Re: [PATCH] x86_64/bug: Handle __WARN_printf() trap in early_fixup_exception()

[kernel test robot]

Hi Hou,

kernel test robot noticed the following build errors:

[auto build test ERROR on linus/master]
[also build test ERROR on v6.19-rc4 next-20260109]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Hou-Wenlong/x86_64-bug-Handle-__WARN_printf-trap-in-early_fixup_exception/20260109-204012
base:   linus/master
patch link:    https://lore.kernel.org/r/97dd5c5b5e92d48ffbc95fb1357dfbbbf0d12a1e.1767960698.git.houwenlong.hwl%40antgroup.com
patch subject: [PATCH] x86_64/bug: Handle __WARN_printf() trap in early_fixup_exception()
config: i386-allnoconfig-bpf (https://download.01.org/0day-ci/archive/20260110/202601100329.ndS6mKRm-lkp@xxxxxxxxx/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260110/202601100329.ndS6mKRm-lkp@xxxxxxxxx/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@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202601100329.ndS6mKRm-lkp@xxxxxxxxx/

All errors (new ones prefixed by >>):

>> arch/x86/mm/extable.c:414:7: error: call to undeclared function 'handle_bug'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     414 |                 if (handle_bug(regs))
         |                     ^
   1 error generated.


vim +/handle_bug +414 arch/x86/mm/extable.c

   376	
   377	/* Restricted version used during very early boot */
   378	void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
   379	{
   380		/* Ignore early NMIs. */
   381		if (trapnr == X86_TRAP_NMI)
   382			return;
   383	
   384		if (early_recursion_flag > 2)
   385			goto halt_loop;
   386	
   387		/*
   388		 * Old CPUs leave the high bits of CS on the stack
   389		 * undefined.  I'm not sure which CPUs do this, but at least
   390		 * the 486 DX works this way.
   391		 * Xen pv domains are not using the default __KERNEL_CS.
   392		 */
   393		if (!xen_pv_domain() && regs->cs != __KERNEL_CS)
   394			goto fail;
   395	
   396		/*
   397		 * The full exception fixup machinery is available as soon as
   398		 * the early IDT is loaded.  This means that it is the
   399		 * responsibility of extable users to either function correctly
   400		 * when handlers are invoked early or to simply avoid causing
   401		 * exceptions before they're ready to handle them.
   402		 *
   403		 * This is better than filtering which handlers can be used,
   404		 * because refusing to call a handler here is guaranteed to
   405		 * result in a hard-to-debug panic.
   406		 *
   407		 * Keep in mind that not all vectors actually get here.  Early
   408		 * page faults, for example, are special.
   409		 */
   410		if (fixup_exception(regs, trapnr, regs->orig_ax, 0))
   411			return;
   412	
   413		if (trapnr == X86_TRAP_UD) {
 > 414			if (handle_bug(regs))

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