Re: --enable-auto-import extension

[egor duda <deo@logos-m.ru>]

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Hi!

Tuesday, 02 July, 2002 Charles Wilson cwilson@ece.gatech.edu wrote:

>> What i was talking about is 64-bit versions of windows where addresses
>> (and so base symbol values and addends are 64-bit). Or if we want to
>> add some other types of relocations. Adding type field will make it
>> possible to add extensions to this feature.

CW> </sheepish> Yeah.  What he said.  <I'll be over here....>

Well, after thinking twice about it i concluded that such flexibility
may be not that good after all. Sure, it allows adding extensions, but
make it hard to check at link-time if runtime support for those
extensions is present. So i think we can stay with simple format of
pseudo relocations for now.

>> Of course. Luckily, all we have to check is that it doesn't change
>> binaries for existing code, 

CW> Hard to do, really -- DLLs get a timestamp in their header, so even 
CW> under ideal conditions you can't do a simple diff on two DLLs...I 
CW> suppose you could make sure that two DLLs differ ONLY in "unimportant" 
CW> ways, like timestamp.

Someone suggested that one can do 'cmp -i 150 old.dll new.dll', or
whatever offset timestamp is located at.

Ok, i've finalized patch and test. I suppose i have a copyright
assignment with FSF for this changes to get incorporated into official
sources. As far as i understand, i have to get an assignment form from
binutils maintainer, right? 

Egor.            mailto:deo@logos-m.ru ICQ 5165414 FidoNet 2:5020/496.19

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2002-07-01  Egor Duda  <deo@logos-m.ru>

	* bfdlink.h (struct bfd_link_info): Add new boolean
	field pei386_runtime_pseudo_reloc.

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Index: bfdlink.h
===================================================================
RCS file: /cvs/uberbaum/include/bfdlink.h,v
retrieving revision 1.20
diff -u -p -2 -r1.20 bfdlink.h
--- bfdlink.h	1 Jul 2002 08:04:47 -0000	1.20
+++ bfdlink.h	2 Jul 2002 07:47:09 -0000
@@ -330,4 +330,9 @@ struct bfd_link_info
   int pei386_auto_import;
 
+  /* Non-zero if runtime relocs for DATA items with non-zero addends
+     in pei386 DLLs should be generated.  Set to 1 if this feature
+     is explicitly requested by the user, -1 if enabled by default.  */
+  int pei386_runtime_pseudo_reloc;
+
   /* True if non-PLT relocs should be merged into one reloc section
      and sorted so that relocs against the same symbol come together.  */

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2002-07-01  Egor Duda  <deo@logos-m.ru>

	* ldmain.c (main): Make runtime relocs disabled by default. Remove
	assignment which has no effect.
	* pe-dll.h (pe_create_import_fixup): Change prototype.
	* pe-dll.c (make_runtime_pseudo_reloc): New function.
	(pe_create_runtime_relocator_reference): Ditto.
	(pe_create_import_fixup): Handle relocations with non-zero addends.
	* emultempl/pe.em: Add options --enable-runtime-pseudo-reloc and
	--disable-runtime-pseudo-reloc.
	(make_import_fixup): Handle relocations with non-zero addends. Create
	an external reference to _pei386_runtime_relocator symbol if at least
	one pseudo reloc was created.
	* scripttempl/pe.sc: Handle .rdata_runtime_pseudo_reloc sections.
	Add symbols for application to access them.
	* ld.texinfo: Document --enable-runtime-pseudo-reloc and
	--disable-runtime-pseudo-reloc options.

