[PATCH v2 1/3] [sim/riscv] Add basic semi-hosting support

[<jaydeep.patil@imgtec.com>]

From: Jaydeep Patil <jaydeep.patil@imgtec.com>

Added support for basic semi-hosting calls OPEN, EXIT and GET_CMDLINE.
Added gdb.arch/riscv-exit-getcmd.c to test it.
---
 gdb/testsuite/gdb.arch/riscv-exit-getcmd.c   |  26 +++
 gdb/testsuite/gdb.arch/riscv-exit-getcmd.exp |  27 +++
 sim/riscv/riscv-sim.h                        |  32 +++
 sim/riscv/sim-main.c                         | 230 ++++++++++++++++++-
 4 files changed, 310 insertions(+), 5 deletions(-)
 create mode 100644 gdb/testsuite/gdb.arch/riscv-exit-getcmd.c
 create mode 100644 gdb/testsuite/gdb.arch/riscv-exit-getcmd.exp

diff --git a/gdb/testsuite/gdb.arch/riscv-exit-getcmd.c b/gdb/testsuite/gdb.arch/riscv-exit-getcmd.c
new file mode 100644
index 00000000000..02a97da8643
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-exit-getcmd.c
@@ -0,0 +1,26 @@
+/* This file is part of GDB, the GNU debugger.
+
+   Copyright 2023 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Test basic semi-hosting calls SYS_GET_CMDLINE and SYS_EXIT.  */
+
+int
+main (int argc, char **argv)
+{
+  if (argc != 4)
+    return 1;
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.arch/riscv-exit-getcmd.exp b/gdb/testsuite/gdb.arch/riscv-exit-getcmd.exp
new file mode 100644
index 00000000000..7f5670200c2
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv-exit-getcmd.exp
@@ -0,0 +1,27 @@
+# Copyright 2023 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test basic semi-hosting calls SYS_GET_CMDLINE and SYS_EXIT.
+
+require {istarget "riscv*-*-*"}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} \
+	  {debug quiet}] } {
+    return -1
+}
+
+gdb_test "run 1 2 3" ".*Inferior.*process.*exited normally.*"
diff --git a/sim/riscv/riscv-sim.h b/sim/riscv/riscv-sim.h
index 1bc9aa12156..bb296fa6e62 100644
--- a/sim/riscv/riscv-sim.h
+++ b/sim/riscv/riscv-sim.h
@@ -75,4 +75,36 @@ extern void initialize_env (SIM_DESC, const char * const *argv,
 
 #define RISCV_XLEN(cpu) MACH_WORD_BITSIZE (CPU_MACH (cpu))
 
+#define APPLICATION_EXIT 0x20026
+
+#define SYS_OPEN 0x01
+#define SYS_GET_CMDLINE 0x15
+#define SYS_EXIT 0x18
+
+#define GDB_O_RDONLY 0x000
+#define GDB_O_WRONLY 0x001
+#define GDB_O_RDWR 0x002
+#define GDB_O_APPEND 0x008
+#define GDB_O_CREAT 0x200
+#define GDB_O_TRUNC 0x400
+#define GDB_O_BINARY 0
+
+#define SEMI_HOSTING_SLLI 0x01f01013
+#define SEMI_HOSTING_SRAI 0x40705013
+
+static int gdb_open_modeflags[12] = {
+  GDB_O_RDONLY,
+  GDB_O_RDONLY | GDB_O_BINARY,
+  GDB_O_RDWR,
+  GDB_O_RDWR | GDB_O_BINARY,
+  GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC,
+  GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC | GDB_O_BINARY,
+  GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC,
+  GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC | GDB_O_BINARY,
+  GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND,
+  GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND | GDB_O_BINARY,
+  GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND,
+  GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND | GDB_O_BINARY
+};
+
 #endif
diff --git a/sim/riscv/sim-main.c b/sim/riscv/sim-main.c
index afdfcf50656..8e08eb9fc4e 100644
--- a/sim/riscv/sim-main.c
+++ b/sim/riscv/sim-main.c
@@ -136,6 +136,176 @@ store_csr (SIM_CPU *cpu, const char *name, int csr, unsigned_word *reg,
   TRACE_REGISTER (cpu, "wrote CSR %s = %#" PRIxTW, name, val);
 }
 
