Summary: Adding more info to Pulse webpage Reviewed By: jvillard Differential Revision: D26884576 fbshipit-source-id: a6f13757fmaster
Gabriela Cunha Sampaio
4 years ago
committed by
Facebook GitHub Bot
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### What is Infer:Pulse?
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Pulse is an interprocedural memory safety analysis. Pulse can detect, for instance, [Null dereferences](/docs/next/all-issue-types#nullptr_dereference) in Java. Errors are only reported when all conditions on the erroneous path are true regardless of input. Pulse should gradually replace the original [biabduction](/docs/next/checker-biabduction) analysis of Infer. An example of a Null dereference found by Pulse is given below.
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```java
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class Person {
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Person emergencyContact;
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String address;
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Person getEmergencyContact() {
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return this.emergencyContact;
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}
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}
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class Registry {
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void create() {
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Person p = new Person();
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Person c = p.getEmergencyContact();
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// Null dereference here
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System.out.println(c.address);
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}
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void printContact(Person p) {
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// No null dereference, as we don't know anything about `p`
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System.out.println(p.getEmergencyContact().address);
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}
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}
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```
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How to run pulse for Java:
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```bash
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infer run --pulse -- javac Test.java
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```
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Pulse reports a Null dereference on this file on `create()`, as it tries to access the field `address` of object `c`, and `c` has value `null`. In contrast, Pulse gives no report for `printContact(Person p)`, as we cannot be sure that `p.getEmergencyContact()` will return `null`. Pulse then labels this error as latent and only reports if there is a call to `printContact(Person p)` satisfying the condition for Null dereference.
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### Pulse x Nullsafe
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[Nullsafe](/docs/next/checker-eradicate) is a type checker for `@Nullable` annotations for Java. Classes following the Nullsafe discipline are annotated with `@Nullsafe`.
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Consider the classes `Person` and `Registry` from the previous example. Assuming that class `Person` is annotated with `@Nullsafe`. In this case, we also annotate `getEmergencyContact()` with `@Nullable`, to make explicit that this method can return the `null` value. There is still the risk that classes depending on `Person` have Null dereferences. In this case, Pulse would report a Null dereference on `Registry`. It could also be the case that class `Registry` is annotated with `@Nullsafe`. By default Pulse reports on `@Nullsafe` files too, see the `--pulse-nullsafe-report-npe` option (Facebook-specific: Pulse does not report on `@Nullsafe` files).
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```java
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@Nullsafe(Nullsafe.Mode.LOCAL)
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class Person {
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Person emergencyContact;
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String address;
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@Nullable Person getEmergencyContact() {
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return this.emergencyContact;
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}
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}
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class Registry {
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... // Pulse reports here
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}
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```
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@ -1 +1,96 @@
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Infer reports null dereference bugs in Java, C and Objective-C. The issue is
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about a pointer that can be `null` and it is dereferenced. This leads to a crash
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in all the above languages.
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### Null dereference in Java
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Many of Infer's reports of potential NPE's come from code of the form
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```java
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p = foo(); // foo() might return null
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stuff();
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p.goo(); // dereferencing p, potential NPE
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```
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If you see code of this form, then you have several options.
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<b> If you are unsure whether or not foo() will return null </b>, you should
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ideally i. Change the code to ensure that foo() can not return null ii. Add a
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check for whether p is null, and do something other than dereferencing p when it
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is null.
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Sometimes, in case ii it is not obvious what you should do when p is null. One
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possibility (a last option) is to throw an exception, failing early. This can be
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done using checkNotNull as in the following code:
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```java
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// code idiom for failing early
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import static com.google.common.base.Preconditions.checkNotNull;
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//... intervening code
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p = checkNotNull(foo()); // foo() might return null
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stuff();
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p.goo(); // dereferencing p, potential NPE
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```
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The call checkNotNull(foo()) will never return null; in case foo() returns null
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it fails early by throwing an NPE.
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<b> If you are absolutely sure that foo() will not be null </b>, then if you
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land your diff this case will no longer be reported after your diff makes it to
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master.
