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

[Mikael Vidstedt]

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](https://bugs.openjdk.java.net/browse/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}

-------------

Commit messages:
 - 8283059: Uninitialized warning in check_code.c with GCC 11.2

Changes: https://git.openjdk.java.net/jdk/pull/7794/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7794&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283059
  Stats: 22 lines in 1 file changed: 5 ins; 0 del; 17 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7794.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7794/head:pull/7794

PR: https://git.openjdk.java.net/jdk/pull/7794