Annotation of wikisrc/users/haad/ddb_howto.mdwn, revision 1.4

1.1       wiki        1: [[!meta title="NetBSD Developer Cheatsheet"]]
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                      3: [[!toc]]
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                      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.
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                      9: ## Finding where the bug is
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                     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:
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1.3       sevan      13:     Stopped in pid 496.1 (gdb) at netbsd:breakpoint+0x5: leave
1.1       wiki       14: 
1.3       sevan      15: First, you need to find the address of the breakpoint function in the running kernel image with the [[!template id=man name="nm" section="1"]] command:
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1.3       sevan      17:     nm netbsd | grep breakpoint
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1.3       sevan      19: Then add `0x5` to the address, and use [[!template id=man name="addr2line" section="1"]] to get the exact line in the kernel source code where you get the crash:
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1.4     ! sevan      21:     addr2line -e netbsd {sum address}
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1.3       sevan      23: In [[!template id=man name="gdb" section="1"]], this can be achieved with the command `info line *(function_name)+0x5`.
1.1       wiki       24: 
                     25: ## What to do if ddb backtrace doesn't work
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                     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.
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1.3       sevan      29:     db> show all reg
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1.3       sevan      31:     eip 0 cs 0 eflags 0 esp 0xcb741b70
1.1       wiki       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
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1.3       sevan      35:     x /Lx 0xcb741b70,20
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1.3       sevan      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.
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1.3       sevan      39: The command `x /I c06428fc` will then translate the function address to it's name with the symbol table lookup.
1.2       gson       40: 
                     41: ## What to do if gdb cannot backtrace through trap()
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1.3       sevan      43: Use `source .../sys/arch/i386/gdbscripts/stack` gdb script and run `stack`. See also [PR 10313](http://gnats.netbsd.org/10313).
1.2       gson       44: 
                     45: ## How to rebuild /boot
1.1       wiki       46: 
                     47: (This example assumes you are running NetBSD-i386)
                     48: 
                     49:     * Make sure you have the tools built
                     50:     * sys/arch/i386/stand/boot and enter $TOOLDIR/bin/nbmake-i386

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