Nabble - ccache

Re: Build Safety

2009-09-25T06:58:19Z

Thanks!

I also realised that each developer builds their own compiler from source, so the modification date will also be different. However, I can think of ways that this can be solved, like using relative paths for the includes. I think that initially though, we will get a nice improvement from using a local cache for each machine :-)

Cheers for your help!

Tom

________________________________

From: Vincent Dupuis [mailto:vincedupuis@...]
Sent: 25 September 2009 14:50
To: Dalton, Tom
Subject: RE: [ccache] Build Safety

Tom,

you are right. ccache is independent of your project/component setup.
it is source file (compile) based.

for each file compiled
build a key (see below 1-4)
if the key is found return the .o
else add the new key and the new .o in the cache

Remember that if the file is exactly the same but the compiler option
are not (#2) like the -I option (include path). It will not retrieve the cached file.
So your makefile needs to use relative path or all user need to use the same include paths.

V

> Date: Fri, 25 Sep 2009 14:56:48 +0200
> From: tom.dalton@...
> To: ccache@...
> Subject: Re: [ccache] Build Safety
>
> Thanks Vincent, that is very useful. I have one more clarification on
> why I think using a shared cache will be useful (if it works!)
>
> We have several sub-projects, A, B, C, D.
> Our developers (and their development/build machines) can move around
> between the sub-projects.
>
>
> Subproject A and B 1 use gcc3, subproject C and D use gcc4.
> Subproject A uses libraryX v1, subprojects B,C,D use libraryX v2.
>
> So effectively there are 3 configurations, (gcc3 libX1), (gcc3 libX2),
> (gcc4 libX2).
>
> Now if each developer has a local cache, then each developer needs to do
> each compile at least once, before the cache is populated. But if each
> subproject has 10 developers, and the cache is shared, then only 1
> developer needs to build the subproject, and then all the other
> developers will get lots of cache hits when they compile.
>
> From my point of view, it is easier to configure a single, large shared
> cache across all developers than to set up a single cache for each
> subproject team. Also, in the above example, subprojects C and D have
> the same configuration and so could actually use the same cache.
>
> My issue is that the real scenario is much more complex, with each
> subproject being comprised many components, which in turn are components
> etc. So identifying the configurations is not trivial. I suspect that in
> reality, each project has some compilation in common with some of the
> other projects, but it's hard to tell which. So if ccache can cope with
> using a network-shared cache, then having one single (large) cache would
> give maximum efficiency across all the projects, as any
> cache-partitioning I impose (per-project or per-developer or
> per-machine).
>
> I hope that makes sense, but I don't know how ccache actually reads the
> cache. In effect, is it safe to use the same shared cache on multiple
> machines? If not, then is it safe to run a parallel build (e.g. make -j
> 2) on a local machine with a local cache, as presumably that has the
> same implications wrt. multiple concurrent cache updates.
>
> Thanks for your help!
>
> Tom
>
>
> ________________________________
>
> From: Vincent Dupuis [mailto:vincedupuis@...]
> Sent: 25 September 2009 13:18
> To: Dalton, Tom
> Cc: ccache@...
> Subject: RE: [ccache] Build Safety
>
>
> Hi, and welcome to ccache!
>
> > Date: Fri, 25 Sep 2009 10:22:14 +0200
> > From: tom.dalton@...
> > To: ccache@...
> > Subject: [ccache] Build Safety
> >
> > Hi,
> >
> > I think I know the answer to this question, but I want a
> second opinion!
> >
> > In the past, I have used the Clearcase version control system,
> which has
> > it's own make system, clearmake. Clearmake provides some build
> caching
> > functionality (which it terms wink-ins), that allows it to
> 'wink-in'
> > build objects from other users views. I have experienced a lot
> of
> > problems with this system, because clearcase wouldn't detect
> that two
> > users were building the same file in a different environment
> (e.g.
> > external libraries at different versions. This caused me all
> sorts of
> > issues.
>
> That's why it is not very used.
>
> > Is it possible for inconsistent environments between builds to
> cause
> > ccache to incorrectly use a cached object instead of
> recompiling? For
> > example, different builds of gcc, different external libraries
> etc? What
> > circumstances could cause this?
>
> for each compile ccache makes a key with the following
> information:
>
> 1. the pre-processor output from running the compiler
> with -E
> 2. the command line options
> 3. the real compilers size and modification time
> 4. any stderr output generated by the compiler
>
> if something changes then it recompiles and recache the new
> key/.o
> so if you use a different external librairies, #1 and maybe #2
> can change.
>
> > Secondly, if there is not much that can break ccache, is it
> possible to
> > use a shared cache (e.g. on an nfs-shared disk) to allow many
> users on
> > many hosts to cache build results across several versions of a
> single
> > product? (which will mean different gcc versions, libraries,
> even
> > kernels.)
>
> if each users use different gcc versions, libraries, even
> kernels, then
> sharing the cache is not useful. It's better to use it locally.
> Try to compile
> your product from scratch witch ccache and recompile (clean
> before) and
> compare the time. (ie: time make all). Here is my current stats
> at this moment:
>
> cache directory
> /home/vince/projects/raaf/ccache
> cache hit 16462
> cache miss 11307
> called for link 70
> compile failed 63
> preprocessor error 4
> not a C/C++ file 1198
> files in cache 8779
> cache size 793.5 Mbytes
> max cache size 976.6 Mbytes
>
> like you see, I skip compilation of 16462 files locally.
>
>
> > Thanks for your help - ccache sounds really useful, but I want
> to make
> > sure there's no 'traps'!
> >
> > Thanks,
> >
> > Tom
> > _______________________________________________
> > ccache mailing list
> > ccache@...
> > https://lists.samba.org/mailman/listinfo/ccache
>
>
> ________________________________
>
> Naviguez plus vite avec Internet Explorer 8 Ici.
> <http://go.microsoft.com/?linkid=9655263>
>
> _______________________________________________
> ccache mailing list
> ccache@...
> https://lists.samba.org/mailman/listinfo/ccache

