[PATCH v2] xen/arch/x86: Fix early boot command line parsing

[PATCH v2] xen/arch/x86: Fix early boot command line parsing

[Daniel Kiper]

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@oracle.com>
---
 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
-- 
1.7.10.4

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

[Andrew Cooper]

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@oracle.com>

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@citrix.com>

> ---
>  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

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

[Keir Fraser]

On 03/12/2013 20:32, "Andrew Cooper" <andrew.cooper3@citrix.com> 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@oracle.com>
> 
> 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@citrix.com>

Acked-by: Keir Fraser <keir@xen.org>

>> ---
>>  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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