Go 1.26 changed all Windows syscall wrappers in zsyscall_windows.go
to use SyscallN instead of fixed-argument Syscall/Syscall6/etc. The
SyscallN function now has a body that calls an unexported syscalln
function (provided by runtime via //go:linkname).
TinyGo's existing createSyscall compiler builtin used call.Args[2:]
to extract syscall arguments, but for variadic SyscallN the SSA
representation passes args as a slice value (not individual args),
causing call.Args[2:] to be empty -- resulting in zero arguments
being passed to Windows API calls and 0xc0000005 access violations.
Fix this by:
1. Excluding syscall.SyscallN from builtin interception, letting
Go 1.26's function body compile normally (it calls syscalln)
2. Adding a new createSyscalln compiler builtin that intercepts
syscall.syscalln and correctly handles the variadic slice:
- Generates a switch on the arg count n (0-18 cases)
- Each case loads args from the slice via GEP/Load
- Wraps calls with SetLastError(0)/GetLastError() as before
- Handles i386 stdcall conventions
3. Adding runtime stubs for both Go versions:
- go1.26: syscall.syscalln stub (body intercepted by compiler)
- pre-go1.26: syscall.SyscallN stub (linker satisfaction)
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