On Wed, Oct 10, 2018 at 03:39:07PM +0100, Szabolcs Nagy wrote: > On 10/10/18 15:10, Eugene Syromiatnikov wrote: > > * What's the reasoning behind capping syscall arguments to 32 bit? x32 > > and MIPS N32 do not have such a restriction (and do not need special > > wrappers for syscalls that pass 64-bit values as a result, except > > when they do, as it is the case for preadv2 on x32); moreover, that > > would lead to insurmountable difficulties for AArch64 ILP32 tracers > > that try to trace LP64 tracees, as it would be impossible to pass > > 64-bit addresses to process_vm_{read,write} or ptrace PEEK/POKE. > > but that's necessarily the case for all ilp32 abis: > the userspace syscall function receives 32bit > arguments so even if the kernel abi takes 64bit > args you cannot use that from c code. (the libc > does not even know which args should be sign or > zero extended.) glibc's syscall() prototype has kernel_ulong_t as its arguments (more specifically, to __syscall_ulong_t, which is 64-bit wide on x32; it should also have kernel_long_t as its return type instead of long, but that's another story), so it works perfectly fine in case of x32. > process_vm_readv/writev is limited by the ilp32 > iovec struct, not by the syscall arguments. Right, on x32/N32 this issue is worked around by the usage of the respective x86_64/N64 call, and it looks like another thing that is impossible with AArch64 ilp32. > ptrace is specified to take void* addr argument, > and void* is 32bit on all ilp32 targets. > so again on the c language level there is no > way around the 32bit limitation. Which is an issue.