[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 07/12] xen/arm: cpuerrata: Match register size with value size in check_workaround_*
On Wed, 17 Apr 2019, Julien Grall wrote: > Hi, > > On 4/17/19 9:28 PM, Stefano Stabellini wrote: > > On Wed, 27 Mar 2019, Julien Grall wrote: > > > Clang is pickier than GCC for the register size in asm statement. It > > > expects the register size to match the value size. > > > > > > The asm statement expects a 32-bit (resp. 64-bit) value on Arm32 > > > (resp. Arm64) whereas the value is a boolean (Clang consider to be > > > 32-bit). > > > > > > It would be possible to impose 32-bit register for both architecture > > > but this require the code to use __OP32. However, it does not really > > > improve the assembly generated. Instead, replace switch the variable > > > to use register_t. > > > > > > Signed-off-by: Julien Grall <julien.grall@xxxxxxx> > > > --- > > > xen/include/asm-arm/cpuerrata.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/xen/include/asm-arm/cpuerrata.h > > > b/xen/include/asm-arm/cpuerrata.h > > > index 55ddfda272..88ef3ca934 100644 > > > --- a/xen/include/asm-arm/cpuerrata.h > > > +++ b/xen/include/asm-arm/cpuerrata.h > > > @@ -14,7 +14,7 @@ static inline bool check_workaround_##erratum(void) > > > \ > > > return false; \ > > > else \ > > > { \ > > > - bool ret; \ > > > + register_t ret; \ > > > \ > > > asm volatile (ALTERNATIVE("mov %0, #0", \ > > > "mov %0, #1", \ > > > > This is OK. Could you please also change the return statement below? > > Maybe something like: > > > > return unlikely(!!ret); > Why? The compiler will implicitly convert the int to bool. 0 will turn to > false, all the other will be true. > > We actually been actively removing !! when the type is bool (see the example > in get_paged_frame in common/grant_table.c). Really? Too bad, I loved the explicit conversions to bool. This is a matter of code style, not correctness, so usually I wouldn't care much. But I went to read MISRA-C to figure out if there are any differences from that point of view. From Rule 10.3, it looks like it is not compliant, because they say that: bool_t bla = 0; is not MISRA-C compliant. While: int c = 1; bool_t bla = c == 0; is compliant. So, if I read this right: return !!ret //compliant return ret; //not compliant I am not 100% sure though. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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