RFR: 8283059: Uninitialized warning in check_code.c with GCC 11.2 [v2]

[David Holmes]

On Fri, 18 Mar 2022 02:39:23 GMT, Mikael Vidstedt <mikael at openjdk.org> wrote:

>> Note: this PR replaces the one I messed up earlier.
>> 
>> Background, from JBS:
>> 
>> src/java.base/share/native/libverify/check_code.c: In function 'read_all_code':
>> src/java.base/share/native/libverify/check_code.c:942:5: error: 'lengths' may be used uninitialized [-Werror=maybe-uninitialized]
>> 942 | check_and_push(context, lengths, VM_MALLOC_BLK);
>> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> src/java.base/share/native/libverify/check_code.c:4145:13: note: by argument 2 of type 'const void *' to 'check_and_push' declared here
>> 4145 | static void check_and_push(context_type *context, const void *ptr, int kind)
>> | ^~~~~~~~~~~~~~
>> 
>> Because the second argument of check_and_push is "const void*" GCC assumes that the malloc:ed data, which has not yet been initialized, will not be/can not be modified later which in turn suggests it may be used without ever being initialized.
>> 
>> The same general issue was addressed in JDK-8266168, presumably for GCC 11.1.
>> 
>> Details:
>> 
>> Instead of sprinkling more calloc calls around or using pragmas/gcc attributes I chose to change the check_and_push function to take a (non-const) void* argument, and provide a new wrapper function check_and_push_const which handles the const argument case. For the (non-const) VM_MALLOC_BKP that means the pointer never needs to go through a const conversion.
>> 
>> To avoid having multiple ways of solving the same problem I also chose to revert the change made in JDK-8266168, reverting the calloc back to a malloc call.
>> 
>> Testing:
>> 
>> tier1 + builds-tier{2,3,4,5}
>
> Mikael Vidstedt has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use const char for check_and_push_string_utf

Looks good!

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Marked as reviewed by dholmes (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/7859