Re: [Xen-devel] [PATCH 1/2] x86/boot: fix early error display

[Doug Goldstein <cardoe@xxxxxxxxxx>]

> On Oct 12, 2017, at 4:27 PM, Daniel Kiper <daniel.kiper@xxxxxxxxxx> wrote:
> 
>> On Thu, Oct 12, 2017 at 03:50:06PM -0500, Doug Goldstein wrote:
>> From: David Esler <drumandstrum@xxxxxxxxx>
>> 
>> In 9180f5365524 a change was made to the send_chr function to take in
>> C-strings and print out a character at a time until a NULL was
>> encountered. However there is no code to increment the current character
>> position resulting in an endless loop of the first character. This adds
>> a simple increment.
>> 
>> Reviewed-by: Doug Goldstein <cardoe@xxxxxxxxxx>
>> Signed-off-by: David Esler <drumandstrum@xxxxxxxxx>
>> ---
>> xen/arch/x86/boot/head.S | 1 +
>> 1 file changed, 1 insertion(+)
>> 
>> diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
>> index fd6fc337fe..f48bbbd2e5 100644
>> --- a/xen/arch/x86/boot/head.S
>> +++ b/xen/arch/x86/boot/head.S
>> @@ -174,6 +174,7 @@ not_multiboot:
>>         mov     sym_esi(vga_text_buffer),%edi
>> .Lsend_chr:
>>         mov     (%esi),%bl
>> +        inc     %esi
>>         test    %bl,%bl        # Terminate on '\0' sentinel
>>         je      .Lhalt
>>         mov     $0x3f8+5,%dx   # UART Line Status Register
> 
> I have a feeling that you have tested this on machine without
> VGA text buffer available. Then your fix works. However, if VGA
> text buffer is available then %esi is increased twice. First time
> by inc here and once again by movsb below. So, I think that the
> issue have to be fixed in a bit different way.
> 
> Daniel

Correct. It was an EFI machine with serial only where I saw it in action. David 
has put together a new change and I’ll get it submitted tomorrow.

—
Doug
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