________________________________

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Re: Build Safety

2009-09-25T05:56:48Z

Thanks Vincent, that is very useful. I have one more clarification on
why I think using a shared cache will be useful (if it works!)

We have several sub-projects, A, B, C, D.
Our developers (and their development/build machines) can move around
between the sub-projects.

Subproject A and B 1 use gcc3, subproject C and D use gcc4.
Subproject A uses libraryX v1, subprojects B,C,D use libraryX v2.

So effectively there are 3 configurations, (gcc3 libX1), (gcc3 libX2),
(gcc4 libX2).

Now if each developer has a local cache, then each developer needs to do
each compile at least once, before the cache is populated. But if each
subproject has 10 developers, and the cache is shared, then only 1
developer needs to build the subproject, and then all the other
developers will get lots of cache hits when they compile.

From my point of view, it is easier to configure a single, large shared
cache across all developers than to set up a single cache for each
subproject team. Also, in the above example, subprojects C and D have
the same configuration and so could actually use the same cache.

My issue is that the real scenario is much more complex, with each
subproject being comprised many components, which in turn are components
etc. So identifying the configurations is not trivial. I suspect that in
reality, each project has some compilation in common with some of the
other projects, but it's hard to tell which. So if ccache can cope with
using a network-shared cache, then having one single (large) cache would
give maximum efficiency across all the projects, as any
cache-partitioning I impose (per-project or per-developer or
per-machine).

I hope that makes sense, but I don't know how ccache actually reads the
cache. In effect, is it safe to use the same shared cache on multiple
machines? If not, then is it safe to run a parallel build (e.g. make -j
2) on a local machine with a local cache, as presumably that has the
same implications wrt. multiple concurrent cache updates.

Thanks for your help!

Tom

________________________________

From: Vincent Dupuis [mailto:vincedupuis@...]
Sent: 25 September 2009 13:18
To: Dalton, Tom
Cc: ccache@...
Subject: RE: [ccache] Build Safety

Hi, and welcome to ccache!

> Date: Fri, 25 Sep 2009 10:22:14 +0200
> From: tom.dalton@...
> To: ccache@...
> Subject: [ccache] Build Safety
>
> Hi,
>
> I think I know the answer to this question, but I want a
second opinion!
>
> In the past, I have used the Clearcase version control system,
which has
> it's own make system, clearmake. Clearmake provides some build
caching
> functionality (which it terms wink-ins), that allows it to
'wink-in'
> build objects from other users views. I have experienced a lot
of
> problems with this system, because clearcase wouldn't detect
that two
> users were building the same file in a different environment
(e.g.
> external libraries at different versions. This caused me all
sorts of
> issues.

