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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.08.13 at 17:55, Tim Deegan <tim@xxxxxxx> 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

> Signed-off-by: Tim Deegan <tim@xxxxxxx>
> ---
>  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




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel