On 2015/05/27 15:09, AKASHI Takahiro wrote: > Sorry for not replying soon. > > On 04/24/2015 06:27 PM, Jiri Kosina wrote: >> On Fri, 24 Apr 2015, AKASHI Takahiro wrote: >> >>> This patchset enables livepatch support on arm64. >>> >>> Livepatch was merged in v4.0, and allows replacying a function dynamically >>> based on ftrace framework, but it also requires -mfentry option of gcc. >>> Currently arm64 gcc doesn't support it, but by adding a helper function to >>> ftrace, we will be able to support livepatch on arch's which don't support >>> this option. >>> >>> I submit this patchset as RFC since I'm not quite sure that I'm doing >>> in the right way, or we should definitely support -fentry instead. >> >> I don't have arm64 cross-compiler handy, could you please copy/paste how >> does function prologue, generated by gcc -pg on arm64 look like? > > As other people said, my current patch has some drawbacks and was far from > perfect. > I talked to a toolchain guy in Linaro, and he suggested that, instead of x86 > specific -mfentry option, we should add a new generic option, -fprolog-pad=N. > > It works as if "-pg -mfentry -mrecord-mcount -mnop-mcount" were specified on a > command line, but actually puts N nop instructions at the very beginning of > a function. > (Please note that -mrecord-mcount and -mnop-mcount options have been added > in x86 gcc to make it easier to implement ftrace and others.)
Ah, that's a cool idea :) Note that it also will need to take care of debuginfo. Previously -mfentry had broken the debuginfo about function prologue. > While it is not clear that this new option will be implemented soon (in > gcc-6), > once it is supported on aarch64, I will update and re-post my livepatch patch > as well as DYNAMIC_TRACE_WITH_REGS ftrace. Thank you! -- Masami HIRAMATSU Linux Technology Research Center, System Productivity Research Dept. Center for Technology Innovation - Systems Engineering Hitachi, Ltd., Research & Development Group E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
