# Checksum incorrectly uses signed values 3 messages from 2012-06-14 to 2012-06-14. Participants: Brendan Brewster, Tomas Carnecky. Thread: https://gitlist.dev/t/30801 ## Brendan Brewster, 2012-06-14 01:16 Subject: Checksum incorrectly uses signed values Message-ID: URL: https://gitlist.dev/e/CA%2B-ctj5M4XraOQJfWRVVFmRrNsUZUJyt63_Oi__OJCcYMC%3Dciw%40mail.gmail.com ``` Hi, I initially reported this issue to another developer thinking the issue resided there but after some testing and discussion, have found that the issue is not there but possibly here :) The issue, in summary, is that 7-zip was unable to untar a tar created via a "git archive" whereas gnu tar can. It seem that it may be the case that git is incorrectly using signed values when creating the checksum. As Igor commented in the other aforementioned thread, "[t]hey use 'char' (that is 'signed char' by default in most compilers). BUT correct TAR must use sum of unsigned values." Please see the following: 1) The thread previously opened with Igor/7-Zip: http://sourceforge.net/projects/sevenzip/forums/forum/45798/topic/5322604 2) http://www.gnu.org/software/tar/manual/html_node/Checksumming.html 3) TAR source code:      tar_checksum       and      simple_finish_header       functions. 4) GIT source code that calculates checksum: ustar_header_chksum function in archive-tar.c. For reference, here is the snippet of the git source code in question: git-git-f623ca1\archive-tar.c static unsigned int ustar_header_chksum(const struct ustar_header *header) {        const char *p = (const char *)header;        unsigned int chksum = 0;        while (p < header->chksum)                chksum += *p++;        chksum += sizeof(header->chksum) * ' ';        p += sizeof(header->chksum);        while (p < (const char *)header + sizeof(struct ustar_header))                chksum += *p++;        return chksum; } Can someone please look into this and possibly redirect if needed? Thanks, Brendan ``` ## Tomas Carnecky, 2012-06-14 04:35 Subject: Re: Checksum incorrectly uses signed values Message-ID: <1339648521-ner-3801@calvin> URL: https://gitlist.dev/e/1339648521-ner-3801%40calvin In-Reply-To: ``` On Wed, 13 Jun 2012 21:16:21 -0400, Brendan Brewster wrote: > Hi, > > The issue, in summary, is that 7-zip was unable to untar a tar created > via a "git archive" whereas gnu tar can. It seem that it may be the > case that git is incorrectly using signed values when creating the > checksum. > > Can someone please look into this and possibly redirect if needed? That was reported a day ago and Junio already wrote a patch. See http://article.gmane.org/gmane.comp.version-control.git/199911. tom ``` ## Brendan Brewster, 2012-06-14 14:50 Subject: Re: Checksum incorrectly uses signed values Message-ID: URL: https://gitlist.dev/e/CA%2B-ctj5tXQmeHcZ5CC74O5QSyOH1sEYTSL-f3Rcc4MtqmGnTgA%40mail.gmail.com In-Reply-To: ``` On Thu, Jun 14, 2012 at 12:39 AM, Brendan Brewster wrote: > Hi Tomas/Junio, > > Yes, that is definitely it. The referenced 7-zip thread was my own > that I tried to report today; I guess that's what I get for going on > vacation and not getting a chance to submit my report here until after > getting back :) > > Thanks, this is good news. I will report back to Igor on this. > > Thanks again, > Brendan > > On Thu, Jun 14, 2012 at 12:35 AM, Tomas Carnecky > wrote: >> On Wed, 13 Jun 2012 21:16:21 -0400, Brendan Brewster wrote: >>> Hi, >>> >>> The issue, in summary, is that 7-zip was unable to untar a tar created >>> via a "git archive" whereas gnu tar can. It seem that it may be the >>> case that git is incorrectly using signed values when creating the >>> checksum. >>> >>> Can someone please look into this and possibly redirect if needed? >> >> That was reported a day ago and Junio already wrote a patch. See >> http://article.gmane.org/gmane.comp.version-control.git/199911. >> >> tom Pushing this to the mailing list (sorry for the top post initially). -Brendan ```