Qiuhao Li <qiuhao...@outlook.com> writes: > Currently, we split the write commands' data from the middle. If it does not > work, try to move the pivot "left" and retry until there is no space left. > But, this is complete for ram writes but not for IO writes. > > For example, there is an IO write command: > > write addr uuxxxxuu > > u is the unnecessary byte for the crash. Unlike ram write commands, in most > case, a split IO write won't trigger the same crash, So if we split from the > middle, we will get: > > write addr uu (will be removed in next round) > write addr xxxxuu > > For xxxxuu, since split it from the middle and retry to the leftmost byte > won't get the same crash, we will be stopped from removing the last two > bytes. >
Good catch! I missed this case. > Therefore, we should split QTest writes from the rightmost byte. > > Tested with Bug 1908062. Refined vs. Original result: > > outl 0xcf8 0x8000081c outl 0xcf8 0x8000081c > outb 0xcfc 0xc3 outb 0xcfc 0xc3 > outl 0xcf8 0x8000082f outl 0xcf8 0x8000082f > outl 0xcf8 0x80000804 outl 0xcf8 0x80000804 > outl 0xcfc 0x9b2765be outl 0xcfc 0x9b2765be > write 0xc300001024 0x2 0x0055 write 0xc300001024 0x2 0x0055 > write 0xc300001028 0x1 0x5a write 0xc300001028 0x1 0x5a > write 0xc30000101c 0x1 0x01 write 0xc30000101c 0x1 0x01 > writel 0xc30000100c 0x2a6f6c63 writel 0xc30000100c 0x2a6f6c63 > write 0xc300001018 0x1 0xa4 <-- write 0xc300001016 0x3 0xa4a4a4 > write 0x5c 0x1 0x19 write 0x5c 0x1 0x19 > write 0xc300003002 0x1 0x8a write 0xc300003002 0x1 0x8a > Can we wrap-around to the right when we hit the end of the input on the left, instead of going byte-by-byte? Otherwise, i think we would need O(n) operations to reach the leftmost in a write, rather than O(logN). i.e. xxxxuu -> xxx xuu -> xx xxuu -> x xxxuu -> xxxxu u I think the case where we would need to wrap around the entire input usually happens for smaller writes, so it shouldn't slow the minimizer down too much -Alex > Signed-off-by: Qiuhao Li <qiuhao...@outlook.com> > --- > scripts/oss-fuzz/minimize_qtest_trace.py | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/scripts/oss-fuzz/minimize_qtest_trace.py > b/scripts/oss-fuzz/minimize_qtest_trace.py > index d3b09e6567..855c3bcb54 100755 > --- a/scripts/oss-fuzz/minimize_qtest_trace.py > +++ b/scripts/oss-fuzz/minimize_qtest_trace.py > @@ -140,7 +140,7 @@ def minimize_trace(inpath, outpath): > > # 3.) If it is a qtest write command: write addr len data, try to > split > # it into two separate write commands. If splitting the write down > the > - # middle does not work, try to move the pivot "left" and retry, until > + # rightmost does not work, try to move the pivot "left" and retry, > until > # there is no space left. The idea is to prune unneccessary bytes > from > # long writes, while accommodating arbitrary MemoryRegion access > sizes > # and alignments. > @@ -149,7 +149,7 @@ def minimize_trace(inpath, outpath): > length = int(newtrace[i].split()[2], 16) > data = newtrace[i].split()[3][2:] > if length > 1: > - leftlength = int(length/2) > + leftlength = length - 1 > rightlength = length - leftlength > newtrace.insert(i+1, "") > while leftlength > 0: > -- > 2.25.1