From 8e418f9e54a3a0d8f15b75ad1ad43ae925fea7e0 Mon Sep 17 00:00:00 2001
From: Tim Newsome <tim@sifive.com>
Date: Sun, 1 May 2016 13:18:03 -0700
Subject: [PATCH] Implement single memory read access.

Prevent unaligned accesses in memory read.

Also change how exceptions in Debug Mode are signaled.
---
 debug_rom/debug_rom.S |  20 +++++---
 debug_rom/debug_rom.h |  33 ++++++------
 riscv/gdbserver.cc    | 113 ++++++++++++++++++++++++++++++++++++------
 riscv/processor.cc    |   6 ++-
 4 files changed, 133 insertions(+), 39 deletions(-)

diff --git a/debug_rom/debug_rom.S b/debug_rom/debug_rom.S
index b1fa8bd..35dd406 100755
--- a/debug_rom/debug_rom.S
+++ b/debug_rom/debug_rom.S
@@ -29,15 +29,14 @@ entry:  j       _entry
 resume:
         j       _resume
 exception:
-        # Flip the LSB of the first word in Debug RAM so the debugger can know
-        # that we hit an exception.
-        lw      s1, (DEBUG_RAM)(zero)
-        xori    s1, s1, 1
-        sw      s1, (DEBUG_RAM)(zero)
-
-        # Fall through to resume.
+        # Set the last word of Debug RAM to all ones, to indicate that we hit
+        # an exception.
+        li      s0, ~0
+        j       _resume2
 
 _resume:
+        li      s0, 0
+_resume2:
         # Clear debug interrupt.
         csrr    s1, CSR_MHARTID
         sw      s1, CLEARDEBINT(zero)
@@ -58,6 +57,11 @@ restore_64:
 restore_128:
         nop     #lq      s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 16)(zero)
 
+        # s0 contains ~0 if we got here through an exception, and 0 otherwise.
+        # Store this to the last word in Debug RAM so the debugger can tell if
+        # an exception occurred.
+        sw      s0, (DEBUG_RAM + DEBUG_RAM_SIZE - 4)(zero)
+
 check_halt:
         csrr    s0, DCSR
         andi    s0, s0, (1<<DCSR_HALT_OFFSET)
@@ -68,7 +72,7 @@ exit:
         # Restore s0.
         csrr    s0, DSCRATCH
         # TODO: dret?
-        mret
+        sret
 
