Move simple_search_memory to gdbsupport/search.cc

This moves the simple_search_memory function to a new file,
gdbsupport/search.cc.  The API is slightly changed to make it more
general.  This generality is useful for wiring it to gdbserver, and
also for unit testing.

gdb/ChangeLog
2020-10-07  Tom Tromey  <tromey@adacore.com>

	* target.h (simple_search_memory): Don't declare.
	* target.c (simple_search_memory): Move to gdbsupport.
	(default_search_memory): Update.
	* remote.c (remote_target::search_memory): Update.

gdbsupport/ChangeLog
2020-10-07  Tom Tromey  <tromey@adacore.com>

	* Makefile.in: Rebuild.
	* Makefile.am (libgdbsupport_a_SOURCES): Add search.cc.
	* search.h: New file.
	* search.cc: New file.

5 files changed, 173 insertions, 1 deletions

diff --git a/gdbsupport/ChangeLog b/gdbsupport/ChangeLog
index 05462e6..adcc53a 100644
--- a/gdbsupport/ChangeLog
+++ b/gdbsupport/ChangeLog
@@ -1,3 +1,10 @@
+2020-10-07  Tom Tromey  <tromey@adacore.com>
+
+	* Makefile.in: Rebuild.
+	* Makefile.am (libgdbsupport_a_SOURCES): Add search.cc.
+	* search.h: New file.
+	* search.cc: New file.
+
 2020-10-02  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* event-loop.h (debug_event_loop): New variable declaration.
diff --git a/gdbsupport/Makefile.am b/gdbsupport/Makefile.am
index 9763c96..9f4ec93 100644
--- a/gdbsupport/Makefile.am
+++ b/gdbsupport/Makefile.am
@@ -65,6 +65,7 @@ libgdbsupport_a_SOURCES = \
     run-time-clock.cc \
     safe-strerror.cc \
     scoped_mmap.cc \
+    search.cc \
     signals.cc \
     signals-state-save-restore.cc \
     tdesc.cc \
diff --git a/gdbsupport/Makefile.in b/gdbsupport/Makefile.in
index 0223f6d..044ef15 100644
--- a/gdbsupport/Makefile.in
+++ b/gdbsupport/Makefile.in
@@ -156,7 +156,7 @@ am_libgdbsupport_a_OBJECTS = agent.$(OBJEXT) btrace-common.$(OBJEXT) \
 	netstuff.$(OBJEXT) new-op.$(OBJEXT) pathstuff.$(OBJEXT) \
 	print-utils.$(OBJEXT) ptid.$(OBJEXT) rsp-low.$(OBJEXT) \
 	run-time-clock.$(OBJEXT) safe-strerror.$(OBJEXT) \
-	scoped_mmap.$(OBJEXT) signals.$(OBJEXT) \
+	scoped_mmap.$(OBJEXT) search.$(OBJEXT) signals.$(OBJEXT) \
 	signals-state-save-restore.$(OBJEXT) tdesc.$(OBJEXT) \
 	thread-pool.$(OBJEXT) xml-utils.$(OBJEXT) $(am__objects_1)
 libgdbsupport_a_OBJECTS = $(am_libgdbsupport_a_OBJECTS)
@@ -388,6 +388,7 @@ libgdbsupport_a_SOURCES = \
     run-time-clock.cc \
     safe-strerror.cc \
     scoped_mmap.cc \
+    search.cc \
     signals.cc \
     signals-state-save-restore.cc \
     tdesc.cc \
@@ -492,6 +493,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/run-time-clock.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/safe-strerror.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/scoped_mmap.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/search.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/selftest.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/signals-state-save-restore.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/signals.Po@am__quote@
diff --git a/gdbsupport/search.cc b/gdbsupport/search.cc
new file mode 100644
index 0000000..f10c570
--- /dev/null
+++ b/gdbsupport/search.cc
@@ -0,0 +1,120 @@
+/* Target memory searching
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+#include "gdbsupport/common-defs.h"
+
+#include "gdbsupport/search.h"
+#include "gdbsupport/byte-vector.h"
+
+/* This implements a basic search of memory, reading target memory and
+   performing the search here (as opposed to performing the search in on the
+   target side with, for example, gdbserver).  */
+
+int
+simple_search_memory
+  (gdb::function_view<target_read_memory_ftype> read_memory,
