[PATCH 1/2] kexec: add phys_offset field
ext-mika.1.westerberg at nokia.com
Wed Apr 28 10:01:33 EDT 2010
On Tue, Apr 27, 2010 at 03:08:54PM +0200, ext Dave Anderson wrote:
> ----- "Mika Westerberg" <ext-mika.1.westerberg at nokia.com> wrote:
> > Idea here was to make sure that virtual addresses in PT_LOAD segments are
> > calculated correctly based on PHYS_OFFSET field. For example with OMAP3,
> > physical memory starts at 0x80000000 so for 0xc0000000 (PAGE_OFFSET)
> > we get:
> > phdr->p_vaddr = 0x80000000 + 0xc0000000 = 0x40000000
> > which is not correct. But taking PHYS_OFFSET into equation we get
> > phdr->p_vaddr = 0x80000000 + 0xc0000000 - 0x80000000 = 0xc0000000
> > which is correct.
> Yes, I understand completely -- we've been there... ;-)
> The issue is that there would be a disconnect between the actual kernel
> virtual addresses used in the vmlinux file vs. your "calculated" virtual
> addresses in the header, and to me that goes against the grain of what
> the p_vaddr field is supposed to mean.
> The ELF spec defines them:
> p_vaddr This member gives the virtual address at which the first
> byte of the segment resides in memory.
> p_paddr On systems for which physical addressing is relevant, this
> member is reserved for the segment's physical address.
> Because System V ignores physical addressing for application
> programs, this member has unspecified contents for executable
> files and shared objects.
> To me, the term "virtual address" means the virtual addresses used by the
> executable. Your scheme "calculates" a p_vaddr based upon the p_paddr.
Sorry, I have to ask some clarifications to understand this.
If the kernel image is linked at virtual address 0xc0008000 which is the case
with ARM kernel for example. Then how following is legitimate kernel virtual
phdr->p_vaddr = mstart + elf_info->page_offset;
if the first physical memory region starts for example at 0x80000000, and
PAGE_OFFSET is 0xc0000000 we get:
phdr->p_vaddr = 0x80000000 + 0xc0000000
this results virtual address 0x40000000 (in 32-bit) for the kernel direct mapped
region, which I think is not the same as used by the executable (the vmlinux
% objdump -h vmlinux
vmlinux: file format elf32-little
Idx Name Size VMA LMA File off Algn
0 .note.gnu.build-id 00000024 00000000 00000000 00008000 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
1 .init 0001f6ed c0008000 c0008000 00010000 2**5
CONTENTS, ALLOC, LOAD, CODE
2 .text 0031706a c0028000 c0028000 00030000 2**6
CONTENTS, ALLOC, LOAD, READONLY, CODE
Am I missing something?
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