Re: My git repo is broken, how to fix it ?

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mar 22, 2007, 16:29 UTC
Message-ID: <Pine.LNX.4.64.0703220924590.6730@woody.linux-foundation.org>
In-Reply-To: <Pine.LNX.4.64.0703220858400.6730@woody.linux-foundation.org>

On Thu, 22 Mar 2007, Linus Torvalds wrote:

Show 6 quoted lines

> 
> It's also possible that the real bug is that we have some memory scribble 
> internally in git, and that it shows up for you just because Cygwin and/or 
> WinXp has different allocation patterns than other platforms. Do you know 
> if there are any "debugging malloc" libraries for Cygwin? Something like 
> ElectricFence/dmalloc under Linux, or running with valgrind.

Yeehaa! I think I'm on the right trail.

Git people: do this:

	yum install ElectricFence

(or similar, apt-get, whatever), and then apply this patch, and do

	make test

and it will fail in "git-apply"! Which (having read Alexander's corruption sequence once more) must have been what corrupted things for Alexander too!

I've not debugged it any more, but gdb on the core-dump shows:

	(gdb) where
	#0  0x0000003768462331 in SHA1_Update () from /lib64/libcrypto.so.6
	#1  0x0000000000461b0e in write_sha1_file_prepare (buf=0x2ba371737fd0, len=46, type=0x49a50b "blob", sha1=0x7fff395c84a0 "",
	    hdr=0x7fff395c8480 "blob 46", hdrlen=0x7fff395c847c) at sha1_file.c:1823
	#2  0x0000000000461e6f in write_sha1_file (buf=0x2ba371737fd0, len=46, type=0x49a50b "blob", returnsha1=0x2ba371733fe0 "")
	    at sha1_file.c:1962
	#3  0x000000000040aa9a in add_index_file (path=0x2ba371719ffc "one", mode=33188, buf=0x2ba371737fd0, size=46) at builtin-apply.c:2350
	#4  0x000000000040aeb5 in create_file (patch=0x2ba37170cf40) at builtin-apply.c:2451
	#5  0x000000000040af45 in write_out_one_result (patch=0x2ba37170cf40, phase=1) at builtin-apply.c:2475
	#6  0x000000000040b291 in write_out_results (list=0x2ba37170cf40, skipped_patch=0) at builtin-apply.c:2560
	#7  0x000000000040b71c in apply_patch (fd=6, filename=0x7fff395c96ec "patch.file", inaccurate_eof=0) at builtin-apply.c:2676
	#8  0x000000000040bd1b in cmd_apply (argc=3, argv=0x7fff395c8990, unused_prefix=0x0) at builtin-apply.c:2836
	#9  0x0000000000403fbb in handle_internal_command (argc=3, argv=0x7fff395c8990, envp=0x7fff395c89b0) at git.c:322
	#10 0x0000000000404193 in main (argc=3, argv=0x7fff395c8990, envp=0x7fff395c89b0) at git.c:391

so I thought I'd send out this email asap, in case somebody else finds the bug before I do.

Anyway, this looks like a real smoking gun..

		Linus
----

diff --git a/Makefile b/Makefile
index 51c1fed..7e20410 100644
--- a/Makefile
+++ b/Makefile
@@ -123,7 +123,7 @@ uname_P := $(shell sh -c 'uname -p 2>/dev/null || echo not')
 
 # CFLAGS and LDFLAGS are for the users to override from the command line.
 
-CFLAGS = -g -O2 -Wall
+CFLAGS = -g -Wall
 LDFLAGS =
 ALL_CFLAGS = $(CFLAGS)
 ALL_LDFLAGS = $(LDFLAGS)
@@ -647,7 +647,7 @@ prefix_SQ = $(subst ','\'',$(prefix))
 SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
 PERL_PATH_SQ = $(subst ','\'',$(PERL_PATH))
 
-LIBS = $(GITLIBS) $(EXTLIBS)
+LIBS = $(GITLIBS) $(EXTLIBS) -lefence
 
 BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' \
 	-DETC_GITCONFIG='"$(ETC_GITCONFIG_SQ)"' $(COMPAT_CFLAGS)