save registers: fix small problems

- Don't put C code at the beginning of save save_registers macro, as
  it will change the registers in unpredictable ways. Therefore, test
  whether ust_reg_stack_ptr has been initialized in assembly code.
- Save rflags at the begginning of the stub because using the test
  instruction may change its content.

diff --git a/include/ust/processor.h b/include/ust/processor.h
index bc24e7edddc39cd3f938e4388ccd4b416550cc72..ea75be05fff01fef3fd5dd7c702dc938fad979ba 100644 (file)
--- a/include/ust/processor.h
+++ b/include/ust/processor.h
@@ -43,7 +43,6 @@ struct registers {
        int padding; /* 4 bytes */
        short ss;
        short cs;
-       unsigned long rflags;
        unsigned long r15;
        unsigned long r14;
        unsigned long r13;
@@ -59,31 +58,54 @@ struct registers {
        unsigned long rdi;
        unsigned long rbx;
        unsigned long rax;
+       unsigned long rflags;
        unsigned long rsp;
 };
 
 #define save_registers(regsptr) \
-       if(ust_reg_stack_ptr == NULL) { \
-               ust_reg_stack_ptr = (long*)((long)ust_reg_stack)+500; \
-       } \
        asm volatile ( \
             /* save original rsp */ \
             "pushq %%rsp\n\t" \
+            /* push original rflags */ \
+            "pushfq\n\t" \
              /* rax will hold the ptr to the private stack bottom */ \
             "pushq %%rax\n\t" \
             /* rbx will be used to temporarily hold the stack bottom addr */ \
             "pushq %%rbx\n\t" \
             /* rdi is the input to __tls_get_addr, and also a temp var */ \
             "pushq %%rdi\n\t" \
-            /* Start TLS access of private reg stack */ \
+            /* Start TLS access of private reg stack pointer */ \
             ".byte 0x66\n\t" \
             "leaq ust_reg_stack_ptr@tlsgd(%%rip), %%rdi\n\t" \
             ".word 0x6666\n\t" \
             "rex64\n\t" \
             "call __tls_get_addr@plt\n\t" \
             /* --- End TLS access */ \
+            /* check if ust_reg_stack_ptr has been initialized */ \
+            "movq (%%rax),%%rbx\n\t" \
+            "testq %%rbx,%%rbx\n\t" \
+            "jne 1f\n\t" \
+            "movq %%rax,%%rbx\n\t" \
+            /* Start TLS access of private reg stack */ \
+            ".byte 0x66\n\t" \
+            "leaq ust_reg_stack@tlsgd(%%rip), %%rdi\n\t" \
+            ".word 0x6666\n\t" \
+            "rex64\n\t" \
+            "call __tls_get_addr@plt\n\t" \
+            /* --- End TLS access */ \
+            "addq $500,%%rax\n\t" \
+            "movq %%rax,(%%rbx)\n\t" \
+            "movq %%rbx,%%rax\n\t" \
+            /* now the pointer to the private stack is in rax.
+               must add stack size so the ptr points to the stack bottom. */ \
+       "1:\n\t" \
             /* Manually push rsp to private stack */ \
             "addq $-8,(%%rax)\n\t" \
+            "movq 32(%%rsp), %%rdi\n\t" \
+            "movq (%%rax), %%rbx\n\t" \
+            "movq %%rdi, (%%rbx)\n\t" \
+            /* Manually push eflags to private stack */ \
+            "addq $-8,(%%rax)\n\t" \
             "movq 24(%%rsp), %%rdi\n\t" \
             "movq (%%rax), %%rbx\n\t" \
             "movq %%rdi, (%%rbx)\n\t" \
@@ -143,11 +165,6 @@ struct registers {
             "addq $-8,(%%rax)\n\t" \
             "movq (%%rax), %%rbx\n\t" \
             "movq %%r15,(%%rbx)\n\t" \
-            /* deal with rflags */ \
-            "pushfq\n\t" /* push rflags on stack */ \
-            "addq $-8,(%%rax)\n\t" \
-            "movq (%%rax), %%rbx\n\t" \
-            "popq (%%rbx)\n\t" \
             /* push cs */ \
             "addq $-2,(%%rax)\n\t" \
             "movq (%%rax), %%rbx\n\t" \
@@ -164,6 +181,8 @@ struct registers {
             "popq %%rax\n\t" \
             /* cancel push of rsp */ \
             "addq $8,%%rsp\n\t" \
+            /* cancel push of rflags */ \
+            "addq $8,%%rsp\n\t" \
             ::); \
        memcpy(regsptr, (void *)ust_reg_stack_ptr, sizeof(struct registers)); \
        ust_reg_stack_ptr = (void *)(((long)ust_reg_stack_ptr) + sizeof(struct registers));