32bit OPTEE OS System call interface Question

[acy54321]

Hi optee expert

I have a question about system call, because development needs so we will add new system call api for user ta.
My question is system call parameter have limit can not used uint64_t type?
Because I have some problem when use uint64_t type as system call parameter.
In arm32 compiler when use uint64_t type as parameter will use 2 registers to save data(because arm 32 register is 32bit),if can't put in register will save to stack, and I get a problem when system call api define as follows :
void f(int a,int b,int c, uint64_t d)

f(1,2,3,0x123456789);
disassembly will like :
.
strd r2,r3,[sp] will use r2 & r3 combination to 64bit data and save to stack
movs r0,#1
movs r1,#2
movs r3,#3

In lib/libutee/arch/arm/utee_syscalls_a32.S
.macro UTEE_SYSCALL name, scn, num_args
.
.
@ Tell number of arguments passed on the stack
mov r6, #(\num_args - 4)
.
.
=> because my system call only have 4 args so here r6 will 0, because This code default considered args 1~4 will all put in arm 32 register but in our case will put in stack
then in core/arch/arm/tee/arch_svc_a32.S
tee_svc_do_call
.
.
cmp r6, #0
beq .Lno_args
.
.
=> in our case will not use tee_svc_copy_from_user copy stack from user to kernel space,
here cause subsequent code use arg4 will error

I think problem will occur when system call args have uint64_t type and not enough cpu register can't use, will cause same problem(eg. ff(uint64_t a,uint64_t b,uint32_t c) c will get error because no copy stack from user space to kernel space).

Is there a limit 32bit optee system call can't use uint64_t type as System call parameter ??
If not limit, I think have to modify utee_syscalls_a32.S & arch_svc_a32.S mechanism.

[jenswi-linaro]

As long as you follow the guidelines at

optee_os/lib/libutee/include/utee_syscalls.h

Line 40 in 9102ce2

* Arguments must use the native register width, unless it's a signed

you should be OK.

[acy54321]

Ok I understand thank you for answer