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Re: Enable SMP support


From: Almudena Garcia
Subject: Re: Enable SMP support
Date: Sat, 16 Jun 2018 13:17:57 +0200

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 <address@hidden>:
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 <address@hidden>:
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


Attachment: smp.c
Description: Text Data


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