Santosh Sivaraj <santosh@xxxxxxxxxx> writes: > * Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> wrote (on 2017-09-20 16:29:02 +0000): > >> 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! > > Tested patch series on ppc64 sucessfully. > > You may add tested by to the series. > > Tested-by: Santosh Sivaraj <santosh@xxxxxxxxxx> Thanks Santosh. I also gave it a quick spin. I'll give you an ack for the powerpc changes. Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> (powerpc) Thanks for cleaning this up Sergey. cheers -- 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
