diff options
Diffstat (limited to 'en_US.ISO8859-1/books/developers-handbook/kerneldebug')
| -rw-r--r-- | en_US.ISO8859-1/books/developers-handbook/kerneldebug/chapter.sgml | 81 |
1 files changed, 59 insertions, 22 deletions
diff --git a/en_US.ISO8859-1/books/developers-handbook/kerneldebug/chapter.sgml b/en_US.ISO8859-1/books/developers-handbook/kerneldebug/chapter.sgml index 4cf1b19f75..70efe283f2 100644 --- a/en_US.ISO8859-1/books/developers-handbook/kerneldebug/chapter.sgml +++ b/en_US.ISO8859-1/books/developers-handbook/kerneldebug/chapter.sgml @@ -1,7 +1,7 @@ <!-- The FreeBSD Documentation Project - $FreeBSD: doc/en_US.ISO_8859-1/books/handbook/kerneldebug/chapter.sgml,v 1.25 2000/07/14 21:57:34 ben Exp $ + $FreeBSD: doc/en_US.ISO_8859-1/books/handbook/kerneldebug/chapter.sgml,v 1.26 2000/11/07 09:08:11 jkoshy Exp $ --> <chapter id="kerneldebug"> @@ -554,33 +554,70 @@ Debugger (msg=0xf01b0383 "Boot flags requested debugger") full access to the source, running it in gud-mode inside an Emacs window (which gives you an automatic source code display in another Emacs window) etc.</para> + </sect1> + + <sect1> + <title>Debugging Loadable Modules Using GDB</title> - <para>Remote GDB can also be used to debug LKMs. First build the LKM with - debugging symbols:</para> + <para>When debugging a panic that occurred within a module, or + using remote GDB against a machine that uses dynamic modules, + you need to tell GDB how to obtain symbol information for those + modules.</para> - <screen>&prompt.root; <userinput>cd /usr/src/lkm/linux</userinput> + <para>First, you need to build the module(s) with debugging + information:</para> + + <screen>&prompt.root; <userinput>cd /sys/modules/linux</userinput> &prompt.root; <userinput>make clean; make COPTS=-g</userinput></screen> - <para>Then install this version of the module on the target machine, load - it and use <command>modstat</command> to find out where it was - loaded:</para> - - <screen>&prompt.root; <userinput>linux</userinput> -&prompt.root; <userinput>modstat</userinput> -Type Id Off Loadaddr Size Info Rev Module Name -EXEC 0 4 f5109000 001c f510f010 1 linux_mod</screen> - - <para>Take the load address of the module and add 0x20 (probably to - account for the a.out header). This is the address that the module code - was relocated to. Use the <command>add-symbol-file</command> command in - GDB to tell the debugger about the module:</para> - - <screen><prompt>(kgdb)</prompt> <userinput>add-symbol-file /usr/src/lkm/linux/linux_mod.o 0xf5109020</userinput> -add symbol table from file "/usr/src/lkm/linux/linux_mod.o" at -text_addr = 0xf5109020? (y or n) <userinput>y</userinput> + <para>If you are using remote GDB, you can run + <command>kldstat</command> on the target machine to find out + where the module was loaded:</para> + + <screen>&prompt.root; <userinput>kldstat</userinput> +Id Refs Address Size Name + 1 4 0xc0100000 1c1678 kernel + 2 1 0xc0a9e000 6000 linprocfs.ko + 3 1 0xc0ad7000 2000 warp_saver.ko + 4 1 0xc0adc000 11000 linux.ko +</screen> + + <para>If you are debugging a crash dump, you'll need to walk the + <literal>linker_files</literal> list, starting at + <literal>linker_files->tqh_first</literal> and following the + <literal>link.tqe_next</literal> pointers until you find the + entry with the <literal>filename</literal> you are looking for. + The <literal>address</literal> member of that entry is the load + address of the module.</para> + + <para>Next, you need to find out the offset of the text section + within the module:</para> + + <screen>&prompt.root; <userinput>objdump --section-headers /sys/modules/linux/linux.ko | grep text</userinput> + 3 .rel.text 000016e0 000038e0 000038e0 000038e0 2**2 + 10 .text 00007f34 000062d0 000062d0 000062d0 2**2</screen> + + <para>The one you want is the <literal>.text</literal> section, + section 10 in the above example. The fourth numerical field + (sixth field overall) is the offset in hex of the text section + within the file (0x62d0 in our example). Add this to the load + address reported by <command>kldstat</command> to obtain the + address of the module text in memory.</para> + + <para>Take the load address of the module (as reported by + <command>kldstat</command>) and add the offset of the text + section within the module (0x62d0 + 0xc0adc000 = c0ae22d0 in our + example). This is the address that the module code was + relocated to. Use the <command>add-symbol-file</command> + command in GDB to tell the debugger about the module:</para> + + <screen><prompt>(kgdb)</prompt> <userinput>add-symbol-file /sys/modules/linux/linux.ko 0xc0ae22d0</userinput> +add symbol table from file "/sys/modules/linux/linux.ko" at text_addr = 0xc0ae22d0? +(y or n) <userinput>y</userinput> +Reading symbols from /sys/modules/linux/linux.ko...done. <prompt>(kgdb)</prompt></screen> - <para>You now have access to all the symbols in the LKM.</para> + <para>You now have access to all the symbols in the module.</para> </sect1> <sect1> |