On Tue, 25 Jan 2022 15:10:11 GMT, Christian Hagedorn <chaged...@openjdk.org> wrote:
>> When printing the native stack trace on Linux (mostly done for hs_err >> files), it only prints the method with its parameters and a relative offset >> in the method: >> >> Stack: [0x00007f6e01739000,0x00007f6e0183a000], sp=0x00007f6e01838110, >> free space=1020k >> Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native >> code) >> V [libjvm.so+0x620d86] Compilation::~Compilation()+0x64 >> V [libjvm.so+0x624b92] Compiler::compile_method(ciEnv*, ciMethod*, int, >> bool, DirectiveSet*)+0xec >> V [libjvm.so+0x8303ef] >> CompileBroker::invoke_compiler_on_method(CompileTask*)+0x899 >> V [libjvm.so+0x82f067] CompileBroker::compiler_thread_loop()+0x3df >> V [libjvm.so+0x84f0d1] CompilerThread::thread_entry(JavaThread*, >> JavaThread*)+0x69 >> V [libjvm.so+0x1209329] JavaThread::thread_main_inner()+0x15d >> V [libjvm.so+0x12091c9] JavaThread::run()+0x167 >> V [libjvm.so+0x1206ada] Thread::call_run()+0x180 >> V [libjvm.so+0x1012e55] thread_native_entry(Thread*)+0x18f >> >> This makes it sometimes difficult to see where exactly the methods were >> called from and sometimes almost impossible when there are multiple >> invocations of the same method within one method. >> >> This patch improves this by providing source information (filename + line >> number) to the native stack traces on Linux similar to what's already done >> on Windows (see >> [JDK-8185712](https://bugs.openjdk.java.net/browse/JDK-8185712)): >> >> Stack: [0x00007f34fca18000,0x00007f34fcb19000], sp=0x00007f34fcb17110, >> free space=1020k >> Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native >> code) >> V [libjvm.so+0x620d86] Compilation::~Compilation()+0x64 >> (c1_Compilation.cpp:607) >> V [libjvm.so+0x624b92] Compiler::compile_method(ciEnv*, ciMethod*, int, >> bool, DirectiveSet*)+0xec (c1_Compiler.cpp:250) >> V [libjvm.so+0x8303ef] >> CompileBroker::invoke_compiler_on_method(CompileTask*)+0x899 >> (compileBroker.cpp:2291) >> V [libjvm.so+0x82f067] CompileBroker::compiler_thread_loop()+0x3df >> (compileBroker.cpp:1966) >> V [libjvm.so+0x84f0d1] CompilerThread::thread_entry(JavaThread*, >> JavaThread*)+0x69 (compilerThread.cpp:59) >> V [libjvm.so+0x1209329] JavaThread::thread_main_inner()+0x15d >> (thread.cpp:1297) >> V [libjvm.so+0x12091c9] JavaThread::run()+0x167 (thread.cpp:1280) >> V [libjvm.so+0x1206ada] Thread::call_run()+0x180 (thread.cpp:358) >> V [libjvm.so+0x1012e55] thread_native_entry(Thread*)+0x18f >> (os_linux.cpp:705) >> >> For Linux, we need to parse the debug symbols which are generated by GCC in >> DWARF - a standardized debugging format. This patch adds support for DWARF >> 4, the default of GCC 10.x, for 32 and 64 bit architectures (tested with >> x86_32, x86_64 and AArch64). DWARF 5 is not supported as it was still >> experimental and not generated for HotSpot. However, newer GCC version may >> soon generate DWARF 5 by default in which case this parser either needs to >> be extended or the build of HotSpot configured to only emit DWARF 4. >> >> The code follows the parsing steps described in the official DWARF 4 spec: >> https://dwarfstd.org/doc/DWARF4.pdf >> I added references to the corresponding sections throughout the code. >> However, I tried to explain the steps from the DWARF spec directly in the >> code (method names, comments etc.). This allows to follow the code without >> the need to actually deep dive into the spec. >> >> The comments at the `Dwarf` class in the `elf.hpp` file explain in more >> detail how a DWARF file is structured and how the parsing algorithm works to >> get to the filename and line number information. There are more class >> comments throughout the `elf.hpp` file about how different DWARF sections >> are structured and how the parsing algorithm needs to fetch the required >> information. Therefore, I will not repeat the exact workings of the >> algorithm here but refer to the code comments. I've tried to add as much >> information as possible to improve the readability. >> >> Generally, I've tried to stay away from adding any assertions as this code >> is almost always executed when