Finally, we got to write a test function to get the apic_id, and It feels
to run correctly.
Now, we're trying to implement another function, to transform the apic_id
in the kernel cpuid.
I attach the current test function to get apic_id with its test file
2018-06-15 19:36 GMT+02:00 Almudena Garcia <liberamenso10...@gmail.com>:
> Yes, I saw this.
>
> When I test It in Linux, I used a dual core computer. But the snippet
> returns "8" number.
>
> Now I know the reason ;)
>
> 2018-06-15 19:25 GMT+02:00 Richard Braun <rbr...@sceen.net>:
>
>> On Fri, Jun 15, 2018 at 07:18:55PM +0200, Richard Braun wrote:
>> > On Fri, Jun 15, 2018 at 06:27:21PM +0200, Almudena Garcia wrote:
>> > > I'm trying to define the cpu_number() in multiprocessor.
>> > >
>> > > To do this, I tried to use CPUID assembly x86 instruction, to get the
>> CPU
>> > > SMP number.
>> > > The function, in C, is this:
>> > >
>> > > static inline char smp_processor_id(void) {
>> > > char apic_id = 0;
>> > > asm("mov $1, %%eax\n\t"
>> > > "cpuid\n\t"
>> > > "mov %%bh, %0\n\t" : "=g" (apic_id));
>> > > return apic_id;
>> > > }
>> > >
>> > > In Linux, after executing this in a test source, It returns '8'
>> > >
>> > > But, when I try to execute It in Hurd, It shows a segmentation fault.
>> > >
>> > > I attach the test source file
>> > >
>> > >
>> > > Can you help me?
>>
>> Also note here that you're confusing the APIC ID, a device identifier at
>> the hardware level, with the CPU ID, a processor identifier at the kernel
>> level. On some machines, the APIC ID may be higher than or equal to the
>> maximum number of processor installed.
>>
>> --
>> Richard Braun
>>
>
>
#include <stdio.h>
static inline int cpu_number(void) {
long eax = 1, ebx = 0, ecx = 0, edx = 0;
char apic_id = 0;
int cpun = -1;
asm("cpuid" : "=a" (eax), "=b" (ebx), "=c" (ecx), "=d" (edx) : "a" (eax));
apic_id = (char) (ebx >> 24) & 0xff;
printf("eax = %lx, ebx = %lx, ecx = %lx, edx = %lx\n", eax, ebx, ecx, edx);
printf("apic_id = %lx\n", apic_id);
return cpun;
}
int main (void) {
printf("%d\n", cpu_number());
return 0;
}
