106 lines
2.8 KiB
C
106 lines
2.8 KiB
C
|
// SPDX-License-Identifier: GPL-2.0
|
||
|
|
#include <linux/bpf.h>
|
||
|
|
#include <bpf/bpf_helpers.h>
|
||
|
|
#include "bpf_misc.h"
|
||
|
|
|
||
|
|
int main(void);
|
||
|
|
|
||
|
|
struct {
|
||
|
|
__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
|
||
|
|
__uint(max_entries, 1);
|
||
|
|
__uint(key_size, sizeof(__u32));
|
||
|
|
__array(values, void (void));
|
||
|
|
} jmp_table SEC(".maps") = {
|
||
|
|
.values = {
|
||
|
|
[0] = (void *) &main,
|
||
|
|
},
|
||
|
|
};
|
||
|
|
|
||
|
|
__noinline __auxiliary
|
||
|
|
static __naked int sub(void)
|
||
|
|
{
|
||
|
|
asm volatile (
|
||
|
|
"r2 = %[jmp_table] ll;"
|
||
|
|
"r3 = 0;"
|
||
|
|
"call 12;"
|
||
|
|
"exit;"
|
||
|
|
:
|
||
|
|
: __imm_addr(jmp_table)
|
||
|
|
: __clobber_all);
|
||
|
|
}
|
||
|
|
|
||
|
|
__success
|
||
|
|
__arch_x86_64
|
||
|
|
/* program entry for main(), regular function prologue */
|
||
|
|
__jited(" endbr64")
|
||
|
|
__jited(" nopl (%rax,%rax)")
|
||
|
|
__jited(" xorq %rax, %rax")
|
||
|
|
__jited(" pushq %rbp")
|
||
|
|
__jited(" movq %rsp, %rbp")
|
||
|
|
/* tail call prologue for program:
|
||
|
|
* - establish memory location for tail call counter at &rbp[-8];
|
||
|
|
* - spill tail_call_cnt_ptr at &rbp[-16];
|
||
|
|
* - expect tail call counter to be passed in rax;
|
||
|
|
* - for entry program rax is a raw counter, value < 33;
|
||
|
|
* - for tail called program rax is tail_call_cnt_ptr (value > 33).
|
||
|
|
*/
|
||
|
|
__jited(" endbr64")
|
||
|
|
__jited(" cmpq $0x21, %rax")
|
||
|
|
__jited(" ja L0")
|
||
|
|
__jited(" pushq %rax")
|
||
|
|
__jited(" movq %rsp, %rax")
|
||
|
|
__jited(" jmp L1")
|
||
|
|
__jited("L0: pushq %rax") /* rbp[-8] = rax */
|
||
|
|
__jited("L1: pushq %rax") /* rbp[-16] = rax */
|
||
|
|
/* on subprogram call restore rax to be tail_call_cnt_ptr from rbp[-16]
|
||
|
|
* (cause original rax might be clobbered by this point)
|
||
|
|
*/
|
||
|
|
__jited(" movq -0x10(%rbp), %rax")
|
||
|
|
__jited(" callq 0x{{.*}}") /* call to sub() */
|
||
|
|
__jited(" xorl %eax, %eax")
|
||
|
|
__jited(" leave")
|
||
|
|
__jited(" {{(retq|jmp 0x)}}") /* return or jump to rethunk */
|
||
|
|
__jited("...")
|
||
|
|
/* subprogram entry for sub(), regular function prologue */
|
||
|
|
__jited(" endbr64")
|
||
|
|
__jited(" nopl (%rax,%rax)")
|
||
|
|
__jited(" nopl (%rax)")
|
||
|
|
__jited(" pushq %rbp")
|
||
|
|
__jited(" movq %rsp, %rbp")
|
||
|
|
/* tail call prologue for subprogram address of tail call counter
|
||
|
|
* stored at rbp[-16].
|
||
|
|
*/
|
||
|
|
__jited(" endbr64")
|
||
|
|
__jited(" pushq %rax") /* rbp[-8] = rax */
|
||
|
|
__jited(" pushq %rax") /* rbp[-16] = rax */
|
||
|
|
__jited(" movabsq ${{.*}}, %rsi") /* r2 = &jmp_table */
|
||
|
|
__jited(" xorl %edx, %edx") /* r3 = 0 */
|
||
|
|
/* bpf_tail_call implementation:
|
||
|
|
* - load tail_call_cnt_ptr from rbp[-16];
|
||
|
|
* - if *tail_call_cnt_ptr < 33, increment it and jump to target;
|
||
|
|
* - otherwise do nothing.
|
||
|
|
*/
|
||
|
|
__jited(" movq -0x10(%rbp), %rax")
|
||
|
|
__jited(" cmpq $0x21, (%rax)")
|
||
|
|
__jited(" jae L0")
|
||
|
|
__jited(" nopl (%rax,%rax)")
|
||
|
|
__jited(" addq $0x1, (%rax)") /* *tail_call_cnt_ptr += 1 */
|
||
|
|
__jited(" popq %rax")
|
||
|
|
__jited(" popq %rax")
|
||
|
|
__jited(" jmp {{.*}}") /* jump to tail call tgt */
|
||
|
|
__jited("L0: leave")
|
||
|
|
__jited(" {{(retq|jmp 0x)}}") /* return or jump to rethunk */
|
||
|
|
SEC("tc")
|
||
|
|
__naked int main(void)
|
||
|
|
{
|
||
|
|
asm volatile (
|
||
|
|
"call %[sub];"
|
||
|
|
"r0 = 0;"
|
||
|
|
"exit;"
|
||
|
|
:
|
||
|
|
: __imm(sub)
|
||
|
|
: __clobber_all);
|
||
|
|
}
|
||
|
|
|
||
|
|
char __license[] SEC("license") = "GPL";
|