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// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2026 Meta Platforms, Inc and affiliates. */
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include "bpf_misc.h"
/*
* Macro tricks to tersely define for long non-recursive call chains. Add
* computation to the functions prevent tail recursion from reducing the
* stack size to 0.
*/
#define CAT(a, b) a ## b
#define XCAT(a, b) CAT(a, b)
#define F_0 \
__attribute__((noinline)) \
int f0(unsigned long a) \
{ \
volatile long b = a + 16; \
if (a == 0) \
return 0; \
return b; \
}
#define FN(n, prev) \
__attribute__((noinline)) \
int XCAT(f, n)(unsigned long a) \
{ \
volatile long b = XCAT(f, prev)(a - 1); \
if (!b) \
return 0; \
return b + 1; \
}
/* Call chain 33 levels deep. */
#define F_1 F_0 FN(1, 0)
#define F_2 F_1 FN(2, 1)
#define F_3 F_2 FN(3, 2)
#define F_4 F_3 FN(4, 3)
#define F_5 F_4 FN(5, 4)
#define F_6 F_5 FN(6, 5)
#define F_7 F_6 FN(7, 6)
#define F_8 F_7 FN(8, 7)
#define F_9 F_8 FN(9, 8)
#define F_10 F_9 FN(10, 9)
#define F_11 F_10 FN(11, 10)
#define F_12 F_11 FN(12, 11)
#define F_13 F_12 FN(13, 12)
#define F_14 F_13 FN(14, 13)
#define F_15 F_14 FN(15, 14)
#define F_16 F_15 FN(16, 15)
#define F_17 F_16 FN(17, 16)
#define F_18 F_17 FN(18, 17)
#define F_19 F_18 FN(19, 18)
#define F_20 F_19 FN(20, 19)
#define F_21 F_20 FN(21, 20)
#define F_22 F_21 FN(22, 21)
#define F_23 F_22 FN(23, 22)
#define F_24 F_23 FN(24, 23)
#define F_25 F_24 FN(25, 24)
#define F_26 F_25 FN(26, 25)
#define F_27 F_26 FN(27, 26)
#define F_28 F_27 FN(28, 27)
#define F_29 F_28 FN(29, 28)
#define F_30 F_29 FN(30, 29)
#define F_31 F_30 FN(31, 30)
#define F_32 F_31 FN(32, 31)
/* Same, with a 480-byte frame, to exceed the 2 KiB budget of large stacks. */
#define FNB(n, prev) \
__attribute__((noinline)) \
int XCAT(f, n)(unsigned long a) \
{ \
volatile char buf[480] = {}; \
volatile long b = XCAT(f, prev)(a - 1); \
if (!b) \
return 0; \
return b + buf[479] + 1; \
}
#define F_33 F_32 FNB(33, 32)
#define F_34 F_33 FNB(34, 33)
#define F_35 F_34 FNB(35, 34)
#define F_36 F_35 FNB(36, 35)
#define F_37 F_36 FNB(37, 36)
#define CAT2(a, b) a ## b
#define XCAT2(a, b) CAT2(a, b)
#define F(n) XCAT2(F_, n)
F(37)
/* Ensure that even 32 levels deep, the function verifies. */
SEC("syscall")
__success
int global_func_deep_stack_success(struct __sk_buff *skb)
{
return f31(55);
}
/*
* Check we actually honor stack limits (33 * 16 = 528 > 512 = MAX_STACK_DEPTH).
* The stack depth is 16 because the verifier calls round_up_stack_depth() on
* the size.
*/
SEC("syscall")
__load_if_no_large_stack()
__failure __msg("combined stack size of 34 calls")
int global_func_deep_stack_fail(struct __sk_buff *skb)
{
return f32(123);
}
/*
* Five 480-byte frames on top of the chain: 5 * 480 + 33 * 16 = 2928 bytes,
* more than the 2 KiB budget of JITs with large stacks, and more than 512
* bytes after the second frame everywhere else.
*/
SEC("syscall")
__failure __msg("combined stack size of {{[0-9]+}} calls")
int global_func_deep_stack_fail_large(struct __sk_buff *skb)
{
return f37(123);
}
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