Fix VM_Call crash in DLL mode when nargs is 0#66
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742617000027 wants to merge 1 commit intoDefrag-racing:mainfrom
Open
Fix VM_Call crash in DLL mode when nargs is 0#66742617000027 wants to merge 1 commit intoDefrag-racing:mainfrom
742617000027 wants to merge 1 commit intoDefrag-racing:mainfrom
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On ARM64, the compiler transforms the va_arg copy loop into a do-while (check at bottom) without a zero-trip guard. When nargs is 0, the loop never terminates and reads past the stack into the guard page, causing SIGBUS. This affects any VM_Call with nargs=0 in DLL mode, such as CG_CONSOLE_COMMAND and CG_SHUTDOWN. The VM interpreter path already handles this correctly with a `cmp w1, Defrag-racing#1; b.lt skip` guard. Zero-initialize the args array so the memset gives the compiler a separate initialization path, preventing it from folding the guard into the loop and eliminating it.
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Summary
Fixes a crash (SIGBUS) on ARM64 when using native DLL cgame modules (e.g. cgame-proxymod).
On ARM64 with
-O2, the compiler transforms theforloop inVM_Call's DLL path into a do-while loop without a zero-trip guard. Whennargsis 0 (used byCG_CONSOLE_COMMANDandCG_SHUTDOWN), the va_arg copy loop never terminates and reads past the stack into the guard page, causing a SIGBUS crash.The VM interpreter path already handles this correctly — the compiled code includes a
cmp w1, #1; b.lt skipguard before its copy loop.Fix
Zero-initialize the
argsarray withmemset. This gives the compiler a separate initialization path that prevents it from eliminating the loop guard during optimization.Reproduction
vm_cgame 0)Received signal 10(SIGBUS)See also: Jelvan1/cgame-proxymod#14