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FromEric Lacombe <>
SubjectRe: [x86] do_arch_prctl
DateMon, 24 Nov 2008 13:24:53 +0100
Hello,

Does the "doit case" (line 822 in ARCH_GET_FS, function do_arch_prctl) exist
for performance reasons? Else, why "task->thread.fs" (line 824) does not
contain the fs base in the "doit case"?

Can someone explain _precisely_ the lines 835 through 838 (ARCH_GET_GS)?
(I thought that just the line 836 was sufficient, but I
obviously miss the case where MSR_KERNEL_GS_BASE does not reflect the value
requested)

Thanks again for all your previous answers.

Eric

828 case ARCH_GET_GS: {
829 unsigned long base;
830 unsigned gsindex;
831 if (task->thread.gsindex == GS_TLS_SEL)
832 base = read_32bit_tls(task, GS_TLS);
833 else if (doit) {
834 asm("movl %%gs,%0" : "=r" (gsindex));
835 if (gsindex)
836 rdmsrl(MSR_KERNEL_GS_BASE, base);
837 else
838 base = task->thread.gs;
839 }
840 else
841 base = task->thread.gs;
842 ret = put_user(base, (unsigned long __user *)addr);
843 break;
844 }
---
817 case ARCH_GET_FS: {
818 unsigned long base;
819 if (task->thread.fsindex == FS_TLS_SEL)
820 base = read_32bit_tls(task, FS_TLS);
821 else if (doit)
822 rdmsrl(MSR_FS_BASE, base);
823 else
824 base = task->thread.fs;
825 ret = put_user(base, (unsigned long __user *)addr);
826 break;
827 }


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