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MIPS64: Avoid unaligned load in lj_vm_exit_interp. Thanks to Sergey Kaplun. (cherry picked from commit 2aec641e0) MIPS processors originally required all memory accesses to be naturally aligned. If we use ld instruction to load a double-word from the address which is word-aligned, MIPS raises the exception SIGBUS. When exiting the interpreter, if the current function is a fast function, the code in the `lj_vm_exit_interp()` throws SIGBUS. The pc field for the fast function points to the word-aligned bytecodes for ASM fast functions, and PC2PROTO offset is double-word-aligned. The resulting address is somewhere in the dispatch table. Hence, some (odd-indexed) fast function access leads to the BUS error. For other architectures the load from unaligned access is not a problem so there are no exceptions. This patch prevents unaligned memory access by address loading only after fast-function checks. Sergey Kaplun: * added the description and the test for the problem Part of tarantool/tarantool#12134 Reviewed-by: Sergey Bronnikov <sergeyb@tarantool.org> Signed-off-by: Sergey Kaplun <skaplun@tarantool.org> (cherry picked from commit 3ed650fed)
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