README
1Introduction
2
3This document covers the native NetBSD compiler runtime.
4
5Machine independent sources can be found in common. The crtbegin.c in
6that directory is a useful template for deriving compact assembler
7versions. That is preferable to decouple the result from changes in the
8compiler logic.
9
10A new platform should provide the following content in
11arch/${MACHINE_ARCH} or arch/${MACHINE_CPU}:
12- Makefile.inc: provides ELFSIZE corresponding to 32/64bit file format.
13 If using the common C code instead of crtbegin.S also provide a -I option
14 to find crtbegin.h in your arch subdir.
15- crt0.S: provides setup code and the call to ___start.
16- crtbegin.S or crtbegin.h: see below
17- crtend.S: see below, most likely just a copy of an existing architecture
18- crti.S: prefix part of .init/.fini sections, i.e. to ensure stack alignment
19- crtn.S: suffix part of the .init/.fini sections, i.e. return to caller.
20
21
22Overview of the common runtime support
23
24The common runtime support contains two modules, crtbegin and crtend.
25crtbegin is linked before all other object files of the program or
26dynamic library, crtend after all other object files. They frame the
27lists of constructors, destructors, Java types and exception handling frames.
28
29If done correctly, crtend contains no code and is therefore position
30independent. crtendS.o is therefore just a link to crtend.o.
31
32crtbegin should be position-independent code. crtbeginT.o doesn't have
33to be PIC as it is statically linked. The overhead is generally not
34worth the trouble though.
35
36
37Section types:
38.ctor: writeable
39.dtor: writeable
40.eh_frame: read-only if platform allows mixing read-only and read-write
41sections. This is supported by GNU ld.
42.jcr: writeable
43.init: executable
44.fini: executable
45
46
47Non-local symbols:
48
49Weak references:
50- _Jv_RegisterClasses,
51- __cxa_finalize (crtbeginS.o)
52- __deregister_frame_info
53- __register_frame_info
54
55Hidden:
56- __dso_handle: pointer to self for crtbeginS.o, NULL otherwise.
57- __CTOR_LIST_END__
58
59
60Initialisation (called from .init):
61
621. Check that the init code hasn't started already, otherwise bail out.
632. If __register_frame_info is NULL, skip to 4
643. Call __register_frame_info with start of .eh_frame as first argument
65 and a data object of at least 8 pointers as second argument.
664: If _Jv_RegisterClasses is NULL, skip to 6
675: Call _Jv_RegisterClasses with the first pointer of the .jcr section
68 as argument.
696: Iterate from the end of the .ctor section to the start. Skip the
70 terminating NULL and stop when reaching the starting (void *)-1 element.
71 Call the pointers as void (*)(void) functions.
72
73
74Deinitialisation (called from .fini):
75
761. Check if the init code has already started, otherwise bail out.
772. If this is not crtbeginS.o or __cxa_finalize is NULL, skip to 4.
783. Call __cxa_finalize with a pointer into this Dynamic Shared Object (DSO)
79 as first argument.
804. Iterate from the start of the .dtor section to the send. Skip the
81 initial (void *)-1 and stop when reaching the terminating NULL element.
82 Call the pointers as void (*)(void) functions.
835. If __deregister_frame_info is NULL, return.
846. Call __deregister_frame_info with the start of .eh_frame as the argument.
85
86
87Since most of this can easily be done in C code, instead of providing a
88crtbegin.S you can also chose to use the generic C implementation. Provide
89a crtbegin.h file instead of crtbegin.S. In there put inline assembler
90stubs (mostly copied from some other arch) and implement calls to the
91helper functions __do_global_ctors_aux/__do_global_dtors_aux.
92