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List: cfe-commits
Subject: Re: [cfe-commits] r140777 - in /cfe/trunk:
From: Ted Kremenek <kremenek () apple ! com>
Date: 2011-09-30 18:11:52
Message-ID: 11CC5DBD-A69D-4B65-9F41-E05F83A6403C () apple ! com
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The 'format' attribute already states whether or not it takes 'printf' or 'scanf' \
format strings. That's not really the issue here. The issue is whether or not the \
function is a no-op given an empty format string. For a 'scanf' format string, it's \
clearly a no-op given no format string. For a 'printf' format string, that's not \
necessarily the case.
On Sep 30, 2011, at 11:07 AM, Ahmed Charles wrote:
> Without knowing the context perfectly, is it possible to annotate the function in a \
> way that expresses which set of format strings it accepts? Of there are two sets of \
> behaviors from format strings, then having a way to identify each \
> makes sense.
> From: Ted Kremenek
> Sent: 9/30/2011 12:45 AM
> To: Joerg Sonnenberger
> Cc: llvm cfe
> Subject: Re: [cfe-commits] r140777 - in /cfe/trunk: lib/Sema/SemaChecking.cpp \
> test/Sema/format-strings.c
> On Sep 30, 2011, at 12:38 AM, Ted Kremenek wrote:
>
> > On Sep 29, 2011, at 11:51 PM, Joerg Sonnenberger wrote:
> >
> > > On Thu, Sep 29, 2011 at 04:01:39PM -0700, Ted Kremenek wrote:
> > > > This isn't just about printf and scanf, but any function with the format \
> > > > attribute. There are functions with that attribute where this isn't a no-op \
> > > > even when the format string is empty. I saw such a case, which was the \
> > > > motivation for this change.
> > > > That said, the warning definitely is useful for printf and friends when there \
> > > > are no data arguments. I'd like the warning to be the strictest when it can \
> > > > be.
> > >
> > > Why not support -W(no-)format-zero-length like GCC then?
> >
> > Clang does support that, and I don't think it is so simple.
> >
> > Passing -Wno-format-zero-length means the warning never fires at all, even in \
> > legit cases (like the ones you pointed out).
> > Using pragmas to silence the warning within smaller blocks of code is also not \
> > user friendly, as it requires using it on every callsite that the warning \
> > triggers.
>
> Along the pragmas line, the only solution that I know of that would work without \
> silencing the warning outright would be to wrap the original function in a macro \
> that surrounded the function call with _Pragmas that silenced the warning. That's \
> obviously not a great experience.
[Attachment #5 (text/html)]
<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; \
-webkit-line-break: after-white-space; ">The 'format' attribute already states \
whether or not it takes 'printf' or 'scanf' format strings. That's not really \
the issue here. The issue is whether or not the function is a no-op given an \
empty format string. For a 'scanf' format string, it's clearly a no-op given no \
format string. For a 'printf' format string, that's not necessarily the \
case.<div><div><br><div><div>On Sep 30, 2011, at 11:07 AM, Ahmed Charles \
wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><meta \
content="text/html; charset=utf-8" http-equiv="Content-Type"><div><div><div \
style="font-family: Calibri,sans-serif; font-size: 11pt;">Without knowing the context \
perfectly, is it possible to annotate the function in a way that expresses which set \
of format strings it accepts? Of there are two sets of behaviors from format strings, \
then having a way to identify each makes sense.<br> </div></div><hr><span \
style="font-family: Tahoma,sans-serif; font-size: 10pt; font-weight: bold;">From: \
</span><span style="font-family: Tahoma,sans-serif; font-size: 10pt;">Ted \
Kremenek</span><br><span style="font-family: Tahoma,sans-serif; font-size: 10pt; \
font-weight: bold;">Sent: </span><span style="font-family: Tahoma,sans-serif; \
font-size: 10pt;">9/30/2011 12:45 AM</span><br> <span style="font-family: \
Tahoma,sans-serif; font-size: 10pt; font-weight: bold;">To: </span><span \
style="font-family: Tahoma,sans-serif; font-size: 10pt;">Joerg \
Sonnenberger</span><br><span style="font-family: Tahoma,sans-serif; font-size: 10pt; \
font-weight: bold;">Cc: </span><span style="font-family: Tahoma,sans-serif; \
font-size: 10pt;">llvm cfe</span><br> <span style="font-family: Tahoma,sans-serif; \
font-size: 10pt; font-weight: bold;">Subject: </span><span style="font-family: \
Tahoma,sans-serif; font-size: 10pt;">Re: [cfe-commits] r140777 - in /cfe/trunk: \
lib/Sema/SemaChecking.cpp test/Sema/format-strings.c</span><br> <br></div><div \
style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: \
after-white-space; "><div><div>On Sep 30, 2011, at 12:38 AM, Ted Kremenek \
wrote:</div><br class="Apple-interchange-newline"> <blockquote type="cite"><div \
style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: \
after-white-space; "><div><div>On Sep 29, 2011, at 11:51 PM, Joerg Sonnenberger \
wrote:</div><br class="Apple-interchange-newline"> <blockquote type="cite"><span \
class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; \
font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: \
normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; \
text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; \
-webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; \
-webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; \
-webkit-text-stroke-width: 0px; font-size: medium; ">On Thu, Sep 29, 2011 at \
04:01:39PM -0700, Ted Kremenek wrote:<br> <blockquote type="cite">This isn't just \
about printf and scanf, but any function with the format attribute. There are \
functions with that attribute where this isn't a no-op even when the format string is \
empty. I saw such a case, which was the motivation for this change.<br> \
</blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">That \
said, the warning definitely is useful for printf and friends when there are no data \
arguments. I'd like the warning to be the strictest when it can be.<br> \
</blockquote><br>Why not support -W(no-)format-zero-length like GCC \
then?<br></span></blockquote></div><br><div>Clang does support that, and I don't \
think it is so simple.</div><div><br></div><div>Passing -Wno-format-zero-length means \
the warning never fires at all, even in legit cases (like the ones you pointed \
out).</div> <div><br></div><div>Using pragmas to silence the warning within smaller \
blocks of code is also not user friendly, as it requires using it on every callsite \
that the warning triggers.</div></div></blockquote></div><br><div> Along the pragmas \
line, the only solution that I know of that would work without silencing the warning \
outright would be to wrap the original function in a macro that surrounded the \
function call with _Pragmas that silenced the warning. That's obviously not a \
great experience.</div> </div>
</blockquote></div><br></div></div></body></html>
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