Re: [linux-next:master 4278/4736] arch/mips/include/asm/pgtable.h:238:39: error: missing binary operator before token "("

[Zach O'Keefe <zokeefe@google.com>]

On Sep 02 13:19, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   e47eb90a0a9ae20b82635b9b99a8d0979b757ad8
> commit: 2abbc27432878c26759d2913a22a7a15a66b96fd [4278/4736] mm/khugepaged: use minimal bits to store num page < HPAGE_PMD_NR
> config: mips-randconfig-r013-20220901 (https://download.01.org/0day-ci/archive/20220902/202209021349.F73i5d6X-lkp@intel.com/config)
> compiler: mips-linux-gcc (GCC) 12.1.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=2abbc27432878c26759d2913a22a7a15a66b96fd
>         git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>         git fetch --no-tags linux-next master
>         git checkout 2abbc27432878c26759d2913a22a7a15a66b96fd
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All error/warnings (new ones prefixed by >>):
> 
>    In file included from include/linux/pgtable.h:6,
>                     from include/linux/mm.h:29,
>                     from mm/khugepaged.c:4:
> >> arch/mips/include/asm/pgtable.h:238:26: warning: "__builtin_ffs" is not defined, evaluates to 0 [-Wundef]
>      238 | #define PTE_T_LOG2      (__builtin_ffs(sizeof(pte_t)) - 1)
>          |                          ^~~~~~~~~~~~~
>    arch/mips/include/asm/pgtable-32.h:65:43: note: in expansion of macro 'PTE_T_LOG2'
>       65 | # define PGDIR_SHIFT    (2 * PAGE_SHIFT - PTE_T_LOG2 - 1)
>          |                                           ^~~~~~~~~~
>    include/asm-generic/pgtable-nop4d.h:11:33: note: in expansion of macro 'PGDIR_SHIFT'
>       11 | #define P4D_SHIFT               PGDIR_SHIFT
>          |                                 ^~~~~~~~~~~
>    include/asm-generic/pgtable-nopud.h:18:25: note: in expansion of macro 'P4D_SHIFT'
>       18 | #define PUD_SHIFT       P4D_SHIFT
>          |                         ^~~~~~~~~
>    include/asm-generic/pgtable-nopmd.h:20:25: note: in expansion of macro 'PUD_SHIFT'
>       20 | #define PMD_SHIFT       PUD_SHIFT
>          |                         ^~~~~~~~~
>    include/linux/huge_mm.h:109:25: note: in expansion of macro 'PMD_SHIFT'
>      109 | #define HPAGE_PMD_SHIFT PMD_SHIFT
>          |                         ^~~~~~~~~
>    include/linux/huge_mm.h:105:26: note: in expansion of macro 'HPAGE_PMD_SHIFT'
>      105 | #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>          |                          ^~~~~~~~~~~~~~~
>    mm/khugepaged.c:90:5: note: in expansion of macro 'HPAGE_PMD_ORDER'
>       90 | #if HPAGE_PMD_ORDER < 16
>          |     ^~~~~~~~~~~~~~~
> >> arch/mips/include/asm/pgtable.h:238:39: error: missing binary operator before token "("
>      238 | #define PTE_T_LOG2      (__builtin_ffs(sizeof(pte_t)) - 1)
>          |                                       ^
>    arch/mips/include/asm/pgtable-32.h:65:43: note: in expansion of macro 'PTE_T_LOG2'
>       65 | # define PGDIR_SHIFT    (2 * PAGE_SHIFT - PTE_T_LOG2 - 1)
>          |                                           ^~~~~~~~~~
>    include/asm-generic/pgtable-nop4d.h:11:33: note: in expansion of macro 'PGDIR_SHIFT'
>       11 | #define P4D_SHIFT               PGDIR_SHIFT
>          |                                 ^~~~~~~~~~~
>    include/asm-generic/pgtable-nopud.h:18:25: note: in expansion of macro 'P4D_SHIFT'
>       18 | #define PUD_SHIFT       P4D_SHIFT
>          |                         ^~~~~~~~~
>    include/asm-generic/pgtable-nopmd.h:20:25: note: in expansion of macro 'PUD_SHIFT'
>       20 | #define PMD_SHIFT       PUD_SHIFT
>          |                         ^~~~~~~~~
>    include/linux/huge_mm.h:109:25: note: in expansion of macro 'PMD_SHIFT'
>      109 | #define HPAGE_PMD_SHIFT PMD_SHIFT
>          |                         ^~~~~~~~~
>    include/linux/huge_mm.h:105:26: note: in expansion of macro 'HPAGE_PMD_SHIFT'
>      105 | #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>          |                          ^~~~~~~~~~~~~~~
>    mm/khugepaged.c:90:5: note: in expansion of macro 'HPAGE_PMD_ORDER'
>       90 | #if HPAGE_PMD_ORDER < 16
>          |     ^~~~~~~~~~~~~~~
> 
> 
> vim +238 arch/mips/include/asm/pgtable.h
> 
> ^1da177e4c3f41 include/asm-mips/pgtable.h Linus Torvalds 2005-04-16  235  
> 5ff974720abec2 include/asm-mips/pgtable.h Ralf Baechle   2007-08-01  236  #define PGD_T_LOG2	(__builtin_ffs(sizeof(pgd_t)) - 1)
> 5ff974720abec2 include/asm-mips/pgtable.h Ralf Baechle   2007-08-01  237  #define PMD_T_LOG2	(__builtin_ffs(sizeof(pmd_t)) - 1)
> 5ff974720abec2 include/asm-mips/pgtable.h Ralf Baechle   2007-08-01 @238  #define PTE_T_LOG2	(__builtin_ffs(sizeof(pte_t)) - 1)
> ^1da177e4c3f41 include/asm-mips/pgtable.h Linus Torvalds 2005-04-16  239  
> 
> :::::: The code at line 238 was first introduced by commit
> :::::: 5ff974720abec255c17af6f3732dd410d364e367 [MIPS] Fix computation of {PGD,PMD,PTE}_T_LOG2.
> 
> :::::: TO: Ralf Baechle <ralf@linux-mips.org>
> :::::: CC: Ralf Baechle <ralf@linux-mips.org>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://01.org/lkp
> 

Sorry about this - have been trying to figure out what exactly is happening.

AFAICT this config doesn't even build on v5.19 with the repro steps / compiler.

---8<---
	../arch/mips/mm/init.c:454:9: note: in expansion of macro 'BUILD_BUG_ON'
	  454 |         BUILD_BUG_ON(IS_ENABLED(CONFIG_32BIT) && (_PFN_SHIFT > PAGE_SHIFT));
	      |         ^~~~~~~~~~~~
---8<---

Though if I set 64 bit kernel it builds 2abbc27432878c26759d2913a22a7a15a66b96fd
fine - though I haven't gone through all levels of macros to see how that has
changed the expansion of HPAGE_PMD_ORDER.

Seems to be something specific to the "#if" directive as the compiler doesn't
seem to complain about, for example, defining an int[HPAGE_PMD_ORDER] array
in this struct. No fix yet, but just wanted to put this out there so it's known
I'm looking into it.

Thanks,
Zach