Re: [PATCH] iommu/arm-smmu-v3: Fix endianness annotations

[Robin Murphy <robin.murphy@arm.com>]

On 2020-09-18 15:18, Jean-Philippe Brucker wrote:
> When building with C=1, sparse reports some issues regarding endianness
> annotations:
> 
> arm-smmu-v3.c:221:26: warning: cast to restricted __le64
> arm-smmu-v3.c:221:24: warning: incorrect type in assignment (different base types)
> arm-smmu-v3.c:221:24:    expected restricted __le64 [usertype]
> arm-smmu-v3.c:221:24:    got unsigned long long [usertype]
> arm-smmu-v3.c:229:20: warning: incorrect type in argument 1 (different base types)
> arm-smmu-v3.c:229:20:    expected restricted __le64 [usertype] *[assigned] dst
> arm-smmu-v3.c:229:20:    got unsigned long long [usertype] *ent
> arm-smmu-v3.c:229:25: warning: incorrect type in argument 2 (different base types)
> arm-smmu-v3.c:229:25:    expected unsigned long long [usertype] *[assigned] src
> arm-smmu-v3.c:229:25:    got restricted __le64 [usertype] *
> arm-smmu-v3.c:396:20: warning: incorrect type in argument 1 (different base types)
> arm-smmu-v3.c:396:20:    expected restricted __le64 [usertype] *[assigned] dst
> arm-smmu-v3.c:396:20:    got unsigned long long *
> arm-smmu-v3.c:396:25: warning: incorrect type in argument 2 (different base types)
> arm-smmu-v3.c:396:25:    expected unsigned long long [usertype] *[assigned] src
> arm-smmu-v3.c:396:25:    got restricted __le64 [usertype] *
> arm-smmu-v3.c:1349:32: warning: invalid assignment: |=
> arm-smmu-v3.c:1349:32:    left side has type restricted __le64
> arm-smmu-v3.c:1349:32:    right side has type unsigned long
> arm-smmu-v3.c:1396:53: warning: incorrect type in argument 3 (different base types)
> arm-smmu-v3.c:1396:53:    expected restricted __le64 [usertype] *dst
> arm-smmu-v3.c:1396:53:    got unsigned long long [usertype] *strtab
> arm-smmu-v3.c:1424:39: warning: incorrect type in argument 1 (different base types)
> arm-smmu-v3.c:1424:39:    expected unsigned long long [usertype] *[assigned] strtab
> arm-smmu-v3.c:1424:39:    got restricted __le64 [usertype] *l2ptr
> 
> While harmless, they are incorrect and could hide actual errors during
> development. Fix them.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
> 
> There is another false positive due to passing INT_MIN to cmpxchg, and
> __cmpxchg* to truncate them to u8 and u16:
> 
> arch/arm64/include/asm/cmpxchg.h:172:1: warning: cast truncates bits from constant value (ffffffff80000000 becomes 0)
> arch/arm64/include/asm/cmpxchg.h:172:1: warning: cast truncates bits from constant value (ffffffff80000000 becomes 0)
> 
> I haven't found a satisfying fix so far, except adding __force to
> __cmpxchg_case* which could hide actual bugs.

I guess that's a general issue with the switch(sizeof()) idiom of sparse 
not being aware that those cases are unreachable?

Robin.

> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index c192544e874b..83acc1e5888e 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -867,7 +867,7 @@ static void queue_write(__le64 *dst, u64 *src, size_t n_dwords)
>   		*dst++ = cpu_to_le64(*src++);
>   }
>   
> -static void queue_read(__le64 *dst, u64 *src, size_t n_dwords)
> +static void queue_read(u64 *dst, __le64 *src, size_t n_dwords)
>   {
>   	int i;
>   
> @@ -1939,7 +1939,7 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>   		arm_smmu_cmdq_issue_cmd(smmu, &prefetch_cmd);
>   }
>   
> -static void arm_smmu_init_bypass_stes(u64 *strtab, unsigned int nent)
> +static void arm_smmu_init_bypass_stes(__le64 *strtab, unsigned int nent)
>   {
>   	unsigned int i;
>   
> 
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