Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Add shared basic block library #18497

Merged
merged 13 commits into from
Jan 24, 2025
Merged

Add shared basic block library #18497

Show file tree
Hide file tree
Changes from 4 commits
Commits
Show all changes
13 commits
Select commit Hold shift + click to select a range
ce5c886
Rust, Ruby: Add basic block test
paldepind Jan 15, 2025
c051eec
Shared: Add shared basic block library
paldepind Jan 15, 2025
8b20b0d
Shared: Add change note for basic block addition
paldepind Jan 16, 2025
4d05b6a
Shared: Address review comments for shared basic block library
paldepind Jan 17, 2025
53b63be
Actions: Implement added predicates in CFG instantiation
paldepind Jan 17, 2025
e382ffc
Shared: Address review comments for basic block library
paldepind Jan 17, 2025
62a459d
Shared: Address basic block review comments
paldepind Jan 20, 2025
f7e9049
Shared: Implement `getScope` in BB module instead of CFG module
paldepind Jan 20, 2025
9a4bf75
Shared: Add more detailed documentation for `immediatelyControls`
paldepind Jan 20, 2025
e5f419c
Shared: Define `getNode` inside cached module
paldepind Jan 22, 2025
9547a5c
Shared: Update basic block documentation and make minor tweaks
paldepind Jan 22, 2025
a537f34
Shared: Tweak basic block documentation
paldepind Jan 23, 2025
e13a7a2
Merge branch 'main' into shared-basic-block-library
paldepind Jan 24, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
270 changes: 32 additions & 238 deletions csharp/ql/lib/semmle/code/csharp/controlflow/BasicBlocks.qll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,26 +4,20 @@

import csharp
private import ControlFlow::SuccessorTypes
private import semmle.code.csharp.controlflow.internal.ControlFlowGraphImpl as CfgImpl
private import CfgImpl::BasicBlocks as BasicBlocksImpl

/**
* A basic block, that is, a maximal straight-line sequence of control flow nodes
* without branches or joins.
*/
class BasicBlock extends TBasicBlockStart {
/** Gets an immediate successor of this basic block, if any. */
BasicBlock getASuccessor() { result.getFirstNode() = this.getLastNode().getASuccessor() }

final class BasicBlock extends BasicBlocksImpl::BasicBlock {
/** Gets an immediate successor of this basic block of a given type, if any. */
BasicBlock getASuccessorByType(ControlFlow::SuccessorType t) {
result.getFirstNode() = this.getLastNode().getASuccessorByType(t)
}

/** Gets an immediate predecessor of this basic block, if any. */
BasicBlock getAPredecessor() { result.getASuccessor() = this }
BasicBlock getASuccessorByType(ControlFlow::SuccessorType t) { result = this.getASuccessor(t) }

/** Gets an immediate predecessor of this basic block of a given type, if any. */
BasicBlock getAPredecessorByType(ControlFlow::SuccessorType t) {
result.getASuccessorByType(t) = this
result = this.getAPredecessor(t)
}

/**
Expand Down Expand Up @@ -65,23 +59,20 @@ class BasicBlock extends TBasicBlockStart {
}

/** Gets the control flow node at a specific (zero-indexed) position in this basic block. */
ControlFlow::Node getNode(int pos) { bbIndex(this.getFirstNode(), result, pos) }
ControlFlow::Node getNode(int pos) { result = super.getNode(pos) }

/** Gets a control flow node in this basic block. */
ControlFlow::Node getANode() { result = this.getNode(_) }
ControlFlow::Node getANode() { result = super.getANode() }

/** Gets the first control flow node in this basic block. */
ControlFlow::Node getFirstNode() { this = TBasicBlockStart(result) }
ControlFlow::Node getFirstNode() { result = super.getFirstNode() }

/** Gets the last control flow node in this basic block. */
ControlFlow::Node getLastNode() { result = this.getNode(this.length() - 1) }
ControlFlow::Node getLastNode() { result = super.getLastNode() }

/** Gets the callable that this basic block belongs to. */
final Callable getCallable() { result = this.getFirstNode().getEnclosingCallable() }

/** Gets the length of this basic block. */
int length() { result = strictcount(this.getANode()) }