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Index: ld.texinfo
===================================================================
RCS file: /cvs/uberbaum/ld/ld.texinfo,v
retrieving revision 1.70
diff -u -p -2 -r1.70 ld.texinfo
--- ld.texinfo	20 Jun 2002 14:44:10 -0000	1.70
+++ ld.texinfo	2 Jul 2002 11:37:31 -0000
@@ -1794,5 +1794,9 @@ There are several ways to address this d
 data type of the exported variable:
 
-One solution is to force one of the 'constants' to be a variable -- 
+One way is to use --enable-runtime-pseudo-reloc switch. This leaves the task
+of adjusting references in your client code for runtime environment, so
+this method works only when runtime environtment supports this feature.
+
+Second solution is to force one of the 'constants' to be a variable -- 
 that is, unknown and un-optimizable at compile time.  For arrays, 
 there are two possibilities: a) make the indexee (the array's address) 
@@ -1830,5 +1834,5 @@ extern_ll -->
 @end example
 
-A second method of dealing with this difficulty is to abandon
+A third method of dealing with this difficulty is to abandon
 'auto-import' for the offending symbol and mark it with 
 @code{__declspec(dllimport)}.  However, in practice that
@@ -1881,5 +1885,5 @@ void main(int argc, char **argv)@{
 @end example
 
-A third way to avoid this problem is to re-code your 
+A fouth way to avoid this problem is to re-code your 
 library to use a functional interface rather than a data interface
 for the offending variables (e.g. set_foo() and get_foo() accessor
@@ -1890,4 +1894,15 @@ functions).
 Do not attempt to do sophisticalted linking of @code{_symbol} to 
 @code{__imp__symbol} for DATA imports from DLLs.
+
+@kindex --enable-runtime-pseudo-reloc
+@item --enable-runtime-pseudo-reloc
+If your code contains expressions described in --enable-auto-import section,
+that is, DATA imports from DLL with non-zero offset, this switch will create
+a vector of 'runtime pseudo relocations' which can be used by runtime
+environment to adjust references to such data in your client code. 
+
+@kindex --disable-runtime-pseudo-reloc
+@item --disable-runtime-pseudo-reloc
+Do not create pseudo relocations for non-zero offset DATA imports from DLLs.
 
 @kindex --enable-extra-pe-debug
Index: ldmain.c
===================================================================
RCS file: /cvs/uberbaum/ld/ldmain.c,v
retrieving revision 1.49
diff -u -p -2 -r1.49 ldmain.c
--- ldmain.c	1 Jul 2002 08:07:29 -0000	1.49
+++ ldmain.c	2 Jul 2002 11:37:32 -0000
@@ -261,6 +261,6 @@ main (argc, argv)
   link_info.flags = (bfd_vma) 0;
   link_info.flags_1 = (bfd_vma) 0;
-  link_info.pei386_auto_import = false;
   link_info.pei386_auto_import = -1;
+  link_info.pei386_runtime_pseudo_reloc = false;
   link_info.combreloc = true;
   link_info.spare_dynamic_tags = 5;
Index: pe-dll.c
===================================================================
RCS file: /cvs/uberbaum/ld/pe-dll.c,v
retrieving revision 1.41
diff -u -p -2 -r1.41 pe-dll.c
--- pe-dll.c	25 May 2002 20:39:25 -0000	1.41
+++ pe-dll.c	2 Jul 2002 11:37:32 -0000
@@ -142,4 +142,5 @@ static struct sec *edata_s, *reloc_s;
 static unsigned char *edata_d, *reloc_d;
 static size_t edata_sz, reloc_sz;
+static int runtime_pseudo_relocs_created = 0;
 
 typedef struct
@@ -302,4 +303,8 @@ static char *make_import_fixup_mark PARA
 static bfd *make_import_fixup_entry
   PARAMS ((const char *, const char *, const char *, bfd *));
+static bfd *make_runtime_pseudo_reloc
+  PARAMS ((const char *, const char *, int, bfd *));
+static bfd *pe_create_runtime_relocator_reference
+  PARAMS ((bfd *parent));
 static unsigned int pe_get16 PARAMS ((bfd *, int));
 static unsigned int pe_get32 PARAMS ((bfd *, int));
@@ -2068,7 +2073,103 @@ make_import_fixup_entry (name, fixup_nam
 }
 
