Hello RFC 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 [1], 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 section. - dereference_module_function_descriptor(module, addr) dereference a module pointer if it's within the module's .opd section. *** A BIG NOTE *** I don't own ia64/ppc64/parisc64 hardware, so the patches are not tested. Sorry about that! Another note: I need to check what is BPF symbol lookup and do we need to do any dereference there. [1] https://marc.info/?l=linux-kernel&m=150472969730573 Sergey Senozhatsky (5): 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 Documentation/printk-formats.txt | 15 +++++---------- arch/ia64/include/asm/sections.h | 14 +++++++++++++- 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 | 3 +++ arch/parisc/kernel/module.c | 14 ++++++++++++++ arch/parisc/kernel/process.c | 10 ++++++++++ arch/parisc/kernel/vmlinux.lds.S | 2 ++ arch/powerpc/include/asm/module.h | 3 +++ arch/powerpc/include/asm/sections.h | 13 +++++++++++++ arch/powerpc/kernel/module_64.c | 16 ++++++++++++++++ arch/powerpc/kernel/vmlinux.lds.S | 2 ++ include/asm-generic/sections.h | 4 ++-- include/linux/moduleloader.h | 4 ++++ kernel/kallsyms.c | 1 + kernel/module.c | 7 +++++++ lib/vsprintf.c | 5 +---- 18 files changed, 113 insertions(+), 17 deletions(-) -- 2.14.1 -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
