| Message ID | 20220412215220.75677-1-alobakin@pm.me (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | [RESEND] asm-generic: fix __get_unaligned_be48() on 32 bit platforms | expand |
diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h index 8fc637379899..df30f11b4a46 100644 --- a/include/asm-generic/unaligned.h +++ b/include/asm-generic/unaligned.h @@ -143,7 +143,7 @@ static inline void put_unaligned_be48(const u64 val, void *p) static inline u64 __get_unaligned_be48(const u8 *p) { - return (u64)p[0] << 40 | (u64)p[1] << 32 | p[2] << 24 | + return (u64)p[0] << 40 | (u64)p[1] << 32 | (u64)p[2] << 24 | p[3] << 16 | p[4] << 8 | p[5]; }
While testing the new macros for working with 48 bit containers, I faced a weird problem: 32 + 16: 0x2ef6e8da 0x79e60000 48: 0xffffe8da + 0x79e60000 All the bits starting from the 32nd were getting 1d in 9/10 cases. The debug showed: p[0]: 0x00002e0000000000 p[1]: 0x00002ef600000000 p[2]: 0xffffffffe8000000 p[3]: 0xffffffffe8da0000 p[4]: 0xffffffffe8da7900 p[5]: 0xffffffffe8da79e6 that the value becomes a garbage after the third OR, i.e. on `p[2] << 24`. When the 31st bit is 1 and there's no explicit cast to an unsigned, it's being considered as a signed int and getting sign-extended on OR, so `e8000000` becomes `ffffffffe8000000` and messes up the result. Cast the @p[2] to u64 as well to avoid this. Now: 32 + 16: 0x7ef6a490 0xddc10000 48: 0x7ef6a490 + 0xddc10000 p[0]: 0x00007e0000000000 p[1]: 0x00007ef600000000 p[2]: 0x00007ef6a4000000 p[3]: 0x00007ef6a4900000 p[4]: 0x00007ef6a490dd00 p[5]: 0x00007ef6a490ddc1 Fixes: c2ea5fcf53d5 ("asm-generic: introduce be48 unaligned accessors") Signed-off-by: Alexander Lobakin <alobakin@pm.me> --- Resend: target linux-block, expand Ccs a bit include/asm-generic/unaligned.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.35.2