94 lines
4.9 KiB
ArmAsm
94 lines
4.9 KiB
ArmAsm
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/* Run-time exception support */
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#include "swi.h"
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/* .text is used instead of .section .text so it works with arm-aout too. */
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.text
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.align 0
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.global __rt_stkovf_split_big
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.global __rt_stkovf_split_small
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/* The following functions are provided for software stack checking.
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If hardware stack-checking is being used then the code can be
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compiled without the PCS entry checks, and simply rely on VM
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management to extend the stack for a thread.
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The stack extension event occurs when the PCS function entry code
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would result in a stack-pointer beneath the stack-limit register
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value. The system relies on the following map:
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+-----------------------------------+ <-- end of stack block
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| ... |
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| ... |
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| active stack |
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| ... | <-- sp (stack-pointer) somewhere in here
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| ... |
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+-----------------------------------+ <-- sl (stack-limit)
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| stack-extension handler workspace |
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+-----------------------------------+ <-- base of stack block
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The "stack-extension handler workspace" is an amount of memory in
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which the stack overflow support code must execute. It must be
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large enough to deal with the worst case path through the extension
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code. At the moment the compiler expects this to be AT LEAST
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256bytes. It uses this fact to code functions with small local
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data usage within the overflow space.
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In a true target environment We may need to increase the space
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between sl and the true limit to allow for the stack extension
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code, SWI handlers and for undefined instruction handlers of the
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target environment. */
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__rt_stkovf_split_small:
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mov ip,sp @ Ensure we can calculate the stack required
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@ and fall through to...
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__rt_stkovf_split_big:
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@ in: sp = current stack-pointer (beneath stack-limit)
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@ sl = current stack-limit
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@ ip = low stack point we require for the current function
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@ lr = return address into the current function
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@ fp = frame-pointer
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@ original sp --> +----------------------------------+
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@ | pc (12 ahead of PCS entry store) |
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@ current fp ---> +----------------------------------+
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@ | lr (on entry) pc (on exit) |
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@ +----------------------------------+
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@ | sp ("original sp" on entry) |
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@ +----------------------------------+
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@ | fp (on entry to function) |
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@ +----------------------------------+
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@ | |
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@ | ..argument and work registers.. |
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@ | |
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@ current sp ---> +----------------------------------+
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@
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@ The "current sl" is somewhere between "original sp" and "current sp"
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@ but above "true sl". The "current sl" should be at least 256bytes
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@ above the "true sl". The 256byte stack guard should be large enough
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@ to deal with the worst case function entry stacking (160bytes) plus
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@ the stack overflow handler stacking requirements, plus the stack
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@ required for the memory allocation routines.
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@
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@ Normal PCS entry (before stack overflow check) can stack 16
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@ standard registers (64bytes) and 8 floating point registers
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@ (96bytes). This gives a minimum stack guard of 160bytes (excluding
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@ the stack required for the code). (Actually only a maximum of
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@ 14standard registers are ever stacked on entry to a function).
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@
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@ NOTE: Structure returns are performed by the caller allocating a
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@ dummy space on the stack and passing in a "phantom" arg1 into
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@ the function. This means that we do not need to worry about
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@ preserving the stack under "sp" even on function return.
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@
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@ Code should never poke values beneath sp. The sp register
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@ should always be "dropped" first to cover the data. This
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@ protects the data against any events that may try and use
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@ the stack.
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SUB ip, sp, ip @ extra stack required for function
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@ Add stack extension code here. If desired a new stack chunk
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@ can be allocated, and the register state updated suitably.
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@ We now know how much extra stack the function requires.
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@ Terminate the program for the moment:
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swi SWI_Exit
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