On Sat, 13 Jun 2015 08:52:09 +1000, Dave Chinner wrote:
> Yup, that's looking like a toolchain bug. Thread about arm directory
> read corruption:
I think that this is not a toolchain bug, this is related to
Subject: [PATCH v2 1/1] ARM : missing corrupted reg in __do_div_asm
http://www.spinics.net/lists/arm-kernel/msg426684.html
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The problematic line in xfs is:
irecs->br_startblock = XFS_DADDR_TO_FSB(mp, mappedbno)
in xfs_dabuf_map()/fs/xfs/xfs_da_btree.c.
The expansion of it is:
ld = mappedbno >> mp->m_blkbb_log;
do_div(ld, mp->m_sb.sb_agblocks);
startblock = ld << mp->m_sb.sb_agblklog;
ld = mappedbno >> mp->m_blkbb_log;
startblock |= do_div(ld, mp->m_sb.sb_agblocks);
irecs->br_startblock = startblock;
The assembler of these are:
:
bl __do_div64
ldr r1, [sp, #44]
subs r3, r7, #32
orr r1, r1, r2, lsr r5
add r5, sp, #80
str r5, [sp, #64]
ldr r5, [sp, #60]
movpl r1, r2, asl r3
mov r2, r2, asl r7
str r2, [sp, #40]
str r1, [sp, #44]
mov r1, r9
str r5, [sp, #96]
mov r7, #0
ldr r2, [sp, #96]
mov r5, #1
ldr fp, [sp, #64]
str r7, [sp, #84]
mov r9, r2, asr #31
str r7, [sp, #104]
bl __do_div64
:
by GCC 4.7.2 with -O2 option.
Because a result of do_div is stored in the 1st arg (r0),
r0, which is "ld" in the C, must be reloaded after the 1st call of do_div,
before the 2nd call of do_div.
But it is not reloaded in the above assembler.
The problem is macro __do_div_asm, as the patch describes.
I confirmed that the patch fixed this problem.
mov r1, sl
str r2, [sp, #56]
mov r0, fp
bl __do_div64
ldr ip, [sp, #36]
rsb r6, r5, #32
subs r3, r5, #32
ldr r1, [sp, #56]
orr ip, ip, r2, lsr r6
str r7, [sp, #96]
mov r6, #1
str r8, [sp, #80]
mov r0, ip
str r1, [sp, #52]
movpl r0, r2, asl r3
mov r2, r2, asl r5
str r0, [sp, #36]
mov r1, sl
str r2, [sp, #32]
mov r0, fp
bl __do_div64
by GCC 4.7.2 with -O2 option and the patch.
Thank you,
--
UWATOKO
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