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Update the GDB monitor test documentation
The interactive GDB monitor test has changed recently. This patch updates the documentation accordingly. Fixes #126.
This commit is contained in:
Christian Prochaska
Norman Feske
parent
7e00ef96ee
commit
77a7207b42
@ -247,14 +247,14 @@ Working with shared libraries
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=============================
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To get acquainted with GDB monitor, the 'ports' repository comes with two
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example run scripts. The 'gdb_monitor.run' script executes a simple test
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program via GDB monitor. The test program can be found at
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example run scripts. The 'gdb_monitor_interactive.run' script executes a
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simple test program via GDB monitor. The test program can be found at
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'ports/src/test/gdb_monitor/'. When looking behind the scenes, the simple
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program is not simple at all. It uses shared libraries (the libc and libc_log)
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plugin and executes multiple threads. To it is a nice testbed for exercising
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plugin and executes multiple threads. So it is a nice testbed for exercising
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these aspects. The run script can be invoked right from the build directory
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via 'make run/gdb_monitor'. It will execute the scenario on Qemu and use
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the UART to communicate with GDB. Qemu is instructed to redirect the second
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via 'make run/gdb_monitor_interactive'. It will execute the scenario on Qemu and
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use the UART to communicate with GDB. Qemu is instructed to redirect the second
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serial interface to a local socket (using the port 5555):
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! -serial chardev:uart
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! -chardev socket,id=uart,port=5555,host=localhost,server,nowait
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@ -262,62 +262,30 @@ serial interface to a local socket (using the port 5555):
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The used TCP port is then specified to the GDB as remote target:
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! target remote localhost:5555
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The 'gdb_monitor.run' script performs these steps for you and spawns GDB
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in a new terminal window. From within your build directory, execute the
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The 'gdb_monitor_interactive.run' script performs these steps for you and spawns
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GDB in a new terminal window. From within your build directory, execute the
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run script via:
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! make run/gdb_monitor
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! make run/gdb_monitor_interactive
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On startup, GDB monitor halts the target program and waits for GDB to
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connect. Once connected GDB will greet you with a prompt like this:
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connect. Once connected, GDB will greet you with a prompt like this:
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! Reading symbols from /open/build/genode/foc_x86_32/bin/test-gdb_monitor...done.
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! Remote debugging using localhost:5555
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! warning: Unable to find dynamic linker breakpoint function.
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! GDB will be unable to debug shared library initializers
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! and track explicitly loaded dynamic code.
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! 0x00054ac0 in ?? ()
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! (gdb)
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! Breakpoint 2, main () at /.../ports/src/test/gdb_monitor/main.cc:67
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! 67 {
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! (gdb)
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Since 'test-gdb_monitor' is a dynamically linked binary, Genode has started
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the dynamic linker. Because neither the actual binary nor any shared library
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has been loaded so far, GDB cannot determine symbol information. So let's
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start executing the program using the 'c' (continue) command:
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! (gdb) c
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! Continuing.
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The test program will start printing some messages via core's LOG service.
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We can interrupt it by pressing Control-C in the GDB console.
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! ^C
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! Program received signal SIGINT, Interrupt.
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! 0x0005396c in ?? ()
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! (gdb)
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Now that the program has been executed for a while, it is a good time to let
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GDB figure out information about shared libraries using the 'sharedlibrary' command:
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! (gdb) sharedlibrary
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You will see several messages indicating where GDB fetches symbol information
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for each shared library used by the program. To see, what GDB has found out,
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use the 'info shared' command. GDB will respond with a table like this:
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(gdb) info shared
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! From To Syms Read Shared Object Library
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! 0x0009c1b8 0x00100b64 Yes /.../build/var/libcache/libc/libc.lib.so
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! 0x00007c5c 0x00007ecc Yes /.../build/var/libcache/libc_log/libc_log.lib.so
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! 0x0003e704 0x00063748 Yes /.../build/var/libcache/ld/ld.lib.so
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It is telling us the load location of each shared library and informs us
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about having successfully obtained the symbol information for each library.
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Now, with symbol information available, let's set a breakpoint to the 'printf'
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function, which is repeatedly called by the test program using the 'breakpoint'
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command:
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! (gdb) b printf
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! Breakpoint 1 at 0xd503c: file /.../stdio/printf.c, line 49.