+   CORE_ADDR start_addr, ULONGEST search_space_len,
+   const gdb_byte *pattern, ULONGEST pattern_len,
+   CORE_ADDR *found_addrp)
+{
+  const unsigned chunk_size = SEARCH_CHUNK_SIZE;
+  /* Buffer to hold memory contents for searching.  */
+  unsigned search_buf_size;
+
+  search_buf_size = chunk_size + pattern_len - 1;
+
+  /* No point in trying to allocate a buffer larger than the search space.  */
+  if (search_space_len < search_buf_size)
+    search_buf_size = search_space_len;
+
+  gdb::byte_vector search_buf (search_buf_size);
+
+  /* Prime the search buffer.  */
+
+  if (!read_memory (start_addr, search_buf.data (), search_buf_size))
+    {
+      warning (_("Unable to access %s bytes of target "
+		 "memory at %s, halting search."),
+	       pulongest (search_buf_size), hex_string (start_addr));
+      return -1;
+    }
+
+  /* Perform the search.
+
+     The loop is kept simple by allocating [N + pattern-length - 1] bytes.
+     When we've scanned N bytes we copy the trailing bytes to the start and
+     read in another N bytes.  */
+
+  while (search_space_len >= pattern_len)
+    {
+      gdb_byte *found_ptr;
+      unsigned nr_search_bytes
+	= std::min (search_space_len, (ULONGEST) search_buf_size);
+
+      found_ptr = (gdb_byte *) memmem (search_buf.data (), nr_search_bytes,
+				       pattern, pattern_len);
+
+      if (found_ptr != NULL)
+	{
+	  CORE_ADDR found_addr = start_addr + (found_ptr - search_buf.data ());
+
+	  *found_addrp = found_addr;
+	  return 1;
+	}
+
+      /* Not found in this chunk, skip to next chunk.  */
+
+      /* Don't let search_space_len wrap here, it's unsigned.  */
+      if (search_space_len >= chunk_size)
+	search_space_len -= chunk_size;
+      else
+	search_space_len = 0;
+
+      if (search_space_len >= pattern_len)
+	{
+	  unsigned keep_len = search_buf_size - chunk_size;
+	  CORE_ADDR read_addr = start_addr + chunk_size + keep_len;
+	  int nr_to_read;
+
+	  /* Copy the trailing part of the previous iteration to the front
+	     of the buffer for the next iteration.  */
+	  gdb_assert (keep_len == pattern_len - 1);
+	  if (keep_len > 0)
+	    memcpy (&search_buf[0], &search_buf[chunk_size], keep_len);
+
+	  nr_to_read = std::min (search_space_len - keep_len,
+				 (ULONGEST) chunk_size);
+
+	  if (!read_memory (read_addr, &search_buf[keep_len], nr_to_read))
+	    {
+	      warning (_("Unable to access %s bytes of target "
+			 "memory at %s, halting search."),
+		       plongest (nr_to_read),
+		       hex_string (read_addr));
+	      return -1;
+	    }
+
+	  start_addr += chunk_size;
+	}
+    }
+
+  /* Not found.  */
+
+  return 0;
+}
diff --git a/gdbsupport/search.h b/gdbsupport/search.h
new file mode 100644
index 0000000..886d80f
--- /dev/null
+++ b/gdbsupport/search.h
@@ -0,0 +1,42 @@
+/* Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+#ifndef COMMON_SEARCH_H
+#define COMMON_SEARCH_H
+
+#include "gdbsupport/function-view.h"
+
+/* This is needed by the unit test, so appears here.  */
+#define SEARCH_CHUNK_SIZE 16000
+
+/* The type of a callback function that can be used to read memory.
+   Note that target_read_memory is not used here, because gdbserver
+   wants to be able to examine trace data when searching, and
+   target_read_memory does not do this.  */
+
+typedef bool target_read_memory_ftype (CORE_ADDR, gdb_byte *, size_t);
+
+/* Utility implementation of searching memory.  */
+extern int simple_search_memory
+  (gdb::function_view<target_read_memory_ftype> read_memory,
+   CORE_ADDR start_addr,
+   ULONGEST search_space_len,
+   const gdb_byte *pattern,
+   ULONGEST pattern_len,
+   CORE_ADDR *found_addrp);
+
+#endif /* COMMON_SEARCH_H */