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Diffstat (limited to 'c/src/lib/libbsp/arm/armulator/startup/trap.S')
| -rw-r--r-- | c/src/lib/libbsp/arm/armulator/startup/trap.S | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/c/src/lib/libbsp/arm/armulator/startup/trap.S b/c/src/lib/libbsp/arm/armulator/startup/trap.S new file mode 100644 index 0000000000..328fabca5c --- /dev/null +++ b/c/src/lib/libbsp/arm/armulator/startup/trap.S @@ -0,0 +1,93 @@ + /* Run-time exception support */ +#include "swi.h" + +/* .text is used instead of .section .text so it works with arm-aout too. */ + .text + .align 0 + .global __rt_stkovf_split_big + .global __rt_stkovf_split_small + +/* The following functions are provided for software stack checking. + If hardware stack-checking is being used then the code can be + compiled without the PCS entry checks, and simply rely on VM + management to extend the stack for a thread. + + The stack extension event occurs when the PCS function entry code + would result in a stack-pointer beneath the stack-limit register + value. The system relies on the following map: + + +-----------------------------------+ <-- end of stack block + | ... | + | ... | + | active stack | + | ... | <-- sp (stack-pointer) somewhere in here + | ... | + +-----------------------------------+ <-- sl (stack-limit) + | stack-extension handler workspace | + +-----------------------------------+ <-- base of stack block + + The "stack-extension handler workspace" is an amount of memory in + which the stack overflow support code must execute. It must be + large enough to deal with the worst case path through the extension + code. At the moment the compiler expects this to be AT LEAST + 256bytes. It uses this fact to code functions with small local + data usage within the overflow space. + + In a true target environment We may need to increase the space + between sl and the true limit to allow for the stack extension + code, SWI handlers and for undefined instruction handlers of the + target environment. */ + +__rt_stkovf_split_small: + mov ip,sp @ Ensure we can calculate the stack required + @ and fall through to... +__rt_stkovf_split_big: + @ in: sp = current stack-pointer (beneath stack-limit) + @ sl = current stack-limit + @ ip = low stack point we require for the current function + @ lr = return address into the current function + @ fp = frame-pointer + @ original sp --> +----------------------------------+ + @ | pc (12 ahead of PCS entry store) | + @ current fp ---> +----------------------------------+ + @ | lr (on entry) pc (on exit) | + @ +----------------------------------+ + @ | sp ("original sp" on entry) | + @ +----------------------------------+ + @ | fp (on entry to function) | + @ +----------------------------------+ + @ | | + @ | ..argument and work registers.. | + @ | | + @ current sp ---> +----------------------------------+ + @ + @ The "current sl" is somewhere between "original sp" and "current sp" + @ but above "true sl". The "current sl" should be at least 256bytes + @ above the "true sl". The 256byte stack guard should be large enough + @ to deal with the worst case function entry stacking (160bytes) plus + @ the stack overflow handler stacking requirements, plus the stack + @ required for the memory allocation routines. + @ + @ Normal PCS entry (before stack overflow check) can stack 16 + @ standard registers (64bytes) and 8 floating point registers + @ (96bytes). This gives a minimum stack guard of 160bytes (excluding + @ the stack required for the code). (Actually only a maximum of + @ 14standard registers are ever stacked on entry to a function). + @ + @ NOTE: Structure returns are performed by the caller allocating a + @ dummy space on the stack and passing in a "phantom" arg1 into + @ the function. This means that we do not need to worry about + @ preserving the stack under "sp" even on function return. + @ + @ Code should never poke values beneath sp. The sp register + @ should always be "dropped" first to cover the data. This + @ protects the data against any events that may try and use + @ the stack. + + SUB ip, sp, ip @ extra stack required for function + @ Add stack extension code here. If desired a new stack chunk + @ can be allocated, and the register state updated suitably. + + @ We now know how much extra stack the function requires. + @ Terminate the program for the moment: + swi SWI_Exit |