[Bug 14231] New: not_const_pp is causing memory reorder in clang without lto

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=14231

            Bug ID: 14231
           Summary: not_const_pp is causing memory reorder in clang
                    without lto
           Product: Busybox
           Version: 1.33.x
          Hardware: Other
                OS: Other
            Status: NEW
          Severity: critical
          Priority: P5
         Component: Standard Compliance
          Assignee: unassigned at busybox.net
          Reporter: shana at zju.edu.cn
                CC: busybox-cvs at busybox.net
  Target Milestone: ---

In ash.c, there's `not_const_pp` which converts a const pointer to non-const
one. However, this will cause memory reorder and leads to SIGSEV.

Here's the instruction after compiled init_G from ash.c:


    0x491624 <+32>:   bl     0x4472d4                  ; xzalloc at
xfuncs_printf.c:70
    0x491628 <+36>:   bl     0x49e070                  ; OUTLINED_FUNCTION_1
    0x49162c <+40>:   mov    w9, #-0x1
    0x491630 <+44>:   ldr    x21, [x8]
    0x491634 <+48>:   str    x0, [x8]
    0x491638 <+52>:   add    x8, x21, #0x54            ; =0x54
->  0x49163c <+56>:   stp    x8, x8, [x21, #0x20] ;<--- crash point

Here, x8 is the register that stores the addr of `ash_ptr_to_globals_misc`.
It's loaded first to x21 and then store from x0. And thus the reset instruction
crashed since x21 is 0 (addr of `ash_ptr_to_globals_misc` before assigned by
`xzalloc`).

I think the key problem is that in clang 9+, `not_const_pp` has a workaround
that breaks the memory dependency and thus the compiler reorders the memory.

-- 
You are receiving this mail because:
You are on the CC list for the bug.