linux-kernel - [PATCH v2] x86/hyperv: Mark hv_ghcb

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Date:   Fri, 10 Mar 2023 12:44:52 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     linux-hyperv@...r.kernel.org, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, decui@...rosoft.com,
        haiyangz@...rosoft.com, kys@...rosoft.com, wei.liu@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        thomas.lendacky@....com, jpoimboe@...nel.org, peterz@...radead.org,
        kernel-dev@...lia.com, kernel@...ccoli.net,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v2] x86/hyperv: Mark hv_ghcb_terminate() as noreturn

Annotate the function prototype as noreturn to prevent objtool
warnings like:

vmlinux.o: warning: objtool: hyperv_init+0x55c: unreachable instruction

Also, as per Josh's suggestion, add it to the global_noreturns list.
As a comparison, an objdump output without the annotation:

[...]
1b63:  mov    $0x1,%esi
1b68:  xor    %edi,%edi
1b6a:  callq  ffffffff8102f680 <hv_ghcb_terminate>
1b6f:  jmpq   ffffffff82f217ec <hyperv_init+0x9c> # unreachable
1b74:  cmpq   $0xffffffffffffffff,-0x702a24(%rip)
[...]

Now, after adding the __noreturn to the function prototype:

[...]
17df:  callq  ffffffff8102f6d0 <hv_ghcb_negotiate_protocol>
17e4:  test   %al,%al
17e6:  je     ffffffff82f21bb9 <hyperv_init+0x469>
[...]  <many insns>
1bb9:  mov    $0x1,%esi
1bbe:  xor    %edi,%edi
1bc0:  callq  ffffffff8102f680 <hv_ghcb_terminate>
1bc5:  nopw   %cs:0x0(%rax,%rax,1) # end of function

Reported-by: Arnd Bergmann <arnd@...db.de>
Link: https://lore.kernel.org/r/9698eff1-9680-4f0a-94de-590eaa923e94@app.fastmail.com/
Cc: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
---


V2:
- Per Josh's suggestion (thanks!), added the function to the objtool global
table as well.


 arch/x86/include/asm/mshyperv.h | 2 +-
 tools/objtool/check.c           | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 4c4c0ec3b62e..09c26e658bcc 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -212,7 +212,7 @@ int hv_set_mem_host_visibility(unsigned long addr, int numpages, bool visible);
 void hv_ghcb_msr_write(u64 msr, u64 value);
 void hv_ghcb_msr_read(u64 msr, u64 *value);
 bool hv_ghcb_negotiate_protocol(void);
-void hv_ghcb_terminate(unsigned int set, unsigned int reason);
+void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason);
 #else
 static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
 static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f937be1afe65..4b5e03f61f1f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -209,6 +209,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"do_task_dead",
 		"ex_handler_msr_mce",
 		"fortify_panic",
+		"hv_ghcb_terminate",
 		"kthread_complete_and_exit",
 		"kthread_exit",
 		"kunit_try_catch_throw",
-- 
2.39.2