On 06/12/2015 03:10 PM, Josh Poimboeuf wrote: > 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]. Thanks for the pointer. > 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. How does the asmvalidator handle these? > [1] http://www.openwall.com/lists/musl/2015/05/31/5 Thanks, Pedro Alves -- 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
