FreeBSD/armv6z/clang on Raspberry Pi 512MB (with U-Boot + ubldr)

[Adrian Chadd]

.. the compiler should know the alignment for each of those types and
pad the structure appropriately, right?

david - what's the "right" behaviour here? Surely clang should be
inserting 4 bytes of padding before that pointer?



Adrian


On 28 December 2012 08:41, Daisuke Aoyama <aoyama at peach.ne.jp> wrote:
>>>> This is complete version of systimer patch.
>>>> It should fix stopping interrupt and related things such as USB LAN is
>>>> unstable,
>>>> SSH is closed suddenly.
>>>> (I've not yet finished all test at this time, but at least portsnap
>>>> fetch is
>>>> success.
>>>> Now extracting the ports without any problems.)
>
>
> Finished without any problems.
>
>
> I'm checking the alignment of clang now. It seems no difference of location
> of data structure.
> However, access method is different.
>
> I learned clang will combine two loads into one op.
> This is a reason why the alignment seems difference between clang and gcc.
> Also, a reason why clang binary is smaller than gcc code.
>
> According to ARM manual, strd alignment is:
> "The address must be a multiple of eight for doubleword transfers."
>
> uboot/lib/api_public.h:
> ----------------------------------------------------------------------
> struct sys_info {
>        unsigned long           clk_bus;
>        unsigned long           clk_cpu;
>        unsigned long           bar;
>        struct mem_region       *mr;    /* << mr offset is 12!! (not DW
> aligned) */
>        int                     mr_no;  /* number of memory regions */
> };
>
> uboot/lib/glue.c:
> ----------------------------------------------------------------------
> struct sys_info *
> ub_get_sys_info(void)
> {
>        int err = 0;
>
>        memset(&si, 0, sizeof(struct sys_info));
>        si.mr = mr;
>        si.mr_no = UB_MAX_MR;
>        memset(&mr, 0, sizeof(mr));
>
>        if (!syscall(API_GET_SYS_INFO, &err, (u_int32_t)&si))
>                return (NULL);
>
>        return ((err) ? NULL : &si);
> }
>
> ----------------------------------------------------------------------
> clang -O2 output (7 steps):
>        bl      memset            ; ATPCS uses r0-r3 as parameters
>        ldr     r0, .LCPI6_1      ; mr
>        mov     r1, #5            ; UB_MAX_MR
>        mov     r2, #60           ; sizeof(mr)
>        strd    r0, r1, [r5, #12] ; r5 aligned but strd requires DW(8byte)
> alignment (faulted here)
>        mov     r1, #0
>        bl      memset            ;  memset(&mr, 0, sizeof(mr));
>
> clang final binary size(2.8% smaller):
> -rwxr-xr-x  1 root  wheel  235984 Dec 28 23:49 ubldr
> ----------------------------------------------------------------------
> gcc 4.2 -O2 output (9 steps):
>        bl      memset            ; ATPCS uses r0-r3 as parameters
>        ldr     ip, .L162+4       ; mr
>        mov     r3, #5            ; UB_MAX_MR
>        mov     r1, r4            ; r4 is zero
>        mov     r0, ip            ; << what??
>        mov     r2, #60           ; sizeof(mr)
>        str     r3, [r6, #16]     ; r6 aligned same as clang
>        str     ip, [r6, #12]     ; r6 aligned same as clang
>        bl      memset            ;  memset(&mr, 0, sizeof(mr));
>
> gcc final binary size:
> -rwxr-xr-x  1 root  wheel  242810 Dec 28 18:22 ubldr
> ----------------------------------------------------------------------
> I don't know gcc 4.3 or newer, but probably output is more smart.
> It seems that there is no reason to use ip in this case.
>
> Does any one know how to prevent above clang output?
> (or how to solve this issue for all codes.)
>
> Thanks
>
> --
> Daisuke Aoyama
>
>
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