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Message-ID: <BYAPR21MB16888EBB51D1597F9B9C212FD7BA9@BYAPR21MB1688.namprd21.prod.outlook.com>
Date: Fri, 10 Mar 2023 21:17:08 +0000
From: "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"x86@...nel.org" <x86@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Dexuan Cui <decui@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
KY Srinivasan <kys@...rosoft.com>,
"wei.liu@...nel.org" <wei.liu@...nel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"bp@...en8.de" <bp@...en8.de>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"hpa@...or.com" <hpa@...or.com>,
"thomas.lendacky@....com" <thomas.lendacky@....com>,
"jpoimboe@...nel.org" <jpoimboe@...nel.org>,
"peterz@...radead.org" <peterz@...radead.org>,
"kernel-dev@...lia.com" <kernel-dev@...lia.com>,
"kernel@...ccoli.net" <kernel@...ccoli.net>,
Arnd Bergmann <arnd@...db.de>
Subject: RE: [PATCH v2] x86/hyperv: Mark hv_ghcb_terminate() as noreturn
From: Guilherme G. Piccoli <gpiccoli@...lia.com>
>
> Annotate the function prototype as noreturn to prevent objtool
> warnings like:
Just curious: Should the actual function also be updated with
__noreturn? In similar situations, such as snp_abort(), the
__noreturn attribute is both places. I don't know what the
guidance is on this question.
In any case, thanks for doing this cleanup!
Michael
>
>
> Also, as per Josh's suggestion, add it to the global_noreturns list.
> As a comparison, an objdump output without the annotation:
>
> vmlinux.o: warning: objtool: hyperv_init+0x55c: unreachable instruction
> [...]
> 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/all/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
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