+/*	.section	.rdata_runtime_pseudo_reloc
+ 	.long		addend
+ 	.rva		__fuNN_SYM (pointer to reference (address) in text)  */
+
+static bfd *
+make_runtime_pseudo_reloc (name, fixup_name, addend, parent)
+     const char *name ATTRIBUTE_UNUSED;
+     const char *fixup_name;
+     int addend;
+     bfd *parent;
+{
+  asection *rt_rel;
+  unsigned char *rt_rel_d;
+  char *oname;
+  bfd *abfd;
+
+  oname = (char *) xmalloc (20);
+  sprintf (oname, "rtr%06d.o", tmp_seq);
+  tmp_seq++;
+
+  abfd = bfd_create (oname, parent);
+  bfd_find_target (pe_details->object_target, abfd);
+  bfd_make_writable (abfd);
+
+  bfd_set_format (abfd, bfd_object);
+  bfd_set_arch_mach (abfd, pe_details->bfd_arch, 0);
+
+  symptr = 0;
+  symtab = (asymbol **) xmalloc (2 * sizeof (asymbol *));
+  rt_rel = quick_section (abfd, ".rdata_runtime_pseudo_reloc", SEC_HAS_CONTENTS, 2);
+
+  quick_symbol (abfd, "", fixup_name, "", UNDSEC, BSF_GLOBAL, 0);
+
+  bfd_set_section_size (abfd, rt_rel, 8);
+  rt_rel_d = (unsigned char *) xmalloc (8);
+  rt_rel->contents = rt_rel_d;
+  memset (rt_rel_d, 0, 8);
+  bfd_put_32 (abfd, addend, rt_rel_d);
+
+  quick_reloc (abfd, 4, BFD_RELOC_RVA, 1);
+  save_relocs (rt_rel);
+
+  bfd_set_symtab (abfd, symtab, symptr);
+
+  bfd_set_section_contents (abfd, rt_rel, rt_rel_d, 0, 8);
+
+  bfd_make_readable (abfd);
+  return abfd;
+}
+
+/*	.section	.rdata
+ 	.rva		__pei386_runtime_relocator */
+
+static bfd *
+pe_create_runtime_relocator_reference (parent)
+     bfd *parent;
+{
+  asection *extern_rt_rel;
+  unsigned char *extern_rt_rel_d;
+  char *oname;
+  bfd *abfd;
+
+  oname = (char *) xmalloc (20);
+  sprintf (oname, "ertr%06d.o", tmp_seq);
+  tmp_seq++;
+
+  abfd = bfd_create (oname, parent);
+  bfd_find_target (pe_details->object_target, abfd);
+  bfd_make_writable (abfd);
+
+  bfd_set_format (abfd, bfd_object);
+  bfd_set_arch_mach (abfd, pe_details->bfd_arch, 0);
+
+  symptr = 0;
+  symtab = (asymbol **) xmalloc (2 * sizeof (asymbol *));
+  extern_rt_rel = quick_section (abfd, ".rdata", SEC_HAS_CONTENTS, 2);
+
+  quick_symbol (abfd, "", "__pei386_runtime_relocator", "", UNDSEC, BSF_NO_FLAGS, 0);
+
+  bfd_set_section_size (abfd, extern_rt_rel, 4);
+  extern_rt_rel_d = (unsigned char *) xmalloc (4);
+  extern_rt_rel->contents = extern_rt_rel_d;
+
+  quick_reloc (abfd, 0, BFD_RELOC_RVA, 1);
+  save_relocs (extern_rt_rel);
+
+  bfd_set_symtab (abfd, symtab, symptr);
+
+  bfd_set_section_contents (abfd, extern_rt_rel, extern_rt_rel_d, 0, 4);
+
+  bfd_make_readable (abfd);
+  return abfd;
+}
+
 void
-pe_create_import_fixup (rel)
+pe_create_import_fixup (rel, s, addend)
      arelent *rel;
+     asection *s;
+     int addend;
 {
   char buf[300];
@@ -2077,4 +2178,5 @@ pe_create_import_fixup (rel)
   const char *name = sym->name;
   char *fixup_name = make_import_fixup_mark (rel);
+  bfd *b;
 
   sprintf (buf, U ("_nm_thnk_%s"), name);
@@ -2091,12 +2193,36 @@ pe_create_import_fixup (rel)
     }
 