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After continuing the executing via 'c' (continue), you will see that the
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At this point, GDB has acquired symbol information from the loaded shared
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libraries and stopped the program at the beginning of its 'main()' function.
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Now let's set a breakpoint to the 'puts' function, which is called by the test
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program, by using the 'breakpoint' command:
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! (gdb) b puts
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! Breakpoint 3 at 0x106e120: file /.../libc-8.2.0/libc/stdio/puts.c, line 53.
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After continuing the execution via 'c' (continue), you will see that the
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breakpoint will trigger with a message like this:
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! (gdb) c
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! Continuing.
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! [New Thread 2]
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! [Switching to Thread 2]
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!
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! Breakpoint 1, printf (fmt=0x1004144 "Test thread is running, cnt=%d\n")
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! at /.../stdio/printf.c:49
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! 49 ret = vfprintf(stdout, fmt, ap);
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! Breakpoint 3, puts (s=0x10039c0 "in func2()\n")
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! at /.../libc-8.2.0/libc/stdio/puts.c:53
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! 53 {
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Now, you can inspect the source code of the function via the 'list' command,
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inspect the function arguments ('info args' command) or start stepping
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@ -326,68 +294,53 @@ backtrace including several functions located in different shared libraries,
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set another breakpoint at the 'stdout_write' function. This function is
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used by the 'libc_log' backend and provided by the dynamic linker. The
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backtrace will reveal all the intermediate steps throughout the libc when
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'printf' is called.
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'puts' is called.
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! (gdb) b stdout_write
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! Breakpoint 1 at 0x55906: file /.../log_console.cc, line 101.
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! Breakpoint 4 at 0x59d10: file /.../log_console.cc, line 108.
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! (gdb) c
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! Continuing.
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! [New Thread 2]
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! [Switching to Thread 2]
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!
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! Breakpoint 1, stdout_write (s=0x400ff434 "Test thread is running, cnt=8\n")
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! at /.../genode/base/src/base/console/log_console.cc:101
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! 101 {
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! Breakpoint 4, stdout_write (s=0x1015860 "in func2()\n")
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! at /.../genode/base/src/base/console/log_console.cc:108
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! 108 {
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! (gdb) bt
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! #0 stdout_write (s=0x400ff434 "Test thread is running, cnt=8\n")
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! at /.../genode/base/src/base/console/log_console.cc:101
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! #1 0x0000799c in Libc::Log_plugin::write (this=0x8310, fd=0x114ba8,
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! buf=0x3e60, count=30)
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! at /.../genode/libports/src/lib/libc_log/plugin.cc:84
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! #2 0x000f85f8 in _write (libc_fd=1, buf=0x3e60, count=30)
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! at /.../genode/libports/src/lib/libc/file_operations.cc:379
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! #3 0x000d737f in __swrite (cookie=0x105ca8,
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! buf=0x3e60 "Test thread is running, cnt=8\n\006", n=30)
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! at /.../stdio/stdio.c:71
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! #4 0x000d7233 in _swrite (fp=0x105ca8,
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! buf=0x3e60 "Test thread is running, cnt=8\n\006", n=30)
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! at /.../stdio/stdio.c:133
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! #5 0x000d04cb in __sflush (fp=0x105ca8)
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! at /.../stdio/fflush.c:123
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! #6 0x000d052a in __fflush (fp=0x400ff434)
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! at /.../stdio/fflush.c:96
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! #7 0x000d310b in __sfvwrite (fp=0x105ca8, uio=0x400ffdd8)
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! at /.../stdio/fvwrite.c:194
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! #8 0x000d7ea4 in __sprint (fp=0x400ff434, uio=0x400ffdd8)
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! at /.../stdio/vfprintf.c:88
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! #9 0x000dad08 in __vfprintf (fp=0x105ca8,
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! fmt0=0x1003618 "Test thread is running, cnt=%d\n", ap=0x400ffe98 "\b")
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! ---Type <return> to continue, or q <return> to quit---
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! at /.../stdio/vfprintf.c:1179
