From: Peter Zijlstra
> Sent: 10 March 2022 09:05
>
> On Wed, Mar 09, 2022 at 04:30:28PM -0800, Nick Desaulniers wrote:
>
> > I observed the following error when building with
> > CONFIG_LTO_CLANG_FULL=y enabled:
> >
> > ld.lld: error: ld-temp.o <inline asm>:7:2: symbol 'ibt_selftest_ip' is
> > already defined
> > ibt_selftest_ip:
> > ^
> >
> > Seems to come from
> > commit a802350ba65a ("x86/ibt: Add IBT feature, MSR and #CP handling")
> >
> > Commenting out the label in the inline asm, I then observed:
> > vmlinux.o: warning: objtool: identify_cpu()+0x6d0: sibling call from
> > callable instruction with modified stack frame
> > vmlinux.o: warning: objtool: identify_cpu()+0x6e0: stack state
> > mismatch: cfa1=4+64 cfa2=4+8
> > These seemed to disappear when I kept CONFIG_LTO_CLANG_FULL=y but then
> > disabled CONFIG_X86_KERNEL_IBT. (perhaps due to the way I hacked out
> > the ibt_selftest_ip label).
>
> Urgh.. I'm thikning this is a clang bug :/
>
> The code in question is:
>
>
> void ibt_selftest_ip(void); /* code label defined in asm below */
>
> DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
> {
> /* ... */
>
> if (unlikely(regs->ip == (unsigned long)ibt_selftest_ip)) {
> regs->ax = 0;
> return;
> }
>
> /* ... */
> }
>
> bool ibt_selftest(void)
> {
> unsigned long ret;
>
> asm (" lea ibt_selftest_ip(%%rip), %%rax\n\t"
> ANNOTATE_RETPOLINE_SAFE
> " jmp *%%rax\n\t"
> "ibt_selftest_ip:\n\t"
> UNWIND_HINT_FUNC
> ANNOTATE_NOENDBR
> " nop\n\t"
>
> : "=a" (ret) : : "memory");
>
> return !ret;
> }
>
> There is only a single definition of that symbol, the one in the asm.
> The other is a declaration, which is used in the exception handler to
> compare against regs->ip.
LTO has probably inlined it twice.
David
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