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// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2025 Nandakumar Edamana */
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "bpf_misc.h"
/* Intended to test the abstract multiplication technique(s) used by
* the verifier. Using assembly to avoid compiler optimizations.
*/
SEC("fentry/bpf_fentry_test1")
void BPF_PROG(mul_precise, int x)
{
/* First, force the verifier to be uncertain about the value:
* unsigned int a = (bpf_get_prandom_u32() & 0x2) | 0x1;
*
* Assuming the verifier is using tnum, a must be tnum{.v=0x1, .m=0x2}.
* Then a * 0x3 would be m0m1 (m for uncertain). Added imprecision
* would cause the following to fail, because the required return value
* is 0:
* return (a * 0x3) & 0x4);
*/
asm volatile ("\
call %[bpf_get_prandom_u32];\
r0 &= 0x2;\
r0 |= 0x1;\
r0 *= 0x3;\
r0 &= 0x4;\
if r0 != 0 goto l0_%=;\
r0 = 0;\
goto l1_%=;\
l0_%=:\
r0 = 1;\
l1_%=:\
" :
: __imm(bpf_get_prandom_u32)
: __clobber_all);
}
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