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

XENIX Programming adb: Program Debugger
Validating Addresses
Whenever you use an address in a command, adb checks the address to make sure it is
valid. adb uses the segment number, file position, and size values in each map entry to
validate the addresses. If an address is correct, adb carries out the command;
otherwise, it displays an error message.
The first step adb takes when validating an address is to check the segment value to
make sure it belongs to the appropriate map. Segments used with the ? command must
appear in the text segments map; segments used with the I command must appear in the
data segments map. If the value does not belong to the map, adb displays a bad segment
error.
The next step is to check the offset to see if it is in range. The offset must be within
the range
0 < = offset < = segment-size
If it is not in this range, adb displays a bad address error.
If adb is currently accessing memory, the validating segment and offset are used to
access a memory location and no other processing takes place. If adb is accessing files,
it computes an effective file address as follows:
effective-fi le-address = offset + fi le-position
then uses this effective address to read from the corresponding file.
Miscellaneous Features
The following sections explain how to use a number of useful miscellaneous commands
and features of adb.
Combining Comma nds on a Single Line
You can give more than one command on a line by separating the commands with a
semicolon (;). The com mands are performed one at a time, starting at the left. Changes
to the current address and format are carried to the next command. If an error occurs,
the remaining commands are ignored.
One typical combination is to place a ? command after an 1 command. For example,
the commands
?I 'Th'; ?s
search for and display a string that begins with the characters "Th".
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