Re: [PATCH] Powerpc: Add support for openat and fstatat syscalls

["Ulrich Weigand" <Ulrich.Weigand@de.ibm.com>]

"Carl Love" <cel@us.ibm.com> wrote on 12.10.2021 21:13:43:

> So, it says to me that calling newfstatat for both, as Ulrich said, is
> fine.  I do think this is all rather convoluted.  I guess it is one of
> those things that evolved over time into something more convoulted and
> confusing then it should be.
>
> So as you said "...there is not a significant difference between the
> two syscalls".

The two syscalls are similar, but not identical.  In particular, they
differ in the amount of memory that is accessed:

 sys_newfstatat accesses a "struct stat"
    (144 bytes on 64-bit / 88 bytes on 32-bit)
 sys_fstatat64 accesses a "struct stat64"
    (104 bytes on both 64-bit and 32-bit)

Since this affects the memory being recorded, it would actually be
preferable to use the correct system call depending on ABI.

Note that in general, there are more cases of syscall numbers refering
to different system calls depending on the ABI (64-bit vs. 32-bit),
so it would make sense to add support for that in general.

As an example, you may want to look s390_canonicalize_syscall,
which does make the distinction between 64-bit and 32-bit ABI.


Bye,
Ulrich