[klibc] Bug in strrchr

[Bugs Reporter]

Hi,

I am writing to report a bug in the strrchr function of klibc.
The bug is in the C implementation of strrchr as located in the usr/klibc/
directory of the klibc repository. The klibc version was `2.0.11` and the
source code was downloaded from the Linux Kernel Archives
<https://mirrors.edge.kernel.org/pub/linux/libs/klibc/2.0/klibc-2.0.11.tar.gz>
.
Please find a detailed report below.

Linux[0] manpage for strrchr() specifies that the terminating null byte is
considered part of the string, so that if c is specified as '\0', this
function returns a pointer to the terminator. klibc's implementation does
not follow this and thus gives wrong output when `c' is '\0'.
An example input is:
    const char src[] = {128, '\0'};
    char *ret = strrchr(src, 0);
    if (!ret) {
        printf("BUG!\n");
    }

The file that demonstrates the bug can be found here
<https://github.com/compilerai/bug-reports/blob/master/bug_files/klibc_strrchr_bug.c>
.

0: https://man7.org/linux/man-pages/man3/strchr.3.html

Thanks,

Jai Arora, Abhishek Rose, Shubhani Gupta, Sorav Bansal
CompilerAI Research Group
IIT Delhi, India
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