Branch Tracer or btrax for short, is a branch instruction tracer using the branch record mechanism that is the debugging function of Pentium4 and Xeon CPU.
It can trace branch instruction of kernel, driver, application and library without making a change to the kernel source code. Traced log information is analyzed, and branch coverage information and the execution path can be displayed.
btrax consists of the following two parts.
· Tracer of the branch instructions.
· Analyzer of the traced log.
As for the branch instruction tracing part, the development result of another project shown as follows is included excluding the driver of the branch tracer. To facilitate the installation of btrax, these drivers are bundling it to the btrax package. The future, there is a possibility not to be bundled.
· djprobe --- Driver to set hook point without changing the kernel source.
· ctr --- Driver to set hook point to entrance/exit of system calls.
· relayfs --- Driver to transmit a large amount of data from kernel space to user space.
Branch coverage information and the execution path can be displayed by the log analysis part. It is composed by the following programs.
· bt_split --- Trace log splitter.
· bt_coverage --- Branch coverage analyzer.
· bt_execpath --- Execution path analyzer.
Here are some key features of "Branch Tracer":
Getting trace log
btrax supports the application, library, kernel, and driver's trace. In the trace of the application and the kernel, the following points are different.
· application --- Start the application and get pid, and execute the trace command with this pid.
· kernel --- The trace log capacity is limited to the size of the buffer. It traces it from or to an arbitrary symbol/address only by the capacity of the buffer.
Starting or terminating of the kernel trace uses the hook that is inserted by djprobe, and djprobe has the limitation in the hook insert point. Please refer to djprobe's home page for details.
Analyzing trace log
The range of the address to be analyzed can be specified. The following information can be analyzed and referred to.
· branch coverage
· execution path
As the branch coverage information, the function coverage and branch execution coverage can be analyzed.
Moreover, it has an simple repetition check function, and it is possible to display it omitting repeating in the execution path analysis function.
Compile/Execution environment
Because btrax uses the debugging function of Pentium4 and Xeon CPU, the machine equipped with these processors is necessary.
The following are necessary to compile, and to execute btrax.
· Kernel header files necessary for the driver's compilation (kernel-devel package).
· Uncompressed vmlinux (kernel-debuginfo package).
· binutils
Moreover, it is necessary to support the following by the kernel.
· procfs
· kallsyms
· apic
btrax can work on the following environment.
· RedHat Enterprise Linux App Server 4 Update 1 (2.6.9-11.ELsmp)
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