1 // SPDX-License-Identifier: GPL-2.0-only 2 /* Copyright (c) 2026 Meta Platforms, Inc and affiliates. */ 3 #include <linux/bpf.h> 4 #include <bpf/bpf_helpers.h> 5 #include "bpf_misc.h" 6 7 /* 8 * Macro tricks to tersely define for long non-recursive call chains. Add 9 * computation to the functions prevent tail recursion from reducing the 10 * stack size to 0. 11 */ 12 13 #define CAT(a, b) a ## b 14 #define XCAT(a, b) CAT(a, b) 15 16 #define F_0 \ 17 __attribute__((noinline)) \ 18 int f0(unsigned long a) \ 19 { \ 20 volatile long b = a + 16; \ 21 if (a == 0) \ 22 return 0; \ 23 return b; \ 24 } 25 26 #define FN(n, prev) \ 27 __attribute__((noinline)) \ 28 int XCAT(f, n)(unsigned long a) \ 29 { \ 30 volatile long b = XCAT(f, prev)(a - 1); \ 31 if (!b) \ 32 return 0; \ 33 return b + 1; \ 34 } 35 36 /* Call chain 33 levels deep. */ 37 #define F_1 F_0 FN(1, 0) 38 #define F_2 F_1 FN(2, 1) 39 #define F_3 F_2 FN(3, 2) 40 #define F_4 F_3 FN(4, 3) 41 #define F_5 F_4 FN(5, 4) 42 #define F_6 F_5 FN(6, 5) 43 #define F_7 F_6 FN(7, 6) 44 #define F_8 F_7 FN(8, 7) 45 #define F_9 F_8 FN(9, 8) 46 #define F_10 F_9 FN(10, 9) 47 #define F_11 F_10 FN(11, 10) 48 #define F_12 F_11 FN(12, 11) 49 #define F_13 F_12 FN(13, 12) 50 #define F_14 F_13 FN(14, 13) 51 #define F_15 F_14 FN(15, 14) 52 #define F_16 F_15 FN(16, 15) 53 #define F_17 F_16 FN(17, 16) 54 #define F_18 F_17 FN(18, 17) 55 #define F_19 F_18 FN(19, 18) 56 #define F_20 F_19 FN(20, 19) 57 #define F_21 F_20 FN(21, 20) 58 #define F_22 F_21 FN(22, 21) 59 #define F_23 F_22 FN(23, 22) 60 #define F_24 F_23 FN(24, 23) 61 #define F_25 F_24 FN(25, 24) 62 #define F_26 F_25 FN(26, 25) 63 #define F_27 F_26 FN(27, 26) 64 #define F_28 F_27 FN(28, 27) 65 #define F_29 F_28 FN(29, 28) 66 #define F_30 F_29 FN(30, 29) 67 #define F_31 F_30 FN(31, 30) 68 #define F_32 F_31 FN(32, 31) 69 70 #define CAT2(a, b) a ## b 71 #define XCAT2(a, b) CAT2(a, b) 72 73 #define F(n) XCAT2(F_, n) 74 75 F(32) 76 77 /* Ensure that even 32 levels deep, the function verifies. */ 78 SEC("syscall") 79 __success 80 int global_func_deep_stack_success(struct __sk_buff *skb) 81 { 82 return f31(55); 83 } 84 85 /* 86 * Check we actually honor stack limits (33 * 16 = 528 > 512 = MAX_STACK_DEPTH). 87 * The stack depth is 16 because the verifier calls round_up_stack_depth() on 88 * the size. 89 */ 90 SEC("syscall") 91 __failure __msg("combined stack size of 34 calls") 92 int global_func_deep_stack_fail(struct __sk_buff *skb) 93 { 94 return f32(123); 95 } 96