arm32 stack check

arm64 反汇编分析分析了armv8的stack check原理，　这里分析下arm32的原理
基本流程和arm64一致，我们看下arm32如何保存canary值，　
__set_tls

ENTRY(__set_tls)
	 mov ip, r7
	 ldr r7, =__ARM_NR_set_tls
	 swi #0
	 mov r7, ip
	 cmn r0, #(MAX_ERRNO + 1)
	 bxls lr
	 neg r0, r0
	 b __set_errno_internal
END(__set_tls)

# define __get_tls() ({ void** __val; __asm__("mrc p15, 0, %0, c13, c0, 3"
   : "=r"(__val)); __val; })//cp1513_val13
Read User read-only Thread and Process ID Register


extern "C" void** __get_tls() {
	#include "private/__get_tls.h"
	 return __get_tls();
}

也就是通过系统调用去设置tls的指针值，
__get_tlstls

参考
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0344k/Babeihid.html