That's why it is not very used.

> Is it possible for inconsistent environments between builds to
cause
> ccache to incorrectly use a cached object instead of
recompiling? For
> example, different builds of gcc, different external libraries
etc? What
> circumstances could cause this?

for each compile ccache makes a key with the following
information:

1. the pre-processor output from running the compiler
with -E
2. the command line options
3. the real compilers size and modification time
4. any stderr output generated by the compiler

if something changes then it recompiles and recache the new
key/.o
so if you use a different external librairies, #1 and maybe #2
can change.

> Secondly, if there is not much that can break ccache, is it
possible to
> use a shared cache (e.g. on an nfs-shared disk) to allow many
users on
> many hosts to cache build results across several versions of a
single
> product? (which will mean different gcc versions, libraries,
even
> kernels.)

if each users use different gcc versions, libraries, even
kernels, then
sharing the cache is not useful. It's better to use it locally.
Try to compile
your product from scratch witch ccache and recompile (clean
before) and
compare the time. (ie: time make all). Here is my current stats
at this moment:

cache directory
/home/vince/projects/raaf/ccache
cache hit 16462
cache miss 11307
called for link 70
compile failed 63
preprocessor error 4
not a C/C++ file 1198
files in cache 8779
cache size 793.5 Mbytes
max cache size 976.6 Mbytes

like you see, I skip compilation of 16462 files locally.

> Thanks for your help - ccache sounds really useful, but I want
to make
> sure there's no 'traps'!
>
> Thanks,
>
> Tom
> _______________________________________________
> ccache mailing list
> ccache@...
> https://lists.samba.org/mailman/listinfo/ccache

________________________________

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_______________________________________________
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Re: Build Safety

2009-09-25T05:18:19Z

Hi, and welcome to ccache!

> Date: Fri, 25 Sep 2009 10:22:14 +0200
> From: tom.dalton@...
> To: ccache@...
> Subject: [ccache] Build Safety
>
> Hi,
>
> I think I know the answer to this question, but I want a second opinion!
>
> In the past, I have used the Clearcase version control system, which has
> it's own make system, clearmake. Clearmake provides some build caching
> functionality (which it terms wink-ins), that allows it to 'wink-in'
> build objects from other users views. I have experienced a lot of
> problems with this system, because clearcase wouldn't detect that two
> users were building the same file in a different environment (e.g.
> external libraries at different versions. This caused me all sorts of
> issues.

That's why it is not very used.

> Is it possible for inconsistent environments between builds to cause
> ccache to incorrectly use a cached object instead of recompiling? For
> example, different builds of gcc, different external libraries etc? What
> circumstances could cause this?

for each compile ccache makes a key with the following information:1. the pre-processor output from running the compiler with -E
2. the command line options
3. the real compilers size and modification time
4. any stderr output generated by the compilerif something changes then it recompiles and recache the new key/.o
so if you use a different external librairies, #1 and maybe #2 can change.

> Secondly, if there is not much that can break ccache, is it possible to
> use a shared cache (e.g. on an nfs-shared disk) to allow many users on
> many hosts to cache build results across several versions of a single
> product? (which will mean different gcc versions, libraries, even
> kernels.)

if each users use different gcc versions, libraries, even kernels, then
sharing the cache is not useful. It's better to use it locally. Try to compile
your product from scratch witch ccache and recompile (clean before) and
compare the time. (ie: time make all). Here is my current stats at this moment:

cache directory /home/vince/projects/raaf/ccache
cache hit 16462
cache miss 11307
called for link 70
compile failed 63
preprocessor error 4
not a C/C++ file 1198
files in cache 8779
cache size 793.5 Mbytes
max cache size 976.6 Mbytes

like you see, I skip compilation of 16462 files locally.

> Thanks for your help - ccache sounds really useful, but I want to make
> sure there's no 'traps'!
>
> Thanks,
>
> Tom
> _______________________________________________
> ccache mailing list
> ccache@...
> https://lists.samba.org/mailman/listinfo/ccache

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Build Safety

2009-09-25T01:22:14Z

Hi,

I think I know the answer to this question, but I want a second opinion!

