[Beignet] [PATCH 3/4] Add a mem stream class to support ELF write.

[junyan.he at inbox.com]

From: Junyan He <junyan.he at intel.com>

Elf writer need to make sure seekp function work, while
sstream fails it. Implement wmemstreambuf to support
mem ostream which can support seek out of the range.

Signed-off-by: Junyan He <junyan.he at intel.com>
---
 backend/src/CMakeLists.txt              |   1 +
 backend/src/backend/gen_program_elf.cpp | 124 ++++++++++++++++++++++++++++++++
 2 files changed, 125 insertions(+)
 create mode 100644 backend/src/backend/gen_program_elf.cpp

diff --git a/backend/src/CMakeLists.txt b/backend/src/CMakeLists.txt
index 7c1f4db..90db85b 100644
--- a/backend/src/CMakeLists.txt
+++ b/backend/src/CMakeLists.txt
@@ -128,6 +128,7 @@ set (GBE_SRC
     backend/gen9_context.hpp
     backend/gen9_context.cpp
     backend/gen_program.cpp
+    backend/gen_program_elf.cpp
     backend/gen_program.hpp
     backend/gen_program.h
     backend/gen7_instruction.hpp
diff --git a/backend/src/backend/gen_program_elf.cpp b/backend/src/backend/gen_program_elf.cpp
new file mode 100644
index 0000000..efd45fe
--- /dev/null
+++ b/backend/src/backend/gen_program_elf.cpp
@@ -0,0 +1,124 @@
+/*
+ * Copyright © 2012 Intel Corporation
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+#include "ocl_common_defines.h"
+#include "elfio/elfio.hpp"
+#include "backend/gen_program.hpp"
+#include "backend/gen_program.hpp"
+#include <algorithm>
+#include <sstream>
+#include <streambuf>
+
+namespace gbe
+{
+/* The elf writer need to make sure seekp function work, so sstream
+   can not work, and we do not want the fostream to generate the real
+   file. We just want to keep the elf image in the memory. Implement
+   a simple streambuf write only class here. */
+class wmemstreambuf : public std::streambuf
+{
+public:
+  wmemstreambuf(size_t size) : max_writed(0)
+  {
+    buf_ = static_cast<char *>(::malloc(size));
+    memset(buf_, 0, size);
+    buf_size_ = size;
+    setbuf(buf_, buf_size_);
+  }
+  ~wmemstreambuf()
+  {
+    if (buf_)
+      ::free(buf_);
+  }
+
+  char *getcontent(size_t &total_sz)
+  {
+    total_sz = max_writed;
+    return buf_;
+  }
+
+protected:
+  char *buf_;
+  std::streamsize buf_size_;
+  std::streamsize max_writed;
+
+  virtual std::streambuf *setbuf(char *s, std::streamsize n)
+  {
+    auto const begin(s);
+    auto const end(s + n);
+    setp(begin, end);
+    return this;
+  }
+
+  virtual std::streampos seekpos(std::streampos pos,
+                                 std::ios_base::openmode which =
+                                   ::std::ios_base::in | ::std::ios_base::out)
+  {
+    if (which != std::ios_base::out) {
+      assert(0);
+      return pos_type(off_type(-1));
+    }
+
+    if (pos >= epptr() - pbase()) {
+      auto old_size = buf_size_;
+      while (buf_size_ < pos) {
+        buf_size_ *= 2;
+      }
+
+      buf_ = static_cast<char *>(::realloc(buf_, buf_size_));
+      memset(buf_ + old_size, 0, buf_size_ - old_size);
+      setbuf(buf_, buf_size_);
+    } else {
+      setp(pbase(), epptr());
+    }
+
+    pbump(pos);
+    return pos;
+  }
+
+  virtual int sync() { return 0; }
+  virtual int overflow(int c) { return c; };
+
+  virtual std::streamsize xsgetn(const char *s, std::streamsize count)
+  {
+    assert(0);
+    return traits_type::eof();
+  }
+
+  virtual std::streamsize xsputn(const char *s, std::streamsize const count)
+  {
+    if (epptr() - pptr() < count) {
+      auto old_pos = pptr() - pbase();
+      while (buf_size_ < (pptr() - pbase()) + count) {
+        buf_size_ *= 2;
+      }
+      buf_ = static_cast<char *>(::realloc(buf_, buf_size_));
+      memset(buf_ + old_pos, 0, buf_size_ - old_pos);
+      setbuf(buf_, buf_size_);
+      pbump(old_pos);
+    }
+
+    std::memcpy(pptr(), s, count);
+    if (pptr() - pbase() + count > max_writed)
+      max_writed = pptr() - pbase() + count;
+
+    pbump(count);
+
+    return count;
+  }
+};
+} /* namespace gbe */
-- 
2.7.4