From: Mukesh R <[email protected]> Sent: Friday, October 17, 2025
4:58 PM
>
> On 10/17/25 15:57, Wei Liu wrote:
> > On Fri, Oct 17, 2025 at 10:33:00PM +0000, Wei Liu wrote:
> >> On Mon, Oct 06, 2025 at 03:42:02PM -0700, Mukesh Rathor wrote:
> >> [...]
> >>> Mukesh Rathor (6):
> >>> x86/hyperv: Rename guest crash shutdown function
> >>> hyperv: Add two new hypercall numbers to guest ABI public header
> >>> hyperv: Add definitions for hypervisor crash dump support
> >>> x86/hyperv: Add trampoline asm code to transition from hypervisor
> >>> x86/hyperv: Implement hypervisor RAM collection into vmcore
> >>> x86/hyperv: Enable build of hypervisor crashdump collection files
> >>>
> >>
> >> Applied to hyperv-next. Thanks.
> >
> > This breaks i386 build.
> >
> > /work/linux-on-hyperv/linux.git/arch/x86/hyperv/hv_init.c: In function
> > ?hyperv_init?:
> > /work/linux-on-hyperv/linux.git/arch/x86/hyperv/hv_init.c:557:17: error:
> > implicit declaration of function ?hv_root_crash_init?
> > [-Werror=implicit-function-declaration]
> > 557 | hv_root_crash_init();
> > | ^~~~~~~~~~~~~~~~~~
> >
> > That's because CONFIG_MSHV_ROOT is only available on x86_64. And the
> > crash feature is guarded by CONFIG_MSHV_ROOT.
> >
> > Applying the following diff fixes the build.
>
>
> Thanks. A bit surprising tho that CONFIG_MSHV_ROOT doesn't have
> hard dependency on x86_64. It should, no?
CONFIG_MSHV_ROOT *does* have a hard dependency on X86_64.
But the problem is actually more pervasive than just 32-bit builds. Because
of the hard dependency, 32-bit builds imply CONFIG_MSHV_ROOT=n, which is
the real problem. In arch/x86/include/asm/mshyperv.h the declaration for
hv_root_crash_init() is available only when CONFIG_MSHV_ROOT is defined
(m or y). There's a stub hv_root_crash_init() if CONFIG_MSHV_ROOT is defined
and CONFIG_CRASH_DUMP=n, but not if CONFIG_MSHV_ROOT=n. The solution
is to add a stub when CONFIG_MSHV_ROOT=n, as below:
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 76582affefa8..a5b258d268ed 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -248,6 +248,8 @@ void hv_crash_asm_end(void);
static inline void hv_root_crash_init(void) {}
#endif /* CONFIG_CRASH_DUMP */
+#else /* CONFIG_MSHV_ROOT */
+static inline void hv_root_crash_init(void) {}
#endif /* CONFIG_MSHV_ROOT */
#else /* CONFIG_HYPERV */
Annoyingly, this solution duplicates the hv_root_crash_init() stub. So
an alternate approach that changes a few more lines of code is this:
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 76582affefa8..1342d55c2545 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -237,18 +237,14 @@ static __always_inline u64 hv_raw_get_msr(unsigned int
reg)
}
int hv_apicid_to_vp_index(u32 apic_id);
-#if IS_ENABLED(CONFIG_MSHV_ROOT)
-
-#ifdef CONFIG_CRASH_DUMP
+#if IS_ENABLED(CONFIG_MSHV_ROOT) && IS_ENABLED(CONFIG_CRASH_DUMP)
void hv_root_crash_init(void);
void hv_crash_asm32(void);
void hv_crash_asm64(void);
void hv_crash_asm_end(void);
-#else /* CONFIG_CRASH_DUMP */
+#else /* CONFIG_MSHV_ROOT && CONFIG_CRASH_DUMP */
static inline void hv_root_crash_init(void) {}
-#endif /* CONFIG_CRASH_DUMP */
-
-#endif /* CONFIG_MSHV_ROOT */
+#endif /* CONFIG_MSHV_ROOT && CONFIG_CRASH_DUMP */
#else /* CONFIG_HYPERV */
static inline void hyperv_init(void) {}
Michael
