gdb: move bfd_open_from_target_memory to gdb_bfd

This function allows to create a BFD handle using an accessible memory
range in a target memory.  It is currently contained in a JIT module but
this functionality may be of wider usefullness - for example, reading
ELF binaries contained within a core dump.

gdb/ChangeLog:
2020-12-07  Mihails Strasuns  <mihails.strasuns@intel.com>

	* jit.c (mem_bfd*, bfd_open_from_target_memory): Removed.
	* gdb_bfd.h (gdb_bfd_open_from_target_memory): New function.
	* gdb_bfd.c (mem_bfd*, gdb_bfd_open_from_target_memory): New functions.

1 files changed, 85 insertions, 0 deletions

diff --git a/gdb/gdb_bfd.c b/gdb/gdb_bfd.c
index a61656a..0ea82c9 100644
--- a/gdb/gdb_bfd.c
+++ b/gdb/gdb_bfd.c
@@ -207,6 +207,91 @@ gdb_bfd_has_target_filename (struct bfd *abfd)
   return is_target_filename (bfd_get_filename (abfd));
 }
 
+/* For `gdb_bfd_open_from_target_memory`.  */
+
+struct target_buffer
+{
+  CORE_ADDR base;
+  ULONGEST size;
+};
+
+/* For `gdb_bfd_open_from_target_memory`.  Opening the file is a no-op.  */
+
+static void *
+mem_bfd_iovec_open (struct bfd *abfd, void *open_closure)
+{
+  return open_closure;
+}
+
+/* For `gdb_bfd_open_from_target_memory`.  Closing the file is just freeing the
+   base/size pair on our side.  */
+
+static int
+mem_bfd_iovec_close (struct bfd *abfd, void *stream)
+{
+  xfree (stream);
+
+  /* Zero means success.  */
+  return 0;
+}
+
+/* For `gdb_bfd_open_from_target_memory`.  For reading the file, we just need to
+   pass through to target_read_memory and fix up the arguments and return
+   values.  */
+
+static file_ptr
+mem_bfd_iovec_pread (struct bfd *abfd, void *stream, void *buf,
+		     file_ptr nbytes, file_ptr offset)
+{
+  int err;
+  struct target_buffer *buffer = (struct target_buffer *) stream;
+
+  /* If this read will read all of the file, limit it to just the rest.  */
+  if (offset + nbytes > buffer->size)
+    nbytes = buffer->size - offset;
+
+  /* If there are no more bytes left, we've reached EOF.  */
+  if (nbytes == 0)
+    return 0;
+
+  err = target_read_memory (buffer->base + offset, (gdb_byte *) buf, nbytes);
+  if (err)
+    return -1;
+
+  return nbytes;
+}
+
+/* For `gdb_bfd_open_from_target_memory`.  For statting the file, we only
+   support the st_size attribute.  */
+
+static int
+mem_bfd_iovec_stat (struct bfd *abfd, void *stream, struct stat *sb)
+{
+  struct target_buffer *buffer = (struct target_buffer*) stream;
+
+  memset (sb, 0, sizeof (struct stat));
+  sb->st_size = buffer->size;
+  return 0;
+}
+
+/* See gdb_bfd.h.  */
+
+gdb_bfd_ref_ptr
+gdb_bfd_open_from_target_memory (CORE_ADDR addr, ULONGEST size,
+				 const char *target,
+				 const char *filename)
+{
+  struct target_buffer *buffer = XNEW (struct target_buffer);
+
+  buffer->base = addr;
+  buffer->size = size;
+  return gdb_bfd_openr_iovec (filename ? filename : "<in-memory>", target,
+			      mem_bfd_iovec_open,
+			      buffer,
+			      mem_bfd_iovec_pread,
+			      mem_bfd_iovec_close,
+			      mem_bfd_iovec_stat);
+}
 
 /* Return the system error number corresponding to ERRNUM.  */