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compiler, runtime: fix SyscallN handling for Windows on Go 1.26+

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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)
This commit is contained in:
deadprogram
2026-04-10 12:15:58 +02:00
committed by Ron Evans
parent 2d477e069d
commit ddacdfacd5
4 changed files with 164 additions and 1 deletions
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compiler/compiler.go
+5 -1
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@@ -1980,10 +1980,14 @@ func (b *builder) createFunctionCall(instr *ssa.CallCommon) (llvm.Value, error)
return b.emitSV64Call(instr.Args, getPos(instr))
case strings.HasPrefix(name, "(device/riscv.CSR)."):
return b.emitCSROperation(instr)
case strings.HasPrefix(name, "syscall.Syscall") || strings.HasPrefix(name, "syscall.RawSyscall") || strings.HasPrefix(name, "golang.org/x/sys/unix.Syscall") || strings.HasPrefix(name, "golang.org/x/sys/unix.RawSyscall"):
case (strings.HasPrefix(name, "syscall.Syscall") || strings.HasPrefix(name, "syscall.RawSyscall") || strings.HasPrefix(name, "golang.org/x/sys/unix.Syscall") || strings.HasPrefix(name, "golang.org/x/sys/unix.RawSyscall")) && name != "syscall.SyscallN":
if b.GOOS != "darwin" {
return b.createSyscall(instr)
}
case name == "syscall.syscalln":
if b.GOOS == "windows" {
return b.createSyscalln(instr)
}
case strings.HasPrefix(name, "syscall.rawSyscallNoError") || strings.HasPrefix(name, "golang.org/x/sys/unix.RawSyscallNoError"):
return b.createRawSyscallNoError(instr)
case name == "runtime.supportsRecover":