linux-kernel - [PATCH v2 1/1] x86/mm: Check if PTRS_PER

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Message-ID: <20250306092658.378837-1-andriy.shevchenko@linux.intel.com>
Date: Thu,  6 Mar 2025 11:25:41 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	kernel test robot <lkp@...el.com>
Subject: [PATCH v2 1/1] x86/mm: Check if PTRS_PER_PMD is defined before use

Compiler (GCC) is not happy about PTRS_PER_PMD being undefined
(note, clang also issues the quite similar warning)

In file included from arch/x86/kernel/head_32.S:29:
arch/x86/include/asm/pgtable_32.h:59:5: error: "PTRS_PER_PMD" is not defined, evaluates to 0 [-Werror=undef]
   59 | #if PTRS_PER_PMD > 1

Add a check to make sure PTRS_PER_PMD is defined before use.

The documentation for GCC 7.5.0+ says that:

	if defined BUFSIZE && BUFSIZE >= 1024

    can generally be simplified to just #if BUFSIZE >= 1024, since if BUFSIZE
    is not defined, it will be interpreted as having the value zero.

But in the same time the last paragraph points out that

    It will warn wherever your code uses this feature.

which is what we met here.

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/r/202412152358.l9RJiVaH-lkp@intel.com/
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---

v2: made the commit message more accurate by citing the documentation (Dave)

 arch/x86/include/asm/pgtable_32.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable_32.h b/arch/x86/include/asm/pgtable_32.h
index 7d4ad8907297..3c0523588f59 100644
--- a/arch/x86/include/asm/pgtable_32.h
+++ b/arch/x86/include/asm/pgtable_32.h
@@ -56,7 +56,7 @@ do {						\
  * With PAE paging (PTRS_PER_PMD > 1), we allocate PTRS_PER_PGD == 4 pages for
  * the PMD's in addition to the pages required for the last level pagetables.
  */
-#if PTRS_PER_PMD > 1
+#if defined(PTRS_PER_PMD) && (PTRS_PER_PMD > 1)
 #define PAGE_TABLE_SIZE(pages) (((pages) / PTRS_PER_PMD) + PTRS_PER_PGD)
 #else
 #define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)
-- 
2.47.2