[haiku-bugs] Re: [Haiku] #10509: Stack is not aligned
- From: "pulkomandy" <trac@xxxxxxxxxxxx>
- Date: Mon, 17 Feb 2014 19:00:50 -0000
#10509: Stack is not aligned
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Reporter: pulkomandy | Owner: axeld
Type: enhancement | Status: new
Priority: normal | Milestone: R1/alpha5
Component: System/Kernel | Version: R1/Development
Resolution: | Keywords:
Blocked By: | Blocking:
Has a Patch: 0 | Platform: x86
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Comment (by pulkomandy):
Sorry, I'm not too familiar with this code. Modifying
{{{arch_randomize_stack_pointer}}} is ok. However, in
{{{arch_thread_enter_userspace}}}, the stackTop is decremented by12
already, as the "args" are pushed on the stack. Wouldn't that break the
alignment?
In the current code, it means we get {{{stackTop % 16 == 4}}}, and
modifying {{{arch_randomize_stack_pointer}}} to substract 4 from the
aligned value would lead to {{{stackTop % 16 == 0}}} after the push. Still
not what we want. If I change {{{arch_randomize_stack_pointer}}} so the
alignment gets correct after the push, then get_signal_stack, which
doesn't appear to push anything, would be misaligned.
I'm not sure how to adjust the stack size, either. Callers use
{{{thread->signal_stack_size}}} and {{{thread->signal_stack_base}}}, and
the respective {{{user_}}} fields. These are allocated in
{{{create_thread_user_stack}}}, and may even be provided by the user. Is
it needed to increase the stack size there, or is it acceptable to lose
some bytes because of the alignment without adjusting it?
--
Ticket URL: <https://dev.haiku-os.org/ticket/10509#comment:5>
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