Optimized trampoline design for fast software tracing

A system, comprising:

• a CPU;
• a computer readable storage medium;
• program instructions stored on the computer readable storage medium for execution by the CPU to perform operations for tracing computer software program execution, the operations comprising:
• copying a software instruction stored in a memory location representing an instrumentation point within an original instruction stream of the computer software program;
• replacing the original instruction with a jump instruction at the instrumentation point, the jump instruction causing program control to branch to a multi-level trampoline that includes at least a first-level trampoline and a second-level trampoline;
• the first-level trampoline as loaded being specific to one software tracing probe of multiple different software tracing probes, and the first-level trampoline having a smaller kernel footprint size than the second-level trampoline;
• the second-level trampoline as loaded being generic to the multiple different software tracing probes;
• the first-level trampoline performing initial software-tracing house-keeping operations to preserve partial CPU state, and branching to the second-level trampoline while passing identifying information thereto about the first-level trampoline's one software tracing probe;
• the second-level trampoline performing additional software-tracing house-keeping operations to preserve a remainder of the CPU state, performing software tracing operations in accordance with the first-level trampoline's one software tracing probe, restoring the CPU state that it previously preserved, and returning program control to the first-level trampoline;
• the original software instruction being executed out-of-line or emulated by the first-level trampoline, the second-level trampoline, or any other trampoline that may be part of the multi-level trampoline;
• and
• the first-level trampoline restoring the CPU state that it previously preserved, and returning program control to the original instruction stream of the computer software program at an instruction determined by a result of the out-of-line execution or emulation of the original instruction.

A computer program product, comprising:

• a computer readable storage medium;
• program instructions stored on the computer readable storage medium for execution by a CPU to perform operations for tracing computer software program execution, the operations comprising:
• copying a software instruction stored in a memory location representing an instrumentation point within an original instruction stream of the computer software program;
• replacing the original instruction with a jump instruction at the instrumentation point, the jump instruction causing program control to branch to a multi-level trampoline that includes at least a first-level trampoline and a second-level trampoline;
• the first-level trampoline as loaded being specific to one software tracing probe of multiple different software tracing probes, and the first-level trampoline having a smaller kernel footprint size than the second-level trampoline;
• the second-level trampoline as loaded being generic to the multiple different software tracing probes;
• the first-level trampoline performing initial software-tracing house-keeping operations to preserve partial CPU state, and branching to the second-level trampoline while passing identifying information thereto about the first-level trampoline's one software tracing probe;
• the second-level trampoline performing additional software-tracing house-keeping operations to preserve a remainder of the CPU state, performing software tracing operations in accordance with the first-level trampoline's one software tracing probe, restoring the CPU state that it previously preserved, and returning program control to the first-level trampoline;
• the original software instruction being executed out-of-line or emulated by the first-level trampoline, the second-level trampoline, or any other trampoline that may be part of the multi-level trampoline;
• and
• the first-level trampoline restoring the CPU state that it previously preserved, and returning program control to the original instruction stream of the computer software program at an instruction determined by a result of the out-of-line execution or emulation of the original instruction.