diff mbox

Build compiler checksum from object files v2

Message ID 1286477963-17915-1-git-send-email-andi@firstfloor.org
State New
Headers show

Commit Message

Andi Kleen Oct. 7, 2010, 6:59 p.m. UTC 
From: Andi Kleen <ak@linux.intel.com>

Linking the compiler first to generate the compiler checksum
is extremly costly on a LTO bootstrap build. The link phase
has to recompile everything.

Change the checksum computation to run the checksum over the
object files and a file containing the link options instead.
This should be about as good and is much faster.

Based on discussions with various people.

Passed bootstrap and test suite on x86_64-linux. Ok to commit?

v2: Fix changelog, handle Objective C/C++ too, use move-if-change,
    Remove PHONY

gcc/

2010-10-07  Andi Kleen  <ak@linux.intel.com>

	* Makefile.in (MOSTLYCLEANFILES): Remove cc1*dummy, add
	checksum-options.
	(checksum-options): Add.
	(cc1-dummy): Remove.
	(cc1-checksum): Change to run checksum over object files
	and options only.
	* dummy-checksum.c: Remove.
	* genchecksum.c: Update copyright.
	(usage): Allow multiple arguments.
	(BLOCKSIZE): Add.
	(dosum): Change for incremental checksum. Remove C output.
	(main): Iterate over all argument files. Add C output.

gcc/cp

2010-10-07  Andi Kleen  <ak@linux.intel.com>

	* Make-lang.in (c++_OBJS): Remove dummy-checksum.o.
	(cc1plus-dummy): Remove.
	(cc1plus-checksum): Change to run checksum over object files
        and options only.

gcc/objc

2010-10-07  Andi Kleen  <ak@linux.intel.com>

	* Make-lang.in (cc1obj-dummy): Remove.
	(cc1obj-checksum): Change to run checksum over object files
        and options only.

gcc/objcp

2010-10-07  Andi Kleen  <ak@linux.intel.com>

	* Make-lang.in (cc1objplus-dummy): Remove.
	(cc1objplus-checksum): Change to run checksum over object files
        and options only.
---
 gcc/Makefile.in        |   20 +++++++------
 gcc/cp/Make-lang.in    |   14 ++++----
 gcc/dummy-checksum.c   |    3 --
 gcc/genchecksum.c      |   73 ++++++++++++++++++++++++++++++++++++++----------
 gcc/objc/Make-lang.in  |   12 +++----
 gcc/objcp/Make-lang.in |   13 ++++----
 6 files changed, 87 insertions(+), 48 deletions(-)
 delete mode 100644 gcc/dummy-checksum.c

Comments

Andi Kleen Oct. 11, 2010, 10:22 a.m. UTC | #1 
Andi Kleen <andi@firstfloor.org> writes:

> From: Andi Kleen <ak@linux.intel.com>
>
> Linking the compiler first to generate the compiler checksum
> is extremly costly on a LTO bootstrap build. The link phase
> has to recompile everything.

Ping? Is this ok to commit? 

I believe parts have been already acked in v1, but the final
v2 still needs a review.