-  {
-    extern char * pe_data_import_dll;
-    char * dll_symname = pe_data_import_dll ? pe_data_import_dll : "unknown";
+  if (addend == 0 || link_info.pei386_runtime_pseudo_reloc)
+    {
+      extern char * pe_data_import_dll;
+      char * dll_symname = pe_data_import_dll ? pe_data_import_dll : "unknown";
 
-    bfd *b = make_import_fixup_entry (name, fixup_name, dll_symname,
-				      output_bfd);
-    add_bfd_to_link (b, b->filename, &link_info);
-  }
+      b = make_import_fixup_entry (name, fixup_name, dll_symname, output_bfd);
+      add_bfd_to_link (b, b->filename, &link_info);
+    }
+
+  if (addend != 0)
+    {
+      if (link_info.pei386_runtime_pseudo_reloc)
+	{
+	  if (pe_dll_extra_pe_debug)
+	    printf ("creating runtime pseudo-reloc entry for %s (addend=%d)\n",
+		   fixup_name, addend);
+	  b = make_runtime_pseudo_reloc (name, fixup_name, addend, output_bfd);
+	  add_bfd_to_link (b, b->filename, &link_info);
+	  if (runtime_pseudo_relocs_created == 0)
+	    {
+	      b = pe_create_runtime_relocator_reference (output_bfd);
+	      add_bfd_to_link (b, b->filename, &link_info);
+	    }
+	  runtime_pseudo_relocs_created++;
+	} 
+      else
+	{
+	  einfo (_("%C: variable '%T' can't be auto-imported. Please read the documentation for ld's --enable-auto-import for details.\n"),
+		 s->owner, s, rel->address, sym->name);
+	  einfo ("%X");
+	}
+    }
 }
 
Index: pe-dll.h
===================================================================
RCS file: /cvs/uberbaum/ld/pe-dll.h,v
retrieving revision 1.8
diff -u -p -2 -r1.8 pe-dll.h
--- pe-dll.h	8 Jun 2002 07:39:45 -0000	1.8
+++ pe-dll.h	2 Jul 2002 11:37:32 -0000
@@ -51,4 +51,4 @@ extern void pe_walk_relocs_of_symbol PAR
 					      int (*cb) (arelent *, asection *)));
 
-extern void pe_create_import_fixup PARAMS ((arelent * rel));
+extern void pe_create_import_fixup PARAMS ((arelent * rel, asection * s, int addend));
 #endif /* PE_DLL_H */
Index: emultempl/pe.em
===================================================================
RCS file: /cvs/uberbaum/ld/emultempl/pe.em,v
retrieving revision 1.65
diff -u -p -2 -r1.65 pe.em
--- emultempl/pe.em	1 Jul 2002 08:07:31 -0000	1.65
+++ emultempl/pe.em	2 Jul 2002 11:37:37 -0000
@@ -175,4 +175,5 @@ gld_${EMULATION_NAME}_before_parse()
   config.has_shared = 1;
   link_info.pei386_auto_import = -1;
+  link_info.pei386_runtime_pseudo_reloc = false;
 
 #if (PE_DEF_SUBSYSTEM == 9) || (PE_DEF_SUBSYSTEM == 2)
@@ -223,4 +224,8 @@ gld_${EMULATION_NAME}_before_parse()
 #define OPTION_ENABLE_EXTRA_PE_DEBUG	(OPTION_DLL_DISABLE_AUTO_IMPORT + 1)
 #define OPTION_EXCLUDE_LIBS		(OPTION_ENABLE_EXTRA_PE_DEBUG + 1)
+#define OPTION_DLL_ENABLE_RUNTIME_PSEUDO_RELOC	\
+				(OPTION_EXCLUDE_LIBS + 1)
+#define OPTION_DLL_DISABLE_RUNTIME_PSEUDO_RELOC	\
+				(OPTION_DLL_ENABLE_RUNTIME_PSEUDO_RELOC + 1)
 
