Re: [XEN PATCH 09/11] x86/msi: address violation of MISRA C Rule 20.7 and coding style

From: Jan Beulich <jbeulich@suse.com>
To: Nicola Vetrini <nicola.vetrini@bugseng.com>
Cc: sstabellini@kernel.org, michal.orzel@amd.com,
	xenia.ragiadakou@amd.com, ayan.kumar.halder@amd.com,
	consulting@bugseng.com, andrew.cooper3@citrix.com,
	roger.pau@citrix.com, bertrand.marquis@arm.com, julien@xen.org,
	xen-devel@lists.xenproject.org
Subject: Re: [XEN PATCH 09/11] x86/msi: address violation of MISRA C Rule 20.7 and coding style
Date: Tue, 26 Mar 2024 11:05:41 +0100	[thread overview]
Message-ID: <f2d393e9-6b70-4998-9d85-e070d6bba556@suse.com> (raw)
In-Reply-To: <c924aa0d5b3b6adbb24cc638f739173cbc41862c.1711118582.git.nicola.vetrini@bugseng.com>

On 22.03.2024 17:01, Nicola Vetrini wrote:
> MISRA C Rule 20.7 states: "Expressions resulting from the expansion
> of macro parameters shall be enclosed in parentheses". Therefore, some
> macro definitions should gain additional parentheses to ensure that all
> current and future users will be safe with respect to expansions that
> can possibly alter the semantics of the passed-in macro parameter.
> 
> While at it, the style of these macros has been somewhat uniformed.

Hmm, yes, but they then still leave more to be desired. I guess I can see
though why you don't want to e.g. ...

> --- a/xen/arch/x86/include/asm/msi.h
> +++ b/xen/arch/x86/include/asm/msi.h
> @@ -147,33 +147,34 @@ int msi_free_irq(struct msi_desc *entry);
>   */
>  #define NR_HP_RESERVED_VECTORS 	20
>  
> -#define msi_control_reg(base)		(base + PCI_MSI_FLAGS)
> -#define msi_lower_address_reg(base)	(base + PCI_MSI_ADDRESS_LO)
> -#define msi_upper_address_reg(base)	(base + PCI_MSI_ADDRESS_HI)
> -#define msi_data_reg(base, is64bit)	\
> -	( (is64bit == 1) ? base+PCI_MSI_DATA_64 : base+PCI_MSI_DATA_32 )
> -#define msi_mask_bits_reg(base, is64bit) \
> -	( (is64bit == 1) ? base+PCI_MSI_MASK_BIT : base+PCI_MSI_MASK_BIT-4)
> +#define msi_control_reg(base)        ((base) + PCI_MSI_FLAGS)
> +#define msi_lower_address_reg(base)  ((base) + PCI_MSI_ADDRESS_LO)
> +#define msi_upper_address_reg(base)  ((base) + PCI_MSI_ADDRESS_HI)
> +#define msi_data_reg(base, is64bit) \
> +    (((is64bit) == 1) ? (base) + PCI_MSI_DATA_64 : (base) + PCI_MSI_DATA_32)
> +#define msi_mask_bits_reg(base, is64bit)                \
> +    (((is64bit) == 1) ? (base) + PCI_MSI_MASK_BIT       \
> +                      : (base) + PCI_MSI_MASK_BIT - 4)

... drop the bogus == 1 in these two, making them similar to ...

>  #define msi_pending_bits_reg(base, is64bit) \
> -	((base) + PCI_MSI_MASK_BIT + ((is64bit) ? 4 : 0))
> -#define msi_disable(control)		control &= ~PCI_MSI_FLAGS_ENABLE
> +    ((base) + PCI_MSI_MASK_BIT + ((is64bit) ? 4 : 0))

... this.

> +#define msi_disable(control) (control) &= ~PCI_MSI_FLAGS_ENABLE

Doesn't this need an outer pair of parentheses, too?

>  #define multi_msi_capable(control) \
> -	(1 << ((control & PCI_MSI_FLAGS_QMASK) >> 1))
> +    (1 << (((control) & PCI_MSI_FLAGS_QMASK) >> 1))
>  #define multi_msi_enable(control, num) \
> -	control |= (((fls(num) - 1) << 4) & PCI_MSI_FLAGS_QSIZE);
> -#define is_64bit_address(control)	(!!(control & PCI_MSI_FLAGS_64BIT))
> -#define is_mask_bit_support(control)	(!!(control & PCI_MSI_FLAGS_MASKBIT))
> +    (control) |= (((fls(num) - 1) << 4) & PCI_MSI_FLAGS_QSIZE);

And this, together with dropping the bogus semicolon?

There also look to be cases where MASK_EXTR() / MASK_INSR() would want using,
in favor of using open-coded numbers.

> +#define is_64bit_address(control) (!!((control) & PCI_MSI_FLAGS_64BIT))
> +#define is_mask_bit_support(control) (!!((control) & PCI_MSI_FLAGS_MASKBIT))
>  #define msi_enable(control, num) multi_msi_enable(control, num); \
> -	control |= PCI_MSI_FLAGS_ENABLE
> -
> -#define msix_control_reg(base)		(base + PCI_MSIX_FLAGS)
> -#define msix_table_offset_reg(base)	(base + PCI_MSIX_TABLE)
> -#define msix_pba_offset_reg(base)	(base + PCI_MSIX_PBA)
> -#define msix_enable(control)	 	control |= PCI_MSIX_FLAGS_ENABLE
> -#define msix_disable(control)	 	control &= ~PCI_MSIX_FLAGS_ENABLE
> -#define msix_table_size(control) 	((control & PCI_MSIX_FLAGS_QSIZE)+1)
> -#define msix_unmask(address)	 	(address & ~PCI_MSIX_VECTOR_BITMASK)
> -#define msix_mask(address)		(address | PCI_MSIX_VECTOR_BITMASK)
> +                                 (control) |= PCI_MSI_FLAGS_ENABLE

This again is suspiciously missing outer parentheses; really here, with
the earlier statement, it look like do { ... } while ( 0 ) or ({ ... })
are wanted.

> +#define msix_control_reg(base)       ((base) + PCI_MSIX_FLAGS)
> +#define msix_table_offset_reg(base)  ((base) + PCI_MSIX_TABLE)
> +#define msix_pba_offset_reg(base)    ((base) + PCI_MSIX_PBA)
> +#define msix_enable(control)         (control) |= PCI_MSIX_FLAGS_ENABLE
> +#define msix_disable(control)        (control) &= ~PCI_MSIX_FLAGS_ENABLE

Outer parentheses missing for these two again?

Jan