/**
* Holds if this basic block immediately dominates basic block `bb`.
*
Expand All @@ -103,7 +94,7 @@ class BasicBlock extends TBasicBlockStart {
* basic block on line 4 (all paths from the entry point of `M`
* to `return s.Length;` must go through the null check).
*/
predicate immediatelyDominates(BasicBlock bb) { bbIDominates(this, bb) }
predicate immediatelyDominates(BasicBlock bb) { super.immediatelyDominates(bb) }

/**
* Holds if this basic block strictly dominates basic block `bb`.
Expand All @@ -126,7 +117,7 @@ class BasicBlock extends TBasicBlockStart {
* basic block on line 4 (all paths from the entry point of `M`
* to `return s.Length;` must go through the null check).
*/
predicate strictlyDominates(BasicBlock bb) { bbIDominates+(this, bb) }
predicate strictlyDominates(BasicBlock bb) { super.strictlyDominates(bb) }

/**
* Holds if this basic block dominates basic block `bb`.
Expand Down Expand Up @@ -178,15 +169,7 @@ class BasicBlock extends TBasicBlockStart {
* `Console.Write(x);`. Also, the basic block starting on line 2
* does not dominate the basic block on line 6.
*/
predicate inDominanceFrontier(BasicBlock df) {
this.dominatesPredecessor(df) and
not this.strictlyDominates(df)
}

/**
* Holds if this basic block dominates a predecessor of `df`.
*/
private predicate dominatesPredecessor(BasicBlock df) { this.dominates(df.getAPredecessor()) }
predicate inDominanceFrontier(BasicBlock df) { super.inDominanceFrontier(df) }

/**
* Gets the basic block that immediately dominates this basic block, if any.
Expand All @@ -208,7 +191,7 @@ class BasicBlock extends TBasicBlockStart {
* the basic block online 4 (all paths from the entry point of `M`
* to `return s.Length;` must go through the null check.
*/
BasicBlock getImmediateDominator() { bbIDominates(result, this) }
BasicBlock getImmediateDominator() { result = super.getImmediateDominator() }

/**
* Holds if this basic block strictly post-dominates basic block `bb`.
Expand All @@ -234,7 +217,7 @@ class BasicBlock extends TBasicBlockStart {
* line 3 (all paths to the exit point of `M` from `return s.Length;`
* must go through the `WriteLine` call).
*/
predicate strictlyPostDominates(BasicBlock bb) { bbIPostDominates+(this, bb) }
predicate strictlyPostDominates(BasicBlock bb) { super.strictlyPostDominates(bb) }

/**
* Holds if this basic block post-dominates basic block `bb`.
Expand Down Expand Up @@ -262,10 +245,7 @@ class BasicBlock extends TBasicBlockStart {
* This predicate is *reflexive*, so for example `Console.WriteLine("M");`
* post-dominates itself.
*/
predicate postDominates(BasicBlock bb) {
this.strictlyPostDominates(bb) or
this = bb
}
predicate postDominates(BasicBlock bb) { super.postDominates(bb) }

/**
* Holds if this basic block is in a loop in the control flow graph. This
Expand All @@ -274,230 +254,44 @@ class BasicBlock extends TBasicBlockStart {
* necessary back edges are unreachable.
*/
predicate inLoop() { this.getASuccessor+() = this }

/** Gets a textual representation of this basic block. */
string toString() { result = this.getFirstNode().toString() }

/** Gets the location of this basic block. */
Location getLocation() { result = this.getFirstNode().getLocation() }
}

/**
* Internal implementation details.
*/
cached
private module Internal {
/** Internal representation of basic blocks. */
cached
newtype TBasicBlock = TBasicBlockStart(ControlFlow::Node cfn) { startsBB(cfn) }

/** Holds if `cfn` starts a new basic block. */
private predicate startsBB(ControlFlow::Node cfn) {
not exists(cfn.getAPredecessor()) and exists(cfn.getASuccessor())
or
cfn.isJoin()
or
cfn.getAPredecessor().isBranch()
or
/*
* In cases such as
* ```csharp
* if (b)
* M()
* ```
* where the `false` edge out of `b` is not present (because we can prove it
* impossible), we still split up the basic block in two, in order to generate
* a `ConditionBlock` which can be used by the guards library.
*/

exists(cfn.getAPredecessorByType(any(ControlFlow::SuccessorTypes::ConditionalSuccessor s)))
}

