[PATCH] D38797: [analyzer] CStringChecker: pr34460: Admit that some casts are hard to model.
This revision was automatically updated to reflect the committed changes.
Closed by commit rL315742: [analyzer] CStringChecker: pr34460: Avoid a crash
when a cast is not modeled. (authored by dergachev).
Changed prior to commit:
https://reviews.llvm.org/D38797?vs=118597=118964#toc
Repository:
rL LLVM
https://reviews.llvm.org/D38797
Files:
cfe/trunk/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
cfe/trunk/test/Analysis/bstring.cpp
cfe/trunk/test/Analysis/casts.c
Index: cfe/trunk/test/Analysis/casts.c
===
--- cfe/trunk/test/Analysis/casts.c
+++ cfe/trunk/test/Analysis/casts.c
@@ -123,3 +123,29 @@
int x = (int) p;
clang_analyzer_eval(++x < 10); // no-crash // expected-warning{{UNKNOWN}}
}
+
+void multiDimensionalArrayPointerCasts() {
+ static int x[10][10];
+ int *y1 = &(x[3][5]);
+ char *z = ((char *) y1) + 2;
+ int *y2 = (int *)(z - 2);
+ int *y3 = ((int *)x) + 35; // This is offset for [3][5].
+
+ clang_analyzer_eval(y1 == y2); // expected-warning{{TRUE}}
+
+ // FIXME: should be FALSE (i.e. equal pointers).
+ clang_analyzer_eval(y1 - y2); // expected-warning{{UNKNOWN}}
+ // FIXME: should be TRUE (i.e. same symbol).
+ clang_analyzer_eval(*y1 == *y2); // expected-warning{{UNKNOWN}}
+
+ clang_analyzer_eval(*((char *)y1) == *((char *) y2)); // expected-warning{{TRUE}}
+
+ clang_analyzer_eval(y1 == y3); // expected-warning{{TRUE}}
+
+ // FIXME: should be FALSE (i.e. equal pointers).
+ clang_analyzer_eval(y1 - y3); // expected-warning{{UNKNOWN}}
+ // FIXME: should be TRUE (i.e. same symbol).
+ clang_analyzer_eval(*y1 == *y3); // expected-warning{{UNKNOWN}}
+
+ clang_analyzer_eval(*((char *)y1) == *((char *) y3)); // expected-warning{{TRUE}}
+}
Index: cfe/trunk/test/Analysis/bstring.cpp
===
--- cfe/trunk/test/Analysis/bstring.cpp
+++ cfe/trunk/test/Analysis/bstring.cpp
@@ -1,8 +1,35 @@
// RUN: %clang_analyze_cc1 -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
+// RUN: %clang_analyze_cc1 -DUSE_BUILTINS -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
+// RUN: %clang_analyze_cc1 -DVARIANT -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
+// RUN: %clang_analyze_cc1 -DUSE_BUILTINS -DVARIANT -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
#include "Inputs/system-header-simulator-cxx.h"
#include "Inputs/system-header-simulator-for-malloc.h"
+// This provides us with four possible mempcpy() definitions.
+// See also comments in bstring.c.
+
+#ifdef USE_BUILTINS
+#define BUILTIN(f) __builtin_##f
+#else /* USE_BUILTINS */
+#define BUILTIN(f) f
+#endif /* USE_BUILTINS */
+
+#ifdef VARIANT
+
+#define __mempcpy_chk BUILTIN(__mempcpy_chk)
+void *__mempcpy_chk(void *__restrict__ s1, const void *__restrict__ s2,
+size_t n, size_t destlen);
+
+#define mempcpy(a,b,c) __mempcpy_chk(a,b,c,(size_t)-1)
+
+#else /* VARIANT */
+
+#define mempcpy BUILTIN(mempcpy)
+void *mempcpy(void *__restrict__ s1, const void *__restrict__ s2, size_t n);
+
+#endif /* VARIANT */
+
void clang_analyzer_eval(int);
int *testStdCopyInvalidatesBuffer(std::vector v) {
@@ -36,3 +63,17 @@
return buf;
}
+
+namespace pr34460 {
+short a;
+class b {
+ int c;
+ long g;
+ void d() {
+int e = c;
+f += e;
+mempcpy(f, , g);
+ }
+ unsigned *f;
+};
+}
Index: cfe/trunk/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
===
--- cfe/trunk/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
+++ cfe/trunk/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
@@ -1050,31 +1050,22 @@
// If this is mempcpy, get the byte after the last byte copied and
// bind the expr.
