Re: [PATCH v2 04/12] x86/hvm: Reduce stack usage from HVMTRACE_ND()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.09.2021 19:25, Andrew Cooper wrote:
> v2:
>  * Adjust callers of HVMTRACE_ND() too

What does this refer to? The sole difference to v1 that I can spot
is ...

>  * Drop _d[] for the 0 case.

... the one corresponding to this line, i.e. ...

> --- a/xen/include/asm-x86/hvm/trace.h
> +++ b/xen/include/asm-x86/hvm/trace.h
> @@ -67,38 +67,30 @@
>  #define TRACE_2_LONG_4D(_e, d1, d2, d3, d4, ...) \
>      TRACE_6D(_e, d1, d2, d3, d4)
>  
> -#define HVMTRACE_ND(evt, modifier, cycles, count, d1, d2, d3, d4, d5, d6) \
> +#define HVMTRACE_ND(evt, modifier, cycles, ...)                           \
>      do {                                                                  \
>          if ( unlikely(tb_init_done) && DO_TRC_HVM_ ## evt )               \
>          {                                                                 \
> -            struct {                                                      \
> -                u32 d[6];                                                 \
> -            } _d;                                                         \
> -            _d.d[0]=(d1);                                                 \
> -            _d.d[1]=(d2);                                                 \
> -            _d.d[2]=(d3);                                                 \
> -            _d.d[3]=(d4);                                                 \
> -            _d.d[4]=(d5);                                                 \
> -            _d.d[5]=(d6);                                                 \
> +            uint32_t _d[] = { __VA_ARGS__ };                              \
>              __trace_var(TRC_HVM_ ## evt | (modifier), cycles,             \
> -                        sizeof(*_d.d) * count, &_d);                      \
> +                        sizeof(_d), sizeof(_d) ? _d : NULL);              \

... the addition of a conditional operator here (which I assume was
something a particular compiler didn't like in v1). FAOD - I'm fine
with the change, but I fear I'm overlooking something (again).

Jan