On Thu, Jun 01, 2017 at 06:57:24AM -0700, Andy Lutomirski wrote: > On Wed, May 31, 2017 at 10:44 PM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > Some asm (and inline asm) code does special things to the stack which > > objtool can't understand. (Nor can GCC or GNU assembler, for that > > matter.) In such cases we need a facility for the code to provide > > annotations, so the unwinder can unwind through it. > > > > This provides such a facility, in the form of CFI hints. They're > > similar to the GNU assembler .cfi* directives, but they give more > > information, and are needed in far fewer places, because objtool can > > fill in the blanks by following branches and adjusting the stack pointer > > for pushes and pops. > > Two minor suggestions: > > Could you prefix these with something other than "CFI_"? For those of > use who have read the binutils manual, using "CFI_" sounds awfully > like .cfi_, and people might expect the semantics to be the same. The intention was that even if this undwarf thing doesn't work out, the CFI_ macros could still be used by objtool to generate proper DWARF. Would prefixing them with CFI_HINT_ be better? Or UNWIND_HINT_? > > +#define CFI_HINT(cfa_reg, cfa_offset, type) \ > > + "999: \n\t" \ > > Have you checked if 999 is used elsewhere? My personal preference is to use: > > .Ldescriptive_text_\@: > > instead of a hopefully-unique number. I never researched the history, > but I suspect that the convention of using large numbers came from > early binutils versions that didn't have \@, but we use \@ fairly > extensively in the kernel these days, so it would seem that we no > longer support binutils versions that old. Yeah, that would be a lot better, thanks. -- 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