In the past, I have used the Clearcase version control system, which has
it's own make system, clearmake. Clearmake provides some build caching
functionality (which it terms wink-ins), that allows it to 'wink-in'
build objects from other users views. I have experienced a lot of
problems with this system, because clearcase wouldn't detect that two
users were building the same file in a different environment (e.g.
external libraries at different versions. This caused me all sorts of
issues.

Is it possible for inconsistent environments between builds to cause
ccache to incorrectly use a cached object instead of recompiling? For
example, different builds of gcc, different external libraries etc? What
circumstances could cause this?

Secondly, if there is not much that can break ccache, is it possible to
use a shared cache (e.g. on an nfs-shared disk) to allow many users on
many hosts to cache build results across several versions of a single
product? (which will mean different gcc versions, libraries, even
kernels.)

Thanks for your help - ccache sounds really useful, but I want to make
sure there's no 'traps'!

Thanks,

Tom
_______________________________________________
ccache mailing list
ccache@...
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Re: Questions about CCACHE and shared cache

2009-09-15T14:59:42Z

Vincent Dupuis wrote:

> Hi,
>
> I would like to share the cache of our continuous build server in read only.
>
> I think I need to set those variables:
>
> On each developer machine.
>
> CCACHE_READONLY = 1
> CCACHE_NOLINK = 1
> CCACHE_DIR = /share/builds/ccache
> CCACHE_TEMPDIR = /tmp/ccache
> CCACHE_LOGFILE = /tmp/ccache/ccache.log
> CCACHE_NOSTATS = 1
>
> On the build server.
>
> CCACHE_DIR = /share/builds/ccache
> CCACHE_RECACHE = 1
> CCACHE_LOGFILE = /buildResults/yyyymmdd/ccache.log
>
>

I don't see why CCACHE_RECACHE is necessary. The files are cached only
if they need to be. This option will just slow down your build server.

> Questions:
>
> The CCACHE_NOLINK variable is not listed in the ccache
> environment variables in the man page.
> Is it a special variable reserved for sharing the cache?
>
>
There is no CCACHE_NOLINK env variable in the source that I can see. The
latest debian version of the documentation has a patch to fix these docs
and corrects it to unsetting CCACHE_HARDLINK.

> When using the CCACHE_READONLY on the developper
> machine, are the stats are off by default because the
> stats are written in the cache?
> Do I need to set the CCACHE_NOSTATS?
>
> Do the log file will work locally on the developer computer
> even if with the CCACHE_NOSTATS?
>
> In the man page, it is written:
> The default is the same as CCACHE_DIR. Note that the
> CCACHE_TEMPDIR path must be on the same filesystem
> as the CCACHE_DIR path, so that renames of files between
> the two directories can work
> I'm not sure what does it means in my situation. Did I set
> correctly the CCACHE_TEMPDIR varible on the developer's machine?

Use df on each directory path to see if the filesystems match.
> ccache uses the "real compilers size and modification time"
> in is hash. What does it means? Executable size?
> Modification time of what?
>
Yes executable size and time stamp of the executable file.

> Do I need to set the CCACHE_TEMPDIR on the server side?
>
> How ccache deals with the current working directory?
> The developers and the server current working directory can
> be different and so the debugging information inside.
>
> How ccache deals with the macros '__FILE__' , '__DATE__' ,
> '__TIME__' ?
>
>
>

When the preprocessor gives different output for those variables, then
you get a cache miss.

William

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Re: [PATCH] flag for using relative directories

2009-09-10T18:04:42Z

Hi, I'm new to ccache and was asking myself the question:
how ccache handles the -I directives.

Your solution is good.
I tough ccache would ignore the -I option since it affects
only the preprocessor and ccache use it to build the hash.

Would it be correct and safe to have an option to ignore -I option ?

Regards,
Vincent

Andrea Bittau wrote:

It is common for developers in a shared environment to compile the same
code, but in a different location [e.g. their home] and furthermore, to
use absolute path-names in their includes flags. This results in two
different outputs from the preprocessor, even though the same file is
included [just different path], making it impossible to share a cache.
CCACHE_UNIFY could be used to get rid of the comments from the
preprocessor, but the problem here is of different nature: we do not
wish to UNIFY, and have side-effects such as wrong line information, but
rather just use relative paths so that the output of two preprocesses is
the same.

