Re: [PATCH v2] LoongArch: Libvtv add loongarch support.

[Lulu Cheng <chenglulu@loongson.cn>]

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在 2022/10/12 上午4:57, Caroline Tice 写道:
> I think that if VTV_PAGE_SIZE is not set to the actual size being used 
> by the system,  it could result in some unexpected failures.  I 
> believe the right thing to do in this case, since the size may vary, 
> is to get the actual size being used by the system and use that in the 
> definition of VTV_PAGE_SIZE.  So in include/vtv-permission.h you 
> would have something like:
>
> +#elif defined(__loongarch_lp64)
> +#define VTV_PAGE_SIZE sysconf(_SC_PAGE_SIZE)
>
> Then you would have the accurate, correct size for the current system, 
> and there would be no need to update the
> check in vtv_malloc.cc at all.


     /* Page-aligned symbol to mark beginning of .vtable_map_vars 
section.  */
     char _vtable_map_vars_start []
     __attribute__ ((__visibility__ ("protected"), used, 
aligned(VTV_PAGE_SIZE),
             section(".vtable_map_vars")))
       = { };

The above code is in the libgcc/vtv_start.c file. Alignment (aligned 
(alignment) ) must be an
integer constant power of 2. So setting VTV_PAGE_SIZE as a variable is 
not advisable.


As xiruoyao notes, the default value for the LoongArch Linux kernel 
configuration is 16KB.

So let's set VTV_PAGE_SIZE to 16KB first and I will indicate in the 
submission information

that only 16KB pages are supported.