Valgrind does not check out of bound write in arrays, unless these arrays are
malloc-ed
(and so valgrind can detect the write out of the limit of the malloc-ed block).
Valgrind used to contain an experimental tool (sgcheck) that did such stack
array checks,
but it had several limitations and problems, and was removed.
Thanks
Philippe
On Mon, 2022-09-26 at 14:13 -0600, Grant Schoep wrote:
> So I noticed something in my code that looked wrong to me, but valgrind
> didn't report
> anything. I made a small example of it, and still no findings. I'm sure this
> code is
> reading/writing past its array. But valgind doesn't say anything.
>
> I'm I not understanding something or is this a bug.
>
> Using:
> valgrind-3.19.0, gcc 4.8.5, CentOS 7
>
> I also tried
> valgrind-3.19.0, gcc 7.3.1, Amazon Linux 2
>
> Here is the code.
> ------
> #include <string.h>
> #include <stdio.h>
>
> int main()
> {
> char retStr[32];
>
> // this is bad right? 40 bytes when above was 32?
> memset(retStr, 'F', 40);
>
> // These are "writing" past the allocated memory?
> retStr[32] = 'A';
> retStr[33] = 'B';
>
> // These should be fine
> printf("*********** retStr is %c\n", retStr[30]);
> printf("*********** retStr is %c\n", retStr[31]);
>
> // These are reading past allocated memory?
> printf("*********** retStr is %c\n", retStr[32]);
> printf("*********** retStr is %c\n", retStr[33]);
>
> return 0;
> }
> ---
>
>
> Compiled:
> "gcc filename.cxx"
>
> Ran via this command
> "valgrind ./a.out"
>
>
>
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