Re: [RFC PATCH 07/15] strbuf.c: placate -fanalyzer in strbuf_grow()

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Jun 4, 2022, 16:21 UTC
Message-ID: <220604.86czfowg81.gmgdl@evledraar.gmail.com>
In-Reply-To: <870925774.539833.1654346793623@apps.talktalk.co.uk>

On Sat, Jun 04 2022, Phillip Wood wrote:

> Hi Ævar
>
> [This is an old address that I only have webmail access to, please use
> phillip.wood@dunelm.org.uk when cc'ing me]

Hrm, I just grabbed it from an old commit of yours I found. Consider sending in a patch to update .mailmap :)

Show 32 quoted lines

>> On 03 June 2022 at 19:37 Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
>> 
>> 
>> Change the strbuf_grow() function so that GCC v12's -fanalyze doesn't
>> yell at us about sb->buf[0] dereferencing NULL, this also makes this
>> code easier to follow.
>> 
>> This BUG() should be unreachable since the state of our "sb->buf" and
>> "sb->alloc" goes hand-in-hand, but -fanalyzer isn't smart enough to
>> know that, and adding the BUG() also makes it clearer to human readers
>> that that's what happens here.
>> 
>> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
>> ---
>>  strbuf.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/strbuf.c b/strbuf.c
>> index dd9eb85527a..61c4630aeeb 100644
>> --- a/strbuf.c
>> +++ b/strbuf.c
>> @@ -97,6 +97,8 @@ void strbuf_grow(struct strbuf *sb, size_t extra)
>>  	if (new_buf)
>>  		sb->buf = NULL;
>>  	ALLOC_GROW(sb->buf, sb->len + extra + 1, sb->alloc);
>> +	if (new_buf && !sb->buf)
>> +		BUG("for a new buffer ALLOC_GROW() should always do work!");
>
> This is a bit ugly, have you tried adding
> __attribute__((malloc (free), returns_nonnull))
> to xmalloc() and xrealloc() ?
>

Will try to experiment with that, perhaps GCC can be massaged to grok this somehow.

I do vaguely remember (but couldn't track down where it was) that we have some config for coverity for this function, due to it also having trouble with it.