linux-kernel - Re: [tip:WIP.x86/pti-upstream 38/50] arch/x86/include/asm/mmu_context.h:73:18: error: 'LDT_BASE

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Date:   Sat, 16 Dec 2017 18:50:24 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     kbuild test robot <fengguang.wu@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>, kbuild-all@...org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        tipbuild@...or.com, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [tip:WIP.x86/pti-upstream 38/50] arch/x86/include/asm/mmu_context.h:73:18:
 error: 'LDT_BASE_ADDR' undeclared

On Sat, Dec 16, 2017 at 3:35 PM, kbuild test robot
<fengguang.wu@...el.com> wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.x86/pti-upstream
> head:   78e4da51f7c77587cc6f419af4f63a21b289bdb7
> commit: 7e482cfe4a23ead21215423c4566c8516ba21025 [38/50] x86/pti: Put the LDT in its own PGD if PTI is on
> config: i386-randconfig-h0-12170619 (attached as .config)
> compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026
> reproduce:
>         git checkout 7e482cfe4a23ead21215423c4566c8516ba21025
>         # save the attached .config to linux build tree
>         make ARCH=i386
>
> All errors (new ones prefixed by >>):
>
>    In file included from arch/x86//kernel/apic/ipi.c:16:0:
>    arch/x86/include/asm/mmu_context.h: In function 'ldt_slot_va':
>>> arch/x86/include/asm/mmu_context.h:73:18: error: 'LDT_BASE_ADDR' undeclared (first use in this function)
>      return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
>                      ^~~~~~~~~~~~~
>    arch/x86/include/asm/mmu_context.h:73:18: note: each undeclared identifier is reported only once for each function it appears in
> --
>    In file included from arch/x86//kernel/cpu/common.c:22:0:
>    arch/x86/include/asm/mmu_context.h: In function 'ldt_slot_va':
>>> arch/x86/include/asm/mmu_context.h:73:18: error: 'LDT_BASE_ADDR' undeclared (first use in this function)
>      return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
>                      ^~~~~~~~~~~~~
>    arch/x86/include/asm/mmu_context.h:73:18: note: each undeclared identifier is reported only once for each function it appears in
>    In file included from arch/x86//kernel/cpu/common.c:22:0:
>    arch/x86/include/asm/mmu_context.h:74:1: warning: control reaches end of non-void function [-Wreturn-type]
>     }
>     ^
>
> vim +/LDT_BASE_ADDR +73 arch/x86/include/asm/mmu_context.h
>
>     70
>     71  static inline void *ldt_slot_va(int slot)
>     72  {
>   > 73          return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
>     74  }
>     75
>

I would fix this like this:

index b7ffd45b22f7..3c7042877e63 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -70,7 +70,11 @@ struct ldt_struct {

 static inline void *ldt_slot_va(int slot)
 {
+#ifdef CONFIG_X86_64
        return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
+#else
+       BUG();
+#endif
 }

Ingo or Thomas, want to do that manually?  It's probably easier than
folding in a patch.