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// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include "bpf_misc.h"
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, 1);
__type(key, __u32);
__type(value, __u32);
} map_array SEC(".maps");
SEC("socket")
__description("invalid map type for tail call")
__failure __msg("expected prog array map for tail call")
__failure_unpriv
__naked void invalid_map_for_tail_call(void)
{
asm volatile (" \
r2 = %[map_array] ll; \
r3 = 0; \
call %[bpf_tail_call]; \
exit; \
" :
: __imm(bpf_tail_call),
__imm_addr(map_array)
: __clobber_all);
}
struct {
__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
__uint(max_entries, 1);
__uint(key_size, sizeof(__u32));
__uint(value_size, sizeof(__u32));
} jmp_table SEC(".maps");
__used __naked
static int subprog_tail_call(void)
{
asm volatile (" \
r2 = %[jmp_table] ll; \
r3 = 0; \
call %[bpf_tail_call]; \
r0 = 0; \
exit; \
" :
: __imm(bpf_tail_call),
__imm_addr(jmp_table)
: __clobber_all);
}
/*
* A tail call unwinds only the frame of the subprog doing it, so the
* frames of its callers stay on the stack. With up to 33 tail calls in
* a chain the verifier caps the stack those frames may add up to at
* 256 bytes.
*/
SEC("tc")
__description("tail call from subprog with 240 bytes of caller stack")
__success
__naked void tail_call_caller_stack_ok(void)
{
asm volatile (" \
r2 = 42; \
*(u64 *)(r10 - 240) = r2; \
call subprog_tail_call; \
r0 = 0; \
exit; \
" ::: __clobber_all);
}
SEC("tc")
__description("tail call from subprog with 256 bytes of caller stack")
__failure
__msg("tail_calls are not allowed when call stack of previous frames is 256 bytes. Too large")
__naked void tail_call_caller_stack_too_large(void)
{
asm volatile (" \
r2 = 42; \
*(u64 *)(r10 - 256) = r2; \
call subprog_tail_call; \
r0 = 0; \
exit; \
" ::: __clobber_all);
}
char _license[] SEC("license") = "GPL";
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