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### Null dereference in C
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Here is an example of an inter-procedural null dereference bug in C:
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```c
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struct Person {
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int age;
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int height;
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int weight;
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};
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int get_age(struct Person *who) {
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return who->age;
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}
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int null_pointer_interproc() {
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struct Person *joe = 0;
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return get_age(joe);
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}
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```
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### Null dereference in Objective-C
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In Objective-C, null dereferences are less common than in Java, but they still
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happen and their cause can be hidden. In general, passing a message to nil does
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not cause a crash and returns `nil`, but dereferencing a pointer directly does
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cause a crash as well as calling a `nil` block.C
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```objectivec
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-(void) foo:(void (^)())callback {
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callback();
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}
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-(void) bar {
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[self foo:nil]; //crash
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}
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```
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Moreover, there are functions from the libraries that do not allow `nil` to be
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passed as argument. Here are some examples:
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```objectivec
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-(void) foo {
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NSString *str = nil;
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NSArray *animals = @[@"horse", str, @"dolphin"]; //crash
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}
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-(void) bar {
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CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); //can return NULL
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...
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CFRelease(colorSpace); //crashes if called with NULL
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}
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```
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@ -1,97 +0,0 @@
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Infer reports null dereference bugs in C, Objective-C and Java. The issue is
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about a pointer that can be `null` and it is dereferenced. This leads to a crash
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in all the above languages.
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### Null dereference in C
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Here is an example of an inter-procedural null dereference bug in C:
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```c
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struct Person {
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int age;
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int height;
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int weight;
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};
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int get_age(struct Person *who) {
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return who->age;
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}
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int null_pointer_interproc() {
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struct Person *joe = 0;
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return get_age(joe);
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}
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```
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### Null dereference in Objective-C
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In Objective-C, null dereferences are less common than in Java, but they still
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happen and their cause can be hidden. In general, passing a message to nil does
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not cause a crash and returns `nil`, but dereferencing a pointer directly does
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cause a crash as well as calling a `nil` block.C
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```objectivec
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-(void) foo:(void (^)())callback {
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callback();
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}
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-(void) bar {
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[self foo:nil]; //crash
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}
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```
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Moreover, there are functions from the libraries that do not allow `nil` to be
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passed as argument. Here are some examples:
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```objectivec
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-(void) foo {
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NSString *str = nil;
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NSArray *animals = @[@"horse", str, @"dolphin"]; //crash
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}
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-(void) bar {
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CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); //can return NULL
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...
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CFRelease(colorSpace); //crashes if called with NULL
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}
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```
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### Null dereference in Java
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Many of Infer's reports of potential NPE's come from code of the form
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```java
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p = foo(); // foo() might return null
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stuff();
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p.goo(); // dereferencing p, potential NPE
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```
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If you see code of this form, then you have several options.
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<b> If you are unsure whether or not foo() will return null </b>, you should
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ideally i. Change the code to ensure that foo() can not return null ii. Add a
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check for whether p is null, and do something other than dereferencing p when it
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is null.
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Sometimes, in case ii it is not obvious what you should do when p is null. One
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possibility (a last option) is to throw an exception, failing early. This can be
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done using checkNotNull as in the following code:
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```java
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// code idiom for failing early
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import static com.google.common.base.Preconditions.checkNotNull;
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//... intervening code
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p = checkNotNull(foo()); // foo() might return null
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stuff();
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p.goo(); // dereferencing p, potential NPE
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```
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The call checkNotNull(foo()) will never return null; in case foo() returns null
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it fails early by throwing an NPE.
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<b> If you are absolutely sure that foo() will not be null </b>, then if you
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land your diff this case will no longer be reported after your diff makes it to
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master. In the future we might include analysis directives (hey, analyzer, p is
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not null!) like in Hack that tell the analyzer the information that you know,
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but that is for later.
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@ -0,0 +1,20 @@
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---
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title: "Config Impact Analysis"
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description: "[EXPERIMENTAL] Collects function that are called without config checks."
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---
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[EXPERIMENTAL] Collects function that are called without config checks.
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Activate with `--config-impact-analysis`.
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Supported languages:
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- C/C++/ObjC: Experimental
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- Java: Experimental
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- C#/.Net: Experimental
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This checker collects functions whose execution isn't gated by certain pre-defined gating functions. The set of gating functions is hardcoded and empty by default for now, so to use this checker, please modify the code directly in [FbGKInteraction.ml](https://github.com/facebook/infer/tree/master/infer/src/opensource).
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## List of Issue Types
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The following issue types are reported by this checker:
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- [CONFIG_IMPACT](/docs/next/all-issue-types#config_impact)
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