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[Qemu-devel] [Bug 1655700] Re: disas/libvixl/vixl/invalset.h: possible d
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [Bug 1655700] Re: disas/libvixl/vixl/invalset.h: possible dodgy code in binary search ? |
Date: |
Mon, 16 Jan 2017 17:46:44 -0000 |
That doesn't look like a bounds check to me, so I think your checker is
producing false positives.
libvixl is third-party code in any case, so stylistic questions are
better directed to them upstream. But I think the difference between
this code and a standard binary search is (as the comment says) that it
ignores invalid elements in the array.
** Changed in: qemu
Status: New => Invalid
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https://bugs.launchpad.net/bugs/1655700
Title:
disas/libvixl/vixl/invalset.h: possible dodgy code in binary search ?
Status in QEMU:
Invalid
Bug description:
[qemu/disas/libvixl/vixl/invalset.h:442]: (style) Array index 'low' is used
before limits check.
Source code is
while (!IsValid(elements[low]) && (low < high)) ++low;
Also:
qemu/disas/libvixl/vixl/invalset.h:450]: (style) Array index 'middle'
is used before limits check.
The source code is
while (!IsValid(elements[high]) && (low < high)) --high;
Mind you, these lines of code look similar but didn't get reported:
while (!IsValid(elements[middle]) && (middle < high - 1)) ++middle;
while (!IsValid(elements[middle]) && (low + 1 < middle)) --middle;
Given that binary search is notoriously tricky to get correct and a standard
C library routine
I am puzzled as to why the standard library routine didn't get used, with of
course a custom
comparison function.
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