On Fri, Jun 12, 2015 at 12:18:16PM +0100, Pedro Alves wrote: > On 06/11/2015 03:10 PM, Josh Poimboeuf wrote: > > > C would definitely make more sense when analyzing object code. In fact, > > asmvalidate is written in C. But then I guess we'd have to re-implement > > the .cfi stuff and populate the DWARF sections manually instead of > > letting the assembler do it. > > Was doing all this directly in the assembler considered? That is, > e.g., add some knob that makes it error/warn in the same conditions > you're making the validator catch. For tail calls, you'd e.g., add > some new ".nonlocal" directive that you'd use to whitelist the > following jump. And then if it's possible run a CFI generator > as a separate step over the source, it sounds like it should also > be possible to have the assembler do it instead too (again with > some new high level directive to trigger/help it). In general I think doing these types of things in the assembler would be a good idea. Missing or inaccurate debug data for asm code seems to be a common problem for other projects as well. As Andy pointed out, they're doing similar things in musl [1]. So it might be useful to add an option to the assembler which validates that the code conforms to certain structural rules, and then inserts frame pointer and/or .cfi directives. That said, the kernel has much more custom features than other projects. There are some sneaky macros, like _ASM_EXTABLE and ALTERNATIVE, which hide code in various sections. Unless we're able to somehow either stop using these macros or isolate them to a few places, I doubt that such a general purpose assembler option would work. [1] http://www.openwall.com/lists/musl/2015/05/31/5 -- 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