 
 _entry:
diff --git a/debug_rom/debug_rom.h b/debug_rom/debug_rom.h
index f8aa2e0..8b5ea69 100644
--- a/debug_rom/debug_rom.h
+++ b/debug_rom/debug_rom.h
@@ -1,18 +1,19 @@
 static const unsigned char debug_rom_raw[] = {
-  0x6f, 0x00, 0xc0, 0x05, 0x6f, 0x00, 0x00, 0x01, 0x83, 0x24, 0x00, 0xc0,
-  0x93, 0xc4, 0x14, 0x00, 0x23, 0x20, 0x90, 0xc0, 0xf3, 0x24, 0x50, 0xf1,
-  0x23, 0x2c, 0x90, 0xee, 0x0f, 0x00, 0xf0, 0x0f, 0xf3, 0x24, 0x00, 0xf1,
-  0x63, 0xc6, 0x04, 0x00, 0x83, 0x24, 0xc0, 0xc3, 0x6f, 0x00, 0x80, 0x01,
-  0x93, 0x94, 0x14, 0x00, 0x63, 0xc6, 0x04, 0x00, 0x83, 0x34, 0x80, 0xc3,
-  0x6f, 0x00, 0x80, 0x00, 0x13, 0x00, 0x00, 0x00, 0x73, 0x24, 0x00, 0x79,
-  0x13, 0x74, 0x84, 0x00, 0x63, 0x04, 0x04, 0x00, 0x6f, 0x00, 0x40, 0x05,
-  0x73, 0x24, 0x20, 0x79, 0x73, 0x00, 0x20, 0x10, 0x73, 0x10, 0x24, 0x79,
-  0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x74, 0x00, 0x13, 0x04, 0xd4, 0xff,
-  0x63, 0x16, 0x04, 0x02, 0x73, 0x24, 0x00, 0xf1, 0x63, 0x46, 0x04, 0x00,
-  0x23, 0x2e, 0x90, 0xc2, 0x67, 0x00, 0x00, 0xc0, 0x13, 0x14, 0x14, 0x00,
-  0x63, 0x46, 0x04, 0x00, 0x23, 0x3c, 0x90, 0xc2, 0x67, 0x00, 0x00, 0xc0,
-  0x13, 0x00, 0x00, 0x00, 0x67, 0x00, 0x00, 0xc0, 0x73, 0x24, 0x50, 0xf1,
-  0x23, 0x20, 0x80, 0xf0, 0x73, 0x60, 0x04, 0x79, 0x73, 0x24, 0x00, 0x79,
-  0x13, 0x74, 0x04, 0x40, 0xe3, 0x0c, 0x04, 0xfe, 0x6f, 0xf0, 0x1f, 0xfc
+  0x6f, 0x00, 0x00, 0x06, 0x6f, 0x00, 0xc0, 0x00, 0x13, 0x04, 0xf0, 0xff,
+  0x6f, 0x00, 0x80, 0x00, 0x13, 0x04, 0x00, 0x00, 0xf3, 0x24, 0x40, 0xf1,
+  0x23, 0x24, 0x90, 0x10, 0x0f, 0x00, 0xf0, 0x0f, 0xf3, 0x24, 0x00, 0xf1,
+  0x63, 0xc6, 0x04, 0x00, 0x83, 0x24, 0xc0, 0x43, 0x6f, 0x00, 0xc0, 0x01,
+  0x93, 0x94, 0x14, 0x00, 0x63, 0xc6, 0x04, 0x00, 0x83, 0x34, 0x80, 0x43,
+  0x6f, 0x00, 0xc0, 0x00, 0x13, 0x00, 0x00, 0x00, 0x23, 0x2e, 0x80, 0x42,
+  0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x84, 0x00, 0x63, 0x04, 0x04, 0x00,
+  0x6f, 0x00, 0x40, 0x05, 0x73, 0x24, 0x20, 0x79, 0x73, 0x00, 0x00, 0x10,
+  0x73, 0x10, 0x24, 0x79, 0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x74, 0x00,
+  0x13, 0x04, 0xd4, 0xff, 0x63, 0x16, 0x04, 0x02, 0x73, 0x24, 0x00, 0xf1,
+  0x63, 0x46, 0x04, 0x00, 0x23, 0x2e, 0x90, 0x42, 0x67, 0x00, 0x00, 0x40,
+  0x13, 0x14, 0x14, 0x00, 0x63, 0x46, 0x04, 0x00, 0x23, 0x3c, 0x90, 0x42,
+  0x67, 0x00, 0x00, 0x40, 0x13, 0x00, 0x00, 0x00, 0x67, 0x00, 0x00, 0x40,
+  0x73, 0x24, 0x40, 0xf1, 0x23, 0x20, 0x80, 0x10, 0x73, 0x60, 0x04, 0x79,
+  0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x04, 0x40, 0xe3, 0x0c, 0x04, 0xfe,
+  0x6f, 0xf0, 0x1f, 0xfc
 };
-static const unsigned int debug_rom_raw_len = 180;
+static const unsigned int debug_rom_raw_len = 184;
diff --git a/riscv/gdbserver.cc b/riscv/gdbserver.cc
index e7aa99c..35a408e 100644
--- a/riscv/gdbserver.cc
+++ b/riscv/gdbserver.cc
@@ -104,15 +104,38 @@ static uint32_t sd(unsigned int src, unsigned int base, uint16_t offset)
     MATCH_SD;
 }
 
-static uint32_t ld(unsigned int src, unsigned int base, uint16_t offset)
+static uint32_t ld(unsigned int rd, unsigned int base, uint16_t offset)
 {
-  return (bits(offset, 11, 5) << 25) |
-    (bits(src, 4, 0) << 20) |
+  return (bits(offset, 11, 0) << 20) |
     (base << 15) |
-    (bits(offset, 4, 0) << 7) |
+    (bits(rd, 4, 0) << 7) |
     MATCH_LD;
 }
 
+static uint32_t lw(unsigned int rd, unsigned int base, uint16_t offset)
+{
+  return (bits(offset, 11, 0) << 20) |
+    (base << 15) |
+    (bits(rd, 4, 0) << 7) |
+    MATCH_LW;
+}
+
+static uint32_t lh(unsigned int rd, unsigned int base, uint16_t offset)
+{
+  return (bits(offset, 11, 0) << 20) |
+    (base << 15) |
+    (bits(rd, 4, 0) << 7) |
+    MATCH_LH;
+}
+
+static uint32_t lb(unsigned int rd, unsigned int base, uint16_t offset)
+{
+  return (bits(offset, 11, 0) << 20) |
+    (base << 15) |
+    (bits(rd, 4, 0) << 7) |
+    MATCH_LB;
+}
+
 static uint32_t fsd(unsigned int src, unsigned int base, uint16_t offset)
 {
   return (bits(offset, 11, 5) << 25) |
@@ -415,6 +438,77 @@ class register_read_op_t : public operation_t
     unsigned int reg;
 };
 
