On Fri, 26 Feb 2021 22:01:09 GMT, Calvin Cheung <cche...@openjdk.org> wrote:
>> Hi, Please review >> >> Added jcmd option for dumping CDS archive during application runtime. >> Before this change, user has to dump shared archive in two steps: first run >> application with >> `java -XX:DumpLoadedClassList=<classlist> .... ` >> to collect shareable class names and saved in file `<classlist>` , then >> `java -Xshare:dump -XX:SharedClassListFile=<classlist> >> -XX:SharedArchiveFile=<archivefile> ...` >> With this change, user can use jcmd to dump CDS without going through >> above steps. Also user can choose a moment during the app runtime to dump >> an archive. >> The bug is associated with the CSR: >> https://bugs.openjdk.java.net/browse/JDK-8259798 which has been approved. >> New added jcmd option: >> `jcmd <pid or AppName> VM.cds static_dump <filename>` >> or >> `jcmd <pid or AppName> VM.cds dynamic_dump <filename>` >> To dump dynamic archive, requires start app with newly added flag >> `-XX:+RecordDynamicDumpInfo`, with this flag, some information related to >> dynamic dump like loader constraints will be recorded. Note the dumping >> process changed some object memory locations so for dumping dynamic archive, >> can only done once for a running app. For static dump, user can dump >> multiple times against same process. >> The file name is optional, if the file name is not supplied, the file >> name will take format of `java_pid<number>_static.jsa` or >> `java_pid<number>_dynamic.jsa` for static and dynamic respectively. The >> `<number>` is the application process ID. >> >> Tests: tier1,tier2,tier3,tier4 >> >> Thanks >> Yumin > > src/hotspot/share/memory/metaspaceShared.cpp line 783: > >> 781: char* start = buffer + strlen(buffer); >> 782: snprintf(start, buff_len, "%s ", arg); >> 783: } > > Maybe move the above function to the StringUtils class under share/utilities? > Use `os::snprintf()` instead of `snprintf()`? The calculation is also wrong, this would overflow. You need: char* start = buffer + strlen(buffer); snprintf(start, buff_len - (start - buffer), "%s ", arg); - and maybe add an assert that strlen(buf) < bufflen. - and as Ioi wrote, I'd use either one of os::snprintf or jio_snprintf since both guarantee zero termination on truncation. - or, just use strncat() ------------- PR: https://git.openjdk.java.net/jdk/pull/2737
