Handling argc==0 in the kernel [LWN.net]

Handling argc==0 in the kernel

Posted Mar 28, 2022 21:41 UTC (Mon) by fest3er (guest, #60379)
In reply to: Handling argc==0 in the kernel by matthias
Parent article: Handling argc==0 in the kernel

"According to the C standard argv is a argc+1 sized array, where argv[argc] == NULL. If argc is 0, argv[1] uses an index outside of the bounds of the array."

Hmmm. Off-by-one seems to rear its head here. If argc is 0, then argv[] should contain 0+1 elements, thus only argv[0] exists and should be null and argv[1] is out-of-bounds.

Aside, why are people saying that argv is the same as argv[0]? Isn't argv the address of the array, and argv[0] the address of the zeroeth argument (or null to indicate the end of the array)? Thus, shouldn't argv always be a valid pointer to an array and the array always contain at least the terminating NULL pointer?

And when the kernel constructs the argv array, does it use its memory or the user's memory?

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Handling argc==0 in the kernel

Posted Mar 29, 2022 12:51 UTC (Tue) by jem (subscriber, #24231) [Link]

>Hmmm. Off-by-one seems to rear its head here. If argc is 0, then argv[] should contain 0+1 elements, thus only argv[0] exists and should be null and argv[1] is out-of-bounds.

Yes, of course. If argc is 0, then the argument vector is empty and only contains the terminating NULL at index 0. You can't expect to find anything of interest in argv[1].

>And when the kernel constructs the argv array, does it use its memory or the user's memory?

The argv array is in the process (user) address space. You can print the address of argv if you are interested to find out where it is located.