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5 BPF ABI Recommended Conventions and Guidelines 5 BPF ABI Recommended Conventions and Guidelines v1.0
6 ============================================== 6 ===================================================
7 7
8 This is version 1.0 of an informational docume 8 This is version 1.0 of an informational document containing recommended
9 conventions and guidelines for producing porta 9 conventions and guidelines for producing portable BPF program binaries.
10 10
11 Registers and calling convention 11 Registers and calling convention
12 ================================ 12 ================================
13 13
14 BPF has 10 general purpose registers and a rea 14 BPF has 10 general purpose registers and a read-only frame pointer register,
15 all of which are 64-bits wide. 15 all of which are 64-bits wide.
16 16
17 The BPF calling convention is defined as: 17 The BPF calling convention is defined as:
18 18
19 * R0: return value from function calls, and ex 19 * R0: return value from function calls, and exit value for BPF programs
20 * R1 - R5: arguments for function calls 20 * R1 - R5: arguments for function calls
21 * R6 - R9: callee saved registers that functio 21 * R6 - R9: callee saved registers that function calls will preserve
22 * R10: read-only frame pointer to access stack 22 * R10: read-only frame pointer to access stack
23 23
24 R0 - R5 are scratch registers and BPF programs 24 R0 - R5 are scratch registers and BPF programs needs to spill/fill them if
25 necessary across calls. 25 necessary across calls.
26 26
27 The BPF program needs to store the return valu 27 The BPF program needs to store the return value into register R0 before doing an
28 ``EXIT``. 28 ``EXIT``.
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