// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)

#include <bpf/bpf.h>
#include "disasm.h"

struct print_insn_context {
        char scratch[16];
        char *buf;
        size_t sz;
};

static void print_insn_cb(void *private_data, const char *fmt, ...)
{
        struct print_insn_context *ctx = private_data;
        va_list args;

        va_start(args, fmt);
        vsnprintf(ctx->buf, ctx->sz, fmt, args);
        va_end(args);
}

static const char *print_call_cb(void *private_data, const struct bpf_insn *insn)
{
        struct print_insn_context *ctx = private_data;

        /* For pseudo calls verifier.c:jit_subprogs() hides original
         * imm to insn->off and changes insn->imm to be an index of
         * the subprog instead.
         */
        if (insn->src_reg == BPF_PSEUDO_CALL) {
                snprintf(ctx->scratch, sizeof(ctx->scratch), "%+d", insn->off);
                return ctx->scratch;
        }

        return NULL;
}

struct bpf_insn *disasm_insn(struct bpf_insn *insn, char *buf, size_t buf_sz)
{
        struct print_insn_context ctx = {
                .buf = buf,
                .sz = buf_sz,
        };
        struct bpf_insn_cbs cbs = {
                .cb_print       = print_insn_cb,
                .cb_call        = print_call_cb,
                .private_data   = &ctx,
        };
        char *tmp, *pfx_end, *sfx_start;
        bool double_insn;
        int len;

        print_bpf_insn(&cbs, insn, true);
        /* We share code with kernel BPF disassembler, it adds '(FF) ' prefix
         * for each instruction (FF stands for instruction `code` byte).
         * Remove the prefix inplace, and also simplify call instructions.
         * E.g.: "(85) call foo#10" -> "call foo".
         * Also remove newline in the end (the 'max(strlen(buf) - 1, 0)' thing).
         */
        pfx_end = buf + 5;
        sfx_start = buf + max((int)strlen(buf) - 1, 0);
        if (strncmp(pfx_end, "call ", 5) == 0 && (tmp = strrchr(buf, '#')))
                sfx_start = tmp;
        len = sfx_start - pfx_end;
        memmove(buf, pfx_end, len);
        buf[len] = 0;
        double_insn = insn->code == (BPF_LD | BPF_IMM | BPF_DW);
        return insn + (double_insn ? 2 : 1);
}