+class memory_read_op_t : public operation_t
+{
+  public:
+    memory_read_op_t(gdbserver_t& gdbserver, reg_t addr, unsigned int length) :
+      operation_t(gdbserver), addr(addr), length(length) {};
+
+    bool start()
+    {
+      // address goes in S0
+      access_size = (addr % length);
+      if (access_size == 0)
+        access_size = length;
+
+      gs.write_debug_ram(0, ld(S0, 0, (uint16_t) DEBUG_RAM_START + 16));
+      switch (access_size) {
+        case 1:
+          gs.write_debug_ram(1, lb(S1, S0, 0));
+          break;
+        case 2:
+          gs.write_debug_ram(1, lh(S1, S0, 0));
+          break;
+        case 4:
+          gs.write_debug_ram(1, lw(S1, S0, 0));
+          break;
+        case 8:
+          gs.write_debug_ram(1, ld(S1, S0, 0));
+          break;
+        default:
+          gs.send_packet("E12");
+          return true;
+      }
+      gs.write_debug_ram(2, sd(S1, 0, (uint16_t) DEBUG_RAM_START + 24));
+      gs.write_debug_ram(3, jal(0, (uint32_t) (DEBUG_ROM_RESUME - (DEBUG_RAM_START + 4*3))));
+      gs.write_debug_ram(4, addr);
+      gs.write_debug_ram(5, addr >> 32);
+      gs.set_interrupt(0);
+
+      gs.start_packet();
+
+      return false;
+    }
+
+    bool step()
+    {
+      char buffer[3];
+      reg_t value = ((uint64_t) gs.read_debug_ram(7) << 32) | gs.read_debug_ram(6);
+      for (unsigned int i = 0; i < access_size; i++) {
+        sprintf(buffer, "%02x", (unsigned int) (value & 0xff));
+        gs.send(buffer);
+        value >>= 8;
+      }
+      length -= access_size;
+      addr += access_size;
+
+      if (length == 0) {
+        gs.end_packet();
+        return true;
+      } else {
+        gs.write_debug_ram(4, addr);
+        gs.write_debug_ram(5, addr >> 32);
+        gs.set_interrupt(0);
+        return false;
+      }
+    }
+
+  private:
+    reg_t addr;
+    unsigned int length;
+    unsigned int access_size;
+};
+
 ////////////////////////////// gdbserver itself
 
 gdbserver_t::gdbserver_t(uint16_t port, sim_t *sim) :
@@ -764,16 +858,7 @@ void gdbserver_t::handle_memory_read(const std::vector<uint8_t> &packet)
   if (*iter != '#')
     return send_packet("E11");
 
-  start_packet();
-  char buffer[3];
-  processor_t *p = sim->get_core(0);
-  mmu_t* mmu = sim->debug_mmu;
-
-  for (reg_t i = 0; i < length; i++) {
-    sprintf(buffer, "%02x", mmu->load_uint8(address + i));
-    send(buffer);
-  }
-  end_packet();
+  set_operation(new memory_read_op_t(*this, address, length));
 }
 
 void gdbserver_t::handle_memory_binary_write(const std::vector<uint8_t> &packet)
diff --git a/riscv/processor.cc b/riscv/processor.cc
index 7f3ba42..f09eea8 100644
--- a/riscv/processor.cc
+++ b/riscv/processor.cc
@@ -206,9 +206,13 @@ void processor_t::enter_debug_mode(uint8_t cause)
 
 void processor_t::take_trap(trap_t& t, reg_t epc)
 {
-  if (debug)
+  if (debug) {
     fprintf(stderr, "core %3d: exception %s, epc 0x%016" PRIx64 "\n",
             id, t.name(), epc);
+    if (t.has_badaddr())
+      fprintf(stderr, "core %3d:           badaddr 0x%016" PRIx64 "\n", id,
+          t.get_badaddr());
+  }
 
   if (t.cause() == CAUSE_BREAKPOINT &&
           sim->gdbserver && sim->gdbserver->connected()) {
-- 
2.30.2