[PATCH v3 38/57] tcg/riscv: Support softmmu unaligned accesses

[Richard Henderson]

The system is required to emulate unaligned accesses, even if the
hardware does not support it.  The resulting trap may or may not
be more efficient than the qemu slow path.  There are linux kernel
patches in flight to allow userspace to query hardware support;
we can re-evaluate whether to enable this by default after that.

In the meantime, softmmu now matches useronly, where we already
assumed that unaligned accesses are supported.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/riscv/tcg-target.c.inc | 48 ++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc
index 8522561a28..3e4c91cce7 100644
--- a/tcg/riscv/tcg-target.c.inc
+++ b/tcg/riscv/tcg-target.c.inc
@@ -924,12 +924,13 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, 
TCGReg *pbase,
 
 #ifdef CONFIG_SOFTMMU
     unsigned s_bits = opc & MO_SIZE;
+    unsigned s_mask = (1u << s_bits) - 1;
     int mem_index = get_mmuidx(oi);
     int fast_ofs = TLB_MASK_TABLE_OFS(mem_index);
     int mask_ofs = fast_ofs + offsetof(CPUTLBDescFast, mask);
     int table_ofs = fast_ofs + offsetof(CPUTLBDescFast, table);
-    TCGReg mask_base = TCG_AREG0, table_base = TCG_AREG0;
-    tcg_target_long compare_mask;
+    int compare_mask;
+    TCGReg addr_adj;
 
     ldst = new_ldst_label(s);
     ldst->is_ld = is_ld;
@@ -938,14 +939,33 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, 
TCGReg *pbase,
 
     QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0);
     QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -(1 << 11));
-    tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP0, mask_base, mask_ofs);
-    tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP1, table_base, table_ofs);
+    tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP0, TCG_AREG0, mask_ofs);
+    tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP1, TCG_AREG0, table_ofs);
 
     tcg_out_opc_imm(s, OPC_SRLI, TCG_REG_TMP2, addr_reg,
                     TARGET_PAGE_BITS - CPU_TLB_ENTRY_BITS);
     tcg_out_opc_reg(s, OPC_AND, TCG_REG_TMP2, TCG_REG_TMP2, TCG_REG_TMP0);
     tcg_out_opc_reg(s, OPC_ADD, TCG_REG_TMP2, TCG_REG_TMP2, TCG_REG_TMP1);
 
+    /*
+     * For aligned accesses, we check the first byte and include the alignment
+     * bits within the address.  For unaligned access, we check that we don't
+     * cross pages using the address of the last byte of the access.
+     */
+    addr_adj = addr_reg;
+    if (a_bits < s_bits) {
+        addr_adj = TCG_REG_TMP0;
+        tcg_out_opc_imm(s, TARGET_LONG_BITS == 32 ? OPC_ADDIW : OPC_ADDI,
+                        addr_adj, addr_reg, s_mask - a_mask);
+    }
+    compare_mask = TARGET_PAGE_MASK | a_mask;
+    if (compare_mask == sextreg(compare_mask, 0, 12)) {
+        tcg_out_opc_imm(s, OPC_ANDI, TCG_REG_TMP1, addr_adj, compare_mask);
+    } else {
+        tcg_out_movi(s, TCG_TYPE_TL, TCG_REG_TMP1, compare_mask);
+        tcg_out_opc_reg(s, OPC_AND, TCG_REG_TMP1, TCG_REG_TMP1, addr_adj);
+    }
+
     /* Load the tlb comparator and the addend.  */
     tcg_out_ld(s, TCG_TYPE_TL, TCG_REG_TMP0, TCG_REG_TMP2,
                is_ld ? offsetof(CPUTLBEntry, addr_read)
@@ -953,29 +973,17 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, 
TCGReg *pbase,
     tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP2, TCG_REG_TMP2,
                offsetof(CPUTLBEntry, addend));
 
-    /* We don't support unaligned accesses. */
-    if (a_bits < s_bits) {
-        a_bits = s_bits;
-    }
-    /* Clear the non-page, non-alignment bits from the address.  */
-    compare_mask = (tcg_target_long)TARGET_PAGE_MASK | a_mask;
-    if (compare_mask == sextreg(compare_mask, 0, 12)) {
-        tcg_out_opc_imm(s, OPC_ANDI, TCG_REG_TMP1, addr_reg, compare_mask);
-    } else {
-        tcg_out_movi(s, TCG_TYPE_TL, TCG_REG_TMP1, compare_mask);
-        tcg_out_opc_reg(s, OPC_AND, TCG_REG_TMP1, TCG_REG_TMP1, addr_reg);
-    }
-
     /* Compare masked address with the TLB entry. */
     ldst->label_ptr[0] = s->code_ptr;
     tcg_out_opc_branch(s, OPC_BNE, TCG_REG_TMP0, TCG_REG_TMP1, 0);
 
     /* TLB Hit - translate address using addend.  */
+    addr_adj = addr_reg;
     if (TARGET_LONG_BITS == 32) {
-        tcg_out_ext32u(s, TCG_REG_TMP0, addr_reg);
-        addr_reg = TCG_REG_TMP0;
+        addr_adj = TCG_REG_TMP0;
+        tcg_out_ext32u(s, addr_adj, addr_reg);
     }
-    tcg_out_opc_reg(s, OPC_ADD, TCG_REG_TMP0, TCG_REG_TMP2, addr_reg);
+    tcg_out_opc_reg(s, OPC_ADD, TCG_REG_TMP0, TCG_REG_TMP2, addr_adj);
     *pbase = TCG_REG_TMP0;
 #else
     if (a_mask) {
-- 
2.34.1