+/* Read 4 or 8 bytes of data from the core memory.  ADDR and (INDEX * XLEN)
+   form the base address.  */
+static uintptr_t
+get_core_data (SIM_CPU *cpu, unsigned_word addr, unsigned_word index)
+{
+  uintptr_t param;
+  int xlen = RISCV_XLEN (cpu);
+  struct riscv_sim_cpu *riscv_cpu = RISCV_SIM_CPU (cpu);
+
+  if (xlen == 64)
+    param = sim_core_read_unaligned_8 (cpu, riscv_cpu->pc, read_map,
+		addr + (index * 8));
+  else
+    param = sim_core_read_unaligned_4 (cpu, riscv_cpu->pc, read_map,
+		addr + (index * 4));
+
+  return param;
+}
+
+/* Write string in HOST_BUF at CORE_ADDR.  The length of string is LEN.  */
+static void
+set_core_string (SIM_CPU *cpu, unsigned_word core_addr, char *host_buf,
+		 int len)
+{
+  struct riscv_sim_cpu *riscv_cpu = RISCV_SIM_CPU (cpu);
+  for (int i = 0; i < len; i++)
+    {
+      sim_core_write_unaligned_1 (cpu, riscv_cpu->pc, write_map,
+				  core_addr + i, host_buf[i]);
+    }
+}
+
+/* Read string of length LEN at address ADDR.  */
+static char *
+get_core_string_with_len (SIM_CPU *cpu, unsigned_word addr,
+			  unsigned_word len)
+{
+  struct riscv_sim_cpu *riscv_cpu = RISCV_SIM_CPU (cpu);
+  char * str;
+  str = (char *) malloc (len + 1);
+
+  for (int i = 0; i < len; i++)
+    {
+      str[i] = sim_core_read_unaligned_1 (cpu, riscv_cpu->pc, read_map,
+					  addr + i);
+    }
+  str[len] = 0;
+
+  return str;
+}
+
+/* SYS_OPEN
+   Register a1 points to a buffer containing:
+   Index 0: Pointer: Address of the file name string.
+   Index 1: Integer: File open flags.
+   Index 2: Integer: Length of the file name string.
+   File handle is returned through register a0.  */
+static void
+semihosting_open (SIM_CPU *cpu)
+{
+  uintptr_t fname_addr;
+  uintptr_t flags;
+  uintptr_t fname_len;
+  char *name;
+  struct riscv_sim_cpu *riscv_cpu = RISCV_SIM_CPU (cpu);
+
+  fname_addr = (uintptr_t) get_core_data (cpu, riscv_cpu->a1, 0);
+  flags = (uintptr_t) get_core_data (cpu, riscv_cpu->a1, 1);
+  fname_len = (uintptr_t) get_core_data (cpu, riscv_cpu->a1, 2);
+
+  if (fname_len <= 0)
+    {
+      riscv_cpu->a0 = -1;
+      return;
+    }
+
+  name = get_core_string_with_len (cpu, fname_addr, fname_len);
+  riscv_cpu->a0 = sim_io_open (CPU_STATE (cpu), name,
+			       gdb_open_modeflags[flags]);
+  free (name);
+}
+
+/* SYS_EXIT.  In case of RV32, register a1 holds the application stop reason
+   and the exit code is decided based on it.  Otherwise, register a1 points to
+   a buffer containing:
+   Index 0: Integer: Application stop reason (ignored)
+   Index 1: Integer: Exit code.  */
+static void
+semihosting_exit (SIM_CPU *cpu)
+{
+  uintptr_t app_code, exit_code;
+  SIM_DESC sd = CPU_STATE (cpu);
+  struct riscv_sim_cpu *riscv_cpu = RISCV_SIM_CPU (cpu);
+  if (RISCV_XLEN (cpu) == 32)
+    {
+      app_code = riscv_cpu->a1;
+      if (app_code == APPLICATION_EXIT)
+	exit_code = 0;
+      else
+	exit_code = 1;
+    }
+  else
+    exit_code = (uintptr_t) get_core_data (cpu, riscv_cpu->a1, 1);
+  riscv_cpu->a0 = exit_code;
+  sim_engine_halt (sd, cpu, NULL, riscv_cpu->pc, sim_exited, exit_code);
+}
+
+/* SYS_GET_CMDLINE.  Write command line arguments to a buffer.  Arguments
+   passed to "run" command are stored in STATE_PROG_ARGV member of SIM_DESC.
+   Register a1 points to a buffer containing:
+   Index 0: Pointer: Buffer to store command line arguments
+   Index 1: Integer: Maximum length of the buffer.  */
+static void
+semihosting_get_cmdline (SIM_CPU *cpu)
+{
+  int i = 0, len = 0, total_len = 0;
+  uintptr_t buf_addr, max_buf_len;
+  SIM_DESC sd = CPU_STATE (cpu);
+  char *space = " ";
+  struct riscv_sim_cpu *riscv_cpu = RISCV_SIM_CPU (cpu);
+
+  char **prog_argv = STATE_PROG_ARGV (sd);
+  if (prog_argv == NULL)
+    {
+      riscv_cpu->a0 = 1; /* Return non-zero to indicate error.  */
