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Re: [musl] Re: [PATCHv3 00/24] ILP32 support in ARM64

On Thu, Feb 12, 2015 at 09:12:34AM +0100, Szabolcs Nagy wrote:
> * Szabolcs Nagy <> [2015-02-11 20:05:37 +0100]:
> > (i think this is also a problem if userspace code uses syscall(2) directly,
> > libc cannot possibly know where to signextend and the kernel side does not
> > do the fixup right now)
> nobody picked up this issue, is this resolved?
> ie. if userspace calls syscall(SYS_foo,...) directly with 32bit
> longs does it always work out correctly on the kernel side?

I think the only way to solve this is to have syscall wrappers in the
kernel rather than glibc.

> the sign extension is a problem for signed long arguments,
> i only found these in the kernel:
> fs/buffer.c:SYSCALL_DEFINE2(bdflush, int, func, long, data)

This is part of the deprecated syscalls, it is not used on new user

> fs/open.c:SYSCALL_DEFINE2(truncate, const char __user *, path, long, length)

The kernel uses a long (64-bit) here and the user ABI defines this as an
off_t. With x32, this should be a long long (__kernel_long_t), so not a

> fs/aio.c:SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
> fs/aio.c-               struct iocb __user * __user *, iocbpp)
> fs/aio.c:SYSCALL_DEFINE5(io_getevents, aio_context_t, ctx_id,
> fs/aio.c-               long, min_nr,
> fs/aio.c-               long, nr,

These would need some int->long conversion for nr, min_nr (it may be
done in x32 glibc already but as you said it would not work via
syscall() directly).

> kernel/ptrace.c:SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
> kernel/ptrace.c-                unsigned long, data)

The pid in user space would be pid_t which is 32-bit. The kernel seems
to use it as pid_t afterwards, so looks safe. For addr and data, I guess
it needs wrappers to zero the top part.

> ipc/syscall.c:SYSCALL_DEFINE6(ipc, unsigned int, call, int, first, unsigned long, second,
> ipc/syscall.c-          unsigned long, third, void __user *, ptr, long, fifth)

ipc(2) shows the first, second, third as ints. I guess some kernel
wrapper is needed here as well.


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