 static struct option longopts[] = {
@@ -264,4 +269,6 @@ static struct option longopts[] = {
   {"disable-auto-import", no_argument, NULL, OPTION_DLL_DISABLE_AUTO_IMPORT},
   {"enable-extra-pe-debug", no_argument, NULL, OPTION_ENABLE_EXTRA_PE_DEBUG},
+  {"enable-runtime-pseudo-reloc", no_argument, NULL, OPTION_DLL_ENABLE_RUNTIME_PSEUDO_RELOC},
+  {"disable-runtime-pseudo-reloc", no_argument, NULL, OPTION_DLL_DISABLE_RUNTIME_PSEUDO_RELOC},
 #endif
   {NULL, no_argument, NULL, 0}
@@ -353,4 +360,8 @@ gld_${EMULATION_NAME}_list_options (file
                                        __imp_sym for DATA references\n"));
   fprintf (file, _("  --disable-auto-import              Do not auto-import DATA items from DLLs\n"));
+  fprintf (file, _("  --enable-runtime-pseudo-reloc      Work around auto-import limitations by\n\
+                                       adding pseudo-relocations resolved at runtime.\n"));
+  fprintf (file, _("  --disable-runtime-pseudo-reloc     Do not add runtime pseudo-relocations for\n\
+                                       auto-imported DATA.\n"));
   fprintf (file, _("  --enable-extra-pe-debug            Enable verbose debug output when building\n\
                                        or linking to DLLs (esp. auto-import)\n"));
@@ -634,4 +645,10 @@ gld_${EMULATION_NAME}_parse_args(argc, a
       link_info.pei386_auto_import = 0;
       break;
+    case OPTION_DLL_ENABLE_RUNTIME_PSEUDO_RELOC:
+      link_info.pei386_runtime_pseudo_reloc = 1;
+      break;
+    case OPTION_DLL_DISABLE_RUNTIME_PSEUDO_RELOC:
+      link_info.pei386_runtime_pseudo_reloc = 0;
+      break;
     case OPTION_ENABLE_EXTRA_PE_DEBUG:
       pe_dll_extra_pe_debug = 1;
@@ -881,12 +898,5 @@ make_import_fixup (rel, s)
       }
 
-    if (addend == 0)
-      pe_create_import_fixup (rel);
-    else
-      {
-        einfo (_("%C: variable '%T' can't be auto-imported. Please read the documentation for ld's --enable-auto-import for details.\n"),
-               s->owner, s, rel->address, sym->name);
-        einfo ("%X");
-      }
+    pe_create_import_fixup (rel, s, addend);
   }
 
Index: scripttempl/pe.sc
===================================================================
RCS file: /cvs/uberbaum/ld/scripttempl/pe.sc,v
retrieving revision 1.5
diff -u -p -2 -r1.5 pe.sc
--- scripttempl/pe.sc	16 Jan 2002 01:48:43 -0000	1.5
+++ scripttempl/pe.sc	2 Jul 2002 11:37:37 -0000
@@ -86,4 +86,7 @@ SECTIONS
     ${R_RDATA}
     *(.eh_frame)
+    ___RUNTIME_PSEUDO_RELOC_LIST__ = .; __RUNTIME_PSEUDO_RELOC_LIST__ = . ;
+    *(.rdata_runtime_pseudo_reloc)
+    ___RUNTIME_PSEUDO_RELOC_LIST_END__ = .; __RUNTIME_PSEUDO_RELOC_LIST_END__ = . ;
   }
 

[-- Attachment #6: crtest.c --]
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#include <stdio.h>
#include <stdlib.h>
#include "crtest.h"

