[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_*
Hi, On 18/04/2019 19:23, Stefano Stabellini wrote: 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. And if you read that rule the following would also be non-compliant bool is_nonzero(int b) { return b; }I know this example is pretty exaggerated but then does it mean the following code is also non-compliant? bool is_nonzero(int b) { if (b) return true; else return false; } If it is considered compliant, then it does not make sense. Cheers, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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