Thanks,
-Andi

>
> Change the checksum computation to run the checksum over the
> object files and a file containing the link options instead.
> This should be about as good and is much faster.
>
> Based on discussions with various people.
>
> Passed bootstrap and test suite on x86_64-linux. Ok to commit?
>
> v2: Fix changelog, handle Objective C/C++ too, use move-if-change,
>     Remove PHONY
>
> gcc/
>
> 2010-10-07  Andi Kleen  <ak@linux.intel.com>
>
> 	* Makefile.in (MOSTLYCLEANFILES): Remove cc1*dummy, add
> 	checksum-options.
> 	(checksum-options): Add.
> 	(cc1-dummy): Remove.
> 	(cc1-checksum): Change to run checksum over object files
> 	and options only.
> 	* dummy-checksum.c: Remove.
> 	* genchecksum.c: Update copyright.
> 	(usage): Allow multiple arguments.
> 	(BLOCKSIZE): Add.
> 	(dosum): Change for incremental checksum. Remove C output.
> 	(main): Iterate over all argument files. Add C output.
>
> gcc/cp
>
> 2010-10-07  Andi Kleen  <ak@linux.intel.com>
>
> 	* Make-lang.in (c++_OBJS): Remove dummy-checksum.o.
> 	(cc1plus-dummy): Remove.
> 	(cc1plus-checksum): Change to run checksum over object files
>         and options only.
>
> gcc/objc
>
> 2010-10-07  Andi Kleen  <ak@linux.intel.com>
>
> 	* Make-lang.in (cc1obj-dummy): Remove.
> 	(cc1obj-checksum): Change to run checksum over object files
>         and options only.
>
> gcc/objcp
>
> 2010-10-07  Andi Kleen  <ak@linux.intel.com>
>
> 	* Make-lang.in (cc1objplus-dummy): Remove.
> 	(cc1objplus-checksum): Change to run checksum over object files
>         and options only.
> ---
>  gcc/Makefile.in        |   20 +++++++------
>  gcc/cp/Make-lang.in    |   14 ++++----
>  gcc/dummy-checksum.c   |    3 --
>  gcc/genchecksum.c      |   73 ++++++++++++++++++++++++++++++++++++++----------
>  gcc/objc/Make-lang.in  |   12 +++----
>  gcc/objcp/Make-lang.in |   13 ++++----
>  6 files changed, 87 insertions(+), 48 deletions(-)
>  delete mode 100644 gcc/dummy-checksum.c
>
> diff --git a/gcc/Makefile.in b/gcc/Makefile.in
> index 3d936f6..d3dbef9 100644
> --- a/gcc/Makefile.in
> +++ b/gcc/Makefile.in
> @@ -1489,10 +1489,10 @@ BACKEND = main.o @TREEBROWSER@ libbackend.a $(CPPLIB) $(LIBDECNUMBER)
>  MOSTLYCLEANFILES = insn-flags.h insn-config.h insn-codes.h \
>   insn-output.c insn-recog.c insn-emit.c insn-extract.c insn-peep.c \
>   insn-attr.h insn-attrtab.c insn-opinit.c insn-preds.c insn-constants.h \
> - tm-preds.h tm-constrs.h \
> + tm-preds.h tm-constrs.h checksum-options \
>   tree-check.h min-insn-modes.c insn-modes.c insn-modes.h \
>   genrtl.h gt-*.h gtype-*.h gtype-desc.c gtyp-input.list \
> - xgcc$(exeext) cpp$(exeext) cc1$(exeext) cc1*-dummy$(exeext) $(EXTRA_PASSES) \
> + xgcc$(exeext) cpp$(exeext) cc1$(exeext) $(EXTRA_PASSES) \
>   $(EXTRA_PARTS) $(EXTRA_PROGRAMS) gcc-cross$(exeext) \
>   $(SPECS) collect2$(exeext) lto-wrapper$(exeext) \
