Hi... 2010/9/10 loody <miloody@xxxxxxxxx>: > Is it the limitation of kernel source debugging? > ( cannot print out the value of variable) Ehm..not sure, but one thing for sure: debugger can only see as much information as the ones that exists inside the kernel image. In this case: symbol table, a table that describe the relation between a function or variable or anything and its location in memory (before relocation, so it's more like an offset). > I guess it maybe due to kernel image is impossible include frame information. > (actually I don't quite well understand what is the frame used for, > but from google, it seems the key point that gdb can watch the value > of parameter) Although I am not 100% sure here, you might try enable "Compile kernel with debug info" inside kernel hacking menu during kernel configuration (and quite possibly you need to recompile your kernel). or...as alternative, if you use stock kernel from your distro, install the kernel image from "debug info" repository. It basically add -g to the gcc, thus embedding so called DWARF information to the final kernel image. It would be a great help for any debugger to locate the symbol in memory. As for the "value optimized out", quite likely it's "erased" since compiler thinks it's not actually used. Why compiler do this (when we use -O1 or O2 etc)? Simple, to conserve space and speed up execution. So if you still see -O<something> in your CFLAGS inside the main Makefile, you may also try to delete it. -g and -O are not a good combination. NB: Frame pointer? Generally it's a "variable" (actually it's processor register) reserved to record the stack boundary during function call. perhaps you recall that when we call a function, we push the passed parameters into stack? along with the current instruction pointer (current address of executed instruction)? frame pointer mark this boundary. What's the difference? Enabling this...and you'll get better stack tracing (also known as back tracing). it's a procedure to trace which function calls which function and where exactly it's called. Does it clear your doubts? -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
