Setjmp/longjmp

Q: How deeply does Rust in Action: Systems programming concepts and techniques cover setjmp/longjmp?

Explains saved contexts, skipped stack frames, recursive behavior, and LLVM declarations, but stops short of full intrinsic implementation details.

As explained in Rust in Action: Systems programming concepts and techniques

longjmp is a non-local control-flow function or compiler intrinsic that restores an execution context previously saved by setjmp.

setjmp marks a location and saves an execution context; longjmp restores that context, transferring control non-locally instead of returning through each intervening call. This escape route can reach error-handling code when an error or interrupt occurs deep in a call stack. section 12.9

A Rust implementation connects the control-flow mechanism to LLVM and operating-system facilities:

Declare LLVM's setjmp and longjmp intrinsics with extern "C" signatures and link_name attributes. section 12.9.2
Use the required link_llvm_intrinsics crate feature and call the declared functions inside unsafe code. section 12.9.2
Store the jump buffer and shutdown flag in mutable global state, with the example restricted to non-Windows targets. section 12.9.5

Escaping recursive calls

A recursive dive() call normally prints increasing depth markers and then prints them again while returning. With longjmp, control can leave after the third call, skip the remaining stack frames, and continue in main(), producing an early-return message followed by finishing. section 12.9

Table 12.3 Comparing the intended output from listing 12.13 and listing 12.17 (view table figure)

Listing 12.13 produces a symmetrical pattern. Each level is caused by a nested call to `dive()`, which is removed when the calls return.	Listing 12.17 produces a much different pattern. After a few calls to `dive()`, control teleports back to `main()` without returning the calls to `dive()`.
# ## ### #### ##### ### ## `#`	# ## ### early return! finishing!

Compare ordinary recursive unwinding with longjmp's direct transfer to main() through the contrasting depth-marker output. section 12.9

How Rust in Action: Systems programming concepts and techniques covers it

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Also explained in

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Modern C, Third EditionA long jump is a nonlocal control transfer that can move execution across function-call boundaries.
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Modern Csetjmp is a C library macro that saves an execution context and returns zero initially or a nonzero value when control later returns through longjmp.

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Related concepts

jmp_bufuses · jmp_buf is an opaque C library-defined type representing a saved execution environment for setjmp and longjmp.
macrokind of · A macro is a named construct that expands or transforms source code, commands, or templates before or during execution.
exceptionaddresses · An exception is a runtime signal or object representing an abnormal condition that interrupts ordinary program flow and may be handled or propagated.
performance optimizationcontrasts with · Performance optimization is the systematic modification of software or its operating conditions to improve measured execution speed, responsiveness, throughput, or resource efficiency while preserving required behavior.
stack frameuses · A stack frame is a runtime record that holds the local context and execution state for one active function or method invocation.
compiler intrinsickind of · A compiler intrinsic is a compiler-recognized language construct exposing a low-level operation through a special implementation rather than ordinary source code.

This explainer was generated by Manning's knowledge graph from the text of Rust in Action: Systems programming concepts and techniques. The section links point to the parts of the book it draws on.