How GDB knows a breakpoint is hit?

kceiwH
2009-08-19T15:28:31Z

Hi,

I wonder how GDB knows it should stop the inferior when a breakpoint
is hit. I try to read the code but only to find how GDB creates a
breakpoint. I thought GDB might change some instructions of inferior
so that when the inferior executes the modified instructions, GDB
should know. But what the function "create_breakpoint" does is to add
a breakpoint to the list "breakpoint_chain". It is not what I thought.
So I am confused. Does GDB monitor each instruction of the inferior
and check whether there is a breakpoint and stop the inferior before
the instruction is executed? If so, how GDB monitor the inferior? And
it will be too slow. Could anybody tell how GDB handle it and plus the
codes. Thanks in advance.

Regards,

Mao