Re: Issue of step by step debugging of OVMF SEC code in QEMU

[Andrew Fish <afish@apple.com>]

It is generally hard to debug across x86 processor mode transitions, and to debug 16-bit real mode code with modern tools. There are a few places in the x86 that still require 16-bit real mode for handoffs (like the reset vector) so you tend to hit this issue more in debugging firmware.

Thanks,

Andrew Fish


> On Aug 3, 2017, at 8:41 PM, wang xiaofeng <winggundum82@163.com> wrote:
> 
> Hi  Andrew,
>     THe problem is solved, after the SEC code switch to protected mode, gdb can work well now
> 
> 
> 
> 
> 
> 
> At 2017-08-04 11:26:16, "wang xiaofeng" <winggundum82@163.com> wrote:
> HI Andrew,
>      How can I adjust the debugger to correct mode? Or I have to enable the debug after swtich to protected mode?
> 
> 
> 
> 
> 
> 
> At 2017-08-04 10:57:16, "Andrew Fish" <afish@apple.com <mailto:afish@apple.com>> wrote:
> >The reset vector is 16-bit real mode, so you have the debugger in the wrong mode. The code should transition to 32 bit protected early in the flow.
> >
> >Sent from my iPhone
> >
> >> On Aug 3, 2017, at 7:47 PM, wang xiaofeng <winggundum82@163.com <mailto:winggundum82@163.com>> wrote:
> >> 
> >> Hello,
> >>       I am tring to add my own SEC code base on OVMF and run on QEMU. Since the code cannot run I need to step to step trace the assembly code .
> >>      The hang point is very early before I can use either UDK or debug serial output. I tried to use gdb to connect to QEMU.I start gdb in another terminal, and issue the following commands:
> >>  (gdb) set architecture i386:x86-64:intel
> >>  (gdb) target remote localhost:1234
> >>   It really stops at the bios first instruction at 0XFFFFFFF0. But gdb shows eip= 0xFFF0 and CS=0xF000(why it not be 0xfff0). After I trigger the command "display /i $pc"
> >>   It shows the assembly code in 0xFFF0 instead of    0XFFFFFFF0, so the information is incorrect.
> >>   Anyone knows how to corrently debug the SEC code ? Other debug tool is also ok.
> >>   Thanks in advance!
> >> 
> >> 
> >> 
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>  
> 
> 
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