#if defined(__CYGWIN__)
#  define HAVE_FORK
#endif

#if !defined(RUNTIME_PSEUDO_RELOC_SUPPORT)
#include <windows.h>
typedef struct
  {
    DWORD addend;
    DWORD target;
  }
runtime_pseudo_reloc;

extern runtime_pseudo_reloc __RUNTIME_PSEUDO_RELOC_LIST__;
extern runtime_pseudo_reloc __RUNTIME_PSEUDO_RELOC_LIST_END__;
extern void* _data_start__;
extern void* _image_base__;

void
_pei386_runtime_relocator (runtime_pseudo_reloc* start, runtime_pseudo_reloc* end)
{
  DWORD reloc_target;
  runtime_pseudo_reloc* r;
  for (r = start; r < end; r++)
    {
      printf ("ptr=%x, addend=%d\n", (long)r->target, r->addend);
      reloc_target = (DWORD) &_image_base__ + r->target;
      printf ("reloc target=%x\n", reloc_target);
      *((DWORD*) reloc_target) += r->addend;
    }
}
#endif

void
print_data ()
{
  printf ("data=%d %d %c\n", foo[0].x, foo[1].y[2], foo[1].z[1]);
}

int
main ()
{
  int pid;
#if !defined(RUNTIME_PSEUDO_RELOC_SUPPORT)
  _pei386_runtime_relocator (&__RUNTIME_PSEUDO_RELOC_LIST__,
                             &__RUNTIME_PSEUDO_RELOC_LIST_END__);
#endif
#if defined(RUNTIME_PSEUDO_RELOC_SUPPORT) && defined(HAVE_FORK)
  switch (pid = fork ())
    {
    case -1:
      perror ("fork");
      break;
    case 0:
      printf ("child: ");
      print_data ();
      break;
    default:
      wait (NULL);
      printf ("parent: ");
      print_data ();
      break;
    }
#else
  print_data ();
#endif
  return 0;
}

[-- Attachment #7: crtest.h --]
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typedef struct
  {
    int x;
    int y[3];
    char z[3];
  }
foo_t;

extern foo_t foo[2];

[-- Attachment #8: crtest_dll.c --]
[-- Type: application/octet-stream, Size: 128 bytes --]

#include "crtest.h"

foo_t foo[2] = { {1, {11, 12, 13}, {'a', 'b', 'c'}},
                 {2, {21, 22, 23}, {'d', 'e', 'f'}}};

[-- Attachment #9: Makefile --]
[-- Type: application/octet-stream, Size: 867 bytes --]

# mingw
# CC=gcc -mno-cygwin
# CFLAGS=-g3 -I . -DNO_RUNTIME_PSEUDO_RELOC_SUPPORT

# cygwin w/o runtime pseudo reloc support
CC=gcc
CFLAGS=-g3 -I . -DNO_RUNTIME_PSEUDO_RELOC_SUPPORT

# cygwin with runtime pseudo reloc support
# CC=gcc
# CFLAGS=-g3 -I . -DRUNTIME_PSEUDO_RELOC_SUPPORT

DLL_LDFLAGS=-Wl,--export-all-symbols -Wl,--out-implib=libcrtest.dll.a
EXE_LDFLAGS=-Wl,--enable-auto-import -Wl,--enable-runtime-pseudo-reloc
# DEBUG_LDFLAGS=-Wl,--enable-extra-pe-debug -Wl,--verbose

all: crtest.exe crtest.dll

crtest_dll.o: crtest_dll.c
	$(CC) $(CFLAGS) -c $<

crtest.o: crtest.c
	$(CC) $(CFLAGS) -c $<

crtest.dll libcrtest.dll.a: crtest_dll.o
	$(CC) -shared -o crtest.dll $(DLL_LDFLAGS) $<

crtest.exe: crtest.o libcrtest.dll.a
	$(CC) $(EXE_LDFLAGS) $(DEBUG_LDFLAGS) -o crtest.exe crtest.o -L. -lcrtest

.PHONY: clean

clean:
	rm -f *.o *.a crtest.exe crtest.dll