On Fri, Dec 15, 2017 at 07:40:09PM +1000, Nicholas Piggin wrote: > On Tue, 12 Dec 2017 08:05:01 -0600 > Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > > On Tue, Dec 12, 2017 at 12:39:12PM +0100, Torsten Duwe wrote: > > > Hi all, > > > > > > The "Power Architecture 64-Bit ELF V2 ABI" says in section 2.3.2.3: > > > > > > [...] There are several rules that must be adhered to in order to ensure > > > reliable and consistent call chain backtracing: > > > > > > * Before a function calls any other function, it shall establish its > > > own stack frame, whose size shall be a multiple of 16 bytes. > > > > What about leaf functions? If a leaf function doesn't establish a stack > > frame, and it has inline asm which contains a blr to another function, > > this ABI is broken. Oops, I meant to say "bl" instead of "blr". > > Also, even for non-leaf functions, is it possible for GCC to insert the > > inline asm before it sets up the stack frame? (This is an occasional > > problem on x86.) > > Inline asm must not have control transfer out of the statement unless > it is asm goto. Can inline asm have calls to other functions? > > Also, what about hand-coded asm? > > Should follow the same rules if it uses the stack. How is that enforced? > > > To me this sounds like the equivalent of HAVE_RELIABLE_STACKTRACE. > > > This patch may be unneccessarily limited to ppc64le, but OTOH the only > > > user of this flag so far is livepatching, which is only implemented on > > > PPCs with 64-LE, a.k.a. ELF ABI v2. > > > > In addition to fixing the above issues, the unwinder also needs to > > detect interrupts (i.e., preemption) and page faults on the stack of a > > blocked task. If a function were preempted before it created a stack > > frame, or if a leaf function blocked on a page fault, the stack trace > > will skip the function's caller, so such a trace will need to be > > reported to livepatch as unreliable. > > I don't think there is much problem there for powerpc. Stack frame > creation and function call with return pointer are each atomic. What if the function is interrupted before it creates the stack frame? -- 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
