Messages in this thread | | | From | Sami Tolvanen <> | Date | Mon, 1 Mar 2021 14:14:51 -0800 | Subject | Re: [x86, build] 6dafca9780: WARNING:at_arch/x86/kernel/ftrace.c:#ftrace_verify_code |
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On Sun, Feb 28, 2021 at 11:25 PM kernel test robot <oliver.sang@intel.com> wrote: > > > Greeting, > > FYI, we noticed the following commit (built with clang-13): > > commit: 6dafca97803309c3cb5148d449bfa711e41ddef2 ("x86, build: use objtool mcount") > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
Thanks for the report, I'm able to reproduce the warning.
> [ 4.764496] ------------[ ftrace bug ]------------ > [ 4.764847] ftrace failed to modify > [ 4.764852] do_sys_open (kbuild/src/consumer/fs/open.c:1186) > [ 4.765483] actual: 0f:1f:44:00:00 > [ 4.765784] Setting ftrace call site to call ftrace function > [ 4.766193] ftrace record flags: 50000001 > [ 4.766490] (1) R > [ 4.766490] expected tramp: ffffffff81037af0 > [ 4.766959] ------------[ cut here ]------------
Basically, the problem is that ftrace_replace_code() expects to find ideal_nops[NOP_ATOMIC5] here, which in this case is 66:66:66:66:90, while objtool has replaced the __fentry__ call with 0f:1f:44:00:00.
As ideal_nops changes depending on kernel config and hardware, when CC_USING_NOP_MCOUNT is defined we could either change ftrace_nop_replace() to always use P6_NOP5, or skip ftrace_verify_code() in ftrace_replace_code() for FTRACE_UPDATE_MAKE_CALL.
Steven, Peter, any thoughts?
Sami
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