Re: [Crash-utility] [PATCH V2] RISCV64: Use va_kernel_pa_offset in VTOP()

在 2023/8/14 16:27, lijiang 写道: > +static void > +riscv64_get_va_kernel_pa_offset(struct machine_specific *ms) > +{ > + unsigned long kernel_version = riscv64_get_kernel_version(); > + > + /* > + * Since Linux v6.4 phys_base is not the physical start of > the kernel, > + * trying to use "va_kernel_pa_offset" to determine the > offset between > + * kernel virtual and physical addresses. > + */ > + if (kernel_version >= LINUX(6,4,0)) { > > Is it possible to detect the existence of the symbol > 'linear_mapping_va_to_pa' or 'linear_mapping_pa_to_va' to decide reading > the value of 'va_kernel_pa_offset'? For example: > kernel_symbol_exists()/symbol_exists() > > if (kernel_symbol_exists("linear_mapping_va_to_pa") || > kernel_symbol_exists("linear_mapping_pa_to_va")) { > string = pc->read_vmcoreinfo("NUMBER(va_kernel_pa_offset)"); > ... > } The `linear_mapping_va_to_pa` and `linear_mapping_pa_to_va` symbols will only be exported when the debug option -- CONFIG_DEBUG_VIRTUAL is enabled, otherwise they will expanded as macros. As the kernel Makefile

says: obj-$(CONFIG_DEBUG_VIRTUAL) += physaddr.o Actually, it's hard to extract some explicit infomation from the commit 3335068f8721 and use them as the first `if` condition, so the kernel version checking was the final choice.

> > I saw the commit 3335068f8721 exported two symbols: > > +phys_addr_t linear_mapping_va_to_pa(unsigned long x) > +{ > + BUG_ON(!kernel_map.va_pa_offset); > + > + return ((unsigned long)(x) - kernel_map.va_pa_offset); > +} > +EXPORT_SYMBOL(linear_mapping_va_to_pa); > + > +void *linear_mapping_pa_to_va(unsigned long x) > +{ > + BUG_ON(!kernel_map.va_pa_offset); > + > + return ((void *)((unsigned long)(x) + kernel_map.va_pa_offset)); > +} > +EXPORT_SYMBOL(linear_mapping_pa_to_va);