Re: [PATCH] ftrace: x86: Fix a compile error about get_kernel_nofault()

Haiyue Wang
2025-02-13T10:27:09Z

On 2025/2/13 18:08, Peter Zijlstra wrote:
> On Wed, Feb 12, 2025 at 08:52:27AM -0800, Sami Tolvanen wrote:
>> On Tue, Feb 11, 2025 at 7:49 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>>>
>>> On Tue, 11 Feb 2025 11:09:14 +0100
>>> Peter Zijlstra <peterz@infradead.org> wrote:
>>>
>>>> I was aiming my patch for x86/core, but if there's a reason to expedite
>>>> them, I can stick it in x86/urgent I suppose.
>>>>
>>>> Just need a reason -- what's this compile error nonsense about, my
>>>> kernels build just fine?
>>>
>>> Masami,
>>>
>>> Do you have a config that fails to build without this fix? If so, can you
>>> please reply with it, and then this can go in as a quick fix.
>>
>> x86 builds with both CONFIG_GENDWARFKSYMS and CONFIG_FUNCTION_TRACER
>> are broken without this fix. Here's how to reproduce:
>>
>> $ make defconfig
>> $ ./scripts/config -e DEBUG_INFO -e DEBUG_INFO_DWARF5 -e MODVERSIONS
>> -e GENDWARFKSYMS -e FUNCTION_TRACER
>> $ make olddefconfig && make -j
>> ...
>> In file included from ./arch/x86/include/asm/asm-prototypes.h:2,
>> from <stdin>:3:
>> ./arch/x86/include/asm/ftrace.h: In function ‘arch_ftrace_get_symaddr’:
>> ./arch/x86/include/asm/ftrace.h:46:21: error: implicit declaration of
>> function ‘get_kernel_nofault’ [-Wimplicit-function-declaration]
>> 46 | if (get_kernel_nofault(instr, (u32
>> *)(fentry_ip - ENDBR_INSN_SIZE)))
>> ...
>
> It breaks much sooner, complaining about not having dwarf.h.. let me go
> figure out what package provides that :/
>
> Anyway, thanks, I'll go see if my patch helps here.

It is header file include indirect :-)

https://lore.kernel.org/linux-trace-kernel/20250206131711.ea536f165d5b5980b3909acd@kernel.org/T/#t

File "asm-prototypes.h" is added to entry.S by 'scripts/Makefile.build',
adding the missed declaration header file can also fix the error:

getasmexports = \
{ echo "\#include <linux/kernel.h>" ; \
echo "\#include <linux/string.h>" ; \
+ echo "\#include <linux/uaccess.h>"; \
echo "\#include <asm/asm-prototypes.h>" ; \
$(call getexportsymbols,EXPORT_SYMBOL(\1);) ; }