1 BPF ABI Recommended Conventions and Guidelines v1.0 ¶

This is version 1.0 of an informational document containing recommended conventions and guidelines for producing portable BPF program binaries.

1.1 Registers and calling convention ¶

BPF has 10 general purpose registers and a read-only frame pointer register, all of which are 64-bits wide.

The BPF calling convention is defined as:

R0: return value from function calls, and exit value for BPF programs
R1 - R5: arguments for function calls
R6 - R9: callee saved registers that function calls will preserve
R10: read-only frame pointer to access stack

R0 - R5 are scratch registers and BPF programs needs to spill/fill them if necessary across calls.