From 3aca5b5f1f1617db2220022d9061dcaf129e54c4 Mon Sep 17 00:00:00 2001

From: Mark Wielaard <mark@klomp.org>

Date: Wed, 21 Jun 2023 18:05:12 +0200

Subject: [PATCH] libelf: Replace list of elf_getdata_rawchunk results with a

 tree

elf_getdata_rawchunks did a linear search to see if a chunk was

already fetched. Replace this list with a binary search tree to make

lookup faster when a lot of Elf_Data_Chunk were created.

       * libelf/libelfP.h (Elf_Data_Chunk): Remove next field.

       (struct Elf): Change the rawchunks type from Elf_Data_Chunk *

       to void *.

       * elf_getdata_rawchunk.c (chunk_compare): New static function.

       (elf_getdata_rawchunk): Use tsearch instead of a manual linked

       list.

       * elf_end.c (free_chunk): New static function.

       (elf_end): Call tdestroy instead of walking linked list.

Signed-off-by: Mark Wielaard <mark@klomp.org>

---

 libelf/elf_end.c              | 22 +++++++++-------

 libelf/elf_getdata_rawchunk.c | 47 +++++++++++++++++++++++++----------

 libelf/libelfP.h              | 13 ++++------

 3 files changed, 52 insertions(+), 30 deletions(-)

diff --git a/libelf/elf_end.c b/libelf/elf_end.c

index 5c451f36..3e5d4c86 100644

--- a/libelf/elf_end.c

+++ b/libelf/elf_end.c

@@ -1,5 +1,6 @@

 /* Free resources associated with Elf descriptor.

    Copyright (C) 1998,1999,2000,2001,2002,2004,2005,2007,2015,2016 Red Hat, Inc.

+   Copyright (C) 2023 Mark J. Wielaard <mark@klomp.org>

    This file is part of elfutils.

    Written by Ulrich Drepper <drepper@redhat.com>, 1998.

@@ -32,12 +33,22 @@

 #endif

 #include <assert.h>

+#include <search.h>

 #include <stddef.h>

 #include <stdlib.h>

 #include "libelfP.h"

+static void

+free_chunk (void *n)

+{

+  Elf_Data_Chunk *rawchunk = (Elf_Data_Chunk *)n;

+  if (rawchunk->dummy_scn.flags & ELF_F_MALLOCED)

+    free (rawchunk->data.d.d_buf);

+  free (rawchunk);

+}

+

 int

 elf_end (Elf *elf)

 {

@@ -112,20 +123,13 @@ elf_end (Elf *elf)

     case ELF_K_ELF:

       {

-	Elf_Data_Chunk *rawchunks

+	void *rawchunks

 	  = (elf->class == ELFCLASS32

 	     || (offsetof (struct Elf, state.elf32.rawchunks)

 		 == offsetof (struct Elf, state.elf64.rawchunks))

 	     ? elf->state.elf32.rawchunks

 	     : elf->state.elf64.rawchunks);

-	while (rawchunks != NULL)

-	  {

-	    Elf_Data_Chunk *next = rawchunks->next;

-	    if (rawchunks->dummy_scn.flags & ELF_F_MALLOCED)

-	      free (rawchunks->data.d.d_buf);

-	    free (rawchunks);

-	    rawchunks = next;

-	  }

+	tdestroy (rawchunks, free_chunk);

 	Elf_ScnList *list = (elf->class == ELFCLASS32

 			     || (offsetof (struct Elf, state.elf32.scns)

diff --git a/libelf/elf_getdata_rawchunk.c b/libelf/elf_getdata_rawchunk.c

index 5a35ccdc..cfd40396 100644

--- a/libelf/elf_getdata_rawchunk.c

+++ b/libelf/elf_getdata_rawchunk.c

@@ -1,6 +1,6 @@

 /* Return converted data from raw chunk of ELF file.

    Copyright (C) 2007, 2014, 2015 Red Hat, Inc.

-   Copyright (C) 2022 Mark J. Wielaard <mark@klomp.org>

+   Copyright (C) 2022, 2023 Mark J. Wielaard <mark@klomp.org>

    This file is part of elfutils.

