linux-kernel - Re: [BUG REPORT] arch/x86/include/asm/uaccess

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Date:   Sat, 15 Apr 2023 19:56:01 +0200
From:   Willy Tarreau <w@....eu>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Jingbo Xu <jefflexu@...ux.alibaba.com>, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [BUG REPORT] arch/x86/include/asm/uaccess_64.h:119: Error: junk
 at end of line

Hi Boris!

On Tue, Mar 14, 2023 at 11:23:16AM +0100, Borislav Petkov wrote:
> On Tue, Mar 14, 2023 at 11:12:13AM +0800, Jingbo Xu wrote:
> > 	gcc (GCC) 6.5.1 20181026 (Alibaba 6.5.1-1)
> 
> Looks like you should complain to whoever patched this gcc and broke it
> in the process. Unless you can reproduce the issue with an official
> compiler...

I got the exact same issue today when building over distcc using locally-
built gcc-7.5 and gcc-6.5 here, though the one from kernel.org/crosstool
didn't have the problem. The only difference I found is the binutils that
the asm comes from. Mine rely on 2.27 while the one from kernel.org is on
2.32.

I produced the .s file then tried to build it and compared. Both .s files
are identical, and only one asm (2.32) assembles it fine. The error is
triggered here:

663:
.pushsection .altinstructions,"a"
 .long 661b - .
 .long 6641f - .
 .4byte ((((((1UL))) << (0)) << 16) | ((18*32+ 4)))
                ^
This is the "L" the asm complains about. If I change it to "1U" it's
happy. Indeed, the difference is here in the introduction of the BIT()
macro in the definition of ALT_FLAG_NOT in your commit 5d1dd961e743
("x86/alternatives: Add alt_instr.flags") merged into 6.3-rc1:

  -#define ALTINSTR_FLAG_INV      (1 << 15)
  -#define ALT_NOT(feat)          ((feat) | ALTINSTR_FLAG_INV)
  +#define ALT_FLAGS_SHIFT                16
  +
  +#define ALT_FLAG_NOT           BIT(0)
  +#define ALT_NOT(feature)       ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature))

And I can confirm that the following patch fixes it for me, now the kernel
builds fine:

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index e2975a32d443..d7da28fada87 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -8,7 +8,7 @@
 
 #define ALT_FLAGS_SHIFT                16
 
-#define ALT_FLAG_NOT           BIT(0)
+#define ALT_FLAG_NOT           (1 << 0)
 #define ALT_NOT(feature)       ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature))
 
 #ifndef __ASSEMBLY__

May I send you a cleaner patch for this ?

Thanks!
Willy