debug-detection

Just trying out some ways to detect debugging from within a debugged program.

Currently, these checks are run:

• test whether environment variable _ ends with /gdb
• checks for existence of environment variables LINES or COLUMNS (gdb adds those)
• checks for breakpoints (INT3 instruction / \xCC opcode) inserted at the start of a function

The _ environment variable is maintained by the shell and means sthg like "last user-run command".
It is only updated when the user runs a new command, not for commands run within another program.
Therefore, this check fails when gdb is not invoked by the user directly, but run from a script.

On some systems, gdb seems to insert its breakpoints after the function prologue.
These are currently not detected.

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Run the no_debug program:

Run normally:

Compile with make, run with ./bin/no_debug.
Or type ./run.sh.

Run in gdb with make && gdb ./bin/no_debug.

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Run with logging:

In order to enable logging, compile with:
LOGGING=2 make clean all.
When compiled this way, the program will print the results of the various
checks for the presence of a debugger along the way.

Alternatively, type ./test.sh to compile with logging enabled and run some
standard tests inside and outside gdb.

If the terminal does not support ANSI escape codes, use:
LOGGING=1 make clean all