On Wed, 27 May 2015, AKASHI Takahiro wrote: > > > 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.)
This is BTW implemented in gcc for various architectures already (see -mhotpatch for s390 or -mprofile-kernel for ppc64). Would be nice to at least try the semantics and format unified in some sense. Thanks, -- Jiri Kosina SUSE Labs -- 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/
