Memory Protection

From SpareMiNT Wiki

Memory protection works on a per-process basis. Unless it uses the specialmode bits in Mxalloc(), a process' entire text+data+bss and any memory it allocates will be of the same type. There are four types of memory:

Private

This is the default protection mode and most programs works as intended in this mode. In this mode the program's memory space is under a very restrictive protection: No one can access the area taken by the program, except the program itself and the operating system. Even interrupt handlers, if any are installed by the program, cannot do that.

Private/Readable

Here the protection is less restrictive: Still, noone can write to the program's area (except the program itself and the operating system), but everybody can safely read data from it. You should set this mode for GEM programs that use the AV protocol, but are not written with the memory protection in mind. ST Guide} is one of good (bad) examples here.

Super

The full name is "Supervisor accessible": The program's area can be accessed by noone (again, except the program itself and the operating system) as long as the "intruder" runs in the CPU user mode. However, any code running in the CPU supervisor mode (as an interrupt handler for example) can access the program's memory space freely. You should set this mode for software, that installs own interrupt handlers. The Dump!module player is a good example.

Global

This mode can be set, if a program does not run under any of the aforementioned protection modes. The program's space is unprotected and anyone can freely access it.

By default, all processes load into private memory. If a program terminates and remains resident with the Ptermres() system call, then its private memory will be converted to Super memory; that's because TSRs won't work in private memory.

Some TSRs may in fact need to be set to load into global memory (if they provide services for user mode programs). There are other programs which need to grant wider access to their memory space: for example, the Gulam CLI is one, because Gulam's children can call Gulam through a pointer found in the system variable space. But Gulam is a bad choice of shell anyway, because you can't run more than one of them. Current versions of STeno also must grant wider access, because it passes data to STalker using shared memory; private/readable is adequate for that.

Programs that load before MiNT does (i.e. in the AUTO folder) will find themselves in global memory. This is the easiest way to be sure that your TSRs will go on working: RAMdisks, FOLDR100, CACHE080, etc. all work when loaded that way.

Notice that a process can grant wider access to its own address space, but it can't change the access permissions of any other process' space. If you set the PRGFLAGS of some process so it loads into global memory, that doesn't mean it can access anybody else's memory, it just means that anybody can access ITS memory.

[edit] FreeMiNT Memory Protection Compatibility list

This list here is not complete. Fell free to update and correct it if something is wrong.

Program	Version	Flags	Reason / Comment
papyrus	7.0x demo	global	if you use OLGA inplace ext.
CAB	2.7 demo	global	if you use OLGA inplace ext.
amail	1.05	global	if you use OLGA inplace ext.
wdialog.prg	2.04	global	(coding)
st-guide	15	readable	(AV protocol)
finder	1.10	readable	(AV protocol)
RSC-View	1.00	readable	(AV protocol)
slay	0.1	readable	(AV protocol)
1st-guide	16.01.1997	readable	(AV protocol)
clock.acc	1.9e	readable	(AV protocol)

These programs seems to work without problems:

Program	Version	Reason / Comment
Thing	1.29	display broken AV clients(!)
CALAMUS SL	98 demo	nice :-)
CAT	4.10	also nice :-)
HDDriver	7.70	also older versions work fine
Diskus	3.61	also older versions work fine
SysInfo	4.50	also older versions work fine
BoxKite	2.13	also older versions work fine
CHKDSK	3.0	it's from ATARI
LHarc Shell	3.10
STZip	2.6
Esscode	6.4
MiNT-Setter	.6	nice FreeMiNT 1.15 tool
FSetter	0.6	nice FreeMiNT 1.15 tool
BreakOut	1.11	it's from ATARI
N.AES
all ported unix tools from F. Naumann
all supported software for FreeMiNT by F. Naumann		like fnramfs, MinixFS & tools, ext2fs & tools, mkfatfs
the MiNT system software		like MiNT-Net, NE2000.xif, GlueSTiK, xconout2.xdd, SPIN!, ...

This is a little outdated list: (feel free to clean up the text and enter better version)

Program	Version	Save	Responsible
7Up	2.32	no	Michael Thaenitz
Alert-Acc.		yes
ApplList	0.4	yes	dl1fdt@amsat.org
Artworx	1.4	no	Christian_Witt@n.maus.de
BoxKite	1.80	yes	Harald_Becker@k.maus.de
CAB	2.6	yes	Alexander_Claus@of2.maus.de
Chatwin	3.08b	yes	Dirk_Haun@lb.maus.de
Clix	3.60	no	Steffen_Engel@pe2.maus.de
Clock-Acc.	1.0	yes	W. Klaren
COPS	1.07	yes	Behne & Behne Systemsoftware GbR
Cypress	1.73	no
DirSort	1.1	yes	Christoph Zwerschke
Diskus	3.11	yes	us@bruker.de
E-Backup	2.01	yes
Everest	3.6D	yes	Oliver Schmidt
FED	1.70	yes
Fiffi	1.05	no	Juergen_Koneczny@m4.maus.de
Finder	1.10	no	Holger_Weets@ol.maus.de
freeBase	1.01	no	Holger_Weets@ol.maus.de
GEMar	3.06	no	Steffen_Engel@pe2.maus.de
GEM-Graph	1.0D	yes	ABC Software
GEMGS	5.10	yes	hristian_Felsch@hh.maus.de
Gemini	1.a	yes	jr@ms.maus.de
GEM-init	0.77	yes	U_Kaiser@t-online.de
GEMJing	1.06	yes
Interface	2.32	yes	Olaf Meisiek
yesnE	1.52	yes	Harald_Becker@k.maus.de
jinnee	1.0	yes	Manfred_Lippert@n.maus.de
Kandinsky	2.5	no	Ulrich Rossgoderer (1)
Les Yper Sound	0.1	yes	Dirk_Haun@lb.maus.de
lps.ttp	1.24	no	uereder@cip.informatik.uni-erlangen.de
MultiStrip	1.3	yes	tommi@linguistik.uni-erlangen.de
MStrip-Config	1.3	no	tommi@linguistik.uni-erlangen.de
MultiTex	5.2	yes
Newsie	0.69a	yes
no!Desk	3.04	no	no! (2)
NovaVDI	2.67	yes	Computerinsel
NVDI	4.11.8	yes	Behne & Behne Systemsoftware GbR
OLGA-Manager	1.3	yes	Thomas_Much@ka2.maus.de
OLGA-Tools	1.0	yes	Thomas_Much@ka2.maus.de
papyrus	5.11	no	R.O.M.
Phoenix	5.0	yes	Gebrueder Geiss/ASH
qed	4.5	yes	Christian_Felsch@hh.maus.de
RCS	2.1	no	ATARI Corp.
RCS	3.0	yes	ATARI Corp.
RSM	2.15	yes	A.Diedering@t-online.de
Scripter	r1	no	Holger_Weets@ol.maus.de
smurf	1.0	yes
SpeedUp	1.91a	yes	tommi@linguistik.uni-erlangen.de
ST-CAD	1.03	yes	MKrutz@t-online.de
Start Me Up!	7.02	yes	Thomas_Much@ka2.maus.de
SysInfo	4.30	yes	Thorsten_Bergner@b.maus.de
TeraDesk	1.01	yes	W. Klaren
TOSWIN2	2.2	yes	Christian_Felsch@hh.maus.de
TWSM/2	2.0	yes	tommi@linguistik.uni-erlangen.de
ZControl	0.24	yes	dl1fdt@amsat.org