[PATCH] x86/tdx: Fix __noreturn build warning around __tdx_hypercall_failed()

[PATCH] x86/tdx: Fix __noreturn build warning around __tdx_hypercall_failed()

[Kai Huang]

LKP reported below build warning:

  vmlinux.o: warning: objtool: __tdx_hypercall+0x128: __tdx_hypercall_failed() is missing a __noreturn annotation

Turns out the __noreturn must be annotated to the function declaration
but not the function body.

Quoted from PeterZ:

---
FWIW, the reason being that...

The point of noreturn is that the caller should know to stop generating
code. For that the declaration needs the attribute, because call sites
typically do not have access to the function definition in C.
---

Fix by moving __noreturn annotation from the __tdx_hypercall_failed()
body to its declaration, which is in <asm/shared/tdx.h>.

Note <asm/shared/tdx.h> is also included by TDX related assembly files.
Include <linux/compiler_attributes.h> only in case of !__ASSEMBLY__
otherwise compiling assembly file would trigger build error.

Also, following the objtool documentation, add __tdx_hypercall_failed()
to "tools/objtool/noreturns.h".

Fixes: c641cfb5c157 ("x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE_CALL")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202309140828.9RdmlH2Z-lkp@intel.com/
Signed-off-by: Kai Huang <kai.huang@intel.com>
---
 arch/x86/coco/tdx/tdx.c           | 2 +-
 arch/x86/include/asm/shared/tdx.h | 4 +++-
 tools/objtool/noreturns.h         | 1 +
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 3e6dbd2199cf..4710d8dd700b 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -38,7 +38,7 @@
 #define TDREPORT_SUBTYPE_0	0
 
 /* Called from __tdx_hypercall() for unrecoverable failure */
-noinstr void __noreturn __tdx_hypercall_failed(void)
+noinstr void __tdx_hypercall_failed(void)
 {
 	instrumentation_begin();
 	panic("TDVMCALL failed. TDX module bug?");
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index b69886ee1c63..f74695dea217 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -56,6 +56,8 @@
 
 #ifndef __ASSEMBLY__
 
+#include <linux/compiler_attributes.h>
+
 /*
  * Used in __tdcall*() to gather the input/output registers' values of the
  * TDCALL instruction when requesting services from the TDX module. This is a
@@ -108,7 +110,7 @@ static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14, u64 r15)
 
 
 /* Called from __tdx_hypercall() for unrecoverable failure */
-void __tdx_hypercall_failed(void);
+void __noreturn __tdx_hypercall_failed(void);
 
 bool tdx_accept_memory(phys_addr_t start, phys_addr_t end);
 
diff --git a/tools/objtool/noreturns.h b/tools/objtool/noreturns.h
index e45c7cb1d5bc..875f8827aa33 100644
--- a/tools/objtool/noreturns.h
+++ b/tools/objtool/noreturns.h
@@ -11,6 +11,7 @@ NORETURN(__kunit_abort)
 NORETURN(__module_put_and_kthread_exit)
 NORETURN(__reiserfs_panic)
 NORETURN(__stack_chk_fail)
+NORETURN(__tdx_hypercall_failed)
 NORETURN(__ubsan_handle_builtin_unreachable)
 NORETURN(arch_call_rest_init)
 NORETURN(arch_cpu_idle_dead)

base-commit: 7b804135d4d1f0a2b9dda69c6303d3f2dcbe9d37
-- 
2.41.0

Re: [PATCH] x86/tdx: Fix __noreturn build warning around __tdx_hypercall_failed()

[Ingo Molnar]

* Kai Huang <kai.huang@intel.com> wrote:

