Re: [PATCH 3/5] powerpc64: Add .opd based function descriptor dereference

Sergey Senozhatsky
2017-09-19T10:31:54Z

On (09/19/17 20:22), Michael Ellerman wrote:
> > On 2017/09/16 12:53PM, Sergey Senozhatsky wrote:
> >> We are moving towards separate kernel and module function descriptor
> >> dereference callbacks. This patch enables it for powerpc64.
> >>
> >> For pointers that belong to the kernel
> >> - Added __start_opd and __end_opd pointers, to track the kernel
> >> .opd section address range;
> >>
> >> - Added dereference_kernel_function_descriptor(). Now we
> >> will dereference only function pointers that are within
> >> [__start_opd, __end_opd];
> >>
> >> For pointers that belong to a module
> >> - Added dereference_module_function_descriptor() to handle module
> >> function descriptor dereference. Now we will dereference only
> >> pointers that are within [module->opd.start, module->opd.end].
> >
> > Would it be simpler to just use kernel_text_address() and dereference
> > everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only
> > dereference function descriptor for non-text symbols") for a related
> > patch.
>
> Yeah that would be a lot simpler and probably work perfectly well.

unlike ppc_function_entry(), printk() can get called on any symbol,
not just function pointers.

for example,

cat /proc/kallsyms | grep shrinker_rwsem
ffffffff81a4b1e0 d shrinker_rwsem

or

cat /proc/kallsyms | grep vm_total_pages
ffffffff81dcd418 B vm_total_pages

and so on.

-ss