update the research of arm

 /*
 # see: https://github.com/winlinvip/simple-rtmp-server/wiki/v1_CN_SrsLinuxArm
- arm-linux-gnueabi-g++ -o jmp jmp.cpp -static
- arm-linux-gnueabi-strip jmp
+    g++ -g -O0 -o jmp jmp.cpp
+    arm-linux-gnueabi-g++ -o jmp jmp.cpp -static
+    arm-linux-gnueabi-strip jmp
 */
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 #include <setjmp.h>
 
+bool func1_ok = false, func2_ok = false;
 jmp_buf env_func1, env_func2;
 
 int sum = 0;
 
 void func1() {
     int ret = setjmp(env_func1);
-    printf("setjmp func1 ret=%d\n", ret);
+    printf("[func1] setjmp ret=%d, sum++=%d\n", ret, sum++);
+    func1_ok = true;
     
-    if (sum <= 0) {
-        return;
-    }
-    
-    if (sum++ > 1000) {
-        return;
-    }
+    sleep(1);
     
     // jmp to func2
-    longjmp(env_func2, 3);
+    if (func2_ok) {
+        longjmp(env_func2, 1);
+    }
 }
 
 void func2() {
     int ret = setjmp(env_func2);
-    printf("setjmp func2 ret=%d\n", ret);
+    printf("[func2] setjmp ret=%d, sum++=%d\n", ret, sum++);
+    func2_ok = true;
     
-    if (sum <= 0) {
-        return;
-    }
+    sleep(1);
     
     // jmp to func1
-    longjmp(env_func1, 2);
+    if (func1_ok) {
+        longjmp(env_func1, 2);
+    }
 }
 
 int main(int argc, char** argv) {
     printf("hello, setjmp/longjmp!\n");
     func1();
-    sum++;
     func2();
     printf("jmp finished, sum=%d\n", sum);
     return 0;

 /*
 # see: https://github.com/winlinvip/simple-rtmp-server/wiki/v1_CN_SrsLinuxArm
- arm-linux-gnueabi-g++ -g -o jmp_sp jmp_sp.cpp -static
- arm-linux-gnueabi-strip jmp_sp
+    g++ -g -O0 -o jmp_sp jmp_sp.cpp
+    arm-linux-gnueabi-g++ -g -o jmp_sp jmp_sp.cpp -static
+    arm-linux-gnueabi-strip jmp_sp
 */
 #include <stdio.h>
 #include <stdlib.h>
 #include <setjmp.h>
 
-int main(int argc, char** argv) {
+jmp_buf env_func1;
+
+void func1()
+{
 #if defined(__amd64__) || defined(__x86_64__)
-    printf("x86_64 sizeof(long int)=%d, sizeof(long)=%d, sizeof(int)=%d\n", (int)sizeof(long int), (int)sizeof(long), (int)sizeof(int));
-#else
-    printf("arm sizeof(long int)=%d, sizeof(long)=%d, sizeof(int)=%d\n", (int)sizeof(long int), (int)sizeof(long), (int)sizeof(int));
-#endif
-    
-    jmp_buf env;
+    register long int rsp0 asm("rsp");
+    printf("in func1, rsp=%#lx, longjmp to func0\n", rsp0);
     
-    int ret = setjmp(env);
-    printf("setjmp func1 ret=%d\n", ret);
+    longjmp(env_func1, 0x101);
     
+    printf("func1 terminated\n");
+#endif
+}
+
+void func0(int* pv0, int* pv1)
+{
+    /**
+    the definition of jmp_buf:
+        typedef struct __jmp_buf_tag jmp_buf[1];
+        struct __jmp_buf_tag {
+             __jmp_buf __jmpbuf;
+             int __mask_was_saved;
+             __sigset_t __saved_mask;
+        };
+    */
 #if defined(__amd64__) || defined(__x86_64__)
-    // typedef lint64_t __jmp_buf[8];
+    /**
+    here, the __jmp_buf is 8*8=64 bytes
+        # if __WORDSIZE == 64
+            typedef long int __jmp_buf[8];
+    */
+    /**
+    the layout for setjmp of x86_64
+        #
+        # The jmp_buf is assumed to contain the following, in order:
+        #       %rbx
+        #       %rsp (post-return)
+        #       %rbp
+        #       %r12
+        #       %r13
+        #       %r14
+        #       %r15
+        #       <return address>
+        #
+    */
+    register long int rsp0 asm("rsp");
+    
+    int ret = setjmp(env_func1);
+    printf("setjmp func0 ret=%d, rsp=%#lx\n", ret, rsp0);
+    
     printf("after setjmp: ");
     for (int i = 0; i < 8; i++) {
-        printf("env[%d]=%#x, ", i, (int)env[0].__jmpbuf[i]);
+        printf("env[%d]=%#x, ", i, (int)env_func1[0].__jmpbuf[i]);
     }
     printf("\n");
 #else
-    // typedef int32_t __jmp_buf[64] __attribute__((__aligned__ (8)));
+    /**
+        /usr/arm-linux-gnueabi/include/bits/setjmp.h
+        #ifndef _ASM
+        The exact set of registers saved may depend on the particular core
+           in use, as some coprocessor registers may need to be saved.  The C
+           Library ABI requires that the buffer be 8-byte aligned, and
+           recommends that the buffer contain 64 words.  The first 28 words
+           are occupied by v1-v6, sl, fp, sp, pc, d8-d15, and fpscr.  (Note
+           that d8-15 require 17 words, due to the use of fstmx.)
+        typedef int __jmp_buf[64] __attribute__((__aligned__ (8)));
+        
+        the layout of setjmp for arm:
+            0-5: v1-v6 
+            6: sl
+            7: fp
+            8: sp
+            9: pc
+            10-26: d8-d15 17words
+            27: fpscr
+    */
+    int ret = setjmp(env_func1);
+    printf("setjmp func1 ret=%d\n", ret);
+    
     printf("after setjmp: ");
     for (int i = 0; i < 64; i++) {
-        printf("env[%d]=%#x, ", i, (int)env[0].__jmpbuf[i]);
+        printf("env[%d]=%#x, ", i, (int)env_func1[0].__jmpbuf[i]);
     }
-    printf("\n");
+    
+    printf("func0 terminated\n");
 #endif
+}
+
+int main(int argc, char** argv) {
+#if defined(__amd64__) || defined(__x86_64__)
+    printf("x86_64 sizeof(long int)=%d, sizeof(long)=%d, sizeof(int)=%d, __WORDSIZE=%d\n", 
+        (int)sizeof(long int), (int)sizeof(long), (int)sizeof(int), (int)__WORDSIZE);
+#else
+    printf("arm sizeof(long int)=%d, sizeof(long)=%d, sizeof(int)=%d\n", 
+        (int)sizeof(long int), (int)sizeof(long), (int)sizeof(int));
+#endif
+
+    int pv0 = 0xf0;
+    int pv1 = 0xf1;
+    func0(&pv0, &pv1);
+    func1();
+    
+    printf("terminated\n");
 
     return 0;
 }