RFR: 8283013: Simplify Arguments::parse_argument() [v3]

[Ioi Lam]

On Wed, 30 Mar 2022 20:34:57 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> src/hotspot/share/runtime/arguments.cpp line 1069:
>> 
>>> 1067: 
>>> 1068:   size_t name_len = size_t(arg - name);
>>> 1069:   JVMFlag* flag = find_jvm_flag(name, name_len);
>> 
>> Consider -XX:@blah
>> I think the name_len could be 0 if the preceding while loop did not increment the arg pointer.
>> But I think it is ok because find_jvm_flag would return NULL on a zero name_len.
>> Is it correct?
>
> The code does handle the case where `name_len==0`, but I added a new check anyway to make the code easier to understand.

I tested a few cases and the results are the same before/after adding the `name_len` check.


$ java -XX:SharedBaseAddress=0x10000000 --version
java 19-internal 2022-09-20
Java(TM) SE Runtime Environment (slowdebug build 19-internal-adhoc.iklam.ken)
Java HotSpot(TM) 64-Bit Server VM (slowdebug build 19-internal-adhoc.iklam.ken, mixed mode)

$ java -XX:XSharedBaseAddress=0x10000000 --version
Unrecognized VM option 'XSharedBaseAddress=0x10000000'
Did you mean 'SharedBaseAddress=<value>'? Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

$ java -XX:@SharedBaseAddress=0x10000000 --version
Unrecognized VM option '@SharedBaseAddress=0x10000000'
Did you mean 'SharedBaseAddress=<value>'? Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

$ java -XX:=0x10000000 --version
Unrecognized VM option '=0x10000000'
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

$ java -XX:@=0x10000000 --version
Unrecognized VM option '@=0x10000000'
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

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PR: https://git.openjdk.java.net/jdk/pull/7916