Re: [PATCH] objtool: Fix SYSCALL instruction handling and INSN_CONTEXT_SWITCH

[Juergen Gross]

On 04.04.25 16:46, Josh Poimboeuf wrote:
> On Fri, Apr 04, 2025 at 12:49:38PM +0200, Peter Zijlstra wrote:
> > On Thu, Apr 03, 2025 at 11:48:13AM -0700, Josh Poimboeuf wrote:
> >
> > > The real problem here is that INSN_CONTEXT_SWITCH is ambiguous.  It can
> > > represent both call semantics (SYSCALL, SYSENTER) and return semantics
> > > (SYSRET, IRET, RETS, RETU).  Those differ significantly: calls preserve
> > > control flow whereas returns terminate it.
> >
> > Does that not rather suggest we should perhaps have INSN_SYSCALL /
> > INSN_SYSRET to replace the single ambiguous thing?
>
> Is there any reason to have INSN_SYSCALL in the first place?

xen_hypercall_pv() needs a syscall which will return after the call of
the hypervisor.

xen_iret() is a special case where the syscall won't return.

Whether objtool has a need for special casing it is another question I
don't feel qualified to answer.


Juergen

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