Re: Source code debugging of OVMF

[Johannes Swoboda <johannes.swoboda@student.tuwien.ac.at>]

Hello Brian,

Unfortunately, if I understand it correctly, this page explains how to 
debug efi-apps (where gdb can simply load the efi-file to load the 
symbols), but this isn't applicable for the ovmf.fd-file itself; gdb 
refuses to open it.

However, this will be of help when I'll look at an efi app.

Thank you and kind regards, Johannes

On 2018-04-16 17:26, Richardson, Brian wrote:
> This page was recently added to the TianoCore wiki. Please let me know
> if this is useful info:
> https://github.com/tianocore/tianocore.github.io/wiki/How-to-debug-OVMF-with-QEMU-using-GDB
> 
> Thanks ... br
> ---
> Brian Richardson, Senior Technical Marketing Engineer, Intel Software
> brian.richardson@intel.com -- @intel_brian (Twitter & WeChat)
> https://software.intel.com/en-us/meet-the-developers/evangelists/team/brian-richardson
> 
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> Johannes Swoboda
> Sent: Monday, April 16, 2018 7:09 AM
> To: edk2-devel@lists.01.org
> Cc: clemens.hlauschek@inso.tuwien.ac.at
> Subject: [edk2] Source code debugging of OVMF
> 
> Hello everyone,
> 
> I'm doing a research project on efi security. I would like to do
> source code debugging of OVMF. I want to step through the OVMF source
> code, set break points, et cetera, preferably with gdb. I want to
> debug the overall boot process. Is that possible?
> 
> I understand I can start qemu with the options -s -S. This gives me a
> virtual machine that awaits connection of a gdb debugger and further
> instructions.
> 
> After connecting with gdb, I can instruct the machine to continue
> execution. Unsurprisingly, there is nothing else I can do, because gdb
> lacks the relevant symbols.
> I tried to read in the OVMF.fd file, as i would do with a binary that
> I would debug, but gdb can't handle the file.
> It seems to be possible to load an efi app with the file command, but
> not this one.
> 
> I found one other person trying to achieve the same five years ago.
> [3] suggests that something like this
>> (gdb) add-symbol-file ../edk2/Build/OvmfX64/DEBUG_GCC5/X64/Shell.debug
>> The address where ../edk2/Build/OvmfX64/DEBUG_GCC5/X64/Shell.debug has
>> been loaded is missing
> might be possible. However, it appears to me this is may contain
> information regarding Shell.efi, an efi-app; but I don't want to debug
> an app. I want to debug the overall boot process.
> 
> I'm quoting some terminal output to clarify what I'm trying to achieve:
> [johannes@johannes-laptop OVMF_efi_hello_world]$ gdb [...]
> (gdb) file OVMF.fd
> "/home/johannes/18S/bakk/uefi_virtual/OVMF_efi_hello_world/OVMF.fd":
> not in executable format: File format not recognized
> (gdb) target remote localhost:1234
> Remote debugging using localhost:1234
> warning: No executable has been specified and target does not support
> determining executable automatically.  Try using the "file" command.
> 0x000000000000fff0 in ?? ()
> (gdb) step
> Cannot find bounds of current function
> (gdb) list
> No symbol table is loaded.  Use the "file" command.
> (gdb) continue
> Continuing.
> [ovmf loads in qemu window]
> 
> I can redirect ovmf debug messages into a text file[1].
> As far as I understand, there is a way to do source code level 
> debugging
> *with* ovmf, to debug efi-apps that are e.g. run via the efi shell[2],
> with the help of SourceLevelDebugPkg[4], but this package cannot be
> used to source level debug the overall boot process, right?
> 
> Is it possible to do source level debugging of ovmf?
> Is it possible to step through ovmf, one instruction or function call 
> at a time?
> How are you ovmf developer debugging it?
> 
> If you could point me to the right direction, that would be great.
> 
> Kind regards,
> Johannes
> 
> [1]: I managed to do so via the qemu options -global
> isa-debugcon.iobase=0x402 -debugcon file:qemu.ovmf.log" as
> demonstrated here
> https://www.linux-kvm.org/downloads/lersek/ovmf-whitepaper-c770f8c.txt
> [2]:https://github.com/tianocore/tianocore.github.io/wiki/OVMF-FAQ#how-do-i-enable-source-level-debugging-with-ovmf
> [3]:
> http://edk2-devel.narkive.com/LRWe2mSQ/using-gdb-on-ovmf-with-symbols
> [4]:
> https://github.com/tianocore/tianocore.github.io/wiki/SourceLevelDebugPkg