Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

On Thu, Aug 27, 2020 at 11:24 PM Florian Weimer [off-list ref] wrote:

* H. J. Lu:

quoted

Can you think of ANY issues of passing more arguments to arch_prctl?

On x32, the glibc arch_prctl system call wrapper only passes two
arguments to the kernel, and applications have no way of detecting that.
musl only passes two arguments on all architectures.  It happens to work
anyway with default compiler flags, but that's an accident.

In the current glibc, there is no arch_prctl wrapper for i386.  There are
arch_prctl wrappers with 2 arguments for x86-64 and x32.  But this isn't an
issue for glibc since glibc is both the provider and the user of the new
arch_prctl extension.  Besides,

long syscall(long number, ...);

is always available.

-- 
H.J.