I've added a new boolean, CCACHE_RELATIVE that will modify all the -I
flags to be relative directories from where ccache is called. An
absolute pathname will be retained if the "common root" between the
working directory and the included path is "/". For example, the
following command line:
/home/sorbo$ gcc -I/common/stuff -I/home/sorbo/includes
will be translated to:
/home/sorbo$ gcc -I/common/stuff -Iincludes

Please consider applying this patch or implementing similar
functionality. This scenario is very common in many work places. The
patch is against ccache v2.4.

This has discussed on this mailing list to some extent, but I am unable
to see attached patches from the web archive, so I had to code something
myself. Also, I don't know what happened to the proposed patches, so I
just redid the work. References:

1) Steve Bennet "[ccache] [PATCH] Better cache reuse across builds in
separate trees":
http://lists.samba.org/archive/ccache/2005q2/000167.html

2) Chris Swiedler "[ccache] ccache and -g"
http://lists.samba.org/archive/ccache/2006q1/000201.html

---

diff -rup ccache-2.4.orig/ccache.c ccache-2.4/ccache.c
--- ccache-2.4.orig/ccache.c 2004-09-13 11:38:30.000000000 +0100
+++ ccache-2.4/ccache.c 2007-06-18 15:10:05.000000000 +0100
@@ -615,6 +615,119 @@ static const char *check_extension(const
return NULL;
}

+/* Transform an incldue path to relative, so that we get more hits */
+static char *relative(char *path)
+{
+ static char result[PATH_MAX];
+ static char *cwd;
+ char *proot, *pp;
+ char *croot, *cp;
+ char *rp;
+
+ /* path is relative */
+ if (*path != '/')
+ return path;
+
+ rp = x_realpath(path);
+ if (!rp) {
+ /* we got two options:
+ 1) remove the -I. gcc works with inexistent paths, but this
+ will screw up our cache.
+
+ 2) Try our best, hoping that path is well formed and won't
+ affect us.
+
+ I do #2 for now, in order to keep compiler generality. Else,
+ return NULL. I prefer #1 though.
+ */
+#if 1
+ rp = x_strdup(path);
+#else
+ return NULL;
+#endif
+ }
+
+ /* init */
+ if (!cwd) {
+ char *x = gnu_getcwd();
+
+ cwd = x_realpath(x);
+ free(x);
+ }
+ result[0] = 0;
+
+ /* step 1 - find common root */
+ cp = croot = cwd;
+ pp = proot = rp;
+ while (*pp && *cp) {
+ if (*pp != *cp)
+ break;
+
+ if (*pp == '/') {
+ proot = pp;
+ croot = cp;
+ }
+ pp++; cp++;
+ }
+
+ /* common root is root - don't relativize */
+ if (croot == cwd) {
+ free(rp);
+ return path;
+ }
+
+ /* same dir */
+ if (*pp == 0 && *cp == 0) {
+ strcpy(result, ".");
+ free(rp);
+ return result;
+ }
+
+ /* parent */
+ if (*pp == 0) {
+ int len = strlen(proot);
+
+ if (strncmp(proot, croot, len) == 0 && croot[len] == '/') {
+ croot++;
+ proot = NULL;
+ }
+ }
+
+ /* subdir */
+ if (*cp == 0) {
+ int len = strlen(croot);
+
+ if (strncmp(croot, proot, len) == 0 && proot[len] == '/') {
+ croot = cp;
+ proot += len;
+ }
+ }
+
+ /* step 2 - cd to common root */
+ while (*croot) {
+ if (*croot++ == '/') {
+ if (strlen(result) + 4 > sizeof(result)) {
+ cc_log("relative: bad len");
+ failed();
+ }
+ strcat(result, "../");
+ }
+ }
+
+ /* step 3 - cd to child (if any) */
+ if (proot) {
+ proot++;
+ if (strlen(result) + strlen(proot) + 1 > sizeof(result)) {
+ cc_log("relative: bad len2");
+ failed();
+ }
+ strcat(result, proot);
+ }
+
+ free(rp);
+
+ return result;
+}