if (IsMempcpy) {
- loc::MemRegionVal destRegVal = destVal.castAs();
-
- // Get the length to copy.
- if (Optional lenValNonLoc = sizeVal.getAs()) {
-// Get the byte after the last byte copied.
-SValBuilder = C.getSValBuilder();
-ASTContext = SvalBuilder.getContext();
-QualType CharPtrTy = Ctx.getPointerType(Ctx.CharTy);
-loc::MemRegionVal DestRegCharVal = SvalBuilder.evalCast(destRegVal,
- CharPtrTy, Dest->getType()).castAs();
-SVal lastElement = C.getSValBuilder().evalBinOpLN(state, BO_Add,
- DestRegCharVal,
- *lenValNonLoc,
- Dest->getType());
-
-// The byte after the last byte copied is the return value.
-state = state->BindExpr(CE, LCtx, lastElement);
- } else {
-// If we don't know how much we copied, we can at least
-
[PATCH] D38797: [analyzer] CStringChecker: pr34460: Admit that some casts are hard to model.
dcoughlin accepted this revision. dcoughlin added a comment. This revision is now accepted and ready to land. This looks good to me. https://reviews.llvm.org/D38797 ___ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[PATCH] D38797: [analyzer] CStringChecker: pr34460: Admit that some casts are hard to model.
NoQ added inline comments.
Comment at: test/Analysis/casts.c:134-139
+ clang_analyzer_eval(y1 == y2); // expected-warning{{TRUE}}
+
+ // FIXME: should be FALSE (i.e. equal pointers).
+ clang_analyzer_eval(y1 - y2); // expected-warning{{UNKNOWN}}
+ // FIXME: should be TRUE (i.e. same symbol).
+ clang_analyzer_eval(*y1 == *y2); // expected-warning{{UNKNOWN}}
Here we have `y1` pointing to `element{element{x, 3}, 5}` vs. both `y2` and
`y3` pointing to `element{x, 35}`. While `y3` is inevitably looking like that,
`y2` could have been same as `y1` if we didn't unwrap multi-dimensional array
elements.
https://reviews.llvm.org/D38797
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[PATCH] D38797: [analyzer] CStringChecker: pr34460: Admit that some casts are hard to model.
NoQ created this revision.
Herald added a subscriber: szepet.
In https://bugs.llvm.org/show_bug.cgi?id=34460 CStringChecker tries to
`evalCast()` a memory region from `void *` to `char *` for the purposes of
modeling `mempcpy()`. The memory region turned out to be an element region of
type `unsigned int` with a symbolic index. For such regions, even such trivial
casts have turned out to be unsupported (modeled as `UnknownVal`), and the
checker crashed upon asserting them to be supported.
I tried to get such trivial cast working for a few days and ended up believing
that it not worth the effort because of:
1. How we represent casts in the SVal hierarchy.
- In our case, the region is an ElementRegion with element type `unsigned
int`, which //essentially// represents a pointer of type `unsigned int *`, not
`void *`. It means that the cast is definitely not a no-op; the region needs to
be modified.
- Now, if the offset was concrete, we already try to replace ElementRegion
with another ElementRegion of the other type, and recompute element index
accordingly. It is only possible if byte offset of the region is divisible by
size of the target type (in our case it is because the target type is `char`).
