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

[Mikael Vidstedt]

> 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

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7859/files
  - new: https://git.openjdk.java.net/jdk/pull/7859/files/c5c60cb2..9f412d0b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7859&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7859&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7859.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7859/head:pull/7859

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