/*
process the compiler options to form the correct set of options
@@ -704,7 +817,7 @@ static void process_args(int argc, char

/* options that take an argument */
{
- const char *opts[] = {"-I", "-include", "-imacros", "-iprefix",
+ const char *opts[] = {"-include", "-imacros", "-iprefix",
"-iwithprefix", "-iwithprefixbefore",
"-L", "-D", "-U", "-x", "-MF",
"-MT", "-MQ", "-isystem", "-aux-info",
@@ -730,6 +843,32 @@ static void process_args(int argc, char
if (opts[j]) continue;
}

+ /* transform paths to relative so that builds in different trees
+ * hit
+ */
+ if (strncmp(argv[i], "-I", 2) == 0) {
+ char *arg = &argv[i][2];
+
+ /* see if arg is not glued */
+ if (*arg == 0) {
+ if (i == argc-1) {
+ cc_log("missing argument to -I\n");
+ stats_update(STATS_ARGS);
+ failed();
+ }
+ i++;
+ arg = argv[i];
+ }
+
+ if (getenv("CCACHE_RELATIVE"))
+ arg = relative(arg);
+ if (!arg)
+ continue;
+ args_add(stripped_args, "-I");
+ args_add(stripped_args, arg);
+ continue;
+ }
+
/* other options */
if (argv[i][0] == '-') {
args_add(stripped_args, argv[i]);
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Questions about CCACHE and shared cache

2009-09-10T07:48:17Z

Hi,

I would like to share the cache of our continuous build server in read only.

I think I need to set those variables:

On each developer machine.

CCACHE_READONLY = 1
CCACHE_NOLINK = 1
CCACHE_DIR = /share/builds/ccache
CCACHE_TEMPDIR = /tmp/ccache
CCACHE_LOGFILE = /tmp/ccache/ccache.log
CCACHE_NOSTATS = 1

On the build server.

CCACHE_DIR = /share/builds/ccache
CCACHE_RECACHE = 1
CCACHE_LOGFILE = /buildResults/yyyymmdd/ccache.log

Questions:

The CCACHE_NOLINK variable is not listed in the ccache
environment variables in the man page.
Is it a special variable reserved for sharing the cache?

When using the CCACHE_READONLY on the developper
machine, are the stats are off by default because the
stats are written in the cache?
Do I need to set the CCACHE_NOSTATS?

Do the log file will work locally on the developer computer
even if with the CCACHE_NOSTATS?

In the man page, it is written:
The default is the same as CCACHE_DIR. Note that the
CCACHE_TEMPDIR path must be on the same filesystem
as the CCACHE_DIR path, so that renames of files between
the two directories can work
I'm not sure what does it means in my situation. Did I set
correctly the CCACHE_TEMPDIR varible on the developer's machine?

ccache uses the "real compilers size and modification time"
in is hash. What does it means? Executable size?
Modification time of what?

Do I need to set the CCACHE_TEMPDIR on the server side?

How ccache deals with the current working directory?
The developers and the server current working directory can
be different and so the debugging information inside.

How ccache deals with the macros '__FILE__' , '__DATE__' ,
'__TIME__' ?

Thanks a lot for helping me.

I know I asked a lot of question ;)

Best Regards,
Vincent

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Re: Possible vulnerability induced by the use of MD4?

2009-07-24T01:34:18Z

2009/7/22 Martin Pool <mbp@...>:
> 2009/7/22 Raphaël Marinier <raphael.marinier@...>:
>> Hello,
>>
>> I was wondering why ccache uses MD4 (which is cryptographically
>> insecure) to decide whether a file should be recompiled.
>
> Because it's much faster than sha256.

Has the impact of the slowness of sha256 compared to MD4 been measured
in ccache?
We can hash with sha256 at more than 100MB/s on a typical computer
(see http://www.cryptopp.com/benchmarks.html for instance).
Isn't that fast enough for ccache? (I'm no expert in ccache)

>> It seems that an attacker could take advantage of that to introduce a
>> vulnerability in the binaries of a software compiled using ccache.
>> Namely, an attacker could do the following:
>> - find two source files A and B such that:
>> * the MD4 hashes of A and B are the same (published attacks to MD4
>> don't allow to do that directly, but since MD4 is deeply broken, it is
>> reasonable to think that it is possible)
>
> Note that they actually have to find two source files A and B such
> that {the result of preprocessing them on the build system, plus the
> command line options, plus the size and modification time of the
> compiler binary, plus the stderr from the preprocessor} will have the
> same hash. That may be harder. At least it depends on knowing
> precisely what build environment will be use, and knowing that no
> relevant headers will change between the two stages.