/**
* Holds if `succ` is a control flow successor of `pred` within
* the same basic block.
*/
private predicate intraBBSucc(ControlFlow::Node pred, ControlFlow::Node succ) {
succ = pred.getASuccessor() and
not startsBB(succ)
}

/**
* Holds if `cfn` is the `i`th node in basic block `bb`.
*
* In other words, `i` is the shortest distance from a node `bb`
* that starts a basic block to `cfn` along the `intraBBSucc` relation.
*/
cached
predicate bbIndex(ControlFlow::Node bbStart, ControlFlow::Node cfn, int i) =
shortestDistances(startsBB/1, intraBBSucc/2)(bbStart, cfn, i)

/**
* Holds if the first node of basic block `succ` is a control flow
* successor of the last node of basic block `pred`.
*/
private predicate succBB(BasicBlock pred, BasicBlock succ) { succ = pred.getASuccessor() }

/** Holds if `dom` is an immediate dominator of `bb`. */
cached
predicate bbIDominates(BasicBlock dom, BasicBlock bb) =
idominance(entryBB/1, succBB/2)(_, dom, bb)

/** Holds if `pred` is a basic block predecessor of `succ`. */
private predicate predBB(BasicBlock succ, BasicBlock pred) { succBB(pred, succ) }

/** Holds if `bb` is an exit basic block that represents normal exit. */
private predicate normalExitBB(BasicBlock bb) {
bb.getANode().(ControlFlow::Nodes::AnnotatedExitNode).isNormal()
}

/** Holds if `dom` is an immediate post-dominator of `bb`. */
cached
predicate bbIPostDominates(BasicBlock dom, BasicBlock bb) =
idominance(normalExitBB/1, predBB/2)(_, dom, bb)
}

private import Internal

/**
* An entry basic block, that is, a basic block whose first node is
* the entry node of a callable.
* an entry node.
*/
class EntryBasicBlock extends BasicBlock {
EntryBasicBlock() { entryBB(this) }
}

/** Holds if `bb` is an entry basic block. */
private predicate entryBB(BasicBlock bb) {
bb.getFirstNode() instanceof ControlFlow::Nodes::EntryNode
}
final class EntryBasicBlock extends BasicBlock, BasicBlocksImpl::EntryBasicBlock { }

/**
* An annotated exit basic block, that is, a basic block that contains
* an annotated exit node.
* An annotated exit basic block, that is, a basic block that contains an
* annotated exit node.
*/
class AnnotatedExitBasicBlock extends BasicBlock {
private boolean isNormal;

AnnotatedExitBasicBlock() {
this.getANode() =
any(ControlFlow::Nodes::AnnotatedExitNode n |
if n.isNormal() then isNormal = true else isNormal = false
)
}

/** Holds if this block represents a normal exit. */
predicate isNormal() { isNormal = true }
}
final class AnnotatedExitBasicBlock extends BasicBlock, BasicBlocksImpl::AnnotatedExitBasicBlock { }

/**
* An exit basic block, that is, a basic block whose last node is
* the exit node of a callable.
* an exit node.
*/
class ExitBasicBlock extends BasicBlock {
ExitBasicBlock() { this.getLastNode() instanceof ControlFlow::Nodes::ExitNode }
}

private module JoinBlockPredecessors {
private import ControlFlow::Nodes
private import semmle.code.csharp.controlflow.internal.ControlFlowGraphImpl as Impl

int getId(JoinBlockPredecessor jbp) {
exists(Impl::AstNode n | result = n.getId() |
n = jbp.getFirstNode().getAstNode()
or
n = jbp.(EntryBasicBlock).getCallable()
)
}

string getSplitString(JoinBlockPredecessor jbp) {
result = jbp.getFirstNode().(ElementNode).getSplitsString()
or
not exists(jbp.getFirstNode().(ElementNode).getSplitsString()) and
result = ""
}
}
final class ExitBasicBlock extends BasicBlock, BasicBlocksImpl::ExitBasicBlock { }

/** A basic block with more than one predecessor. */
class JoinBlock extends BasicBlock {
JoinBlock() { this.getFirstNode().isJoin() }

