Re: [PATCH 1/2] makedumpfile: Adapt code to get value of phys_base

[Baoquan He <bhe@redhat.com>]

On 11/10/16 at 03:57am, Atsushi Kumagai wrote:
> >Kernel code only exports virtual address of phys_base now and it's helpless
> >for Crash and Makedumpfile. Below patch which changes code to export value
> >of phys_base has been posted to upstream. So adapt code to get it.
> >
> >kexec: Change to export the value of phys_base instead of symbol address
> >marc.info/?l=linux-kernel&m=147856863629624&w=2
> >
> >Signed-off-by: Baoquan He <bhe@redhat.com>
> 
> I suspect that this patch will break backward compatibility.
> 
> >---
> > arch/x86_64.c  | 7 +++++--
> > makedumpfile.c | 5 ++---
> > makedumpfile.h | 2 +-
> > 3 files changed, 8 insertions(+), 6 deletions(-)
> >
> >diff --git a/arch/x86_64.c b/arch/x86_64.c
> >index 3ef33ae..8593c1a 100644
> >--- a/arch/x86_64.c
> >+++ b/arch/x86_64.c
> >@@ -61,7 +61,10 @@ get_phys_base_x86_64(void)
> > 	/*
> > 	 * Get the relocatable offset
> > 	 */
> >-	info->phys_base = 0; /* default/traditional */
> >+	if (NUMBER(phys_base) != NOT_FOUND_NUMBER) {
> >+		info->phys_base = NUMBER(phys_base);
> >+		return TRUE;
> >+	}
> >
> > 	for (i = 0; get_pt_load(i, &phys_start, NULL, &virt_start, NULL); i++) {
> > 		if (virt_start >= __START_KERNEL_map) {
> >@@ -189,7 +192,7 @@ vtop4_x86_64(unsigned long vaddr)
> > 	unsigned long pte_paddr, pte;
> > 	unsigned long phys_base;
> >
> >-	if (SYMBOL(phys_base) != NOT_FOUND_SYMBOL)
> >+	if (NUMBER(phys_base) != NOT_FOUND_NUMBER)
> > 		phys_base = info->phys_base;
> > 	else
> > 		phys_base = 0;
> 
> In older kernel, even if get_phys_base_x86_64() calculates info->phys_base
> from PT_LOAD, it will not be used since the kernels export *SYMBOL*(phys_base)
> and phys_base will be always set to 0 here.
> Is this check really needed ? Why don't you just set info->phys_base
> to phys_base ? (Of course, info->phys_base should be initialized with 0
> in get_phys_base_x86_64() in that case.)

You are right. Will change as you suggested and repost.

Thanks
Baoquan

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