+      return;
+    }
+
+  buf_addr = (uintptr_t) get_core_data (cpu, riscv_cpu->a1, 0);
+  max_buf_len = (uintptr_t) get_core_data (cpu, riscv_cpu->a1, 1);
+
+  while (prog_argv[i])
+    {
+      len = strlen (prog_argv[i]);
+      if ((total_len + len) > max_buf_len)
+	break;
+      set_core_string (cpu, buf_addr, prog_argv[i], len);
+      set_core_string (cpu, buf_addr + len, space, 1);
+      len++;	/* Terminate it with space.  */
+      buf_addr += len;
+      total_len += len;
+      i++;
+    }
+  riscv_cpu->a0 = 0;	/* No error.  */
+}
+
+/* Handle semi-hosting calls.  Register a0 contains semi-hosting call number
+   and a1 contains pointer to a buffer containing additional arguments.  */
+static int
+do_semihosting (SIM_CPU *cpu)
+{
+  struct riscv_sim_cpu *riscv_cpu = RISCV_SIM_CPU (cpu);
+  switch (riscv_cpu->a0)
+    {
+    case SYS_OPEN:
+      semihosting_open (cpu);
+      break;
+    case SYS_GET_CMDLINE:
+      semihosting_get_cmdline (cpu);
+      break;
+    case SYS_EXIT:
+      semihosting_exit (cpu);
+      break;
+    default:
+      return -1;	/* Semi-hosting call not supported.  */
+    }
+
+  return 0;
+}
+
 static inline unsigned_word
 ashiftrt (unsigned_word val, unsigned_word shift)
 {
@@ -623,11 +793,60 @@ execute_i (SIM_CPU *cpu, unsigned_word iw, const struct riscv_opcode *op)
       TRACE_INSN (cpu, "fence.i;");
       break;
     case MATCH_EBREAK:
-      TRACE_INSN (cpu, "ebreak;");
-      /* GDB expects us to step over EBREAK.  */
-      sim_engine_halt (sd, cpu, NULL, riscv_cpu->pc + 4, sim_stopped,
-		       SIM_SIGTRAP);
-      break;
+	{
+	  /* If ebreak is at PC 0 then do not check for semi-hosting.  */
+	  if (riscv_cpu->pc != 0)
+	    {
+	      /* RISC-V semi-hosting call is flagged using these three
+		 instructions
+		 slli zero, zero, 0x1f	0x01f01013
+		 ebreak			0x00100073
+		 srai zero, zero, 0x7	0x40705013
+		 Register a0 holds the system call number and a1 holds the
+		 pointer to parameter buffer.  Do not read 4 bytes in one go
+		 as we might read malformed 4 byte instruction.  */
+	      int iw_len;
+	      sim_cia pre_pc = riscv_cpu->pc - 4;
+	      unsigned_word pre_iw;
+	      pre_iw = sim_core_read_aligned_2 (cpu, pre_pc, exec_map, pre_pc);
+	      iw_len = riscv_insn_length (pre_iw);
+	      if (iw_len == 4)
+		pre_iw |= ((unsigned_word) sim_core_read_aligned_2
+			   (cpu, pre_pc, exec_map, pre_pc + 2) << 16);
+
+	      if (pre_iw == SEMI_HOSTING_SLLI)
+		{
+		  sim_cia post_pc = riscv_cpu->pc + 4;
+		  unsigned_word post_iw;
+		  post_iw = sim_core_read_aligned_2 (cpu, post_pc, exec_map,
+						     post_pc);
+		  iw_len = riscv_insn_length (post_iw);
+		  if (iw_len == 4)
+		    post_iw |= ((unsigned_word) sim_core_read_aligned_2
+				(cpu, post_pc, exec_map, post_pc + 2) << 16);
+
+		  if (post_iw == SEMI_HOSTING_SRAI)
+		    {
+		      TRACE_INSN (cpu, "semi-hosting a0=%lx,a1=%lx;",
+				  riscv_cpu->a0, riscv_cpu->a1);
+		      if (do_semihosting (cpu))
+			{
+			  /* Invalid semi-hosting call.  */
+			  TRACE_INSN (cpu, "ebreak;");
+			  sim_engine_halt (sd, cpu, NULL, riscv_cpu->pc,
+					   sim_stopped, SIM_SIGTRAP);
+			}
+		      else
+			pc = pc + 4;	/* post srai.  */
+		      break;
+		    }
+		}
+	    }
+	  TRACE_INSN (cpu, "ebreak;");
+	  sim_engine_halt (sd, cpu, NULL, riscv_cpu->pc, sim_stopped,
+			   SIM_SIGTRAP);
+	  break;
+	}
     case MATCH_ECALL:
       TRACE_INSN (cpu, "ecall;");
       riscv_cpu->a0 = sim_syscall (cpu, riscv_cpu->a7, riscv_cpu->a0,
@@ -990,6 +1209,7 @@ execute_one (SIM_CPU *cpu, unsigned_word iw, const struct riscv_opcode *op)
     case INSN_CLASS_A:
       return execute_a (cpu, iw, op);
     case INSN_CLASS_I:
+    case INSN_CLASS_ZICSR:
       return execute_i (cpu, iw, op);
     case INSN_CLASS_M:
     case INSN_CLASS_ZMMUL:
-- 
2.25.1