(metaschemastr = virJSONValueToString(metaschema, false))) {
> > >          VIR_TEST_VERBOSE("failed to load latest qapi schema\n");
> > > -        ret = -1;
> > >          goto cleanup;
> > 
> > We generally avoid jumps back. Also cleanup really should be at the end. 
> > 
> > Wouldn't be enough just to memset the few structs at the beginning?
> 
> No, this appears to be another GCC regression. IMHO the following should
> not warn, yet it does:

{snip}

> This doesn't appear to be reported to GCC upstream yet

I've filed

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89061
  https://bugzilla.redhat.com/show_bug.cgi?id=1669489


Regards,
Daniel
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