Re: [RFC][PATCH v2 0/7] printk/ia64/ppc64/parisc64: let's deprecate %pF/%pf printk specifiers
From: Santosh Sivaraj
Date: Fri Sep 22 2017 - 01:34:14 EST
* Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> wrote (on 2017-09-20 16:29:02 +0000):
> On some arches C function pointers are indirect and point to
> a function descriptor, which contains the actual pointer to the code.
> This mostly doesn't matter, except for cases when people want to print
> out function pointers in symbolic format, because the usual '%pS/%ps'
> does not work on those arches as expected. That's the reason why we
> have '%pF/%pf', but since it's here because of a subtle ABI detail
> specific to some arches (ppc64/ia64/parisc64) it's easy to misuse
> '%pF/%pf' and '%pS/%ps' (see , for example).
> This patch set attempts to move ia64/ppc64/parisc64 C function
> pointer ABI details out of printk() to arch code. Function dereference
> code now checks if a pointer belongs to a .opd ELF section and dereferences
> that pointer only if it does. The kernel and modules have their own .opd
> sections that's why I use two different ARCH functions: for kernel and
> for module pointer dereference.
> I planned to remove dereference_function_descriptor() entirely,
> but then I discovered a bunch other uses cases (kgdbts, init/main.c,
> extable, etc.), so I decided to keep dereference_function_descriptor()
> around because the main point of this patch set is to deprecate %pF/%pf.
> But at the same time, I think I can go further and handle both kernel
> and module descriptor dereference in dereference_function_descriptor().
> We need a module pointer for module .opd check, so that will come at an
> extra cost of module lookup (may be there will some other issues along
> the way, haven't checked it).
> Right now we've got:
> - dereference_function_descriptor(addr)
> a generic (old) function. it simply attempts to dereference
> whatever pointer we give it.
> - dereference_kernel_function_descriptor(addr)
> dereferences a kernel pointer if it's within the kernel's .opd
> - dereference_module_function_descriptor(module, addr)
> dereference a module pointer if it's within the module's .opd
> *** A BIG NOTE ***
> I don't own ia64/ppc64/parisc64 hardware, so the patches are not
> tested. Sorry about that!
Tested patch series on ppc64 sucessfully.
You may add tested by to the series.
Tested-by: Santosh Sivaraj <santosh@xxxxxxxxxx>
> Another note:
> I need to check what is BPF symbol lookup and do we need to
> do any dereference there.
> -- convert dereference_function_descriptor() to unsigned long
> -- fix kernel descriptor range checks (Helge)
> -- fix parisc module descriptor range check (Helge)
> -- fix ppc64 module range check
> -- add checkpatch patch
> Sergey Senozhatsky (7):
> switch dereference_function_descriptor() to `unsigned long'
> sections: split dereference_function_descriptor()
> ia64: Add .opd based function descriptor dereference
> powerpc64: Add .opd based function descriptor dereference
> parisc64: Add .opd based function descriptor dereference
> symbol lookup: use new kernel and module dereference functions
> checkpatch: add pF/pf deprecation warning
> Documentation/printk-formats.txt | 15 +++++----------
> arch/ia64/include/asm/sections.h | 16 ++++++++++++----
> arch/ia64/kernel/module.c | 13 +++++++++++++
> arch/ia64/kernel/vmlinux.lds.S | 2 ++
> arch/parisc/boot/compressed/vmlinux.lds.S | 2 ++
> arch/parisc/include/asm/sections.h | 4 +++-
> arch/parisc/kernel/module.c | 17 +++++++++++++++++
> arch/parisc/kernel/process.c | 15 ++++++++++++---
> arch/parisc/kernel/vmlinux.lds.S | 2 ++
> arch/parisc/mm/init.c | 4 ++--
> arch/powerpc/include/asm/module.h | 3 +++
> arch/powerpc/include/asm/sections.h | 17 ++++++++++++++---
> arch/powerpc/kernel/module_64.c | 16 ++++++++++++++++
> arch/powerpc/kernel/vmlinux.lds.S | 2 ++
> drivers/misc/kgdbts.c | 2 +-
> include/asm-generic/sections.h | 8 ++++++--
> include/linux/moduleloader.h | 4 ++++
> init/main.c | 2 +-
> kernel/extable.c | 2 +-
> kernel/kallsyms.c | 1 +
> kernel/module.c | 9 ++++++++-
> lib/vsprintf.c | 5 +----
> scripts/checkpatch.pl | 6 ++++--
> 23 files changed, 132 insertions(+), 35 deletions(-)
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