[PATCH] D32346: [clang-tidy] New readability check for strlen argument

[Daniel Marjamäki via Phabricator via cfe-commits]

danielmarjamaki added inline comments.


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Comment at: docs/clang-tidy/checks/readability-strlen-argument.rst:8
+
+In the example code below the developer probably wanted to make room for an extra char in the allocation but misplaced the addition.
+
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JonasToth wrote:
> when the intend was to allocate one more char, he would need to do `strlen(s) + 1`, why is it changed to subtraction then?
If I change it to strlen(s) + 1 then the logic of the program is changed.

If I change it to subtraction then the logic is the same and the program is still wrong, but imho it is easier to see.


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Comment at: docs/clang-tidy/checks/readability-strlen-argument.rst:20
+    char *p = new char[(strlen(s) - 1)]
+    strcpy(p, s);
+
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JonasToth wrote:
> isnt that an overflow?
> an example:
> `strlen(s) == 10` -> `p` will be 9 characters long, since its substracted with `1`.
> 
> the copy operation will then copy the content of `s` into `p`, therefore copying 10 characters into a buffer of length 9.
> 
> as i understand it `strcpy(p, s + 1)` would be correct with the sizes.
yes it is overflow. My intention was to show that strlen(s+1) syntax is dangerous.


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Comment at: test/clang-tidy/readability-strlen-argument.cpp:11
+  X = strlen(Str + 10);
+  // CHECK-FIXES: {{^}}  X = (strlen(Str) - 10);{{$}}
+
----------------
JonasToth wrote:
> sberg wrote:
> > but if any of the first ten chars in Str can be NUL, then the change is bogus?  (I guess I fail to see the reason for this check)
> intersting point. If the Array holds a long list of string concatenated and seperated by `0`, the offsetting would be a valid usecase.
> (are strings in programm executables stored like this?)
> 
> But i have no idea if that is actually a scenario. usually i use `std::string` :)
I think that in theory, you have a point. It would be best that such users don't use this check. I doubt that is a big problem in practice. We don't need to speculate much, I will test this on all debian source code..

It's possible that strings in program executables are stored like that, but I'd say it's ub to calculate the address Str+10 and then dereference that if Str is a string that is 10 bytes long.



Repository:
  rL LLVM

https://reviews.llvm.org/D32346