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

[Juergen Gross <jgross@suse.com>]

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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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