Intel XENIX 286 Programmers Guide (86) - Tenox.tc

XENIX Programming Programming Commands
ad b (continued)
Variables
adb provides a number of variables. Named variables are set initially by adb but are not
used subsequently. Numbered variables are reserved for communication as follows.
0 The last value printed.
1 The last offset part of an instruction source.
2 The previous value of variable 1.
On entry, the following are set from the system header in the core file. If corefile does
not appear to be a core file then these values are set from objfil:
d The data segment size.
e The entry point.
m The execution type.
n The number of segments.
t The text segment size.
Addresses
Addresses in adb refer to either a location in a file or in actual memory. When there is
no current process in memory, adb addresses are computed as file locations, and
requested text and data are read from the objfil and corefile files. When there is a
process, such as after a :r command, addresses are computed as actual memory
locations.
All text and data segments in a program have associated memory map entries. Each
entry has a unique segment number. In addition, each entry has the file position of that
segment's first byte and the physical size of the segment in the file. When a process is
running, a segment's entry has a virtual size that defines the size of the segment in
memory at the current time. This size can change during execution.
When an address is given and no process is running, the file location corresponding to the
address is calculated as
effective-file-address = file-position + offset
If a process is running, the memory location is simply the offset in the given segment.
These addresses are valid if and only if
0 < = offset < = size
where size is physical size for file locations and virtual size for memory locations.
Otherwise, the requested address is not legal.
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