Re: [RFC PATCH 6/7] x86/kexec: Debugging support: Dump registers on exception

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On 11/5/24 13:58, H. Peter Anvin wrote:

Then you can just do the obvious (have your assembly stub point %rdi to the base of the register dump; set the frame order to whatever you'd like, except rip/err/exc, or reverse the order if you prefer by changing the loop):

static inline __noreturn void die(void)
{
     while (1)
         asm volatile("hlt");
}

void dump_register_frame(const unsigned long frame[])
{
     static const char regnames[][5] = {
         "rax:", "rcx:", "rdx:", "rbx:",
         "rsp:", "rbp:", "rsi:", "rdi:",
         "r8: ", "r9: ", "r10:", "r11:",
         "r12:", "r13:", "r14:", "r15:",
         "cr2:", "Exc:", "Err:", "rip:"
     };

     for (size_t i = 0; i < ARRAY_SIZE(regnames); i++) {
         __putstr(regnames[i]);
         __puthex(frame[i]);
         __putstr("\n");
     }

     /* Only return from int3 */
     if (frame[17] != 3)
         die();
}


I don't know if it is necessary, but you can do something like this to make absolutely sure you don't end up with non-relative symbol references:

static inline __constfunc void * sym_addr(const void *sym)
{
	void *addr;
	asm("lea %c1(%%rip),%0" : "=r" (addr) : "i" (sym));
	return addr;
}


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