If it's not divisible, we make two ElementRegions on top of each other, first
with element-type `char` to represent a raw offset, other of the target type to
represent the cast. It means that for symbolic index case, we need to account
for being able to receive such two-element-regions construct in the first
place, and then investigate divisibility of a linear expression of form `a*N +
b`, where `N` is concrete but `a` and `b` are possibly symbolic, to a concrete
type size, which our range constraint manager would never handle.
- In fact, now we not only unpack the top one or two ElementRegions while
computing the offset (that needs to be divisible), but also we unpack all other
top-level element regions (i.e. if we look into a multi-dimensional array; see
`ElementRegion::getAsArrayOffset()`). This was never tested; i added relevant
tests into `casts.c` in this patch to demonstrate the problems caused by that
(which are unrelated to the rest of the patch). I believe that unpacking
multi-dimensional arrays in this way is not ideal; however, i also added tests
that would fail if this behavior is disabled. This needs much more work. Of
course, this work would be even harder if we intend to support symbolic offsets.
2. How we split the responsibilities between entities. When trying to implement
the plan described in 1., i ended up moving a lot of code around and passing
ProgramState through dozens of APIs. We need the state to perform binary
operations on `SVal` objects through `SValBuilder`. Originally, `castRegion()`
resides in `RegionStore` which is not intended to access the program state. It
is trivial to move `castRegion` to `SimpleSValBuilder`, but passing `State`
into it results in a huge cascade of changes in `SValBuilder` method arguments.
I have given up when i had to pass `State` to
`SValBuilder::getConstantVal(const Expr *);`, which seemed ridiculous (it's
constant, why does it depend on the state?). Introducing all this complexity
only to compute an `SVal` that nobody would be able to understand was not worth
the effort, in my opinion.
Hence the quick fix. Code slightly simplified to use a more high-level API.
https://reviews.llvm.org/D38797
Files:
lib/StaticAnalyzer/Checkers/CStringChecker.cpp
test/Analysis/bstring.cpp
test/Analysis/casts.c
Index: test/Analysis/casts.c
===
--- test/Analysis/casts.c
+++ test/Analysis/casts.c
@@ -123,3 +123,29 @@
int x = (int) p;
clang_analyzer_eval(++x < 10); // no-crash // expected-warning{{UNKNOWN}}
}
+
+void multiDimensionalArrayPointerCasts() {
+ static int x[10][10];
+ int *y1 = &(x[3][5]);
+ char *z = ((char *) y1) + 2;
+ int *y2 = (int *)(z - 2);
+ int *y3 = ((int *)x) + 35; // This is offset for [3][5].
+
+ clang_analyzer_eval(y1 == y2); // expected-warning{{TRUE}}
+
+ // FIXME: should be FALSE (i.e. equal pointers).
+ clang_analyzer_eval(y1 - y2); // expected-warning{{UNKNOWN}}
+ // FIXME: should be TRUE (i.e. same symbol).
+ clang_analyzer_eval(*y1 == *y2); // expected-warning{{UNKNOWN}}
+
+ clang_analyzer_eval(*((char *)y1) == *((char *) y2)); // expected-warning{{TRUE}}
+
+ clang_analyzer_eval(y1 == y3); // expected-warning{{TRUE}}
+
+ // FIXME: should be FALSE (i.e. equal pointers).
+ clang_analyzer_eval(y1 - y3); // expected-warning{{UNKNOWN}}
+ // FIXME: should be TRUE (i.e. same symbol).
+ clang_analyzer_eval(*y1 == *y3); // expected-warning{{UNKNOWN}}
+
+ clang_analyzer_eval(*((char *)y1) == *((char *) y3)); // expected-warning{{TRUE}}
+}
Index: test/Analysis/bstring.cpp
===
--- test/Analysis/bstring.cpp
+++ test/Analysis/bstring.cpp
@@ -1,8 +1,35
