Implement printing to file in PassWrapper

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2281,7 +2281,12 @@ extern "C" {
 
     pub fn LLVMRustHasFeature(T: &TargetMachine, s: *const c_char) -> bool;
 
-    pub fn LLVMRustPrintTargetCPUs(T: &TargetMachine, cpu: *const c_char);
+    pub fn LLVMRustPrintTargetCPUs(
+        T: &TargetMachine,
+        cpu: *const c_char,
+        print: unsafe extern "C" fn(out: *mut c_void, string: *const c_char, len: usize),
+        out: *mut c_void,
+    );
     pub fn LLVMRustGetTargetFeaturesCount(T: &TargetMachine) -> size_t;
     pub fn LLVMRustGetTargetFeature(
         T: &TargetMachine,

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -17,8 +17,8 @@ use rustc_session::config::PrintRequest;
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
 use rustc_target::spec::{MergeFunctions, PanicStrategy};
-use std::ffi::{CStr, CString};
 
+use std::ffi::{c_char, c_void, CStr, CString};
 use std::path::Path;
 use std::ptr;
 use std::slice;
@@ -401,7 +401,7 @@ fn print_target_features(out: &mut dyn PrintBackendInfo, sess: &Session, tm: &ll
     writeln!(out, "and may be renamed or removed in a future version of LLVM or rustc.\n");
 }
 
-pub(crate) fn print(req: PrintRequest, out: &mut dyn PrintBackendInfo, sess: &Session) {
+pub(crate) fn print(req: PrintRequest, mut out: &mut dyn PrintBackendInfo, sess: &Session) {
     require_inited();
     let tm = create_informational_target_machine(sess);
     match req {
@@ -411,7 +411,19 @@ pub(crate) fn print(req: PrintRequest, out: &mut dyn PrintBackendInfo, sess: &Se
             // at least as long as the C function
             let cpu_cstring = CString::new(handle_native(sess.target.cpu.as_ref()))
                 .unwrap_or_else(|e| bug!("failed to convert to cstring: {}", e));
-            unsafe { llvm::LLVMRustPrintTargetCPUs(tm, cpu_cstring.as_ptr()) };
+            unsafe extern "C" fn callback(out: *mut c_void, string: *const c_char, len: usize) {
+                let out = &mut *(out as *mut &mut dyn PrintBackendInfo);
+                let bytes = slice::from_raw_parts(string as *const u8, len);
+                write!(out, "{}", String::from_utf8_lossy(bytes));
+            }
+            unsafe {
+                llvm::LLVMRustPrintTargetCPUs(
+                    tm,
+                    cpu_cstring.as_ptr(),
+                    callback,
+                    &mut out as *mut &mut dyn PrintBackendInfo as *mut c_void,
+                );
+            }
         }
         PrintRequest::TargetFeatures => print_target_features(out, sess, tm),
         _ => bug!("rustc_codegen_llvm can't handle print request: {:?}", req),

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -1,5 +1,6 @@
 #include <stdio.h>
 
+#include <iomanip>
 #include <vector>
 #include <set>
 
@@ -306,44 +307,55 @@ static size_t getLongestEntryLength(ArrayRef<KV> Table) {
   return MaxLen;
 }
 
-extern "C" void LLVMRustPrintTargetCPUs(LLVMTargetMachineRef TM, const char* TargetCPU) {
+using PrintBackendInfo = void(void*, const char* Data, size_t Len);
+
+extern "C" void LLVMRustPrintTargetCPUs(LLVMTargetMachineRef TM,
+                                        const char* TargetCPU,
+                                        PrintBackendInfo Print,
+                                        void* Out) {
   const TargetMachine *Target = unwrap(TM);
   const MCSubtargetInfo *MCInfo = Target->getMCSubtargetInfo();
   const Triple::ArchType HostArch = Triple(sys::getDefaultTargetTriple()).getArch();
   const Triple::ArchType TargetArch = Target->getTargetTriple().getArch();
 
+  std::ostringstream Buf;
+
 #if LLVM_VERSION_GE(17, 0)
   const ArrayRef<SubtargetSubTypeKV> CPUTable = MCInfo->getAllProcessorDescriptions();
 #elif defined(LLVM_RUSTLLVM)
   const ArrayRef<SubtargetSubTypeKV> CPUTable = MCInfo->getCPUTable();
 #else
-  printf("Full target CPU help is not supported by this LLVM version.\n\n");
+  Buf << "Full target CPU help is not supported by this LLVM version.\n\n";
   SubtargetSubTypeKV TargetCPUKV = { TargetCPU, {{}}, {{}} };
   const ArrayRef<SubtargetSubTypeKV> CPUTable = TargetCPUKV;
 #endif
   unsigned MaxCPULen = getLongestEntryLength(CPUTable);
 
-  printf("Available CPUs for this target:\n");
+  Buf << "Available CPUs for this target:\n";
   // Don't print the "native" entry when the user specifies --target with a
   // different arch since that could be wrong or misleading.
   if (HostArch == TargetArch) {
     MaxCPULen = std::max(MaxCPULen, (unsigned) std::strlen("native"));
     const StringRef HostCPU = sys::getHostCPUName();
-    printf("    %-*s - Select the CPU of the current host (currently %.*s).\n",
-      MaxCPULen, "native", (int)HostCPU.size(), HostCPU.data());
+    Buf << "    " << std::left << std::setw(MaxCPULen) << "native"
+        << " - Select the CPU of the current host "
+           "(currently " << HostCPU.str() << ").\n";
   }
   for (auto &CPU : CPUTable) {
     // Compare cpu against current target to label the default
     if (strcmp(CPU.Key, TargetCPU) == 0) {
-      printf("    %-*s - This is the default target CPU"
-      " for the current build target (currently %s).",
-        MaxCPULen, CPU.Key, Target->getTargetTriple().str().c_str());
+      Buf << "    " << std::left << std::setw(MaxCPULen) << CPU.Key
+          << " - This is the default target CPU for the current build target "
+             "(currently " << Target->getTargetTriple().str() << ").";
     }
     else {
-      printf("    %-*s", MaxCPULen, CPU.Key);
+      Buf << "    " << CPU.Key;
     }
-    printf("\n");
+    Buf << "\n";
   }
+
+  const auto &BufString = Buf.str();
+  Print(Out, BufString.data(), BufString.size());
 }
 
 extern "C" size_t LLVMRustGetTargetFeaturesCount(LLVMTargetMachineRef TM) {