Date: Fri, 28 Dec 2012 08:47:44 -0800 From: Adrian Chadd <adrian@freebsd.org> To: Daisuke Aoyama <aoyama@peach.ne.jp>, David Chisnall <theraven@freebsd.org> Cc: freebsd-arm@freebsd.org Subject: Re: FreeBSD/armv6z/clang on Raspberry Pi 512MB (with U-Boot + ubldr) Message-ID: <CAJ-VmokH8=CHnPGHtjZTrpuWe1HAjR%2BYRp%2BzGROtS8GcJrCiZA@mail.gmail.com> In-Reply-To: <9ED42265200A41B1BD637682720E0E9D@ad.peach.ne.jp> References: <B5F827FF91C94FF2AFEE00194A2BB2C5@ad.peach.ne.jp> <B508111FCE534B2CBA61F4D1EC1078D3@ad.peach.ne.jp> <E42823D3-D405-40E7-B4CF-75DC947AC119@bluezbox.com> <2BA73CBF02B04DD19D08CDFC556B8750@ad.peach.ne.jp> <BE93F553-E060-45E5-90FE-39AAD1325BAB@bluezbox.com> <F384770FEB784C67BC89AFF7CF57E96C@ad.peach.ne.jp> <1356624694.1144.67.camel@revolution.hippie.lan> <234E1E18AC1C4A3985D6C570F78698E6@ad.peach.ne.jp> <9ED42265200A41B1BD637682720E0E9D@ad.peach.ne.jp>
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.. 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@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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