# [PATCH 0/2] silence clang-3.6 warnings 6 messages from 2015-01-28 to 2015-01-29. Participants: Jeff King, Junio C Hamano. Thread: https://gitlist.dev/t/38467 ## Jeff King, 2015-01-28 17:53 Subject: [PATCH 0/2] silence clang-3.6 warnings Message-ID: <20150128175314.GA13362@peff.net> URL: https://gitlist.dev/e/20150128175314.GA13362%40peff.net ``` I was fooling around with clang-3.6 today (as opposed to 3.5, which is the stock "clang" shipped with Debian), and noticed two new warnings. The first one is a real bug, and the second is just a cleanup (though I agree with clang on it). [1/2]: read_and_strip_branch: fix typo'd address-of operator [2/2]: do not check truth value of flex arrays -Peff ``` ## Jeff King, 2015-01-28 17:57 Subject: [PATCH 1/2] read_and_strip_branch: fix typo'd address-of operator Message-ID: <20150128175735.GA8172@peff.net> URL: https://gitlist.dev/e/20150128175735.GA8172%40peff.net In-Reply-To: <20150128175314.GA13362@peff.net> ``` When we are chomping newlines from the end of a strbuf, we must check "sb.len != 0" before accessing "sb.buf[sb.len - 1]". However, this code mistakenly checks "&sb.len", which is always true (it is a part of an auto struct, so the address is always non-zero). This could lead to us accessing memory outside the strbuf when we read an empty file. Signed-off-by: Jeff King --- This dates back to 8b87cfd (wt-status: move strbuf into read_and_strip_branch(), 2013-03-16), so it is not a bug that needs addressed during the -rc period. This is the most minimal fix, but I kind of wonder if it should just be using strbuf_rtrim (or even strbuf_trim) in the first place. wt-status.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/wt-status.c b/wt-status.c index b54eac5..29666d0 100644 --- a/wt-status.c +++ b/wt-status.c @@ -1140,7 +1140,7 @@ static char *read_and_strip_branch(const char *path) if (strbuf_read_file(&sb, git_path("%s", path), 0) <= 0) goto got_nothing; - while (&sb.len && sb.buf[sb.len - 1] == '\n') + while (sb.len && sb.buf[sb.len - 1] == '\n') strbuf_setlen(&sb, sb.len - 1); if (!sb.len) goto got_nothing; -- 2.3.0.rc1.287.g761fd19 ``` ## Jeff King, 2015-01-28 17:58 Subject: [PATCH 2/2] do not check truth value of flex arrays Message-ID: <20150128175850.GB8172@peff.net> URL: https://gitlist.dev/e/20150128175850.GB8172%40peff.net In-Reply-To: <20150128175314.GA13362@peff.net> ``` There is no point in checking "!ref->name" when ref is a "struct ref". The name field is a flex-array, and there always has a non-zero address. This is almost certainly not hurting anything, but it does cause clang-3.6 to complain. Signed-off-by: Jeff King --- Note that even if "ref" is NULL, this is still going to be "0+offsetof(name)". So short of unsigned pointer wrap-around, I do not think this check can ever do anything. remote-curl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/remote-curl.c b/remote-curl.c index dd63bc2..515ac9b 100644 --- a/remote-curl.c +++ b/remote-curl.c @@ -760,7 +760,7 @@ static int fetch_git(struct discovery *heads, for (i = 0; i < nr_heads; i++) { struct ref *ref = to_fetch[i]; - if (!ref->name || !*ref->name) + if (!