Return to ddb_howto.mdwn CVS log

Up to [NetBSD Developer Wiki] / wikisrc / users / haad

Annotation of wikisrc/users/haad/ddb_howto.mdwn, revision 1.1

1.1     ! wiki        1: [[!meta title="NetBSD Developer Cheatsheet"]]
        !             2: 
        !             3: [[!toc]]
        !             4: 
        !             5: 
        !             6: This article is going to be a collection of random notes which I have found during my development in kernel. I have found that there are some hints which every developer knows, but there is no documentation where newbie can learn them.
        !             7: 
        !             8: 
        !             9: ## Finding where the bug is
        !            10: 
        !            11: When you get a crash in the kernel you want to translate the address from the backtrace to the line in the source code:
        !            12: 
        !            13: Stopped in pid 496.1 (gdb) at netbsd:breakpoint+0x5: leave
        !            14: 
        !            15: First, you need to find the address of the breakpoint function in the running kernel image with the nm(1) command:
        !            16: 
        !            17: nm netbsd | grep breakpoint
        !            18: 
        !            19: Then add 0x5 to the address, and use addr2line(1) to get the exact line in the kernel source code where you get the crash:
        !            20: 
        !            21: addr2line -g netbsd {sum address}
        !            22: 
        !            23: In gdb(1), this can be achieved with the command info line *(function_name)+0x5.
        !            24: 
        !            25: ## What to do if ddb backtrace doesn't work
        !            26: 
        !            27: The DDB backtrace command usually doesn't work when the EIP register was set to NULL, e.g. via a bad function pointer. In this case we can get part of the backtrace by using a different approach.
        !            28: 
        !            29: db> show all reg
        !            30: 
        !            31: eip 0 cs 0 eflags 0 esp 0xcb741b70
        !            32: 
        !            33: We need to find which address was set in the ESP register (this is the stack pointer register on i386). When we have our address we need to use
        !            34: 
        !            35: x /Lx 0xcb741b70,20
        !            36: 
        !            37: to print the first 20 addresses from the stack. To easily find the address of the last function you need to look for an address with 0xc0 at the start.
        !            38: 
        !            39: The command x /I c06428fc will then translate the function address to it's name with the symbol table lookup.
        !            40: What to do if gdb cannot backtrace through trap()
        !            41: 
        !            42: Use ('source') .../sys/arch/i386/gdbscripts/stack gdb script and run 'stack'. See also PR 10313.
        !            43: How to rebuild /boot
        !            44: 
        !            45: (This example assumes you are running NetBSD-i386)
        !            46: 
        !            47:     * Make sure you have the tools built
        !            48:     * sys/arch/i386/stand/boot and enter $TOOLDIR/bin/nbmake-i386