linux-kernel - Re: [tip:x86/core 16/17] vmlinux.o: warning: objtool: do_jit+0x276: relocation to !ENDBR: .noinstr.text+0x6a60

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Message-ID: <20250303094358.GK5880@noisy.programming.kicks-ass.net>
Date: Mon, 3 Mar 2025 10:43:58 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: kernel test robot <lkp@...el.com>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>, Kees Cook <kees@...nel.org>
Subject: Re: [tip:x86/core 16/17] vmlinux.o: warning: objtool: do_jit+0x276:
 relocation to !ENDBR: .noinstr.text+0x6a60

On Mon, Mar 03, 2025 at 10:24:59AM +0100, Peter Zijlstra wrote:
> On Mon, Mar 03, 2025 at 07:47:57AM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/core
> > head:   dfebe7362f6f461d771cdb9ac2c5172a4721f064
> > commit: 0c92385dc05ee9637c04372ea95a11bbf6e010ff [16/17] x86/ibt: Implement FineIBT-BHI mitigation
> > config: x86_64-randconfig-071-20250303 (https://download.01.org/0day-ci/archive/20250303/202503030704.H9KFysNS-lkp@intel.com/config)
> > compiler: clang version 19.1.7 (https://github.com/llvm/llvm-project cd708029e0b2869e80abe31ddb175f7c35361f90)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250303/202503030704.H9KFysNS-lkp@intel.com/reproduce)
> > 
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@...el.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202503030704.H9KFysNS-lkp@intel.com/
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > >> vmlinux.o: warning: objtool: do_jit+0x276: relocation to !ENDBR: .noinstr.text+0x6a60
> 
> Thanks, below seems to cure it for me.
> 
> ---
> Subject: x86/ibt: Make cfi_bhi a constant for FINEIBT_BHI=n
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Mon Mar 3 10:21:47 CET 2025
> 
> Robot yielded a .config that tripped:
> 
>   vmlinux.o: warning: objtool: do_jit+0x276: relocation to !ENDBR: .noinstr.text+0x6a60
> 
> This is the result of using __bhi_args[1] in unreachable code; make
> sure the compiler is able to determine this is unreachable and trigger
> DCE.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202503030704.H9KFysNS-lkp@intel.com/
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Durr, doesn't build with FINEIBT && FINEIBT_BHI=n, let me cure that.