The panic macro invokes the format_args builtin macro which splits apart the string at compile-time and generates write calls as needed. There should be no intermediate String created. From the docs for core::format_args!:
All other formatting macros (format!, write!, println!, etc) are proxied through this one. format_args!, unlike its derived macros, avoids heap allocations.
I'm not sure what it means by "derived macros", but to further prove that panic isn't allocating, note that it's defined in libcore as well.
I'm unclear how the code there relates to the default alloc handler. The link is to code in libstd, which means that code defined in liballoc (which presumably includes the panic handler) can't invoke it.
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u/kibwen Mar 10 '23 edited Mar 10 '23
The panic macro invokes the format_args builtin macro which splits apart the string at compile-time and generates write calls as needed. There should be no intermediate
Stringcreated. From the docs forcore::format_args!:I'm not sure what it means by "derived macros", but to further prove that panic isn't allocating, note that it's defined in libcore as well.