>   gcov-iov$(build_exeext) gcov$(exeext) gcov-dump$(exeext) \
> @@ -1832,14 +1832,16 @@ $(SPECS): xgcc$(exeext)
>  gcc-cross$(exeext): xgcc$(exeext)
>  	cp xgcc$(exeext) gcc-cross$(exeext)
>  
> -dummy-checksum.o : dummy-checksum.c $(CONFIG_H) $(SYSTEM_H)
> +checksum-options:
> +	echo "$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS)" > checksum-options.tmp \
> +	&& $(srcdir)/../move-if-change checksum-options.tmp checksum-options
>  
> -cc1-dummy$(exeext): $(C_OBJS) dummy-checksum.o $(BACKEND) $(LIBDEPS)
> -	+$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ $(C_OBJS) \
> -	  dummy-checksum.o $(BACKEND) $(LIBS) $(BACKENDLIBS)
> -
> -cc1-checksum.c : cc1-dummy$(exeext) build/genchecksum$(build_exeext)
> -	build/genchecksum$(build_exeext) cc1-dummy$(exeext) > $@
> +# compute checksum over all object files and the options
> +cc1-checksum.c : build/genchecksum$(build_exeext) checksum-options \
> +	$(C_OBJS) $(BACKEND) $(LIBDEPS) 
> +	build/genchecksum$(build_exeext) $(C_OBJS) $(BACKEND) $(LIBDEPS) \
> +                     checksum-options > cc1-checksum.c.tmp && 		 \
> +	$(srcdir)/../move-if-change cc1-checksum.c.tmp cc1-checksum.c
>  
>  cc1-checksum.o : cc1-checksum.c $(CONFIG_H) $(SYSTEM_H)
>  
> diff --git a/gcc/cp/Make-lang.in b/gcc/cp/Make-lang.in
> index 4be40b5..fcf2119 100644
> --- a/gcc/cp/Make-lang.in
> +++ b/gcc/cp/Make-lang.in
> @@ -86,17 +86,17 @@ CXX_AND_OBJCXX_OBJS = cp/call.o cp/decl.o cp/expr.o cp/pt.o cp/typeck2.o \
>  # Language-specific object files for C++.
>  CXX_OBJS = cp/cp-lang.o c-family/stub-objc.o $(CXX_AND_OBJCXX_OBJS)
>  
> -c++_OBJS = $(CXX_OBJS) dummy-checksum.o cc1plus-checksum.o cp/g++spec.o
> +c++_OBJS = $(CXX_OBJS) cc1plus-checksum.o cp/g++spec.o
>  
>  # Use strict warnings for this front end.
>  cp-warn = $(STRICT_WARN)
>  
> -cc1plus-dummy$(exeext): $(CXX_OBJS) dummy-checksum.o $(BACKEND) $(LIBDEPS)
> -	$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ \
> -	      $(CXX_OBJS) dummy-checksum.o $(BACKEND) $(LIBS) $(BACKENDLIBS)
> -
> -cc1plus-checksum.c : cc1plus-dummy$(exeext) build/genchecksum$(build_exeext)
> -	build/genchecksum$(build_exeext) cc1plus-dummy$(exeext) > $@
> +# compute checksum over all object files and the options
> +cc1plus-checksum.c : build/genchecksum$(build_exeext) checksum-options \
> +	$(CXX_OBJS) $(BACKEND) $(LIBDEPS) 
> +	build/genchecksum$(build_exeext) $(CXX_OBJS) $(BACKEND) $(LIBDEPS) \
> +                     checksum-options > cc1plus-checksum.c.tmp &&	   \
> +	$(srcdir)/../move-if-change cc1plus-checksum.c.tmp cc1plus-checksum.c
>  
>  cc1plus-checksum.o : cc1plus-checksum.c $(CONFIG_H) $(SYSTEM_H)
>  
> diff --git a/gcc/dummy-checksum.c b/gcc/dummy-checksum.c
> deleted file mode 100644
> index c90f1ca..0000000
> --- a/gcc/dummy-checksum.c
> +++ /dev/null
> @@ -1,3 +0,0 @@
> -#include "config.h"
> -#include "system.h"
> -EXPORTED_CONST unsigned char executable_checksum[16] = { 0 };
