poniedziałek, 22 lutego 2016

EDKII and QEMU - remote debugging with gdb

While working with UEFI debugger can be very helpful. I was using EDKII project to write my UEFI applications and I was testing it with QEMU. I added my application information file to the OvmfPkg module information and this let me to running my program using existing script.
To build OvmfPkg and run QEMU run (in the OvmfPkg folder):
 ./build.sh -A IA32 qemu -s -monitor stdio -debugcon file:debug.log -global isa-debugcon.iobase=0x402  
After start debug.log file will be created where you can read output from UEFI.
We need to know where your application will be loaded (memory address). Run your application in QEMU:
 Shell> fs0:  
 fs0:\> MyApp.efi  
Open debug.log file (in the EDKII directory), and find line with name of your loaded application. You should get something like this:
 Loading driver at 0x00006B75000 EntryPoint=0x00006B75220 MyApp.efi  
And this is our address:
 EntryPoint=0x00006B75220  
Now open second terminal, open directory with your application's debugging symbols and efi file (for me: Build/OvmfIa32/DEBUG_GCC48/IA32/MyApp.debug) and run gdb:
 gdb --tui  
We need to know where particular sections are located. Load efi file and enter info files:
 (gdb) file MyApp.efi  
 Reading symbols from MyApp.efi...(no debugging symbols found)...done.  
 (gdb) info files  
 Symbols from ".../edk2/Build/OvmfIa32/DEBUG_GCC48/IA32/MyApp.efi".  
 Local exec file:  
     `.../Build/OvmfIa32/DEBUG_GCC48/IA32/MyApp.efi', file type pei-i386.  
     Entry point: 0x220  
     0x00000220 - 0x00003a40 is .text  
     0x00003a40 - 0x00004320 is .data  
     0x00004320 - 0x00004520 is .reloc  
We need to calculate our addresses for text and data section. Application is loaded under 0x00006B75220 (entry point) and we know text and data offsets.
text = 0x06B75220
data = 0x06B75220 + 0x00003a40 = 0x06B78C60

Now unload efi file:
 (gdb) file  
 No executable file now.  
 No symbol file now.  
Load symbols:
 (gdb) add-symbol-file MyApp.debug 0x06B75220 -s .data 0x06B78C60
add symbol table from file "MyApp.debug" at
        .text_addr = 0x6b75220
        .data_addr = 0x6b78c60
(y or n) y
Reading symbols from MyApp.debug...done.
You can add some breakpoints, for example:
 break UefiMain  
And attach debugger to the QEMU:
 target remote localhost:1234  
And run QEMU:
 ./build.sh -A IA32 qemu -s -monitor stdio -debugcon file:debug.log -global isa-debugcon.iobase=0x402  
Machine will be paused, type "continue", load your application. Done!



Links:
http://osdevnotes.blogspot.com/2011/05/using-gdb-to-debug-uefi.html
http://wiki.osdev.org/Debugging_UEFI_applications_with_GDB
http://comments.gmane.org/gmane.comp.bios.tianocore.devel/6777

2 komentarze:

  1. My husband and I have been having lots of problems living together, he never gives me attention or makes me happy because he has fallen in love with another woman outside our marriage. I tried my best to make sure that my husband leaves this woman but the more I talk to him about it the more he makes me feel sad and unhappy, My marriage started leading to divorce because he no longer gives me attention. I wanted to forget him but i love him and didn't want to lose him. We have been married for years and he is all I could call a true best friend and best in all, the man that handles my problems perfectly, the man that makes sacrifices for ,my happiness. I wanted him back in my life badly and I was so confused. My Friends told me to buy books about relationships, so I went online for relationship books while I came across a spell caster called Dr Emu. I read testimonies and reviews about him so I contacted him immediately, explained my problems to him. Same day , he casted a spell for me and assured me for 2 days that my husband will return to me and to my greatest surprise the third day my husband came knocking on my door and begged for forgiveness. I am so happy that my love is back again and not only that, we are about to get married again, he proposed. I wouldn't stop talking about him. Contact him today if you need his help via email: emutemple@gmail.com and you will see that your problem will be solved without any delay. Website: https://emutemple.wordpress.com/

    OdpowiedzUsuń