already processing a VM error. Instead, the >> DWARF parser aims to just exit gracefully and possibly omit source >> information for a stack frame instead of risking to stop writing the hs_err >> file when an assertion would have failed. To debug failures, `-Xlog:dwarf` >> can be used with `info`, `debug` or `trace` which provides logging messages >> throughout parsing. >> >> **Testing:** >> Apart from manual testing, I've added two kinds of tests: >> - A JTreg test: Spawns new VMs to let them crash in various ways. The test >> reads the created hs_err files to check if the DWARF parsing could correctly >> find the filename and line number. For normal HotSpot files, I could not >> check against hardcoded filenames and line numbers as they are subject to >> change (especially line number can quickly become different). I therefore >> just added some sanity checks in the form of "found a non-empty file" and >> "found a non-zero line number". On top of that, I added tests that let the >> VM crash in custom C files (which will not change). This enables an >> additional verification of hardcoded filenames and line numbers. >> - Gtests: Directly calling the `get_source()` method which initiates DWARF >> parsing. Tested some special cases, for example, having a buffer that is not >> big enough to store the filename. >> >> On top of that, there are also existing JTreg tests that call >> `-XX:NativeMemoryTracking=detail` which will print a native stack trace with >> the new source information. These tests were also run as part of the >> standard tier testing and can be considered as sanity tests for this >> implementation. >> >> To make tests work in our infrastructure or if some other setups want to >> have debug symbols at different locations, I've added support for an >> additional `_JVM_DWARF_PATH` environment variable. This variable can >> specify a path from which the DWARF symbol file should be read by the parser >> if the default locations do not contain debug symbols (required some `make` >> changes). This is similar to what's done on Windows with `_NT_SYMBOL_PATH`. >> The JTreg test, however, also works if there are no symbols available. In >> that case, the test just skips all the assertion checks for the filename and >> line number. >> >> I haven't run any specific performance testing as this new code is mainly >> executed when an error will exit the VM and only if symbol files are >> available (which is normally not the case when using Java release builds as >> a user). >> >> Special thanks to @tschatzl for giving me some pointers to start based on >> his knowledge from a DWARF 2 parser he once wrote in Pascal and for >> discussing approaches on how to retrieve the source information and to >> @erikj79 for providing help for the changes required for `make`! >> >> Thanks, >> Christian > > Christian Hagedorn has updated the pull request incrementally with two > additional commits since the last revision: > > - Update test/hotspot/jtreg/runtime/ErrorHandling/TestDwarf.java > > Co-authored-by: Erik Joelsson <37597443+erik...@users.noreply.github.com> > - Update test/hotspot/jtreg/runtime/ErrorHandling/TestDwarf.java > > Co-authored-by: Erik Joelsson <37597443+erik...@users.noreply.github.com> Personally, I am in favor of this project. Actually, I were experimenting it with libdwarf. I would like to add some historical background on this topic, just for consideration. We had a dwarf parser over a decade ago, a little after elf parser, but never made to mainline. There were several reasons at the time. Good news, some are no longer applied today :-) - At the time, Solaris still used STABS format, we could not get support from Solaris compiler team. - If one platform does not support a feature, no one can have it. That's why we could have it on Windows from day one, but did not enable it until much later. - Different compiler (and different version of the same compiler) can generate DWARF with different version, may not be compatible with each other, as DWARF allows custom fields. - Maintenance cost to catch up DWARF spec/compiler changes. ------------- PR: https://git.openjdk.java.net/jdk/pull/7126
