source: trunk/libs/newlib/src/libgloss/arm/trap.S @ 478

Last change on this file since 478 was 444, checked in by satin@…, 6 years ago

add newlib,libalmos-mkh, restructure shared_syscalls.h and mini-libc

File size: 4.9 KB
Line 
1#include "arm.h"
2        /* Run-time exception support */
3#ifndef PREFER_THUMB
4#include "swi.h"
5
6/* .text is used instead of .section .text so it works with arm-aout too.  */
7        .text
8        .align 0
9        .global __rt_stkovf_split_big
10        .global __rt_stkovf_split_small
11
12/* The following functions are provided for software stack checking.
13   If hardware stack-checking is being used then the code can be
14   compiled without the PCS entry checks, and simply rely on VM
15   management to extend the stack for a thread.
16
17   The stack extension event occurs when the PCS function entry code
18   would result in a stack-pointer beneath the stack-limit register
19   value.  The system relies on the following map:
20
21        +-----------------------------------+ <-- end of stack block
22        | ...                               |
23        | ...                               |
24        | active stack                      |
25        | ...                               | <-- sp (stack-pointer) somewhere in here
26        | ...                               |
27        +-----------------------------------+ <-- sl (stack-limit)
28        | stack-extension handler workspace |
29        +-----------------------------------+ <-- base of stack block
30
31   The "stack-extension handler workspace" is an amount of memory in
32   which the stack overflow support code must execute.  It must be
33   large enough to deal with the worst case path through the extension
34   code.  At the moment the compiler expects this to be AT LEAST
35   256bytes.  It uses this fact to code functions with small local
36   data usage within the overflow space.
37
38   In a true target environment We may need to increase the space
39   between sl and the true limit to allow for the stack extension
40   code, SWI handlers and for undefined instruction handlers of the
41   target environment.  */
42
43__rt_stkovf_split_small:
44        mov     ip,sp   @ Ensure we can calculate the stack required
45        @ and fall through to...
46__rt_stkovf_split_big:
47        @ in:   sp = current stack-pointer (beneath stack-limit)
48        @       sl = current stack-limit
49        @       ip = low stack point we require for the current function
50        @       lr = return address into the current function
51        @       fp = frame-pointer
52        @               original sp --> +----------------------------------+
53        @                               | pc (12 ahead of PCS entry store) |
54        @               current fp ---> +----------------------------------+
55        @                               | lr (on entry) pc (on exit)       |
56        @                               +----------------------------------+
57        @                               | sp ("original sp" on entry)      |
58        @                               +----------------------------------+
59        @                               | fp (on entry to function)        |
60        @                               +----------------------------------+
61        @                               |                                  |
62        @                               | ..argument and work registers..  |
63        @                               |                                  |
64        @               current sp ---> +----------------------------------+
65        @
66        @ The "current sl" is somewhere between "original sp" and "current sp"
67        @ but above "true sl". The "current sl" should be at least 256bytes
68        @ above the "true sl". The 256byte stack guard should be large enough
69        @ to deal with the worst case function entry stacking (160bytes) plus
70        @ the stack overflow handler stacking requirements, plus the stack
71        @ required for the memory allocation routines.
72        @
73        @ Normal PCS entry (before stack overflow check) can stack 16
74        @ standard registers (64bytes) and 8 floating point registers
75        @ (96bytes). This gives a minimum stack guard of 160bytes (excluding
76        @ the stack required for the code). (Actually only a maximum of
77        @ 14standard registers are ever stacked on entry to a function).
78        @
79        @ NOTE: Structure returns are performed by the caller allocating a
80        @       dummy space on the stack and passing in a "phantom" arg1 into
81        @       the function. This means that we do not need to worry about
82        @       preserving the stack under "sp" even on function return.
83        @
84        @        Code should never poke values beneath sp. The sp register
85        @        should always be "dropped" first to cover the data. This
86        @        protects the data against any events that may try and use
87        @        the stack.
88
89        SUB     ip, sp, ip      @ extra stack required for function
90        @ Add stack extension code here.  If desired a new stack chunk
91        @ can be allocated, and the register state updated suitably.
92
93        @ We now know how much extra stack the function requires.
94        @ Terminate the program for the moment:
95        swi     SWI_Exit
96#endif
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