Provide configurable LLVM cmdline section via target spec

The App Store performs certain sanity checks on bitcode, including that
an acceptable set of command line arguments was used when compiling a
given module. For Rust code to be distributed on the app store with
bitcode rustc must pretend to have the same command line arguments.

Author: thombles

src/librustc_codegen_llvm/back/write.rs

@@ -651,10 +651,10 @@ pub(crate) unsafe fn codegen(
                     "LLVM_module_codegen_embed_bitcode",
                     &module.name[..],
                 );
-                embed_bitcode(cgcx, llcx, llmod, Some(data));
+                embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, Some(data));
             }
         } else if config.emit_obj == EmitObj::ObjectCode(BitcodeSection::Marker) {
-            embed_bitcode(cgcx, llcx, llmod, None);
+            embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, None);
         }
 
         if config.emit_ir {
@@ -777,8 +777,8 @@ pub(crate) unsafe fn codegen(
 /// * __LLVM,__cmdline
 ///
 /// It appears *both* of these sections are necessary to get the linker to
-/// recognize what's going on. For us though we just always throw in an empty
-/// cmdline section.
+/// recognize what's going on. A suitable cmdline value is taken from the
+/// target spec.
 ///
 /// Furthermore debug/O1 builds don't actually embed bitcode but rather just
 /// embed an empty section.
@@ -789,6 +789,7 @@ unsafe fn embed_bitcode(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     llcx: &llvm::Context,
     llmod: &llvm::Module,
+    cmdline: &str,
     bitcode: Option<&[u8]>,
 ) {
     let llconst = common::bytes_in_context(llcx, bitcode.unwrap_or(&[]));
@@ -800,14 +801,15 @@ unsafe fn embed_bitcode(
     llvm::LLVMSetInitializer(llglobal, llconst);
 
     let is_apple = cgcx.opts.target_triple.triple().contains("-ios")
-        || cgcx.opts.target_triple.triple().contains("-darwin");
+        || cgcx.opts.target_triple.triple().contains("-darwin")
+        || cgcx.opts.target_triple.triple().contains("-tvos");
 
     let section = if is_apple { "__LLVM,__bitcode\0" } else { ".llvmbc\0" };
     llvm::LLVMSetSection(llglobal, section.as_ptr().cast());
     llvm::LLVMRustSetLinkage(llglobal, llvm::Linkage::PrivateLinkage);
     llvm::LLVMSetGlobalConstant(llglobal, llvm::True);
 
-    let llconst = common::bytes_in_context(llcx, &[]);
+    let llconst = common::bytes_in_context(llcx, cmdline.as_bytes());
     let llglobal = llvm::LLVMAddGlobal(
         llmod,
         common::val_ty(llconst),

src/librustc_codegen_ssa/back/write.rs

@@ -101,6 +101,7 @@ pub struct ModuleConfig {
     pub emit_ir: bool,
     pub emit_asm: bool,
     pub emit_obj: EmitObj,
+    pub bc_cmdline: String,
 
     // Miscellaneous flags.  These are mostly copied from command-line
     // options.
@@ -213,6 +214,7 @@ impl ModuleConfig {
                 false
             ),
             emit_obj,
+            bc_cmdline: sess.target.target.options.bitcode_llvm_cmdline.clone(),
 
             verify_llvm_ir: sess.verify_llvm_ir(),
             no_prepopulate_passes: sess.opts.cg.no_prepopulate_passes,

src/librustc_target/spec/aarch64_apple_ios.rs

@@ -20,6 +20,17 @@ pub fn target() -> TargetResult {
             max_atomic_width: Some(128),
             abi_blacklist: super::arm_base::abi_blacklist(),
             forces_embed_bitcode: true,
+            // Taken from a clang build on Xcode 11.4.1.
+            // These arguments are not actually invoked - they just have
+            // to look right to pass App Store validation.
+            bitcode_llvm_cmdline: "-triple\0\
+                arm64-apple-ios11.0.0\0\
+                -emit-obj\0\
+                -disable-llvm-passes\0\
+                -target-abi\0\
+                darwinpcs\0\
+                -Os\0"
+                .to_string(),
             ..base
         },
     })

src/librustc_target/spec/mod.rs

@@ -785,6 +785,8 @@ pub struct TargetOptions {
     pub obj_is_bitcode: bool,
     /// Whether the target requires that emitted object code includes bitcode.
     pub forces_embed_bitcode: bool,
+    /// Content of the LLVM cmdline section associated with embedded bitcode.
+    pub bitcode_llvm_cmdline: String,
 
     /// Don't use this field; instead use the `.min_atomic_width()` method.
     pub min_atomic_width: Option<u64>,
@@ -942,6 +944,7 @@ impl Default for TargetOptions {
             has_elf_tls: false,
             obj_is_bitcode: false,
             forces_embed_bitcode: false,
+            bitcode_llvm_cmdline: String::new(),
             min_atomic_width: None,
             max_atomic_width: None,
             atomic_cas: true,
@@ -1282,6 +1285,7 @@ impl Target {
         key!(has_elf_tls, bool);
         key!(obj_is_bitcode, bool);
         key!(forces_embed_bitcode, bool);
+        key!(bitcode_llvm_cmdline);
         key!(max_atomic_width, Option<u64>);
         key!(min_atomic_width, Option<u64>);
         key!(atomic_cas, bool);
@@ -1510,6 +1514,7 @@ impl ToJson for Target {
         target_option_val!(has_elf_tls);
         target_option_val!(obj_is_bitcode);
         target_option_val!(forces_embed_bitcode);
+        target_option_val!(bitcode_llvm_cmdline);
         target_option_val!(min_atomic_width);
         target_option_val!(max_atomic_width);
         target_option_val!(atomic_cas);