On Sat, Apr 25, 2020 at 07:31:40PM +0200, Borislav Petkov wrote:
> Hmm, that's what I was afraid of - having to sprinkle this around. Yah, let's
> wait for compiler guys to have a look here and then maybe I'll convert that
> thing to a macro called
>
> compiler_prevent_tail_call_opt()
>
> or so, so that it can be sprinkled around. ;-\
IOW, something like this (ontop) which takes care of the xen case too.
If it needs to be used by all arches, then I'll split the patch:
---
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 73bf8450afa1..4f275ac7830b 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -273,7 +273,7 @@ static void notrace start_secondary(void *unused)
* boot_init_stack_canary() and must not be checked before tail calling
* another function.
*/
- asm ("");
+ prevent_tail_call_optimization();
}
/**
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 8fb8a50a28b4..f2adb63b2d7c 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -93,6 +93,7 @@ asmlinkage __visible void cpu_bringup_and_idle(void)
cpu_bringup();
boot_init_stack_canary();
cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
+ prevent_tail_call_optimization();
}
void xen_smp_intr_free_pv(unsigned int cpu)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 034b0a644efc..73f889f64513 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -356,4 +356,7 @@ static inline void *offset_to_ptr(const int *off)
/* &a[0] degrades to a pointer: a different type from an array */
#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
+
+#define prevent_tail_call_optimization() asm("")
+
#endif /* __LINUX_COMPILER_H */
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
