[TSan] Improve handling of stack pointer mangling in {set,long}jmp, pt.4

[yln]

Summary

Since we don't clobber %rsi (2nd argument) anymore, we don't have to
save/restore it.

[dvyukov]

Nice!

[yln]

I reverted this, because we are doing a call (%rsi is not a preserved register), so of course we have to save/restore it (even if we don't clobber it ourselves).

compiler-rt/lib/tsan/rtl/tsan_rtl_amd64.S

 ASM_TYPE_FUNCTION(ASM_SYMBOL_INTERCEPTOR(sigsetjmp))
 ASM_SYMBOL_INTERCEPTOR(sigsetjmp):
 #endif
   CFI_STARTPROC
   // save env parameter
   push %rdi
   CFI_ADJUST_CFA_OFFSET(8)
   CFI_REL_OFFSET(%rdi, 0)
-  // save savesigs parameter
-  push %rsi
-  CFI_ADJUST_CFA_OFFSET(8)
-  CFI_REL_OFFSET(%rsi, 0)
-  // align stack frame
-  sub $8, %rsp
-  CFI_ADJUST_CFA_OFFSET(8)
   // obtain SP, store in %rdi, first argument to `void __tsan_setjmp(uptr sp)`
 #if defined(__FreeBSD__) || defined(__NetBSD__)
-  lea 24(%rsp), %rdi
+  lea 8(%rsp), %rdi
 #elif defined(__linux__) || defined(__APPLE__)
-  lea 32(%rsp), %rdi
+  lea 16(%rsp), %rdi
 #else
 # error "Unknown platform"
 #endif
   // call tsan interceptor
   call ASM_SYMBOL(__tsan_setjmp)
-  // unalign stack frame
-  add $8, %rsp
-  CFI_ADJUST_CFA_OFFSET(-8)
-  // restore savesigs parameter
-  pop %rsi
-  CFI_ADJUST_CFA_OFFSET(-8)
-  CFI_RESTORE(%rsi)
   // restore env parameter
   pop %rdi
   CFI_ADJUST_CFA_OFFSET(-8)
   CFI_RESTORE(%rdi)
   // tail jump to libc sigsetjmp
   movl $0, %eax
 #if defined(__NetBSD__)
   movq _ZN14__interception18real___sigsetjmp14E@GOTPCREL(%rip), %rdx

 .globl ASM_SYMBOL_INTERCEPTOR(__sigsetjmp)
 ASM_TYPE_FUNCTION(ASM_SYMBOL_INTERCEPTOR(__sigsetjmp))
 ASM_SYMBOL_INTERCEPTOR(__sigsetjmp):
   CFI_STARTPROC
   // save env parameter
   push %rdi
   CFI_ADJUST_CFA_OFFSET(8)
   CFI_REL_OFFSET(%rdi, 0)
-  // save savesigs parameter
-  push %rsi
-  CFI_ADJUST_CFA_OFFSET(8)
-  CFI_REL_OFFSET(%rsi, 0)
-  // align stack frame
-  sub $8, %rsp
-  CFI_ADJUST_CFA_OFFSET(8)
   // obtain SP, store in %rdi, first argument to `void __tsan_setjmp(uptr sp)`
 #if defined(__FreeBSD__)
-  lea 24(%rsp), %rdi
+  lea 8(%rsp), %rdi
 #else
-  lea 32(%rsp), %rdi
+  lea 16(%rsp), %rdi
 #endif
   // call tsan interceptor
   call ASM_SYMBOL(__tsan_setjmp)
-  // unalign stack frame
-  add $8, %rsp
-  CFI_ADJUST_CFA_OFFSET(-8)
-  // restore savesigs parameter
-  pop %rsi
-  CFI_ADJUST_CFA_OFFSET(-8)
-  CFI_RESTORE(%rsi)
   // restore env parameter
   pop %rdi
   CFI_ADJUST_CFA_OFFSET(-8)
   CFI_RESTORE(%rdi)
   // tail jump to libc sigsetjmp
   movl $0, %eax
   movq _ZN14__interception16real___sigsetjmpE@GOTPCREL(%rip), %rdx
   jmp *(%rdx)
   CFI_ENDPROC
 ASM_SIZE(ASM_SYMBOL_INTERCEPTOR(__sigsetjmp))
 #endif  // !defined(__APPLE__) && !defined(__NetBSD__)
 
 NO_EXEC_STACK_DIRECTIVE
 
 #endif