Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 63 insertions, 0 deletions

diff --git a/linux-user/host/riscv/host-signal.h b/linux-user/host/riscv/host-signal.h
new file mode 100644
index 000000000..a4f170efb
--- /dev/null
+++ b/linux-user/host/riscv/host-signal.h
@@ -0,0 +1,63 @@
+/*
+ * host-signal.h: signal info dependent on the host architecture
+ *
+ * Copyright (c) 2003-2005 Fabrice Bellard
+ * Copyright (c) 2021 Linaro Limited
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef RISCV_HOST_SIGNAL_H
+#define RISCV_HOST_SIGNAL_H
+
+static inline uintptr_t host_signal_pc(ucontext_t *uc)
+{
+    return uc->uc_mcontext.__gregs[REG_PC];
+}
+
+static inline void host_signal_set_pc(ucontext_t *uc, uintptr_t pc)
+{
+    uc->uc_mcontext.__gregs[REG_PC] = pc;
+}
+
+static inline bool host_signal_write(siginfo_t *info, ucontext_t *uc)
+{
+    /*
+     * Detect store by reading the instruction at the program counter.
+     * Do not read more than 16 bits, because we have not yet determined
+     * the size of the instruction.
+     */
+    const uint16_t *pinsn = (const uint16_t *)host_signal_pc(uc);
+    uint16_t insn = pinsn[0];
+
+    /* 16-bit instructions */
+    switch (insn & 0xe003) {
+    case 0xa000: /* c.fsd */
+    case 0xc000: /* c.sw */
+    case 0xe000: /* c.sd (rv64) / c.fsw (rv32) */
+    case 0xa002: /* c.fsdsp */
+    case 0xc002: /* c.swsp */
+    case 0xe002: /* c.sdsp (rv64) / c.fswsp (rv32) */
+        return true;
+    }
+
+    /* 32-bit instructions, major opcodes */
+    switch (insn & 0x7f) {
+    case 0x23: /* store */
+    case 0x27: /* store-fp */
+        return true;
+    case 0x2f: /* amo */
+        /*
+         * The AMO function code is in bits 25-31, unread as yet.
+         * The AMO functions are LR (read), SC (write), and the
+         * rest are all read-modify-write.
+         */
+        insn = pinsn[1];
+        return (insn >> 11) != 2; /* LR */
+    }
+
+    return false;
+}
+
+#endif