Yes, it is of course not very easy, and overall, the attack is very
contrived as you said. (but still, MD4 is broken, so we shouldn't rely
on its security).

--
Raphaël
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Possible vulnerability induced by the use of MD4?

2009-07-21T13:19:09Z

Hello,

I was wondering why ccache uses MD4 (which is cryptographically
insecure) to decide whether a file should be recompiled.

It seems that an attacker could take advantage of that to introduce a
vulnerability in the binaries of a software compiled using ccache.
Namely, an attacker could do the following:
- find two source files A and B such that:
* the MD4 hashes of A and B are the same (published attacks to MD4
don't allow to do that directly, but since MD4 is deeply broken, it is
reasonable to think that it is possible)
* A introduces a vulnerability in the software, whereas B seems
secure (and looks like A)
- make sure A is committed in the repository of the software, and make
sure those who distribute the binaries compile the software with
ccache
- replace A by B, apparently correcting the vulnerability. Now, when
people recompile the software using ccache, the vulnerable source is
not recompiled and may be distributed... (Thus the vulnerability in
the software is corrected, whereas it is still present in the
binaries).

Any thoughts?

--
Raphaël M.
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2009-07-14T11:20:02Z

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regardless

2009-07-13T10:08:03Z

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2009-07-07T12:21:39Z

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Patch for profiling

2009-07-06T04:32:48Z

Hi,
to fix some issue with profiling I added this patch to ccache:

diff -ru ccache-2.4/ccache.c ccache-2.4.my/ccache.c
--- ccache-2.4/ccache.c 2004-09-13 12:38:30.000000000 +0200
+++ ccache-2.4.my/ccache.c 2006-03-27 08:46:24.000000000 +0200
@@ -642,7 +642,9 @@
if (strcmp(argv[i], "-fbranch-probabilities")==0 ||
strcmp(argv[i], "-M") == 0 ||
strcmp(argv[i], "-MM") == 0 ||
- strcmp(argv[i], "-x") == 0) {
+ strcmp(argv[i], "-x") == 0 ||
+ strcmp(argv[i], "-fprofile-arcs") == 0 ||
+ strcmp(argv[i], "-ftest-coverage") == 0) {
cc_log("argument %s is unsupported\n", argv[i]);
stats_update(STATS_UNSUPPORTED);
failed();

Regards
Frediano Ziglio

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2009-07-04T03:38:18Z

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2009-07-03T16:49:32Z

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2009-07-02T04:05:54Z

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2009-06-30T17:01:56Z

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2009-06-23T06:57:52Z

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2009-06-22T20:45:57Z

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Orgasm Guidelines and Suggestions - Achieving Awesome Climxkaes

2009-06-21T03:03:39Z

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Exchanging Links

2009-06-20T11:17:05Z

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Greeat Wall of China wards off ravers

2009-06-11T05:11:15Z

Hii, my photo attached
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Linux embedded computers - became our DISTRIBUTOR

2009-06-08T04:27:00Z

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2009-04-23T15:38:14Z

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Swinger Seduction - How Can I Tell If Our FFriends Want to Play?

2009-04-19T16:01:10Z

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Give Her Multiple Orgasms - Make It A Mooment To Be Reckoned

2009-04-18T11:58:38Z

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Tips Every Guy Needs to Know

2009-04-16T04:41:14Z

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178. Some texts read pritatma, implying one of.
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2009-04-13T12:37:58Z

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How To Give Your Lover MMultiple Orgasms

2009-04-10T11:16:25Z

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colambre could not flatter her so far as to say thou art
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he said: my object in covenant head, directing them how
they are to in the midst of a cauldron of boiling foam.
it.
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2009-04-04T07:08:33Z

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Your Accoount Was Banned

2009-03-30T16:46:30Z

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