On Mon, May 22, 2017 at 02:37:50PM -0700, H. Peter Anvin wrote: > On 05/22/17 14:07, H. Peter Anvin wrote: > > On 05/20/17 13:01, H.J. Lu wrote: > >> On Sat, May 20, 2017 at 9:20 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > >> > >>>> > >>>> (H.J., could we get a binutils feature that allows is to do: > >>>> > >>>> pushq %whatever > >>>> .cfi_adjust_sp -8 > >>>> ... > >>>> popq %whatever > >>>> .cfi_adjust_sp 8 > >>>> > >> > >> Np. Compiler needs to generate this. > >> > > > > For actual assembly we have such a feature, it is called macros. > > > > push/pop is the easy stuff; macros take care of that, but the real pain > > is dealing with the flow of control. > > > > My biggest beef with the CFI directives that gas uses is that there is > that .cfi_remember_state/.cfi_restore_state doesn't have a way to > specify more than one state. That makes it really hard to get sanity > around control flow changes, especially with code that is intentionally > out of line. > > That, and some of the CFI directives seem to be a bit ill-defined in > their definition (are they even applicable to anything other than > DWARF?) They almost seem to be referencing some external specification, > but the only thing I'm finding is the DWARF documentation which is > written in very different terms. > > The best description of what a personality routine is I found in an > article by Ian Lance Taylor. It doesn't seem to be applicable to C as > far as I can tell. So my understanding is that there's stock DWARF (.debug_frame) and then there's souped-up DWARF (.eh_frame), which is basically DWARF with a few extensions. The remember/restore state thing is stock DWARF (DW_CFA_remember_state and DW_CFA_restore_state). The personality routine thing is in the .eh_frame extension which is documented here: http://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html -- Josh -- 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