> diff --git a/gcc/genchecksum.c b/gcc/genchecksum.c
> index 235d4fe..e0c71f4 100644
> --- a/gcc/genchecksum.c
> +++ b/gcc/genchecksum.c
> @@ -1,5 +1,5 @@
>  /* Generate checksums of executables for PCH validation
> -   Copyright (C) 2005, 2007, 2009
> +   Copyright (C) 2005, 2007, 2009, 2010
>     Free Software Foundation, Inc.
>  
>  This file is part of GCC.
> @@ -25,15 +25,18 @@ along with GCC; see the file COPYING3.  If not see
>  static void
>  usage (void)
>  {
> -  fputs ("Usage: genchecksums <filename>\n", stderr);
> +  fputs ("Usage: genchecksums <filename> ...\n", stderr);
>  }
>  
> +/* Important: BLOCKSIZE must be a multiple of 64.  */
> +#define BLOCKSIZE 4096
> +
>  static void
> -dosum (const char *file)
> +dosum (struct md5_ctx *ctx, const char *file)
>  {
>    FILE *f;
> -  unsigned char result[16];
> -  int i;
> +  char buffer[BLOCKSIZE + 72];
> +  size_t sum;
>  
>    f = fopen (file, "rb");
>    if (!f)
> @@ -49,30 +52,70 @@ dosum (const char *file)
>        exit (1);
>      }
>  
> -  if (md5_stream (f, result) != 0
> -      || fclose (f) != 0)
> +  /* Iterate over full file contents.  */
> +  while (1)
> +    {
> +      /* We read the file in blocks of BLOCKSIZE bytes.  One call of the
> +	 computation function processes the whole buffer so that with the
> +	 next round of the loop another block can be read.  */
> +      size_t n;
> +      sum = 0;
> +
> +      /* Read block.  Take care for partial reads.  */
> +      do
> +	{
> +	  n = fread (buffer + sum, 1, BLOCKSIZE - sum, f);
> +
> +	  sum += n;
> +	}
> +      while (sum < BLOCKSIZE && n != 0);
> +      if (n == 0 && ferror (f))
> +        exit (1);
> +
> +      /* If end of file is reached, end the loop.  */
> +      if (n == 0)
> +	break;
> +
> +      /* Process buffer with BLOCKSIZE bytes.  Note that
> +			BLOCKSIZE % 64 == 0
> +       */
> +      md5_process_block (buffer, BLOCKSIZE, ctx);
> +    }
> +
> +  /* Add the last bytes if necessary.  */
> +  if (sum > 0)
> +    md5_process_bytes (buffer, sum, ctx);
> +
> +  if (fclose (f) != 0)
>       {
>        fprintf (stderr, "reading %s: %s\n", file, xstrerror (errno));
>        exit (1);
>      }
> -
> -  puts ("#include \"config.h\"");
> -  puts ("#include \"system.h\"");
> -  fputs ("EXPORTED_CONST unsigned char executable_checksum[16] = { ", stdout);
> -  for (i = 0; i < 16; i++)
> -    printf ("0x%02x%s", result[i], i == 15 ? " };\n" : ", ");
>  }
>  
>  int
>  main (int argc, char ** argv)
>  {
> -  if (argc != 2)
> +  struct md5_ctx ctx;
> +  unsigned char result[16];
> +  int i;
> +
> +  if (argc < 2)
>      {
>        usage ();
>        return 1;
>      }
>  
> -  dosum (argv[1]);
> +  md5_init_ctx (&ctx);
> +  for (i = 1; i < argc; i++) 
> +    dosum (&ctx, argv[i]);
> +  md5_finish_ctx (&ctx, result);
> +
> +  puts ("#include \"config.h\"");
> +  puts ("#include \"system.h\"");
