[haiku-bugs] Re: [Haiku] #10509: Stack is not aligned
- From: "bonefish" <trac@xxxxxxxxxxxx>
- Date: Thu, 06 Feb 2014 14:09:21 -0000
#10509: Stack is not aligned
-----------------------------+----------------------------
Reporter: pulkomandy | Owner: axeld
Type: enhancement | Status: new
Priority: normal | Milestone: Unscheduled
Component: System/Kernel | Version: R1/Development
Resolution: | Keywords:
Blocked By: | Blocking:
Has a Patch: 0 | Platform: x86
-----------------------------+----------------------------
Changes (by bonefish):
* owner: nobody => axeld
* component: System => System/Kernel
Comment:
The initial stack for a new thread is set up in the architecture specific
kernel function `arch_thread_enter_userspace()` ([http://cgit.haiku-
os.org/haiku/tree/src/system/kernel/arch/x86/32/thread.cpp#n217 x86],
[http://cgit.haiku-
os.org/haiku/tree/src/system/kernel/arch/x86/64/thread.cpp#n214 x86-64]).
All that has to be done is align the value of `stackTop` to 16 and offset
it as necessary (note, the stack grows downward, so the address must only
be decreased).
I considered doing that already, but it hadn't been clear to me what that
offset should be. According to the crash report the `movaps` instruction
tries to access 0xffffff48(%ebp), which, I suppose, means that for x86 ebp
(the stack frame pointer) should be offset by 8, which means that for the
initial stack pointer (esp) `esp % 16 == 12` should hold (due to `ebp =
esp - 4`). The `main()` prologue gcc generates seems to agree:
{{{
1ad5: 8d 4c 24 04 lea 0x4(%esp),%ecx
1ad9: 83 e4 f0 and $0xfffffff0,%esp
1adc: ff 71 fc pushl -0x4(%ecx)
1adf: 55 push %ebp
1ae0: 89 e5 mov %esp,%ebp
}}}
I think the best way to implement that is by having
`arch_randomize_stack_pointer()` enforce that property and change all
callers (namely `arch_thread_enter_userspace()` and `get_signal_stack()`)
to supply an address that has already been adjusted to make the needed
room on the stack.
--
Ticket URL: <https://dev.haiku-os.org/ticket/10509#comment:3>
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