Hi Venu,
1. mmap() succeeds even if "offset" argument is a negative value, although
it should return EINVAL in such case.
In such case, it is actually regarded as big positive value
because the type of "off" is "unsigned long" in the kernel.
For example, off=-4096 (-0x1000) is regarded as
off = 0xfffffffffffff000 (x86_64) and as off = 0xfffff000 (x86).
It results in mapping too big offset region.
It is not true always.
Considering your example, say if page size is 4k, then PAGE_MASK = 0xFFF
hence (off& ~PAGE_MASK) will be true and " -EINVAL" will be returned.
Is PAGE_MASK 0xfffffffffffff000 (x86_64) and 0xfffff000 (x86), isn't it?
Or am I missing something?
arch/x86/include/asm/page_types.h
=================================================
...
#define PAGE_SHIFT 12
#define PAGE_SIZE (_AC(1,UL) << PAGE_SHIFT)
#define PAGE_MASK (~(PAGE_SIZE-1))
...
=================================================
Thanks,
Naotaka Hamaguchi
(2012/02/17 18:04), Venu Byravarasu wrote:
The detail of these problems is as follows:
1. mmap() succeeds even if "offset" argument is a negative value, although
it should return EINVAL in such case.
In such case, it is actually regarded as big positive value
because the type of "off" is "unsigned long" in the kernel.
For example, off=-4096 (-0x1000) is regarded as
off = 0xfffffffffffff000 (x86_64) and as off = 0xfffff000 (x86).
It results in mapping too big offset region.
It is not true always.
Considering your example, say if page size is 4k, then PAGE_MASK = 0xFFF
hence (off& ~PAGE_MASK) will be true and " -EINVAL" will be returned.
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