Greetings.
I have merged MIPS port with 4.0.0 release. Now I would like to clean up my code and need to remove many small issues that I did not fix during the porting before making the code public. In fact, most of the current problems are related to toolchains:
1. The first problem is a position independent code. Could you please describe me seL4' vision about it? muclibs is building with -fPIC, but everything else doesn't, right? I have a very tricky set of GCC’ flags, related to MIPS’ GOT, small data, abicalls, pic/non-pic, etc, and many of them are not working together.
2. MIPS assembler has several features, one of them is that the -O0 code requires having an addition space above the top of the stack for 4 registers:
> 43b610: 27bdffe8 addiu sp,sp,-24 <— start of the function
> 43b614: afbf0014 sw ra,20(sp)
> 43b618: afbe0010 sw s8,16(sp)
> 43b61c: afb0000c sw s0,12(sp)
> 43b620: 03a0f021 move s8,sp <— frame stack
> 43b624: afc40018 sw a0,24(s8) <— save 1st arg for a subroutine call
> 43b628: afc5001c sw a1,28(s8) <— save 2nd arg for the subroutine
> 43b62c: afc60020 sw a2,32(s8) <— save 3rd arg for the subroutine
So, each time when I am allocating new stack I should return not top of the stack, but top_of_the_stack - 4*sizeof(seL4_Word). As result, sel4utils_configure_thread_config becomes platform specific. Could you please consider a possibility to put it into the «arch» as sel4utils_arch_init_context, or add something like «sel4utils_arch_configure». Also, it is important: this is an issue only for -O0 code, as far I see, -O2 uses different methods for arguments passing. I am trying to build toolchains which do not use frame pointer this style for -O0 code, but I am not sure about the result.
3. I really like how you redesigned declaration syscalls. Now I have a freedom to modify syscalls and do not care about the mainline declarations because now there are syscall wrappers. However, my toolchain generates very poor code for CONFIG_LIB_SEL4_PUBLIC_SYMBOLS and «DEFAULT» — I have proper working code only for CONFIG_LIB_SEL4_INLINE_INVOCATIONS. What is the conceptual difference of these declaration attributes, what they affect?
4. Could you please tell me what was the C equivalent of this asm code:
.global __syscall
.type __syscall,%function
__syscall:
sub sp, sp, #4
push {r5,r6}
adr r5, 1f
ldr r6, 1f
ldr r5, [r5,r6]
str r5, [sp, #8]
pop {r5, r6}
pop {pc}
.hidden __sysinfo
1: .word __sysinfo-1b
something similar to __syscall6 from libmuslc/arch/<arch>_sel4/syscall_arch.h, right?
Thank you.
P/s Happy new year/merry xmass/happy holidays!
--
Vasily A. Sartakov
sartakov(a)ksyslabs.org