> +  fputs ("EXPORTED_CONST unsigned char executable_checksum[16] = { ", stdout);
> +  for (i = 0; i < 16; i++)
> +    printf ("0x%02x%s", result[i], i == 15 ? " };\n" : ", ");
>  
>    return 0;
>  }
> diff --git a/gcc/objc/Make-lang.in b/gcc/objc/Make-lang.in
> index 08189ef..8259190 100644
> --- a/gcc/objc/Make-lang.in
> +++ b/gcc/objc/Make-lang.in
> @@ -51,13 +51,11 @@ OBJC_OBJS = objc/objc-lang.o objc/objc-act.o
>  
>  objc_OBJS = $(OBJC_OBJS) cc1obj-checksum.o
>  
> -cc1obj-dummy$(exeext): $(OBJC_OBJS) $(C_AND_OBJC_OBJS) dummy-checksum.o $(BACKEND) $(LIBDEPS)
> -	+$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ \
> -	      $(OBJC_OBJS) $(C_AND_OBJC_OBJS) dummy-checksum.o \
> -	      $(BACKEND) $(LIBS) $(BACKENDLIBS)
> -
> -cc1obj-checksum.c : cc1obj-dummy$(exeext) build/genchecksum$(build_exeext)
> -	build/genchecksum$(build_exeext) cc1obj-dummy$(exeext) > $@
> +cc1obj-checksum.c : build/genchecksum$(build_exeext) checksum-options \
> +        $(OBJC_OBJS) $(C_AND_OBJC_OBJS) $(BACKEND) $(LIBDEPS)
> +	build/genchecksum$(build_exeext) $(OBJC_OBJS) $(C_AND_OBJC_OBJS) \
> +        $(BACKEND) $(LIBDEPS) checksum-options > cc1obj-checksum.c.tmp && \
> +	$(srcdir)/../move-if-change cc1obj-checksum.c.tmp cc1obj-checksum.c
>  
>  cc1obj-checksum.o : cc1obj-checksum.c $(CONFIG_H) $(SYSTEM_H)
>  
> diff --git a/gcc/objcp/Make-lang.in b/gcc/objcp/Make-lang.in
> index f9adeac..edc5423 100644
> --- a/gcc/objcp/Make-lang.in
> +++ b/gcc/objcp/Make-lang.in
> @@ -54,13 +54,12 @@ OBJCXX_OBJS = objcp/objcp-act.o objcp/objcp-lang.o objcp/objcp-decl.o \
>  
>  obj-c++_OBJS = $(OBJCXX_OBJS) cc1objplus-checksum.o
>  
> -cc1objplus-dummy$(exeext): $(OBJCXX_OBJS) dummy-checksum.o $(BACKEND) \
> -		$(LIBDEPS)
> -	+$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ \
> -		$(OBJCXX_OBJS) dummy-checksum.o $(BACKEND) $(LIBS) $(BACKENDLIBS)
> -
> -cc1objplus-checksum.c : cc1objplus-dummy$(exeext) build/genchecksum$(build_exeext)
> -	build/genchecksum$(build_exeext) cc1objplus-dummy$(exeext) > $@
> +cc1objplus-checksum.c : build/genchecksum$(build_exeext) checksum-options \
> +	$(OBJCXX_OBJS) $(BACKEND) $(LIBDEPS)
> +	build/genchecksum$(build_exeext) $(OBJCXX_OBJS) $(BACKEND) \
> +		$(LIBDEPS) checksum-options > cc1objplus-checksum.c && \
> +	$(srcdir)/../move-if-change cc1objplus-checksum.c.tmp \
> +	cc1objplus-checksum.c
>  
>  cc1objplus-checksum.o : cc1objplus-checksum.c $(CONFIG_H) $(SYSTEM_H)
Paolo Bonzini Oct. 11, 2010, 11:30 a.m. UTC | #2 
On 10/11/2010 12:22 PM, Andi Kleen wrote:
>> >  From: Andi Kleen<ak@linux.intel.com>
>> >
>> >  Linking the compiler first to generate the compiler checksum
>> >  is extremly costly on a LTO bootstrap build. The link phase
>> >  has to recompile everything.
> Ping? Is this ok to commit?
>
> I believe parts have been already acked in v1, but the final
> v2 still needs a review.

