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由 Rasmus Villemoes 提交于
If ffz() ever returns a value >= 31 then the following shift is undefined behaviour because the literal 1 which gets shifted is treated as signed integer. In practice, the bug is probably harmless, since the first undefined shift count is 31 which results - ignoring UB - in (int)(0x80000000). This gets sign extended so bit 32-63 will be set as well and all subsequent __setup_irq() calls would just end up hitting the -EBUSY branch. However, a sufficiently aggressive optimizer may use the UB of 1<<31 to decide that doesn't happen, and hence elide the sign-extension code, so that subsequent calls can indeed get ffz > 31. In any case, the right thing to do is to make the literal 1UL. [ tglx: For this to happen a single interrupt would have to be shared by 32 devices. Hardware like that does not exist and would have way more problems than that. ] Signed-off-by: NRasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20171030213548.16831-1-linux@rasmusvillemoes.dk
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