[12] RFR: 8214777: Avoid some GCC 8.X strncpy() errors in HotSpot

[David Holmes]

Hi Simon,

On 11/12/2018 4:57 am, Simon Tooke wrote:
> This small patch fixes some simple warnings in Hotspot code, found by
> GCC 8.1

I hate having to change code just to silence faulty tools :(

> Essentially, any code sequence of the pattern
> 
>      int l = strlen(somestring)
>      char* buffer = malloc(l + 1)
>      strncpy(buffer, somestring, l)
>      buffer[l] = 0
> 
> is replaced by
> 
>      int len = strlen(somestring)
>      char* buffer = malloc(len + 1)
>      strncpy(buffer, somestring, len + 1)
> 
> For xmlstream.cpp, this is actually a small inefficiency, as the null
> byte is immediately overwritten; but it makes GCC happy.

For xmlstream and src/hotspot/share/runtime/arguments.cpp I can't 
convince myself that the change is always correct, because (taking the 
arguments example) I'm not sure what "pos-tail" evaluates to and exactly 
what the string might look like, and so whether we're guaranteed to hit 
a Nul-terminator in that case.

        if(tail != NULL) {
           const char* pos = strchr(tail, '=');
           size_t len = (pos == NULL) ? strlen(tail) : pos - tail;
!         char* name = strncpy(NEW_C_HEAP_ARRAY(char, len + 1, 
mtArguments), tail, len + 1);

Aside: note this bug is currently targeted to 13, if it may be pushed to 
12 it needs to be updated first.

Thanks,
David
-----

> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8214777
> Webrev:
> http://cr.openjdk.java.net/~sgehwolf/webrevs/stooke/JDK-8214777/02/webrev/
>