[PATCH v2] coccinelle: assign signed result to unsigned variable

[Andrzej Hajda <a.hajda@samsung.com>]

Assigning signed function result to unsigned variable can indicate error.
To decrease number of false positives patch looks if after assignment
there is also check for negative values of the result.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
---
Hi Julia,

Thanks for the hint. Now it looks much better.
Summarizing this patch has found 20 problems and has 22 false positives [1][2].
unsigned_lesser_than_zero.cocci patch posted earlier has found
40 problems [3][4], and about 80 false positives if I remember correctly.
Few patches were rejected, as developers likes code for testing variable range,
even if its result is always true/false [5][6], but most of kernel patches are
real bug fixes.

Both patches tries to address similar issues, maybe it would be good to merge
them? Especially as their results overlap.
Additionally I thought about adding detecting range checks in
unsigned_lesser_than_zero.cocci, to decrease number of false positives.
Of course it could then miss real bugs. What do you think about it?

[1]: http://permalink.gmane.org/gmane.linux.kernel/2046131
[2]: http://permalink.gmane.org/gmane.linux.kernel/2048070
[3]: http://permalink.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/70031
[4]: http://permalink.gmane.org/gmane.linux.power-management.general/66143
[5]: http://permalink.gmane.org/gmane.linux.kernel.mm/138902
[6]: http://libdivecomputer.org/pipermail/devel/2014-July/000329.html

Regards
Andrzej

---
 .../tests/assign_signed_to_unsigned.cocci          | 45 ++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 scripts/coccinelle/tests/assign_signed_to_unsigned.cocci

diff --git a/scripts/coccinelle/tests/assign_signed_to_unsigned.cocci b/scripts/coccinelle/tests/assign_signed_to_unsigned.cocci
new file mode 100644
index 0000000..efa4e83
--- /dev/null
+++ b/scripts/coccinelle/tests/assign_signed_to_unsigned.cocci
@@ -0,0 +1,45 @@
+/// Assigning signed function result to unsigned variable can indicate error.
+/// To decrease number of false positives patch looks if after assignment
+/// there is also check for negative values of the result.
+///
+// Confidence: High
+// Copyright: (C) 2015 Andrzej Hajda, Samsung Electronics Co., Ltd. GPLv2.
+// URL: http://coccinelle.lip6.fr/
+// Options: --include-headers --all-includes
+
+virtual context
+virtual org
+virtual report
+
+@r@
+typedef bool, u8, u16, u32, u64, s8, s16, s32, s64;
+{char, short, int, long, long long, s8, s16, s32, s64} vs;
+{unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long,
+    size_t, bool, u8, u16, u32, u64} vu;
+position p;
+identifier f;
+statement S1, S2;
+expression e;
+@@
+
+*vu@p = f(...)@vs;
+... when != vu = e;
+if ( \( vu < 0 \| vu <= 0 \) ) S1 else S2
+
+@script:python depends on r && org@
+p << r.p;
+f << r.f;
+vu << r.vu;
+@@
+
+msg = "WARNING: Assigning signed result to unsigned variable: %s = %s(...)" % (vu, f)
+coccilib.org.print_todo(p[0], msg)
+
+@script:python depends on r && report@
+p << r.p;
+f << r.f;
+vu << r.vu;
+@@
+
+msg = "WARNING: Assigning signed result to unsigned variable: %s = %s(...)" % (vu, f)
+coccilib.report.print_report(p[0], msg)
-- 
1.9.1