Re: [Xen-devel] [PATCH v2] xen/arch/x86: Fix early boot command line parsing

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 03/12/2013 20:32, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:

> On 03/12/13 20:28, Daniel Kiper wrote:
>> There is no reliable way to encode NUL character as a character so encode
>> it as a number. Read: http://sourceware.org/binutils/docs/as/Characters.html.
>> Octal and hex encoding do not work on at least one system (GNU assembler
>> version 2.22 (x86_64-linux-gnu) using BFD version (GNU Binutils for Debian)
>> 2.22).
>> Without this fix e.g. no-real-mode option at the end of xen.gz command line
>> is not detected.
>> 
>> v2 - suggestions/fixes:
>>    - add relevant comment to assembly file
>>      (suggested by Andrew Cooper),
>>    - leave encoding of other characters as is for readability
>>      (suggested by Jan Beulich).
>> 
>> Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> 
> I was thinking more along the lines of /* NULL check (as $'\0' == 0x30
> in GAS) */
> 
> Either way, at least it is obvious.
> 
> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

>> ---
>>  xen/arch/x86/boot/cmdline.S |   10 +++++++++-
>>  1 file changed, 9 insertions(+), 1 deletion(-)
>> 
>> diff --git a/xen/arch/x86/boot/cmdline.S b/xen/arch/x86/boot/cmdline.S
>> index 05ffb94..b83975e 100644
>> --- a/xen/arch/x86/boot/cmdline.S
>> +++ b/xen/arch/x86/boot/cmdline.S
>> @@ -138,7 +138,15 @@
>>          call    .Lstrlen
>>          add     $4,%esp
>>          xadd    %eax,%ebx
>> -        cmpb    $'\0',(%ebx)
>> +        /*
>> +         * There is no reliable way to encode NUL character as a character
>> so encode
>> +         * it as a number. Read:
>> http://sourceware.org/binutils/docs/as/Characters.html.
>> +         * Octal and hex encoding do not work on at least one system (GNU
>> assembler
>> +         * version 2.22 (x86_64-linux-gnu) using BFD version (GNU Binutils
>> for Debian) 2.22).
>> +         * Without this fix e.g. no-real-mode option at the end of xen.gz
>> command line
>> +         * is not detected.
>> +         */
>> +        cmpb    $0,(%ebx)
>>          je      3f
>>          cmpb    $' ',(%ebx)
>>          je      3f
> 
> 
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