martong marked an inline comment as done.
martong added inline comments.
================
Comment at: clang/lib/StaticAnalyzer/Core/CheckerHelpers.cpp:114-117
+ const auto MacroIt = llvm::find_if(
+ PP.macros(), [&](const auto &K) { return K.first->getName() == Macro; });
+ if (MacroIt == PP.macro_end())
+ return llvm::None;
----------------
martong wrote:
> Szelethus wrote:
> > NoQ wrote:
> > > martong wrote:
> > > > Szelethus wrote:
> > > > > This seems a bit clunky even for the `Preprocessor` -- how about
> > > > >
> > > > > ```lang=c++
> > > > > const auto *MacroII = PP.getIdentifierInfo(Macro);
> > > > > if (!MacroII)
> > > > > return;
> > > > > const MacroInfo *MI = PP.getMacroInfo(MacroII);
> > > > > assert(MI);
> > > > > ```
> > > > Ok, but we cannot assert on `MI`, because there may be cases when the
> > > > macro is not defined in a TU. In that case we should just return with
> > > > None.
> > > What exactly happens when the macro is `#undef`-ined and redefined? We
> > > get the last redefinition that's valid at the end of the translation
> > > unit, right? Can we check whether there are multiple definitions and
> > > guard against that?
> > Ugh, now that you say it that is a valid concern. I had to deal with that
> > back in the day: https://reviews.llvm.org/D52794?id=171962#inline-476352
> Solving this does not seem easy in my opinion. To handle `#undef`s we should
> build an infrastructure where summaries can reference callable objects. This
> is necessary, because in `evalCall` the value of `EOF` would depend on the
> souce location of the call expression of the function with the summary. Not
> impossible to solve, but certainly introduces complexity. Do you think that
> the redefinition of EOF is so common? I mean maybe it is too much hassle for
> a very rare edge case (?).
The standard library (libc or libc++) should define EOF consitently in stdio.h.
Now, if the application redefines the value of EOF then the code could be
broken, or at least it would not be compatible with libc. Consider the
following code that is perfectly legit if we don't redefine EOF, but if we do:
```
#include <stdio.h>
#include <stdlib.h>
#define EOF -2 // Here be dragons !!!
int main(void)
{
FILE* fp = fopen("test.txt", "r");
int c;
while ((c = fgetc(fp)) != EOF) { // BOOM: Infinite loop !!!
putchar(c);
}
fclose(fp);
}
```
So, redefinition of EOF (or any standard macro) results in broken code.
And this is also a warning:
```
) clang eof-inf.c
eof-inf.c:3:9: warning: 'EOF' macro redefined [-Wmacro-redefined]
#define EOF -2 // Here be dragons !!!
^
/usr/include/x86_64-linux-gnu/bits/libio.h:66:10: note: previous definition is
here
# define EOF (-1)
^
1 warning generated.
```
Repository:
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CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D74473/new/
https://reviews.llvm.org/D74473
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