    This file is free software; you can redistribute it and/or modify

@@ -33,12 +33,28 @@

 #include <assert.h>

 #include <errno.h>

+#include <search.h>

 #include <stdlib.h>

 #include <string.h>

 #include "libelfP.h"

 #include "common.h"

+static int

+chunk_compare (const void *a, const void *b)

+{

+  Elf_Data_Chunk *da = (Elf_Data_Chunk *)a;

+  Elf_Data_Chunk *db = (Elf_Data_Chunk *)b;

+

+  if (da->offset != db->offset)

+    return da->offset - db->offset;

+

+  if (da->data.d.d_size != db->data.d.d_size)

+    return da->data.d.d_size - db->data.d.d_size;

+

+  return da->data.d.d_type - db->data.d.d_type;

+}

+

 Elf_Data *

 elf_getdata_rawchunk (Elf *elf, int64_t offset, size_t size, Elf_Type type)

 {

@@ -75,19 +91,25 @@ elf_getdata_rawchunk (Elf *elf, int64_t offset, size_t size, Elf_Type type)

   rwlock_rdlock (elf->lock);

   /* Maybe we already got this chunk?  */

-  Elf_Data_Chunk *rawchunks = elf->state.elf.rawchunks;

-  while (rawchunks != NULL)

+  Elf_Data_Chunk key;

+  key.offset = offset;

+  key.data.d.d_size = size;

+  key.data.d.d_type = type;

+  Elf_Data_Chunk **found = tsearch (&key, &elf->state.elf.rawchunks,

+				    &chunk_compare);

+  if (found == NULL)

+    goto nomem;

+

+  /* Existing entry.  */

+  if (*found != &key && *found != NULL)

     {

-      if ((rawchunks->offset == offset || size == 0)

-	  && rawchunks->data.d.d_size == size

-	  && rawchunks->data.d.d_type == type)

-	{

-	  result = &rawchunks->data.d;

-	  goto out;

-	}

-      rawchunks = rawchunks->next;

+      result = &(*found)->data.d;

+      goto out;

     }

+  /* New entry.  */

+  *found = NULL;

+

   size_t align = __libelf_type_align (elf->class, type);

   if (elf->map_address != NULL)

     {

@@ -189,8 +211,7 @@ elf_getdata_rawchunk (Elf *elf, int64_t offset, size_t size, Elf_Type type)

   rwlock_unlock (elf->lock);

   rwlock_wrlock (elf->lock);

-  chunk->next = elf->state.elf.rawchunks;

-  elf->state.elf.rawchunks = chunk;

+  *found = chunk;

   result = &chunk->data.d;

  out:

diff --git a/libelf/libelfP.h b/libelf/libelfP.h

index 6624f38a..d3c241e5 100644

--- a/libelf/libelfP.h

+++ b/libelf/libelfP.h

@@ -1,5 +1,6 @@

 /* Internal interfaces for libelf.

    Copyright (C) 1998-2010, 2015, 2016 Red Hat, Inc.

+   Copyright (C) 2023 Mark J. Wielaard <mark@klomp.org>

    This file is part of elfutils.

    Contributed by Ulrich Drepper <drepper@redhat.com>, 1998.

@@ -262,11 +263,7 @@ typedef struct Elf_ScnList

 typedef struct Elf_Data_Chunk

 {

   Elf_Data_Scn data;

-  union

-  {

-    Elf_Scn dummy_scn;

-    struct Elf_Data_Chunk *next;

-  };

+  Elf_Scn dummy_scn;

   int64_t offset;		/* The original raw offset in the Elf image.  */

 } Elf_Data_Chunk;

@@ -324,7 +321,7 @@ struct Elf

       Elf_ScnList *scns_last;	/* Last element in the section list.

 				   If NULL the data has not yet been

 				   read from the file.  */

-      Elf_Data_Chunk *rawchunks; /* List of elf_getdata_rawchunk results.  */

+      void *rawchunks;		/* Tree of elf_getdata_rawchunk results.  */

       unsigned int scnincr;	/* Number of sections allocate the last

 				   time.  */

       int ehdr_flags;		/* Flags (dirty) for ELF header.  */

@@ -343,7 +340,7 @@ struct Elf

       Elf_ScnList *scns_last;	/* Last element in the section list.

 				   If NULL the data has not yet been

 				   read from the file.  */

-      Elf_Data_Chunk *rawchunks; /* List of elf_getdata_rawchunk results.  */

+      void *rawchunks;		/* Tree of elf_getdata_rawchunk results.  */

       unsigned int scnincr;	/* Number of sections allocate the last

 				   time.  */

       int ehdr_flags;		/* Flags (dirty) for ELF header.  */

@@ -368,7 +365,7 @@ struct Elf

       Elf_ScnList *scns_last;	/* Last element in the section list.

 				   If NULL the data has not yet been

 				   read from the file.  */

-      Elf_Data_Chunk *rawchunks; /* List of elf_getdata_rawchunk results.  */

+      void *rawchunks;		/* Tree of elf_getdata_rawchunk results.  */

       unsigned int scnincr;	/* Number of sections allocate the last

 				   time.  */

       int ehdr_flags;		/* Flags (dirty) for ELF header.  */

-- 

2.40.1