Re: [U-Boot] [PATCH v2 07/13] x86: Fix signed shift overflow in MSR_IA32_APICBASE_BASE

On Tue, Aug 28, 2018 at 5:06 AM Bin Meng bmeng.cn@gmail.com wrote:

On Mon, Aug 27, 2018 at 7:19 AM Eugeniu Rosca roscaeugeniu@gmail.com wrote:

...

-#define MSR_IA32_APICBASE_BASE (0xfffff<<12) +#define MSR_IA32_APICBASE_BASE (0xfffffUL << 12)

I don't understand why such warnings is emitted: "left shift of 1048575 by 12 places cannot be represented in type 'int'"

Because it can't.

1 << 30 (fine) 1 << 31 (UB!)

This is good explained in the C standard for ages.

Compilers don't complain this code and Linux kernel has the same definition here.

Someone suppressed those warnings. But they are valid.