Hi Dave,
On Wednesday 25 January 2017 11:59 AM, Dave Young wrote:
> Hi Pratyush
> On 01/25/17 at 10:14am, Pratyush Anand wrote:
>> Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
>> not true and could be misleading, since 0 is a valid physical address.
> I do not know the history of /proc/kcore, so a question is why the
> p_addr was set as 0, if there were some reasons and if this could cause
> some risk or breakage.
>
I do not know why it was 0, which is a valid physical address. But
certainly, it might break some user space tools, and those need to be
fixed. For example, see following code from kexec-tools
kexec/kexec-elf.c:build_mem_phdrs()
435 if ((phdr->p_paddr + phdr->p_memsz) < phdr->p_paddr) {
436 /* The memory address wraps */
437 if (probe_debug) {
438 fprintf(stderr, "ELF address wrap
around\n");
439 }
440 return -1;
441 }
We do not need to perform above check for an invalid physical address.
I think, kexec-tools and makedumpfile will need fixup. I already have
those fixup which will be sent upstream once this patch makes through.
Pro with this approach is that, it will help to calculate variable like
page_offset, phys_base from PT_LOAD even when they are randomized and
therefore will reduce many variable and version specific values in user
space tools.
~Pratyush
