[PATCH] D60039: Fix the bug of garbage collection of siod.

Mon Apr 1 18:24:08 PDT 2019

LuoYuanke added a comment.

In D60039#1450808 <https://reviews.llvm.org/D60039#1450808>, @craig.topper wrote:

> Are sure RBP isn't in the jmp buffer? There's a macro used by setjmp called PTR_MANGLE that can xor the pointer with another variable which can obscure the value. It gets xored again in longjmp to demangle it. But in either case its not a good idea to examine the contents of jmp_buf so I think this is the right fix.

Yes. I'm sure. There is two evidence that shows rbp is not saved in jmp buffer on my machine. First I set a breakpoint before calling setjmp and dump the register in gdb. After calling setjmp, I also dump the memory of jmp buffer and it shows the rbp value is not saved in jmp buffer. Second I disassemble the setjmp code as below and there is no code to save rbp in jmp buffer. Also when app fails, the failed object pointer is the same value of rbp which shows in gdb before setjmp.

  Breakpoint 1, 0x00007ffff6f94040 in _setjmp () from /lib64/libc.so.6
  Missing separate debuginfos, use: debuginfo-install glibc-2.17-196.el7.x86_64
  (gdb) disassemble
  Dump of assembler code for function _setjmp:
  => 0x00007ffff6f94040 <+0>:     xor    %esi,%esi
     0x00007ffff6f94042 <+2>:     jmpq   0x7ffff6f93fa0 <__sigsetjmp>
  End of assembler dump.
  (gdb) disassemble __sigsetjmp
  Dump of assembler code for function __sigsetjmp:
     0x00007ffff6f93fa0 <+0>:     mov    %rbx,(%rdi)
     0x00007ffff6f93fa3 <+3>:     mov    %rbp,%rax
     0x00007ffff6f93fa6 <+6>:     xor    %fs:0x30,%rax
     0x00007ffff6f93faf <+15>:    rol    $0x11,%rax
     0x00007ffff6f93fb3 <+19>:    mov    %rax,0x8(%rdi)
     0x00007ffff6f93fb7 <+23>:    mov    %r12,0x10(%rdi)
     0x00007ffff6f93fbb <+27>:    mov    %r13,0x18(%rdi)
     0x00007ffff6f93fbf <+31>:    mov    %r14,0x20(%rdi)
     0x00007ffff6f93fc3 <+35>:    mov    %r15,0x28(%rdi)
     0x00007ffff6f93fc7 <+39>:    lea    0x8(%rsp),%rdx
     0x00007ffff6f93fcc <+44>:    xor    %fs:0x30,%rdx
     0x00007ffff6f93fd5 <+53>:    rol    $0x11,%rdx
     0x00007ffff6f93fd9 <+57>:    mov    %rdx,0x30(%rdi)
     0x00007ffff6f93fdd <+61>:    mov    (%rsp),%rax
     0x00007ffff6f93fe1 <+65>:    nop
     0x00007ffff6f93fe2 <+66>:    xor    %fs:0x30,%rax
     0x00007ffff6f93feb <+75>:    rol    $0x11,%rax
     0x00007ffff6f93fef <+79>:    mov    %rax,0x38(%rdi)
     0x00007ffff6f93ff3 <+83>:    jmpq   0x7ffff6f94000 <__sigjmp_save>

  (gdb) disassemble __sigjmp_save
  Dump of assembler code for function __sigjmp_save:
     0x00007ffff6f94000 <+0>:     xor    %eax,%eax
     0x00007ffff6f94002 <+2>:     test   %esi,%esi
     0x00007ffff6f94004 <+4>:     push   %rbx
     0x00007ffff6f94005 <+5>:     mov    %rdi,%rbx
     0x00007ffff6f94008 <+8>:     je     0x7ffff6f9401f <__sigjmp_save+31>
     0x00007ffff6f9400a <+10>:    lea    0x48(%rdi),%rdx
     0x00007ffff6f9400e <+14>:    xor    %esi,%esi
     0x00007ffff6f94010 <+16>:    xor    %edi,%edi
     0x00007ffff6f94012 <+18>:    callq  0x7ffff6f94490 <sigprocmask>
     0x00007ffff6f94017 <+23>:    test   %eax,%eax
     0x00007ffff6f94019 <+25>:    sete   %al
     0x00007ffff6f9401c <+28>:    movzbl %al,%eax
     0x00007ffff6f9401f <+31>:    mov    %eax,0x40(%rbx)
     0x00007ffff6f94022 <+34>:    xor    %eax,%eax
     0x00007ffff6f94024 <+36>:    pop    %rbx
     0x00007ffff6f94025 <+37>:    retq
  End of assembler dump.

Repository:
  rT test-suite

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D60039/new/

https://reviews.llvm.org/D60039