Jordan Delong
363d1bb20f
This change is mostly for FB internal organizational reasons. Building is not effected beyond the fact that the target now lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.
59 linhas
2.2 KiB
Plaintext
59 linhas
2.2 KiB
Plaintext
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<h2>Useful gdb Commands</h2>
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info threads
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thread apply [threadno] [all] args
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set follow-fork-mode parent
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set detach-on-fork on
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set print pretty
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handle SIGPIPE nostop noprint pass
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dump binary memory [filename] [start_addr] [end_addr]
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symbol-file [un-stripped binary OR symbol file from strip]
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= b main.no.cpp:55
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If you get "Couldn't get registers" error when starting a program with gdb,
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instead of attaching to a running process, this is because gdb has a bug,
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not able to switch to the main thread/process when it forks:
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[Thread debugging using libthread_db enabled]
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[New Thread 46912496246512 (LWP 30324)]
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[New Thread 1084229952 (LWP 30327)]
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[Thread 1084229952 (LWP 30327) exited]
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Couldn't get registers: No such process.
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Set a break point at line 55 of main.no.cpp, then "r", you will get this,
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[Thread debugging using libthread_db enabled]
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[New Thread 46912496246512 (LWP 30632)]
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[New Thread 1084229952 (LWP 30636)]
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[Thread 1084229952 (LWP 30636) exited]
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<b>[Switching to Thread 46912496246512 (LWP 30632)]</b>
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Breakpoint 1, main (argc=3, argv=0x7fff41b5b138) at sys/main.no.cpp:55
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55 return HPHP::execute_program(argc, argv);
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(gdb) c
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Magically, gdb is able to switch to main thread, attaching to it, then it will
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be able to debug it, even if it forks afterwards.
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<h2> Getting PHP symbols in the JIT under gdb </h2>
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The VM periodically emits DWARF files containing function address
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information for the JIT code it generates. These DWARF files are synced with gdb
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asynchronously (by default every ~128 tracelets). This means that the backtrace
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you see under gdb may contain some unresolved PHP symbols that show up as ??s,
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for symbols that have not been synced.
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There are three ways to resolve this:
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1. pass -v Eval.GdbSyncChunks=1 in the command line. This forces the VM to sync
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debug info synchronously with gdb.
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2. call HPHP::g_context.m_node.m_p->syncGdbState() from the gdb CLI. This
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forces a manual sync of all outstanding symbols to gdb.
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3. if the program has hit a seg fault (or another signal), press continue on
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the CLI. The HHVM signal handler will sync outstanding DWARF symbols to gdb,
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and a subsequent 'bt' should show all symbols.
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