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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/102337] bogus -Wformat-truncation due to incomplete
 sprintf/strlen integration
Date: Wed, 15 Sep 2021 15:21:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102337

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |85741
            Summary|possibly wrong warning      |bogus -Wformat-truncation
                   |about truncation            |due to incomplete
                   |                            |sprintf/strlen integration

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
In the absence of data flow information -Wformat-truncation (and
-Wformat-overflow) uses the sizes of the arrays pointed to by arguments to =
the
%s directive as the upper bound of the lengths of the strings being formatt=
ed.=20
In the test case in comment #0 the results of the first two snprintf calls
computed by GCC are discarded (not used for subsequent data flow analysis) =
and
so the warning assumes that the length of each of the two strings in the la=
st
call to snprintf() is 127 and triggers.  To do better the warning needs to =
be
enhanced to feed the results of snprintf calls to the strlen pass so that t=
hey
are available when computing the lengths of strings in subsequent calls.  T=
his
enhancement is the subject of pr92813 so this bug is effectively a duplicat=
e of
that one.

(Replacing the first two snprintf calls with strcpy avoids the warning beca=
use
string lengths computed by GCC for arguments of strcpy calls are available =
to
the snprintf warning.)


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D85741
[Bug 85741] [meta-bug] bogus/missing -Wformat-overflow=