Re: [Crash-utility] using crash for ARM
On Wed, Oct 03, 2012 at 09:45:51AM -0400, Dave Anderson wrote:
Right -- it looks to be a bug, presuming that ARM is using 1MB pages
for the unity-mapped region:
crash> vtop c0000000 | grep PAGE:
PAGE: 11000 (1MB)
crash> vtop c0100000 | grep PAGE:
PAGE: 11000 (1MB)
crash> vtop c0200000 | grep PAGE:
PAGE: 211000 (1MB)
crash> vtop c0300000 | grep PAGE:
PAGE: 211000 (1MB)
crash> vtop c0400000 | grep PAGE:
PAGE: 411000 (1MB)
crash> vtop c0500000 | grep PAGE:
PAGE: 411000 (1MB)
crash>
The unity-mapped region is mapped using 1MB pages. However, we actually have
(when using the Linux ARM 2-level translation scheme):
see arch/arm/include/asm/pgtable-2level.h:
#define PMD_SHIFT 21
#define PGDIR_SHIFT 21
#define PTRS_PER_PGD 2048
So we have 2048 entries in a PGD instead of 4096 making a PGD entry an array
of "two pointers".
Anyway as you and Paawan suggested it looks like a bug - we always use the
first entry instead of the second given that bit 20 is set in the virtual
address.
Paawan, your fix looks sane to me but can you add a small comment describing
why this is done?