The patch looks okay, but I cannot approve all of it anyway.

Paolo
Richard Biener Oct. 11, 2010, 11:57 a.m. UTC | #3 
On Mon, Oct 11, 2010 at 1:30 PM, Paolo Bonzini <bonzini@gnu.org> wrote:
> On 10/11/2010 12:22 PM, Andi Kleen wrote:
>>>
>>> >  From: Andi Kleen<ak@linux.intel.com>
>>> >
>>> >  Linking the compiler first to generate the compiler checksum
>>> >  is extremly costly on a LTO bootstrap build. The link phase
>>> >  has to recompile everything.
>>
>> Ping? Is this ok to commit?
>>
>> I believe parts have been already acked in v1, but the final
>> v2 still needs a review.
>
> The patch looks okay, but I cannot approve all of it anyway.

Ok.

Thanks,
Richard.

> Paolo
>
diff mbox

Patch

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 3d936f6..d3dbef9 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -1489,10 +1489,10 @@  BACKEND = main.o @TREEBROWSER@ libbackend.a $(CPPLIB) $(LIBDECNUMBER)
 MOSTLYCLEANFILES = insn-flags.h insn-config.h insn-codes.h \
  insn-output.c insn-recog.c insn-emit.c insn-extract.c insn-peep.c \
  insn-attr.h insn-attrtab.c insn-opinit.c insn-preds.c insn-constants.h \
- tm-preds.h tm-constrs.h \
+ tm-preds.h tm-constrs.h checksum-options \
  tree-check.h min-insn-modes.c insn-modes.c insn-modes.h \
  genrtl.h gt-*.h gtype-*.h gtype-desc.c gtyp-input.list \
- xgcc$(exeext) cpp$(exeext) cc1$(exeext) cc1*-dummy$(exeext) $(EXTRA_PASSES) \
+ xgcc$(exeext) cpp$(exeext) cc1$(exeext) $(EXTRA_PASSES) \
  $(EXTRA_PARTS) $(EXTRA_PROGRAMS) gcc-cross$(exeext) \
  $(SPECS) collect2$(exeext) lto-wrapper$(exeext) \
  gcov-iov$(build_exeext) gcov$(exeext) gcov-dump$(exeext) \
@@ -1832,14 +1832,16 @@  $(SPECS): xgcc$(exeext)
 gcc-cross$(exeext): xgcc$(exeext)
 	cp xgcc$(exeext) gcc-cross$(exeext)
 
-dummy-checksum.o : dummy-checksum.c $(CONFIG_H) $(SYSTEM_H)
+checksum-options:
+	echo "$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS)" > checksum-options.tmp \
+	&& $(srcdir)/../move-if-change checksum-options.tmp checksum-options
 
-cc1-dummy$(exeext): $(C_OBJS) dummy-checksum.o $(BACKEND) $(LIBDEPS)
-	+$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ $(C_OBJS) \
-	  dummy-checksum.o $(BACKEND) $(LIBS) $(BACKENDLIBS)
-
-cc1-checksum.c : cc1-dummy$(exeext) build/genchecksum$(build_exeext)
-	build/genchecksum$(build_exeext) cc1-dummy$(exeext) > $@
+# compute checksum over all object files and the options
+cc1-checksum.c : build/genchecksum$(build_exeext) checksum-options \
+	$(C_OBJS) $(BACKEND) $(LIBDEPS) 
+	build/genchecksum$(build_exeext) $(C_OBJS) $(BACKEND) $(LIBDEPS) \
+                     checksum-options > cc1-checksum.c.tmp && 		 \
+	$(srcdir)/../move-if-change cc1-checksum.c.tmp cc1-checksum.c
 
 cc1-checksum.o : cc1-checksum.c $(CONFIG_H) $(SYSTEM_H)
 
diff --git a/gcc/cp/Make-lang.in b/gcc/cp/Make-lang.in
index 4be40b5..fcf2119 100644
--- a/gcc/cp/Make-lang.in
+++ b/gcc/cp/Make-lang.in
@@ -86,17 +86,17 @@  CXX_AND_OBJCXX_OBJS = cp/call.o cp/decl.o cp/expr.o cp/pt.o cp/typeck2.o \
 # Language-specific object files for C++.
 CXX_OBJS = cp/cp-lang.o c-family/stub-objc.o $(CXX_AND_OBJCXX_OBJS)
 
-c++_OBJS = $(CXX_OBJS) dummy-checksum.o cc1plus-checksum.o cp/g++spec.o
+c++_OBJS = $(CXX_OBJS) cc1plus-checksum.o cp/g++spec.o
 
