Cache the text section offset of shared libraries

Each time a dll is loaded, update_solib_list is called.
This in turn calls deep down xfer_partial -> windows_xfer_shared_libraries,
which calls windows_xfer_shared_library for each loaded dll,
and pe_text_section_offset reads the dll for the text section offset.

Also if the data provided by xfer_partial is bigger than 4K,
then all of this is done for each 4K chunk (see target_read_alloc_1).

Caching of the text section offset improves the startup time of
an application with >300 dynamically loaded plugins from 2m10s to 10s.
And the shutdown time improves from 2m to 2s.

gdb/ChangeLog:

2020-01-23  Hannes Domani  <ssbssa@yahoo.de>

	* i386-cygwin-tdep.c (core_process_module_section): Update.
	* windows-nat.c (struct lm_info_windows): Add text_offset.
	(windows_xfer_shared_libraries): Update.
	* windows-tdep.c (windows_xfer_shared_library):
	Add text_offset_cached argument.
	* windows-tdep.h (windows_xfer_shared_library): Update.

1 files changed, 14 insertions, 6 deletions

diff --git a/gdb/windows-tdep.c b/gdb/windows-tdep.c
index 1fc2748..6c9632d 100644
--- a/gdb/windows-tdep.c
+++ b/gdb/windows-tdep.c
@@ -483,19 +483,27 @@ display_tib (const char * args, int from_tty)
 
 void
 windows_xfer_shared_library (const char* so_name, CORE_ADDR load_addr,
+			     CORE_ADDR *text_offset_cached,
 			     struct gdbarch *gdbarch, struct obstack *obstack)
 {
-  CORE_ADDR text_offset;
+  CORE_ADDR text_offset = text_offset_cached ? *text_offset_cached : 0;
 
   obstack_grow_str (obstack, "<library name=\"");
   std::string p = xml_escape_text (so_name);
   obstack_grow_str (obstack, p.c_str ());
   obstack_grow_str (obstack, "\"><segment address=\"");
-  gdb_bfd_ref_ptr dll (gdb_bfd_open (so_name, gnutarget, -1));
-  /* The following calls are OK even if dll is NULL.
-     The default value 0x1000 is returned by pe_text_section_offset
-     in that case.  */
-  text_offset = pe_text_section_offset (dll.get ());
+
+  if (!text_offset)
+    {
+      gdb_bfd_ref_ptr dll (gdb_bfd_open (so_name, gnutarget, -1));
+      /* The following calls are OK even if dll is NULL.
+	 The default value 0x1000 is returned by pe_text_section_offset
+	 in that case.  */
+      text_offset = pe_text_section_offset (dll.get ());
+      if (text_offset_cached)
+	*text_offset_cached = text_offset;
+    }
+
   obstack_grow_str (obstack, paddress (gdbarch, load_addr + text_offset));
   obstack_grow_str (obstack, "\"/></library>");
 }