On July 1, 2026 12:48:34 AM PDT, Peter Zijlstra <[email protected]> wrote: >On Wed, Jul 01, 2026 at 09:27:47AM +0200, Peter Zijlstra wrote: >> On Mon, Jun 29, 2026 at 03:29:50PM -0700, Dave Hansen wrote: >> >> > But, really, if ENTER is so evil and nobody uses it, shouldn't we just >> > have an MSR bit somewhere to tell the CPU to #UD for it rather than >> > playing these stack games? >> >> For supervisor mode only, I suppose. We can't ever get rid of userspace >> ENTER because legacy I suppose. But we can make sure the kernel is >> clean. >> >> So yeah, having a knob to make supervisor-ENTER trap would be useful I >> suppose. > >x86_64-defconfig builds clean with the below :-) > > >diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c >index 1b387d5a195b..9e53db863203 100644 >--- a/tools/objtool/arch/x86/decode.c >+++ b/tools/objtool/arch/x86/decode.c >@@ -642,6 +642,10 @@ int arch_decode_instruction(struct objtool_file *file, >const struct section *sec > > break; > >+ case 0xc8: >+ WARN("ENTER instruction at %s:%lx", sec->name, offset); >+ break; >+ > case 0xc9: > /* > * leave
The problem is that it being a single byte long it can appear in the middle of another instruction. ENTER was primarily designed for languages with nested local scopes, for which it can do quite a bit of work.