 # Use strict warnings for this front end.
 cp-warn = $(STRICT_WARN)
 
-cc1plus-dummy$(exeext): $(CXX_OBJS) dummy-checksum.o $(BACKEND) $(LIBDEPS)
-	$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ \
-	      $(CXX_OBJS) dummy-checksum.o $(BACKEND) $(LIBS) $(BACKENDLIBS)
-
-cc1plus-checksum.c : cc1plus-dummy$(exeext) build/genchecksum$(build_exeext)
-	build/genchecksum$(build_exeext) cc1plus-dummy$(exeext) > $@
+# compute checksum over all object files and the options
+cc1plus-checksum.c : build/genchecksum$(build_exeext) checksum-options \
+	$(CXX_OBJS) $(BACKEND) $(LIBDEPS) 
+	build/genchecksum$(build_exeext) $(CXX_OBJS) $(BACKEND) $(LIBDEPS) \
+                     checksum-options > cc1plus-checksum.c.tmp &&	   \
+	$(srcdir)/../move-if-change cc1plus-checksum.c.tmp cc1plus-checksum.c
 
 cc1plus-checksum.o : cc1plus-checksum.c $(CONFIG_H) $(SYSTEM_H)
 
diff --git a/gcc/dummy-checksum.c b/gcc/dummy-checksum.c
deleted file mode 100644
index c90f1ca..0000000
--- a/gcc/dummy-checksum.c
+++ /dev/null
@@ -1,3 +0,0 @@ 
-#include "config.h"
-#include "system.h"
-EXPORTED_CONST unsigned char executable_checksum[16] = { 0 };
diff --git a/gcc/genchecksum.c b/gcc/genchecksum.c
index 235d4fe..e0c71f4 100644
--- a/gcc/genchecksum.c
+++ b/gcc/genchecksum.c
@@ -1,5 +1,5 @@ 
 /* Generate checksums of executables for PCH validation
-   Copyright (C) 2005, 2007, 2009
+   Copyright (C) 2005, 2007, 2009, 2010
    Free Software Foundation, Inc.
 
 This file is part of GCC.
@@ -25,15 +25,18 @@  along with GCC; see the file COPYING3.  If not see
 static void
 usage (void)
 {
-  fputs ("Usage: genchecksums <filename>\n", stderr);
+  fputs ("Usage: genchecksums <filename> ...\n", stderr);
 }
 
+/* Important: BLOCKSIZE must be a multiple of 64.  */
+#define BLOCKSIZE 4096
+
 static void
-dosum (const char *file)
+dosum (struct md5_ctx *ctx, const char *file)
 {
   FILE *f;
-  unsigned char result[16];
-  int i;
+  char buffer[BLOCKSIZE + 72];
+  size_t sum;
 
   f = fopen (file, "rb");
   if (!f)
@@ -49,30 +52,70 @@  dosum (const char *file)
       exit (1);
     }
 
-  if (md5_stream (f, result) != 0
-      || fclose (f) != 0)
+  /* Iterate over full file contents.  */
+  while (1)
+    {
+      /* We read the file in blocks of BLOCKSIZE bytes.  One call of the
+	 computation function processes the whole buffer so that with the
+	 next round of the loop another block can be read.  */
+      size_t n;
+      sum = 0;
+
+      /* Read block.  Take care for partial reads.  */
+      do
+	{
+	  n = fread (buffer + sum, 1, BLOCKSIZE - sum, f);
+
+	  sum += n;
+	}
+      while (sum < BLOCKSIZE && n != 0);
+      if (n == 0 && ferror (f))
+        exit (1);
+
+      /* If end of file is reached, end the loop.  */
+      if (n == 0)
+	break;
+
+      /* Process buffer with BLOCKSIZE bytes.  Note that
+			BLOCKSIZE % 64 == 0
+       */
+      md5_process_block (buffer, BLOCKSIZE, ctx);
+    }
+
+  /* Add the last bytes if necessary.  */
+  if (sum > 0)
+    md5_process_bytes (buffer, sum, ctx);
+
+  if (fclose (f) != 0)
      {
       fprintf (stderr, "reading %s: %s\n", file, xstrerror (errno));
       exit (1);
     }
-
-  puts ("#include \"config.h\"");
-  puts ("#include \"system.h\"");
-  fputs ("EXPORTED_CONST unsigned char executable_checksum[16] = { ", stdout);
-  for (i = 0; i < 16; i++)
-    printf ("0x%02x%s", result[i], i == 15 ? " };\n" : ", ");
 }
 
 int
 main (int argc, char ** argv)
 {
-  if (argc != 2)
+  struct md5_ctx ctx;
+  unsigned char result[16];
+  int i;
+
+  if (argc < 2)
     {
       usage ();
       return 1;
     }
 
