Why does crash check the program context flags in FILL_PML4() macro
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Hi Dave,
One question:
#define FILL_PML4() { \
if (!(pc->flags & RUNTIME) || ACTIVE()) { \
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I am confused that crash checks the flags in the FILL_PML4() macro, but
not check that in other macros, such as FILL_PGD().
Could you tell me why we need to do this check?
if (!IS_LAST_PML4_READ(vt->kernel_pgd[0])) \
readmem(vt->kernel_pgd[0], KVADDR,
machdep->machspec->pml4, \
PAGESIZE(), "init_level4_pgt", FAULT_ON_ERROR); \
machdep->machspec->last_pml4_read =
(ulong)(vt->kernel_pgd[0]); \
} \
}
Thanks,
dou
----- Original Message -----
Hi Dave,
One question:
#define FILL_PML4() { \
if (!(pc->flags & RUNTIME) || ACTIVE()) { \
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I am confused that crash checks the flags in the FILL_PML4() macro, but
not check that in other macros, such as FILL_PGD().
Good question -- I don't have a really good answer...
I think it's a legacy of an earlier time, but as I recall, the !RUNTIME check
was simply to ensure that it had been initialized at least once during session
initialization. I don't recall the reasoning behind the ACTIVE() check, other
than the fact that while it could never change in a dumpfile, conceivably it may
change during an active session in future kernels? However, I believe that once
FILL_PML4() is called in x86_64_init_kernel_pgd(), it really never needs to be
called again. So it pretty much makes the checks redundantly for the sake of
absolute surety.
Dave
Could you tell me why we need to do this check?
if (!IS_LAST_PML4_READ(vt->kernel_pgd[0])) \
readmem(vt->kernel_pgd[0], KVADDR,
machdep->machspec->pml4, \
PAGESIZE(), "init_level4_pgt", FAULT_ON_ERROR); \
machdep->machspec->last_pml4_read =
(ulong)(vt->kernel_pgd[0]); \
} \
}
Thanks,
dou
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Dou Liyang