/**
* Gets the `i`th predecessor of this join block, with respect to some
* arbitrary order.
*/
cached
JoinBlockPredecessor getJoinBlockPredecessor(int i) {
result =
rank[i + 1](JoinBlockPredecessor jbp |
jbp = this.getAPredecessor()
|
jbp order by JoinBlockPredecessors::getId(jbp), JoinBlockPredecessors::getSplitString(jbp)
)
}
final class JoinBlock extends BasicBlock, BasicBlocksImpl::JoinBasicBlock {
JoinBlockPredecessor getJoinBlockPredecessor(int i) { result = super.getJoinBlockPredecessor(i) }
}

/** A basic block that is an immediate predecessor of a join block. */
class JoinBlockPredecessor extends BasicBlock {
JoinBlockPredecessor() { this.getASuccessor() instanceof JoinBlock }
}

/** A basic block that terminates in a condition, splitting the subsequent control flow. */
class ConditionBlock extends BasicBlock {
ConditionBlock() { this.getLastNode().isCondition() }
final class JoinBlockPredecessor extends BasicBlock, BasicBlocksImpl::JoinPredecessorBasicBlock { }

/**
* Holds if basic block `succ` is immediately controlled by this basic
* block with conditional value `s`. That is, `succ` is an immediate
* successor of this block, and `succ` can only be reached from
* the callable entry point by going via the `s` edge out of this basic block.
*/
pragma[nomagic]
/**
* A basic block that terminates in a condition, splitting the subsequent
* control flow.
*/
final class ConditionBlock extends BasicBlock, BasicBlocksImpl::ConditionBasicBlock {
predicate immediatelyControls(BasicBlock succ, ConditionalSuccessor s) {
succ = this.getASuccessorByType(s) and
forall(BasicBlock pred | pred = succ.getAPredecessor() and pred != this | succ.dominates(pred))
super.immediatelyControls(succ, s)
}

/**
* Holds if basic block `controlled` is controlled by this basic block with
* conditional value `s`. That is, `controlled` can only be reached from
* the callable entry point by going via the `s` edge out of this basic block.
*/
predicate controls(BasicBlock controlled, ConditionalSuccessor s) {
/*
* For this block to control the block `controlled` with `testIsTrue` the following must be true:
* Execution must have passed through the test i.e. `this` must strictly dominate `controlled`.
* Execution must have passed through the `testIsTrue` edge leaving `this`.
*
* Although "passed through the true edge" implies that `this.getATrueSuccessor()` dominates `controlled`,
* the reverse is not true, as flow may have passed through another edge to get to `this.getATrueSuccessor()`
* so we need to assert that `this.getATrueSuccessor()` dominates `controlled` *and* that
* all predecessors of `this.getATrueSuccessor()` are either `this` or dominated by `this.getATrueSuccessor()`.
*
* For example, in the following C# snippet:
* ```csharp
* if (x)
* controlled;
* false_successor;
* uncontrolled;
* ```
* `false_successor` dominates `uncontrolled`, but not all of its predecessors are `this` (`if (x)`)
* or dominated by itself. Whereas in the following code:
* ```csharp
* if (x)
* while (controlled)
* also_controlled;
* false_successor;
* uncontrolled;
* ```
* the block `while controlled` is controlled because all of its predecessors are `this` (`if (x)`)
* or (in the case of `also_controlled`) dominated by itself.
*
* The additional constraint on the predecessors of the test successor implies
* that `this` strictly dominates `controlled` so that isn't necessary to check
* directly.
*/

exists(BasicBlock succ | this.immediatelyControls(succ, s) | succ.dominates(controlled))
super.controls(controlled, s)
}
}
4 changes: 4 additions & 0 deletions csharp/ql/lib/semmle/code/csharp/controlflow/internal/ControlFlowGraphImpl.qll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,10 @@ private module CfgInput implements CfgShared::InputSig<Location> {
t instanceof ST::SuccessorTypes::ExceptionSuccessor or
t instanceof ST::SuccessorTypes::ExitSuccessor
}

int idOfAstNode(AstNode node) { result = node.getId() }

int idOfCfgScope(CfgScope node) { result = idOfAstNode(node) }
}

private module CfgSplittingInput implements CfgShared::SplittingInputSig<Location, CfgInput> {
Expand Down
Loading
Loading