Re: Errors in compilation // xl_cmdimpl.c:2733:11 ...

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 24/08/12 20:12, Ian Campbell wrote:
> On Fri, 2012-08-24 at 19:42 +0100, Andrew Cooper wrote:
>> On 24/08/12 17:43, p.d@gmx.de wrote:
>>> nice time,
>>>
>>> Ian, I'm not sure, but I think after Your patch:
>>> http://xenbits.xen.org/hg/xen-unstable.hg/rev/4ca40e0559c3
>>>
>>> xen-tools (+qemu+seabios) will not be maked :)
>>>
>>> Here are last lines of "make -j7":
>>> ==============================================================
>>> gcc  -O1 -fno-omit-frame-pointer -m64 -g -fno-strict-aliasing -std=gnu99 -Wall -Wstrict-prototypes -Wdeclaration-after-statement -Wno-unused-but-set-variable   -D__XEN_TOOLS__ -MMD -MF ._libxl_save_msgs_callout.o.d  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -fno-optimize-sibling-calls  -Werror -Wno-format-zero-length -Wmissing-declarations -Wno-declaration-after-statement -Wformat-nonliteral -I. -fPIC -pthread -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/libxc -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/include -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/libxc -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/include -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/xenstore -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/include -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/blktap2/control -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/blktap2/include -I/usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/include -include /usr/src/xen_2012_08_24_rev_25779/tools/libxl/../../tools/config.h  -c -o _libxl_save_msgs_callout.o _libxl_save_msgs_callout.c 
>>> xl_cmdimpl.c: In function ‘main_list’:
>>> xl_cmdimpl.c:2733:11: error: ‘hand’ may be used uninitialized in this function [-Werror=uninitialized]
>>> xl_cmdimpl.c:2689:14: note: ‘hand’ was declared here
>>> <snip>
>> Please try the attached patch.  I have fixed the error, and also
>> future-proofed the logic.
>>
>> @Ian: the patch can be slimed down if default_output_format can be
>> guaranteed not to change across the duration of this function call, but
>> my cursory glance at this otherwise-unfamilar codebase cant say for certain.
> It can only change during argument parsing.
>
> gcc is being a bit dumb here since default_output_format is a statically
> initialised enum whose only values are OUTPUT_FORMAT_JSON and
> OUTPUT_FORMAT_SXP.
>
> I suspect that now you have re-written it so that hand is only touched
> iff format == JSON and format is const that initialisation of hand is no
> longer necessary. But nonetheless:
> Acked-by: Ian Campbell <ian.campbell@citrix.com>
>
> Ian.
>

Sadly, hand being touched iff format == JSON was still not enough to
satisfy my version of GCC.

Attached is a far slimmed version which explicitly sets hand to NULL at
the top, and future-proofs the use of hand in the middle of the domain loop.

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


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# HG changeset patch
# Parent 4ca40e0559c33205fb5163b10249a0fd5fda39b9
tools/xl: Fix uninitialized variable error.

c/s 25779:4ca40e0559c3 introduced a compilation error for any build system using
-Werror=uninitialized, such as the default CentOS 5.7 version of gcc.

And with good reason, because if the global libxl default_output_format is
neither OUTPUT_FORMAT_SXP nor OUTPUT_FORMAT_JSON, the variable hand will be used
before being initialised.

The attached patch fixes the warning, and futher fixes the logic to work
correctly when a new OUTPUT_FORMAT is added to xl.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff -r 4ca40e0559c3 tools/libxl/xl_cmdimpl.c
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -2686,7 +2686,7 @@ static void list_domains_details(const l
     uint8_t *data;
     int i, len, rc;
 
-    yajl_gen hand;
+    yajl_gen hand = NULL;
     yajl_gen_status s;
     const char *buf;
     libxl_yajl_length yajl_len = 0;
@@ -2714,10 +2714,10 @@ static void list_domains_details(const l
         CHK_ERRNO(asprintf(&config_source, "<domid %d data>", info[i].domid));
         libxl_domain_config_init(&d_config);
         parse_config_data(config_source, (char *)data, len, &d_config, NULL);
-        if (default_output_format == OUTPUT_FORMAT_SXP)
+        if (default_output_format == OUTPUT_FORMAT_JSON)
+            s = printf_info_one_json(hand, info[i].domid, &d_config);
+        else
             printf_info_sexp(domid, &d_config);
-        else
-            s = printf_info_one_json(hand, info[i].domid, &d_config);
         libxl_domain_config_dispose(&d_config);
         free(data);
         free(config_source);

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