# Request for iOS developers: Testing Swift-based apps for memory corruption using libmalloc

**URL:** <https://forums.swift.org/t/request-for-ios-developers-testing-swift-based-apps-for-memory-corruption-using-libmalloc/66231>\
**Category:** Using Swift\
**Tags:** swift, memory-safety\
**Created:** [July 18, 2023, 4:01pm UTC](https://forums.swift.org/t/request-for-ios-developers-testing-swift-based-apps-for-memory-corruption-using-libmalloc/66231 "2023-07-18T16:01:23Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![yyarashevich](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/yyarashevich/32/27690_2.png) [@yyarashevich](https://forums.swift.org/u/yyarashevich)\
**Post date:** [July 18, 2023, 4:01pm UTC](https://forums.swift.org/t/request-for-ios-developers-testing-swift-based-apps-for-memory-corruption-using-libmalloc/66231/1 "2023-07-18T16:01:23Z")

</div>

The [libmalloc](https://github.com/apple-oss-distributions/libmalloc) provides self inspection facilities to detect corruption. Here is quote from `man malloc`.

```swift
...
ENVIRONMENT
     The following environment variables change the behavior of the allocation-related functions.
...
     MallocCheckHeapStart <s> If set, specifies the number of allocations <s> to wait before begining periodic heap checks every <n> as specified by MallocCheckHeapEach. If MallocCheckHeapStart is set but MallocCheckHeapEach is not
                                      specified, the default check repetition is 1000.

     MallocCheckHeapEach <n> If set, run a consistency check on the heap every <n> operations. MallocCheckHeapEach is only meaningful if MallocCheckHeapStart is also set.

     MallocCheckHeapSleep <t> Sets the number of seconds to sleep (waiting for a debugger to attach) when MallocCheckHeapStart is set and a heap corruption is detected. The default is 100 seconds. Setting this to zero means not to
                                      sleep at all. Setting this to a negative number means to sleep (for the positive number of seconds) only the very first time a heap corruption is detected.

     MallocCheckHeapAbort <b> When MallocCheckHeapStart is set and this is set to a non-zero value, causes abort(3) to be called if a heap corruption is detected, instead of any sleeping.

...

```

When I enable the corruption checker via `MallocCheckHeapStart=X` (for my app it's 1000000), `MallocCheckHeapEach=Y` (for my app it's 1, but it could be 10, 100, or 1000 to lessen the slowdown of the app), `MallocCheckHeapAbort=1`, I consistently get corruption detected in a large app I'm working on within the first few minutes of the app launch. I've also asked a friend who works on a different large, legacy app - they report the same story - corruption is eventually detected.

The problem is, either `libmalloc` is providing false-positive detection or all Swift-based iOS apps are susceptible to subtle memory corruption bugs.

So, I kindly ask any developers who are developing for iOS: could you please check if your app can survive several minutes with `libmalloc` checks enabled without triggering the memory corruption check? I would recommend starting with these initial values:

```swift
MallocCheckHeapStart=100000
MallocCheckHeapEach=100
MallocCheckHeapAbort=1

```

If your app is running too slowly, you can adjust these values.

Thanks a lot in advance to anyone who has read this and tried it on their app!