-  dosum (argv[1]);
+  md5_init_ctx (&ctx);
+  for (i = 1; i < argc; i++) 
+    dosum (&ctx, argv[i]);
+  md5_finish_ctx (&ctx, result);
+
+  puts ("#include \"config.h\"");
+  puts ("#include \"system.h\"");
+  fputs ("EXPORTED_CONST unsigned char executable_checksum[16] = { ", stdout);
+  for (i = 0; i < 16; i++)
+    printf ("0x%02x%s", result[i], i == 15 ? " };\n" : ", ");
 
   return 0;
 }
diff --git a/gcc/objc/Make-lang.in b/gcc/objc/Make-lang.in
index 08189ef..8259190 100644
--- a/gcc/objc/Make-lang.in
+++ b/gcc/objc/Make-lang.in
@@ -51,13 +51,11 @@  OBJC_OBJS = objc/objc-lang.o objc/objc-act.o
 
 objc_OBJS = $(OBJC_OBJS) cc1obj-checksum.o
 
-cc1obj-dummy$(exeext): $(OBJC_OBJS) $(C_AND_OBJC_OBJS) dummy-checksum.o $(BACKEND) $(LIBDEPS)
-	+$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ \
-	      $(OBJC_OBJS) $(C_AND_OBJC_OBJS) dummy-checksum.o \
-	      $(BACKEND) $(LIBS) $(BACKENDLIBS)
-
-cc1obj-checksum.c : cc1obj-dummy$(exeext) build/genchecksum$(build_exeext)
-	build/genchecksum$(build_exeext) cc1obj-dummy$(exeext) > $@
+cc1obj-checksum.c : build/genchecksum$(build_exeext) checksum-options \
+        $(OBJC_OBJS) $(C_AND_OBJC_OBJS) $(BACKEND) $(LIBDEPS)
+	build/genchecksum$(build_exeext) $(OBJC_OBJS) $(C_AND_OBJC_OBJS) \
+        $(BACKEND) $(LIBDEPS) checksum-options > cc1obj-checksum.c.tmp && \
+	$(srcdir)/../move-if-change cc1obj-checksum.c.tmp cc1obj-checksum.c
 
 cc1obj-checksum.o : cc1obj-checksum.c $(CONFIG_H) $(SYSTEM_H)
 
diff --git a/gcc/objcp/Make-lang.in b/gcc/objcp/Make-lang.in
index f9adeac..edc5423 100644
--- a/gcc/objcp/Make-lang.in
+++ b/gcc/objcp/Make-lang.in
@@ -54,13 +54,12 @@  OBJCXX_OBJS = objcp/objcp-act.o objcp/objcp-lang.o objcp/objcp-decl.o \
 
 obj-c++_OBJS = $(OBJCXX_OBJS) cc1objplus-checksum.o
 
-cc1objplus-dummy$(exeext): $(OBJCXX_OBJS) dummy-checksum.o $(BACKEND) \
-		$(LIBDEPS)
-	+$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ \
-		$(OBJCXX_OBJS) dummy-checksum.o $(BACKEND) $(LIBS) $(BACKENDLIBS)
-
-cc1objplus-checksum.c : cc1objplus-dummy$(exeext) build/genchecksum$(build_exeext)
-	build/genchecksum$(build_exeext) cc1objplus-dummy$(exeext) > $@
+cc1objplus-checksum.c : build/genchecksum$(build_exeext) checksum-options \
+	$(OBJCXX_OBJS) $(BACKEND) $(LIBDEPS)
+	build/genchecksum$(build_exeext) $(OBJCXX_OBJS) $(BACKEND) \
+		$(LIBDEPS) checksum-options > cc1objplus-checksum.c && \
+	$(srcdir)/../move-if-change cc1objplus-checksum.c.tmp \
+	cc1objplus-checksum.c
 
 cc1objplus-checksum.o : cc1objplus-checksum.c $(CONFIG_H) $(SYSTEM_H)