Re: [PATCH] x86/process: Silence KASAN warnings in get_wchan()

[Andrey Ryabinin]

On 10/07/2015 11:54 AM, Andrey Ryabinin wrote:
> On 10/06/2015 09:11 PM, Andy Lutomirski wrote:
>>
>> But what's wrong with the GCC attribute mechanism?  Surely GCC ought
>> to be able to generate the code, at least in the simple cases, and the
>> attribute already exists.  The attribute and READ_ONCE_NOCHECK seem
>> like the least messy in the C code.
> 
> The problem with 'no_sanitize_address' attribute is incompatibility with inlining. 
> GCC can't inline function with that attribute into function without it.
> And the contrary is also true - GCC can't inline function without attribute into function with such attribute.
> 
> Failure to inline always_inline function leads to build failure.
> And under CONFIG_OPTIMIZE=n 'inline' means 'always_inline'.
> 
> include/linux/compiler-gcc.h:
> 
> #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||		\
>     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
> #define inline		inline		__attribute__((always_inline)) notrace
> 

Huh, 'inline' effectively means 'always_inline' on every arch, except x86.
This looks like a bug IMO.
Allowing gcc to uninline functions marked 'inline' could be beneficial for some arches/configs.

$ git grep ARCH_SUPPORTS_OPTIMIZED_INLINING
	arch/tile/Kconfig:config ARCH_SUPPORTS_OPTIMIZED_INLINING
	arch/x86/Kconfig:config ARCH_SUPPORTS_OPTIMIZED_INLINING
	include/linux/compiler-gcc.h:#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||           \

$ git grep OPTIMIZE_INLINING
	arch/x86/Kconfig.debug:config OPTIMIZE_INLINING
	arch/x86/configs/i386_defconfig:CONFIG_OPTIMIZE_INLINING=y
	arch/x86/configs/x86_64_defconfig:CONFIG_OPTIMIZE_INLINING=y
	arch/x86/entry/vdso/vdso32/vclock_gettime.c:#undef CONFIG_OPTIMIZE_INLINING
	include/linux/compiler-gcc.h:    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
	kernel/configs/tiny.config:CONFIG_OPTIMIZE_INLINING=y
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