How to print __u128_t in kernel?

[Philipp Hortmann]

On 9/18/21 3:35 PM, Dongliang Mu wrote:
> Hello everyone,
> 
> I encounter one object with __uint128_t type in the following code.
> But I am not sure how to print the content of __uint128_t.
> 
> struct user_fpsimd_state {
> __uint128_t vregs[32];
> __u32 fpsr;
> __u32 fpcr;
> __u32 __reserved[2];
> };
> 
> At first, I would like to use:
> pr_alert("0x%lx %lx\n", i, (uint64_t)(fpreg.vregs[i] >> 64),
> (uint64_t)(fpreg.vregs[i]));
> 
> However, gcc reports error with "-Werror" enabled:
> 
> In function ‘print_fpregs_in_coredump’:
> error: iteration 32 invokes undefined behavior
> [-Werror=aggressive-loop-optimizations]
>     89 |   pr_alert("V%d 0x%lx %lx\n", i, (uint64_t)(fpreg.vregs[i] >> 64),
> 
> Any idea to eliminate this error?
> 
> --
> My best regards to you.
> 
>       No System Is Safe!
>       Dongliang Mu
> 

Hi

I do like this example:
https://lwn.net/Articles/745261/

...
pr_err("%llx%llx\n", (u64) (val >> 64), (u64) val);
pr_err("%llx%llx\n", (u64) (v >> 64), (u64) v);
...

But I have not tried it.

Bye Philipp