> LKP reported below build warning:
> 
>   vmlinux.o: warning: objtool: __tdx_hypercall+0x128: __tdx_hypercall_failed() is missing a __noreturn annotation
> 
> Turns out the __noreturn must be annotated to the function declaration
> but not the function body.
> 
> Quoted from PeterZ:
> 
> ---
> FWIW, the reason being that...
> 
> The point of noreturn is that the caller should know to stop generating
> code. For that the declaration needs the attribute, because call sites
> typically do not have access to the function definition in C.
> ---
> 
> Fix by moving __noreturn annotation from the __tdx_hypercall_failed()
> body to its declaration, which is in <asm/shared/tdx.h>.
> 
> Note <asm/shared/tdx.h> is also included by TDX related assembly files.
> Include <linux/compiler_attributes.h> only in case of !__ASSEMBLY__
> otherwise compiling assembly file would trigger build error.
> 
> Also, following the objtool documentation, add __tdx_hypercall_failed()
> to "tools/objtool/noreturns.h".
> 
> Fixes: c641cfb5c157 ("x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE_CALL")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202309140828.9RdmlH2Z-lkp@intel.com/
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> ---
>  arch/x86/coco/tdx/tdx.c           | 2 +-
>  arch/x86/include/asm/shared/tdx.h | 4 +++-
>  tools/objtool/noreturns.h         | 1 +
>  3 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 3e6dbd2199cf..4710d8dd700b 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -38,7 +38,7 @@
>  #define TDREPORT_SUBTYPE_0	0
>  
>  /* Called from __tdx_hypercall() for unrecoverable failure */
> -noinstr void __noreturn __tdx_hypercall_failed(void)
> +noinstr void __tdx_hypercall_failed(void)
>  {

It's not a bad idea to document the __noreturn nature at the definition 
site either, so I don't think we should remove it.

Thanks,

	Ingo

Re: [PATCH] x86/tdx: Fix __noreturn build warning around __tdx_hypercall_failed()

[Huang, Kai]

On Fri, 2023-09-15 at 14:26 +0200, Ingo Molnar wrote:
> * Kai Huang <kai.huang@intel.com> wrote:
> 
> > LKP reported below build warning:
> > 
> >   vmlinux.o: warning: objtool: __tdx_hypercall+0x128: __tdx_hypercall_failed() is missing a __noreturn annotation
> > 
> > Turns out the __noreturn must be annotated to the function declaration
> > but not the function body.
> > 
> > Quoted from PeterZ:
> > 
> > ---
> > FWIW, the reason being that...
> > 
> > The point of noreturn is that the caller should know to stop generating
> > code. For that the declaration needs the attribute, because call sites
> > typically do not have access to the function definition in C.
> > ---
> > 
> > Fix by moving __noreturn annotation from the __tdx_hypercall_failed()
> > body to its declaration, which is in <asm/shared/tdx.h>.
> > 
> > Note <asm/shared/tdx.h> is also included by TDX related assembly files.
> > Include <linux/compiler_attributes.h> only in case of !__ASSEMBLY__
> > otherwise compiling assembly file would trigger build error.
> > 
> > Also, following the objtool documentation, add __tdx_hypercall_failed()
> > to "tools/objtool/noreturns.h".
> > 
> > Fixes: c641cfb5c157 ("x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE_CALL")
> > Reported-by: kernel test robot <lkp@intel.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202309140828.9RdmlH2Z-lkp@intel.com/
> > Signed-off-by: Kai Huang <kai.huang@intel.com>
> > ---
> >  arch/x86/coco/tdx/tdx.c           | 2 +-
> >  arch/x86/include/asm/shared/tdx.h | 4 +++-
> >  tools/objtool/noreturns.h         | 1 +
> >  3 files changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> > index 3e6dbd2199cf..4710d8dd700b 100644
> > --- a/arch/x86/coco/tdx/tdx.c
> > +++ b/arch/x86/coco/tdx/tdx.c
> > @@ -38,7 +38,7 @@
> >  #define TDREPORT_SUBTYPE_0	0
> >  
> >  /* Called from __tdx_hypercall() for unrecoverable failure */
> > -noinstr void __noreturn __tdx_hypercall_failed(void)
> > +noinstr void __tdx_hypercall_failed(void)
> >  {
> 
> It's not a bad idea to document the __noreturn nature at the definition 
> site either, so I don't think we should remove it.
> 
> 

Thanks for feedback! I'll fix and send out v2.

Since it's a simple fix, I'll send out v2 shortly.