linux-kernel - Re: [tip: objtool/core] x86: Convert unreachable() to BUG()

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Message-ID: <20241216093215.GD12338@noisy.programming.kicks-ass.net>
Date: Mon, 16 Dec 2024 10:32:15 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: linux-kernel@...r.kernel.org
Cc: linux-tip-commits@...r.kernel.org, Josh Poimboeuf <jpoimboe@...nel.org>,
	x86@...nel.org
Subject: Re: [tip: objtool/core] x86: Convert unreachable() to BUG()

On Mon, Dec 02, 2024 at 11:15:21AM -0000, tip-bot2 for Peter Zijlstra wrote:
> The following commit has been merged into the objtool/core branch of tip:
> 
> Commit-ID:     2190966fbc14ca2cd4ea76eefeb96a47d8e390df
> Gitweb:        https://git.kernel.org/tip/2190966fbc14ca2cd4ea76eefeb96a47d8e390df
> Author:        Peter Zijlstra <peterz@...radead.org>
> AuthorDate:    Thu, 28 Nov 2024 10:39:02 +01:00
> Committer:     Peter Zijlstra <peterz@...radead.org>
> CommitterDate: Mon, 02 Dec 2024 12:01:43 +01:00
> 
> x86: Convert unreachable() to BUG()
> 
> Avoid unreachable() as it can (and will in the absence of UBSAN)
> generate fallthrough code. Use BUG() so we get a UD2 trap (with
> unreachable annotation).
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Link: https://lore.kernel.org/r/20241128094312.028316261@infradead.org


Urgh, one got lost:

vmlinux.o: warning: objtool: page_fault_oops() falls through to next function is_prefetch()

---
 arch/x86/mm/fault.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index e6c469b323cc..ac52255fab01 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -678,7 +678,7 @@ page_fault_oops(struct pt_regs *regs, unsigned long error_code,
 			      ASM_CALL_ARG3,
 			      , [arg1] "r" (regs), [arg2] "r" (address), [arg3] "r" (&info));
 
-		unreachable();
+		BUG();
 	}
 #endif