IgnoreUnrecognizedVMOptions and badly specified options (original) (raw)

Dmitry Dmitriev dmitry.dmitriev at oracle.com
Thu Jun 25 17:00:07 UTC 2015

Hello Vladimir,

Thank you for explanation. I just was bit confused about valid VM options but which improperly specified. I look at the Arguments::process_argument function in src/share/vm/runtime/arguments.cpp module and noticed one thing:

817 bool Arguments::process_argument(const char* arg, 818 jboolean ignore_unrecognized, Flag::Flags origin) { 819 820 JDK_Version since = JDK_Version(); 821 822 if (parse_argument(arg, origin) || ignore_unrecognized) { 823 return true; 824 } ... 850 // For locked flags, report a custom error message if available. 851 // Otherwise, report the standard unrecognized VM option. 852 Flag* found_flag = Flag::find_flag((const char*)argname, arg_len, true, true); 853 if (found_flag != NULL) { 854 char locked_message_buf[BUFLEN]; 855 found_flag->get_locked_message(locked_message_buf, BUFLEN); 856 if (strlen(locked_message_buf) == 0) { 857 if (found_flag->is_bool() && !has_plus_minus) { 858 jio_fprintf(defaultStream::error_stream(), 859 "Missing +/- setting for VM option '%s'\n", argname); 860 } else if (!found_flag->is_bool() && has_plus_minus) { 861 jio_fprintf(defaultStream::error_stream(), 862 "Unexpected +/- setting in VM option '%s'\n", argname); 863 } else { 864 jio_fprintf(defaultStream::error_stream(), 865 "Improperly specified VM option '%s'\n", argname); 866 } 867 } else { 868 jio_fprintf(defaultStream::error_stream(), "%s", locked_message_buf); 869 } 870 } else { 871 jio_fprintf(defaultStream::error_stream(), 872 "Unrecognized VM option '%s'\n", argname); 873 Flag* fuzzy_matched = Flag::fuzzy_match((const char*)argname, arg_len, true); 874 if (fuzzy_matched != NULL) { 875 jio_fprintf(defaultStream::error_stream(), 876 "Did you mean '%s%s%s'? ", 877 (fuzzy_matched->is_bool()) ? "(+/-)" : "", 878 fuzzymatched->name, 879 (fuzzymatched->isbool()) ? "" : "="); 880 } 881 } 882 883 // allow for commandline "commenting out" options like -XX:#+Verbose 884 return arg[0] == '#'; 885 }

If "-XX:+IgnoreUnrecongnizedVMOptions" is specified, then "ignore_unrecognized" will be true and "if" statement on line 822 will always be true. I just think that a better place to check "ignore_unrecognized" is on "else" branch on line 867(for locked flags) and on "else" branch on line 870(where we actually found unrecognized option). If "ignore_unrecognized" is true, then return true in this case, otherwise execute code in these "else" branches. It's my thoughts about that. In this case improperly specified options will be catched(lines 857-866).

Thanks, Dmitry

On 25.06.2015 17:45, Vladimir Kozlov wrote:

It is not intentional but difficult to implement. It was added to allow specify options which are not defined in running VM. For example when C2 option is specified but Client VM (which has only C1) is run. We can do more smarter things here, I agree, by trying to verify options before ignoring it. But it will not help with misspelled options, I think.

Regards, Vladimir On 6/25/15 5:17 AM, Dmitry Dmitriev wrote: Hello,

Working with JVM command line options I noticed that "IgnoreUnrecognizedVMOptions" option allow to hide options with bad values. "IgnoreUnrecognizedVMOptions" allow to ignore unrecognized options, but it also allow to ignore improperly specified VM Options which are processed in general way, i.e. "-XX:" options processed by Arguments::processargument function(hotspot/src/share/vm/runtime/arguments.cpp module). I will be very appreciated if someone can describe this behavior or state that this is intentional. Example for numeric and boolean options: 1) Bad numeric option with and without "-XX:+IgnoreUnrecongnizedVMOptions" java -XX:MaxRAMFraction=-1 -version Improperly specified VM option 'MaxRAMFraction=-1' Error: Could not create the Java Virtual Machine. Error: A fatal exception has occurred. Program will exit. java -XX:MaxRAMFraction=-1 -XX:+IgnoreUnrecognizedVMOptions -version java version "1.8.040" Java(TM) SE Runtime Environment (build 1.8.040-b26) Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode) 2) Bad boolean option with and without "-XX:+IgnoreUnrecongnizedVMOptions" java -XX:UseG1GC -version Missing +/- setting for VM option 'UseG1GC' Error: Could not create the Java Virtual Machine. Error: A fatal exception has occurred. Program will exit. java -XX:UseG1GC -XX:+IgnoreUnrecognizedVMOptions -version java version "1.8.040" Java(TM) SE Runtime Environment (build 1.8.040-b26) Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode) So, as we see when "-XX:+IgnoreUnrecongnizedVMOptions" is used, bad "-XX:MaxRAMFraction=-1" and "-XX:UseG1GC" are ignored. I don't know is this behavior intentional or not, but HotSpot works in that way. So, can someone tell me this is intentional? Or this behavior is wrong? Thank you, Dmitry

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