runtime (avr): fix infinite longjmp loop if stack is aligned to 256 bytes #5111
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…ytes The setjmp code sets r24 to 0 and checks if it is still 0 when it finishes. This usually works because tinygo_longjmp stores the lower half of the stack pointer into r24. However, r24 will be set to 0 if the stack is aligned to 256 bytes when entering the setjmp. Manually set r24 to 1 in tinygo_longjmp to fix this issue.
deadprogram
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Dec 5, 2025
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Another impressive find @niaow 🔍
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Another reference on why we need to do this: https://docs.rs/crate/avr-libc/latest/source/avr-libc/libc/stdlib/setjmp.S#131 |
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The setjmp code sets
r24to 0 and checks if it is still 0 when it finishes. This usually works becausetinygo_longjmpstores the lower half of the stack pointer intor24. However,r24will be set to 0 if the stack is aligned to 256 bytes when entering the setjmp.Manually set
r24to 1 intinygo_longjmpto fix this issue.