There is typically only one (or a small set) of hardware instruction pointer breakpoints. Every time the CPU is about to execute an instruction, it compares IP to the IP breakpoint register (or set of registers) and if they match, a debug exception is thrown. These are what you must use to debug the BIOS/bootloader executing in-place from ROM with a JTAG or XDP hardware debugger attached. Later, software can add the proper exception handler once enough of the hardware platform is configured. (Not all architectures exit power-on reset with exceptions enabled or even exception vectors mapped to a valid memory location.)
If the code you are debugging is executing out of write-able memory, then your debugger can support an effectively infinite list of breakpoints by writing some instruction that causes an exception to be thrown anywhere you want a break, then handling that exception by looking up the faulting instruction address in your breakpoint list.
Most processors also give you hardware data access breakpoints as well. These typically sit on the CPU's data bus interface and can fire when the address or data that's about to hit the bus match the respective breakpoint registers. There is usually an option to only trap reads, writes, or both. Sometimes you get interesting things like a mask register that lets you trap on a whole block of memory.
One of the most interesting hardware debug features of modern processors is the branch trace which keeps a running list of the last N branch instructions that lets you reconstruct a "how did we get here" story.
Do you know if VMs like the JVM depend on hardware features also? I suspect that would be more an optimization, not a necessity though, since they should be able to de-optimize jitted native code on stack frames containing breakpoints?
If the code you are debugging is executing out of write-able memory, then your debugger can support an effectively infinite list of breakpoints by writing some instruction that causes an exception to be thrown anywhere you want a break, then handling that exception by looking up the faulting instruction address in your breakpoint list.
Most processors also give you hardware data access breakpoints as well. These typically sit on the CPU's data bus interface and can fire when the address or data that's about to hit the bus match the respective breakpoint registers. There is usually an option to only trap reads, writes, or both. Sometimes you get interesting things like a mask register that lets you trap on a whole block of memory.
One of the most interesting hardware debug features of modern processors is the branch trace which keeps a running list of the last N branch instructions that lets you reconstruct a "how did we get here" story.