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! #10 0x000db29f in vfprintf (fp=0x105ca8,
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! fmt0=0x1003618 "Test thread is running, cnt=%d\n", ap=0x400ffe98 "\b")
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! at /.../stdio/vfprintf.c:351
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! #11 0x000d61f0 in printf (fmt=0x1003618 "Test thread is running, cnt=%d\n")
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! at /.../stdio/printf.c:49
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! #12 0x0100086a in func3 (this=0x1015914)
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! at /.../genode/ports/src/test/gdb_monitor/main.cc:28
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! #13 Test_thread::entry (this=0x1015914)
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! at /.../genode/ports/src/test/gdb_monitor/main.cc:38
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! #14 0x00059333 in Genode::Thread_base::_thread_start ()
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! at /.../genode/base-foc/src/base/thread/thread_bootstrap.cc:39
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! #15 0x00000000 in ?? ()
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! #0 stdout_write (s=0x1015860 "in func2()\n")
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! at /.../genode/base/src/base/console/log_console.cc:108
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! #1 0x010c3701 in (anonymous namespace)::Plugin::write (this=0x10c4378,
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! fd=0x10c0fa8, buf=0x6590, count=11)
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! at /.../genode/libports/src/lib/libc_log/plugin.cc:93
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! #2 0x010937bf in _write (libc_fd=1, buf=0x6590, count=11)
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! at /.../genode/libports/src/lib/libc/file_operations.cc:406
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! #3 0x0106ec4f in __swrite (cookie=0x10a1048, buf=0x6590 "in func2()\n", n=11)
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! at /.../genode/libports/contrib/libc-8.2.0/libc/stdio/stdio.c:71
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! #4 0x0106ef5a in _swrite (fp=0x10a1048, buf=0x6590 "in func2()\n", n=11)
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! at /.../genode/libports/contrib/libc-8.2.0/libc/stdio/stdio.c:133
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! #5 0x01067598 in __sflush (fp=0x10a1048)
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! at /.../genode/libports/contrib/libc-8.2.0/libc/stdio/fflush.c:123
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! #6 0x010675f8 in __fflush (fp=0x10a1048)
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! at /.../genode/libports/contrib/libc-8.2.0/libc/stdio/fflush.c:96
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! #7 0x0106a223 in __sfvwrite (fp=0x10a1048, uio=0x1015a44)
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! at /.../genode/libports/contrib/libc-8.2.0/libc/stdio/fvwrite.c:194
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! #8 0x0106e1ad in puts (s=0x10039c0 "in func2()\n")
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! at /.../genode/libports/contrib/libc-8.2.0/libc/stdio/puts.c:68
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! #9 0x0100041d in func2 ()
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! at /.../genode/ports/src/test/gdb_monitor/main.cc:51
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! #10 0x01000444 in func1 ()
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! at /.../genode/ports/src/test/gdb_monitor/main.cc:60
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! #11 0x01000496 in main ()
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! at /.../genode/ports/src/test/gdb_monitor/main.cc:70
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To inspect a specific call frame, switch to a particular frame by using
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the number printed in the backtrace. For example, to print the local
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variables of the call frame 5:
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! (gdb) f 5
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! #5 0x000d04cb in __sflush (fp=0x105ca8)
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! at /.../stdio/fflush.c:123
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! 123 t = _swrite(fp, (char *)p, n);
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! #5 0x01067598 in __sflush (fp=0x10a1048)
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! at /.../libc-8.2.0/libc/stdio/fflush.c:123
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! 123 t = _swrite(fp, (char *)p, n);
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! (gdb) info locals
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! p = 0x3e60 "Test thread is running, cnt=8\n\006"
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! n = 30
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! t = 1074787380
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! p = 0x6590 "in func2()\n"
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! n = 11
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! t = <optimized out>
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The test program consists of multiple threads. To see which threads there are,
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use the 'info thread' command. To switch another thread, use the 'thread'
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@ -398,7 +351,8 @@ Inspecting a Genode service
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===========================
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As a reference for debugging a native Genode service, the 'debug_nitpicker.run'
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script provides a ready-to-use scenario. You can invoke it via 'make run/debug_nitpicker'.
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script provides a ready-to-use scenario. You can invoke it via
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'make run/debug_nitpicker'.
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Nitpicker is a statically linked program. Hence, no special precautions are
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needed to obtain its symbol information. As a stress test for GDB monitor,
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