Re: AArch64 ILP32 strcmp bug

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 20/07/2020 14:52, Kinsey Moore wrote:
> Hi,
> It appears that the hand-coded assembly in AArch64 strcmp does not sanitize the incoming address parameters in x0 and x1 when compiled for AArch64 ILP32. Based on my reading of the AArch64 Procedure Call Specification and GCC's output for similar function signatures, the callee is responsible for sanitization of the pointer addresses. I encountered this because I have a struct containing a pointer and length returned from another function that happens to get packed into a single register (x0) and GCC passes this unmodified into strcmp as the first argument.
> 
> According to the aapcs64: "Any part of a register or a stack slot that is not used for an argument (padding bits) has unspecified content at the callee entry point."
> 
> I suspect this is a problem for the majority of hand-written AArch64 assembly in newlib.
> 
> Please let me know if I missed something.
> 
> Thanks,
> Kinsey Moore
> 

Apologies, somehow this message got marked as read although it never
received a response.

I don't think we've really added support for ILP32 to newlib.  This may
just be one corner of a fairly large can of worms.

The Arm/AArch64 optimized assembly routines are really just copies
(provided that they've been kept up-to-date) of the code that Arm
publishes as part of its Arm Optimized Routines package
(https://github.com/ARM-software/optimized-routines); but even those do
not have ILP32 support at this time.  The best place to address this is
to raise an issue there.

R.