Breakpoints and function prologues

📚 Official Books Advanced Apple Debugging
1

On page 127 of v1.0, the book shows a breakpoint set in the Xcode GUI in the first image with the result being that the debugger breaks at the start of the function prologue (0x100006b70) as shown in the second image in the book.

However, when I do this (Xcode 3.3.2 build 8E2002, lldb 370.0.42, Swift 3.1), the debugger breaks after the function prologue as seen below (this would be at address 0x100006b83 in the book’s image).

lldb breakpoint.png960×282 83 KB

I’m not sure if I’m doing something wrong with the breakpoint creation or if this is just a change in behavior due to the different software versions, but it will lead to an unexpected crash for readers who are following the directions as written. In order to avoid the crash, the reader will need to be instructed to set rip to the address after the prologue in aGoodMethod (i.e. 0x100003a23, rather than 0x100003a10 in the book). You may want to add some text covering this in future revisions of the book.

2

Gah! I just realized that this was happening due to a typo in the settings set target.skip-prologue false line in my .lldbinit. I didn’t realize it until I fired up lldb at the command line and got the error message.

3

Thanks for highlighting that @wneumann. I’ll add a note reminding readers about that LLDB setting in the next release