4ea9e6e3a6
A new command, run_on_start, for things to do before GRUB starts executing. Currently, this is setting up the loading of module symbols as they are loaded and allowing user-defined script to be run if a command named "onstart" exists. On some platforms, notably x86, software breakpoints set in GDB before the GRUB image is loaded will be cleared when the image is loaded. This is because the breakpoints work by overwriting the memory of the break- point location with a special instruction which when hit will cause the debugger to stop execution. Just before execution is resumed by the debugger, the original instruction bytes are put back. When a breakpoint is set before the GRUB image is loaded, the special debugger instruction will be written to memory and when the GRUB image is loaded by the firmware, which has no knowledge of the debugger, the debugger instruction is overwritten. To the GDB user, GDB will show the breakpoint as set, but it will never be hit. Furthermore, GDB now becomes confused, such that even deleting and re-setting the breakpoint after the GRUB image is loaded will not allow for a working breakpoint. To work around this, in run_on_start, first a watchpoint is set on _start, which will be triggered when the firmware starts loading the GRUB image. When the _start watchpoint is hit, the current breakpoints are saved to a file and then deleted by GDB before they can be overwritten by the firmware and confuse GDB. Then a temporary software breakpoint is set on _start, which will get triggered when the firmware hands off to GRUB to execute. In that breakpoint load the previously saved and deleted breakpoints now that there is no worry of them getting overwritten by the firmware. This is needed for runtime_load_module to work when it is run before the GRUB image is loaded. Note that watchpoints are generally types of hardware breakpoints on x86, so its deleted as soon as it gets triggered so that a minimal set of hardware breakpoints are used, allowing more for the user. Signed-off-by: Glenn Washburn <development@efficientek.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'