linux-kernel - Re: [PATCH V2] riscv: Fixup compile error BUILD_BUG

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Date:   Mon, 29 Jun 2020 16:22:50 -0700 (PDT)
From:   Palmer Dabbelt <palmerdabbelt@...gle.com>
To:     mhiramat@...nel.org
CC:     guoren@...nel.org, greentime.hu@...ive.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>, anup@...infault.org,
        linux-csky@...r.kernel.org, zong.li@...ive.com,
        guoren@...ux.alibaba.com
Subject:     Re: [PATCH V2] riscv: Fixup compile error BUILD_BUG_ON failed

On Sun, 28 Jun 2020 09:25:24 PDT (-0700), mhiramat@...nel.org wrote:
> On Sun, 28 Jun 2020 16:07:37 +0000
> guoren@...nel.org wrote:
>
>> From: Guo Ren <guoren@...ux.alibaba.com>
>>
>> Unfortunately, the current code couldn't be compiled:
>>
>>   CC      arch/riscv/kernel/patch.o
>> In file included from ./include/linux/kernel.h:11,
>>                  from ./include/linux/list.h:9,
>>                  from ./include/linux/preempt.h:11,
>>                  from ./include/linux/spinlock.h:51,
>>                  from arch/riscv/kernel/patch.c:6:
>> In function ‘fix_to_virt’,
>>     inlined from ‘patch_map’ at arch/riscv/kernel/patch.c:37:17:
>> ./include/linux/compiler.h:392:38: error: call to ‘__compiletime_assert_205’ declared with attribute error: BUILD_BUG_ON failed: idx >= __end_of_fixed_addresses
>>   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>>                                       ^
>> ./include/linux/compiler.h:373:4: note: in definition of macro ‘__compiletime_assert’
>>     prefix ## suffix();    \
>>     ^~~~~~
>> ./include/linux/compiler.h:392:2: note: in expansion of macro ‘_compiletime_assert’
>>   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>>   ^~~~~~~~~~~~~~~~~~~
>> ./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
>>  #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>>                                      ^~~~~~~~~~~~~~~~~~
>> ./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
>>   BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
>>   ^~~~~~~~~~~~~~~~
>> ./include/asm-generic/fixmap.h:32:2: note: in expansion of macro ‘BUILD_BUG_ON’
>>   BUILD_BUG_ON(idx >= __end_of_fixed_addresses);
>>   ^~~~~~~~~~~~
>>
>> Because fix_to_virt(, idx) needs a const value, not a dynamic variable of
>> reg-a0 or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".
>
> Looks good to me :)
>
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Is there a configuration that runs into this bug?  It's not showing up for me,
and I generally try to add regressions to my test suite.

> Thanks!
>
>>
>> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
>> Cc: Masami Hiramatsu <mhiramat@...nel.org>
>> Cc: Zong Li <zong.li@...ive.com>
>> ---
>> Changelog V2:
>>  - Use __always_inline as same as fix_to_virt
>>  - Use const "const unsigned int" for 2th param
>>
>> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
>> ---
>>  arch/riscv/kernel/patch.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
>> index d4a64df..3179a4e 100644
>> --- a/arch/riscv/kernel/patch.c
>> +++ b/arch/riscv/kernel/patch.c
>> @@ -20,7 +20,12 @@ struct patch_insn {
>>  };
>>
>>  #ifdef CONFIG_MMU
>> -static void *patch_map(void *addr, int fixmap)
>> +/*
>> + * The fix_to_virt(, idx) needs a const value (not a dynamic variable of
>> + * reg-a0) or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".
>> + * So use '__always_inline' and 'const unsigned int fixmap' here.
>> + */
>> +static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
>>  {
>>  	uintptr_t uintaddr = (uintptr_t) addr;
>>  	struct page *page;
>> @@ -37,7 +42,6 @@ static void *patch_map(void *addr, int fixmap)
>>  	return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
>>  					 (uintaddr & ~PAGE_MASK));
>>  }
>> -NOKPROBE_SYMBOL(patch_map);
>>
>>  static void patch_unmap(int fixmap)
>>  {
>> --
>> 2.7.4
>>