Re: [PATCH] xen/x86: don't use '.ifnes' in bug frame construction.

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 30/08/13 09:29, Jan Beulich wrote:
>>>> On 29.08.13 at 17:55, Tim Deegan <tim@xen.org> wrote:
>> Spotted because it breaks the clang build for LLVM <3.2.  .ifnes is
>> not right here as it will choke on a string with embedded quotes.
>>
>> .ifnb would be better except that LLVM <3.2 doesn't support that either.
>> It should be possible to use something like !!msg or !!msg[0] instead
>> of a separate flag, but I gave up trying to find something that would
>> make it through CPP, asm() and gas as a usable constant. :|
> I'm not really opposed to this (albeit I dislike redundancy like this),
> but I'd really like to understand (also for the sake of my own
> education, including to avoid introducing similar breakage in the
> future) where the problem was, and how gcc+gas manage to
> accept what you appear to have found broken in general (i.e. not
> just for clang as I understand it).
>
> And yes, I would have preferred (and used) .ifnb if I hadn't recalled
> it having been me adding the support for it for binutils 2.17, while at
> least one of the so far lowest common denominator distros (SLE10)
> is only at 2.16.<something> (which appears to have the needed
> support, but it would seem wrong to draw the line at some
> intermediary release); not sure what binutils version RHEL5 uses.
>
> Jan

My CentOS 5.7 environment claims binutils 2.17.50

~Andrew

>
>> Signed-off-by: Tim Deegan <tim@xen.org>
>> ---
>>  xen/include/asm-x86/bug.h |   14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/xen/include/asm-x86/bug.h b/xen/include/asm-x86/bug.h
>> index 148975f..e5dd559 100644
>> --- a/xen/include/asm-x86/bug.h
>> +++ b/xen/include/asm-x86/bug.h
>> @@ -25,7 +25,7 @@ struct bug_frame {
>>  #define BUGFRAME_bug    2
>>  #define BUGFRAME_assert 3
>>  
>> -#define BUG_FRAME(type, line, ptr, msg) do {                                 
>> \
>> +#define BUG_FRAME(type, line, ptr, second_frame, msg) do {                  
>>  \
>>      BUILD_BUG_ON((line) >> (BUG_LINE_LO_WIDTH + BUG_LINE_HI_WIDTH));         
>> \
>>      asm volatile ( ".Lbug%=: ud2\n"                                         
>>  \
>>                     ".pushsection .bug_frames.%c0, \"a\", @progbits\n"       
>>  \
>> @@ -33,7 +33,7 @@ struct bug_frame {
>>                     ".Lfrm%=:\n"                                             
>>  \
>>                     ".long (.Lbug%= - .Lfrm%=) + %c4\n"                       
>> \
>>                     ".long (%c1 - .Lfrm%=) + %c3\n"                           
>> \
>> -                   ".ifnes \"" msg "\", \"\"\n"                              
>> \
>> +                   ".if " #second_frame "\n"                                
>>  \
>>                     ".long 0, %c2 - .Lfrm%=\n"                                
>> \
>>                     ".endif\n"                                               
>>  \
>>                     ".popsection"                                            
>>  \
>> @@ -44,12 +44,14 @@ struct bug_frame {
>>                       "i" (((line) >> BUG_LINE_LO_WIDTH) << BUG_DISP_WIDTH)); \
>>  } while (0)
>>  
>> -#define WARN() BUG_FRAME(BUGFRAME_warn, __LINE__, __FILE__, "")
>> -#define BUG()  BUG_FRAME(BUGFRAME_bug,  __LINE__, __FILE__, "")
>>  
>> -#define run_in_exception_handler(fn) BUG_FRAME(BUGFRAME_run_fn, 0, fn, "")
>> +#define WARN() BUG_FRAME(BUGFRAME_warn, __LINE__, __FILE__, 0, NULL)
>> +#define BUG()  BUG_FRAME(BUGFRAME_bug,  __LINE__, __FILE__, 0, NULL)
>>  
>> -#define assert_failed(msg) BUG_FRAME(BUGFRAME_assert, __LINE__, __FILE__, 
>> msg)
>> +#define run_in_exception_handler(fn) BUG_FRAME(BUGFRAME_run_fn, 0, fn, 0, 
>> NULL)
>> +
>> +#define assert_failed(msg)                                      \
>> +    BUG_FRAME(BUGFRAME_assert, __LINE__, __FILE__, 1, msg)
>>  
>>  extern const struct bug_frame __start_bug_frames[],
>>                                __stop_bug_frames_0[],
>> -- 
>> 1.7.10.4
>
>
>
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