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On powerpc we can build the kernel with two different ABIs for mcount(), which is used by ftrace. Kernels built with one ABI do not know how to load modules built with the other ABI. The new style ABI is called "mprofile-kernel", for want of a better name. Currently if we build a module using the old style ABI, and the kernel with mprofile-kernel, when we load the module we'll oops something like: # insmod autofs4-no-mprofile-kernel.ko ftrace-powerpc: Unexpected instruction f8810028 around bl _mcount ------------[ cut here ]------------ WARNING: CPU: 6 PID: 3759 at ../kernel/trace/ftrace.c:2024 ftrace_bug+0x2b8/0x3c0 CPU: 6 PID: 3759 Comm: insmod Not tainted 4.11.0-rc3-gcc-5.4.1-00017-g5a61ef74f269 #11 ... NIP [c0000000001eaa48] ftrace_bug+0x2b8/0x3c0 LR [c0000000001eaff8] ftrace_process_locs+0x4a8/0x590 Call Trace: alloc_pages_current+0xc4/0x1d0 (unreliable) ftrace_process_locs+0x4a8/0x590 load_module+0x1c8c/0x28f0 SyS_finit_module+0x110/0x140 system_call+0x38/0xfc ... ftrace failed to modify [<d000000002a31024>] 0xd000000002a31024 actual: 35:65:00:48 We can avoid this by including in the vermagic whether the kernel/module was built with mprofile-kernel. Which results in: # insmod autofs4-pg.ko autofs4: version magic '4.11.0-rc3-gcc-5.4.1-00017-g5a61ef74f269 SMP mod_unload modversions ' should be '4.11.0-rc3-gcc-5.4.1-00017-g5a61ef74f269-dirty SMP mod_unload modversions mprofile-kernel' insmod: ERROR: could not insert module autofs4-pg.ko: Invalid module format Fixes: 8c50b72a3b4f ("powerpc/ftrace: Add Kconfig & Make glue for mprofile-kernel") Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Acked-by: Balbir Singh <bsingharora@gmail.com> Acked-by: Jessica Yu <jeyu@redhat.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.