大型机汇编HLASM调试工具XDC及基本概念理解之一 内存保护
背景：今天翻看了多年前做过的大型机汇编项目，后来因为中美关系此项目就中断了。但在学习过程中有很多总结发布出来，希望对还在做这种项目的人有点帮助（很有可能全国都没几个了，大型机+汇编都是冷门）。
1. 0S 表示protection key==0, s表示store-protected
2. 0f: protection key为0, fetch-protected
3. CQM#MAIN创建的DUMMY SDA, protection key==7
Storage Protect Key Display
The DISPLAY command shows the storage protection key as a single hexadecimal digit
appearing to the right of the address/offset field, running down the entirety of
the display. If the storage area is fetch-protected, then the letter f is displayed
next to the storage key. If the storage area is store-protected, then the letter s
is displayed next to the fetch-protected indicator.
The "store-protected" indicator, s, is displayed whenever z/XDC detects that the
storage being displayed has one or another of the following special protections:
- Low Address Protection (LAP): This is a special kind of protection that the
Operating System uses to specifically protect the first 512 bytes of both real
and virtual storage. It prevents the storage from being altered by any program,
regardless of that program's state or key. (LAP does not apply to data space
storage.)
- Page Protection: This is a kind of protection that applies to the following
areas of storage:
- The Pageable Link Pack Area (PLPA)
- The read-only areas of the System Nucleus (IEASYS0x)
- Any area of storage that has been set to "read-only" by the PGSER or
IARVSERV macros.
When a page of storage has been marked as being "read-only", that storage
cannot be directly altered by any program, regardless of that program's state
or key. (Note, "Page Protection" does not apply to real storage. Thus, it
cannot protect a virtual storage page when that page is accessed via its real
address.)
- Access List Entry Protection: When an address space or a data space is accessed
via an ALET that "points to" an Access List Entry (ALE) having its "fetch only"
flag on, then accesses via that ALE are store protected. Note, accesses to that
same space via a different ALE might not be store protected.