*ref->name) die("cannot fetch by sha1 over smart http"); packet_buf_write(&preamble, "%s %s\n", sha1_to_hex(ref->old_sha1), ref->name); -- 2.3.0.rc1.287.g761fd19 ``` ## Junio C Hamano, 2015-01-28 20:42 Subject: Re: [PATCH 1/2] read_and_strip_branch: fix typo'd address-of operator Message-ID: URL: https://gitlist.dev/e/xmqq1tmehc25.fsf%40gitster.dls.corp.google.com In-Reply-To: <20150128175735.GA8172@peff.net> ``` Jeff King writes: > When we are chomping newlines from the end of a strbuf, we > must check "sb.len != 0" before accessing "sb.buf[sb.len - 1]". > However, this code mistakenly checks "&sb.len", which is > always true (it is a part of an auto struct, so the address > is always non-zero). This could lead to us accessing memory > outside the strbuf when we read an empty file. > > Signed-off-by: Jeff King > --- > This dates back to 8b87cfd (wt-status: move strbuf into > read_and_strip_branch(), 2013-03-16), so it is not a bug that needs > addressed during the -rc period. > > This is the most minimal fix, but I kind of wonder if it should just be > using strbuf_rtrim (or even strbuf_trim) in the first place. Yeah. Or strbuf_chomp(), which does not exist ;-) It is tempting to apply this directly to maint and merge up immediately, as there is no way this 1-byte change will break things (of course that is not necessarily true for random 1-byte changes, though). It sometimes gets really hard to resist that temptation during the pre-release freeze period. > wt-status.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/wt-status.c b/wt-status.c > index b54eac5..29666d0 100644 > --- a/wt-status.c > +++ b/wt-status.c > @@ -1140,7 +1140,7 @@ static char *read_and_strip_branch(const char *path) > if (strbuf_read_file(&sb, git_path("%s", path), 0) <= 0) > goto got_nothing; > > - while (&sb.len && sb.buf[sb.len - 1] == '\n') > + while (sb.len && sb.buf[sb.len - 1] == '\n') > strbuf_setlen(&sb, sb.len - 1); > if (!sb.len) > goto got_nothing; ``` ## Jeff King, 2015-01-28 22:57 Subject: Re: [PATCH 1/2] read_and_strip_branch: fix typo'd address-of operator Message-ID: <20150128225755.GA15719@peff.net> URL: https://gitlist.dev/e/20150128225755.GA15719%40peff.net In-Reply-To: ``` On Wed, Jan 28, 2015 at 12:42:26PM -0800, Junio C Hamano wrote: > > This is the most minimal fix, but I kind of wonder if it should just be > > using strbuf_rtrim (or even strbuf_trim) in the first place. > > Yeah. Or strbuf_chomp(), which does not exist ;-) This is not the first time I've seen this chomp/trim distinction come up. However, the thing that has prevented me from writing strbuf_chomp is that the trim is almost always a more reasonable choice. Take this instance. We are opening and reading a whole file. Surely we need to drop the final newline, which is not interesting. But we are not just doing that; we are dropping _all_ trailing newlines. So "foo\n\n" becomes "foo". But "foo\n \n" does not. That doesn't make much sense. IOW, I would venture to say that chomping like this falls into one of two categories: 1. You want to clean up any extraneous cruft. Multiple lines, extra whitespace, etc. 2. You want to read one line, but don't want the trailing newline. And strbuf_getline already handles case (2). End mini-rant. :) > It is tempting to apply this directly to maint and merge up > immediately, as there is no way this 1-byte change will break things > (of course that is not necessarily true for random 1-byte changes, > though). > > It sometimes gets really hard to resist that temptation during the > pre-release freeze period. That's part of why I did the simplest fix instead of strbuf_rtrim. To tempt you. :) -Peff ``` ## Junio C Hamano, 2015-01-29 06:22 Subject: Re: [PATCH 1/2] read_and_strip_branch: fix typo'd address-of operator Message-ID: URL: https://gitlist.dev/e/xmqqy4omds1u.fsf%40gitster.dls.corp.google.com In-Reply-To: <20150128225755.GA15719@peff.net> ``` Jeff King writes: > This is not the first time I've seen this chomp/trim distinction come > up. However, the thing that has prevented me from writing strbuf_chomp > is that the trim is almost always a more reasonable choice. > ... > End mini-rant. :) Thanks. ```