target/riscv: zicfilp `lpad` impl and branch tracking

Implements setting lp expected when `jalr` is encountered and implements
`lpad` instruction of zicfilp. `lpad` instruction is taken out of
auipc x0, <imm_20>. This is an existing HINTNOP space. If `lpad` is
target of an indirect branch, cpu checks for 20 bit value in x7 upper
with 20 bit value embedded in `lpad`. If they don't match, cpu raises a
sw check exception with tval = 2.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Co-developed-by: Jim Shu <jim.shu@sifive.com>
Co-developed-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241008225010.1861630-8-debug@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/target/riscv/insn_trans/trans_rvi.c.inc b/target/riscv/insn_trans/trans_rvi.c.inc
index fab5c06..638fc0f 100644
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -36,6 +36,49 @@ static bool trans_lui(DisasContext *ctx, arg_lui *a)
     return true;
 }
 
+static bool trans_lpad(DisasContext *ctx, arg_lpad *a)
+{
+    /*
+     * fcfi_lp_expected can set only if fcfi was eanbled.
+     * translate further only if fcfi_lp_expected set.
+     * lpad comes from NOP space anyways, so return true if
+     * fcfi_lp_expected is false.
+     */
+    if (!ctx->fcfi_lp_expected) {
+        return true;
+    }
+
+    ctx->fcfi_lp_expected = false;
+    if ((ctx->base.pc_next) & 0x3) {
+        /*
+         * misaligned, according to spec we should raise sw check exception
+         */
+        tcg_gen_st_tl(tcg_constant_tl(RISCV_EXCP_SW_CHECK_FCFI_TVAL),
+                      tcg_env, offsetof(CPURISCVState, sw_check_code));
+        gen_helper_raise_exception(tcg_env,
+                      tcg_constant_i32(RISCV_EXCP_SW_CHECK));
+        return true;
+    }
+
+    /* per spec, label check performed only when embedded label non-zero */
+    if (a->label != 0) {
+        TCGLabel *skip = gen_new_label();
+        TCGv tmp = tcg_temp_new();
+        tcg_gen_extract_tl(tmp, get_gpr(ctx, xT2, EXT_NONE), 12, 20);
+        tcg_gen_brcondi_tl(TCG_COND_EQ, tmp, a->label, skip);
+        tcg_gen_st_tl(tcg_constant_tl(RISCV_EXCP_SW_CHECK_FCFI_TVAL),
+                      tcg_env, offsetof(CPURISCVState, sw_check_code));
+        gen_helper_raise_exception(tcg_env,
+                      tcg_constant_i32(RISCV_EXCP_SW_CHECK));
+        gen_set_label(skip);
+    }
+
+    tcg_gen_st8_tl(tcg_constant_tl(0), tcg_env,
+                  offsetof(CPURISCVState, elp));
+
+    return true;
+}
+
 static bool trans_auipc(DisasContext *ctx, arg_auipc *a)
 {
     TCGv target_pc = dest_gpr(ctx, a->rd);
@@ -75,6 +118,18 @@ static bool trans_jalr(DisasContext *ctx, arg_jalr *a)
     gen_set_gpr(ctx, a->rd, succ_pc);
 
     tcg_gen_mov_tl(cpu_pc, target_pc);
+    if (ctx->fcfi_enabled) {
+        /*
+         * return from functions (i.e. rs1 == xRA || rs1 == xT0) are not
+         * tracked. zicfilp introduces sw guarded branch as well. sw guarded
+         * branch are not tracked. rs1 == xT2 is a sw guarded branch.
+         */
+        if (a->rs1 != xRA && a->rs1 != xT0 && a->rs1 != xT2) {
+            tcg_gen_st8_tl(tcg_constant_tl(1),
+                          tcg_env, offsetof(CPURISCVState, elp));
+        }
+    }
+
     lookup_and_goto_ptr(ctx);
 
     if (misaligned) {