linux-kernel - [RFC] vsprintf: compile error on %09pK

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Date:   Mon, 03 Apr 2023 19:46:17 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     "pmladek@...e.com" <pmladek@...e.com>,
        "senozhatsky@...omium.org" <senozhatsky@...omium.org>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jaewon31.kim@...il.com" <jaewon31.kim@...il.com>,
        GyeongHwan Hong <gh21.hong@...sung.com>
Subject: [RFC] vsprintf: compile error on %09pK

Hello

I've just changed %09lx to %09pK on my driver code to hide the address, but I
faced compiler error. The %9pK without 0 worked.

Is there restriction on %pK which does now allow %0 ? I've wondered whether I
did wrong or it is a printk problem.

To show easily I tried to add pr_info("%09pK\n", nodemask); in page_alloc.c
Then here's what I did.

$ ARCH=x86 make x86_64_defconfig ; make mm/page_alloc.o
#
# No change to .config
#
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  CC      mm/page_alloc.o
In file included from ./include/asm-generic/bug.h:22:0,
                 from ./arch/x86/include/asm/bug.h:87,
                 from ./include/linux/bug.h:5,
                 from ./include/linux/mmdebug.h:5,
                 from ./include/linux/mm.h:6,
                 from mm/page_alloc.c:19:
mm/page_alloc.c: In function ‘__alloc_pages’:
./include/linux/kern_levels.h:5:18: error: '0' flag used with ‘%p’ gnu_printf format [-Werror=format=]
 #define KERN_SOH "\001"  /* ASCII Start Of Header */
                  ^
./include/linux/printk.h:427:11: note: in definition of macro ‘printk_index_wrap’
   _p_func(_fmt, ##__VA_ARGS__);    \
           ^
./include/linux/printk.h:528:2: note: in expansion of macro ‘printk’
  printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
  ^
./include/linux/kern_levels.h:14:19: note: in expansion of macro ‘KERN_SOH’
 #define KERN_INFO KERN_SOH "6" /* informational */
                   ^
./include/linux/printk.h:528:9: note: in expansion of macro ‘KERN_INFO’
  printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
         ^
mm/page_alloc.c:5564:2: note: in expansion of macro ‘pr_info’
  pr_info("%09pK\n", nodemask);
  ^

Jaewon Kim