On Thu, 2016-01-28 at 16:32 +0100, Torsten Duwe wrote: > From: Petr Mladek <pmladek@xxxxxxxx> > > Livepatch works on x86_64 and s390 only when the ftrace call > is at the very beginning of the function. But PPC is different. > We need to handle TOC and save LR there before calling the > global ftrace handler. > > Now, the problem is that the extra operations have different > length on PPC depending on the used gcc version. It is > 4 instructions (16 bytes) before gcc-6 and only 3 instructions > (12 bytes) with gcc-6. > > This patch tries to detect the offset a generic way during > build. It assumes that the offset of the ftrace location > is the same for all functions. It modifies the existing > recordmcount tool that is able to find read mcount locations > directly from the object files. It adds an option -p > to print the first found offset. > > The recordmcount tool is then used in the kernel/livepatch > subdirectory to generate a header file. It defines > a constant that is used to compute the ftrace location > from the function address. > > Finally, we have to enable the C implementation of the > recordmcount tool to be used on PPC and S390. It seems > to work fine there. It should be more reliable because > it reads the standardized elf structures. The old perl > implementation uses rather complex regular expressions > to parse objdump output and is therefore much more tricky. I'm still missing something, I'm getting offset as 8 When I run, I get scripts/recordmcount -p kernel/livepatch/core.o #define KLP_FTRACE_LOCATION 8 scripts/recordmcount -p kernel/livepatch/ftrace-test.o #define KLP_FTRACE_LOCATION 8 My sample fails as well, since the expected offset is 16. I guess the script is being run against a not so good test. A quick hack (no signoff below, its just an experiment), seems to do the trick for the provided sample-livepatch. It is hacky because it uses the sample object and due to lack of a better description of srctree, it uses srctree/../.. I suspect the usage of recordmcount needs to be revisited diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile index 65a44b68..10b5f38 100644 --- a/kernel/livepatch/Makefile +++ b/kernel/livepatch/Makefile @@ -2,7 +2,7 @@ obj-$(CONFIG_LIVEPATCH) += livepatch.o livepatch-objs := core.o -always := $(hostprogs-y) ftrace-test.o +always := $(hostprogs-y) $(srctree)/../../samples/livepatch/livepatch-sample.o # dependencies on generated files need to be listed explicitly $(obj)/core.o: $(obj)/livepatch-ftrace.h @@ -10,7 +10,7 @@ $(obj)/core.o: $(obj)/livepatch-ftrace.h quiet_cmd_livepatch-rmcount = RMCOUNT $@ cmd_livepatch-rmcount = $(objtree)/scripts/recordmcount -p $< > $@ -$(obj)/livepatch-ftrace.h: $(obj)/ftrace-test.o $(objtree)/scripts/recordmcount +$(obj)/livepatch-ftrace.h: $(obj)/../../samples/livepatch/livepatch-sample.o $(objtree)/scripts/recordmcount $(call if_changed,livepatch-rmcount) targets += livepatch-ftrace.h -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
