Messages in this thread Patch in this message | | | Date | Mon, 19 Mar 2018 16:20:53 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 2/2] x86/unwind: Make CONFIG_UNWINDER_ORC=y the default in kconfig for 64-bit |
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On Mon, Mar 19, 2018 at 01:31:30PM -0700, Matthias Kaehlcke wrote: > > The ORC unwinder relies on objtool, which reverse engineers the compiled > > code. This is objtool's first exposure to clang, so I'm not at all > > surprised if it's getting confused. > > > > Send me one of the .o files and I can take a quick look to see how bad > > it is, but I'm guessing it's going to be a lot of work to make objtool > > compatible with clang (and unfortunately I won't have the bandwidth to > > work on that in the near term.) > > > > In the meantime I'd recommend that you use frame pointers (and > > CONFIG_STACK_VALIDATION=n) for clang-compiled kernels. > > Thanks for your assessment! > > dvo_ch7017.o is attached.
Here's a (surprisingly easy) fix for this particular issue, though I'd be shocked if there weren't a bunch more issues lurking elsewhere. Let me know how it goes.
BTW, one thing I noticed in the .o file is that most of the functions' stacks are aligned to 16 bytes. It might be worth checking if the clang -mstack-alignment=8 option is getting set, and if so, if it's working properly. Otherwise, with aligned stacks, the frame pointer is forced, which defeats most of the benefits of ORC.
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 92b6a2c21631..f02df714c18e 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1386,6 +1386,17 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state) state->vals[op->dest.reg].offset = -state->stack_size; } + else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP && + cfa->base == CFI_BP) { + + /* + * mov %rbp, %rsp + * + * Restore the original stack pointer (clang). + */ + state->stack_size = -state->regs[CFI_BP].offset; + } + else if (op->dest.reg == cfa->base) { /* mov %reg, %rsp */
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