Use more accurate ELF flags on MIPS

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -270,45 +270,61 @@ pub(super) fn elf_os_abi(sess: &Session) -> u8 {
 
 pub(super) fn elf_e_flags(architecture: Architecture, sess: &Session) -> u32 {
     match architecture {
-        Architecture::Mips => {
-            let arch = match sess.target.options.cpu.as_ref() {
-                "mips1" => elf::EF_MIPS_ARCH_1,
-                "mips2" => elf::EF_MIPS_ARCH_2,
+        Architecture::Mips | Architecture::Mips64 | Architecture::Mips64_N32 => {
+            // "N32" indicates an "ILP32" data model on a 64-bit MIPS CPU
+            // like SPARC's "v8+", x86_64's "x32", or the watchOS "arm64_32".
+            let is_32bit = architecture == Architecture::Mips;
+            let mut e_flags = match sess.target.options.cpu.as_ref() {
+                "mips1" if is_32bit => elf::EF_MIPS_ARCH_1,
+                "mips2" if is_32bit => elf::EF_MIPS_ARCH_2,
                 "mips3" => elf::EF_MIPS_ARCH_3,
                 "mips4" => elf::EF_MIPS_ARCH_4,
                 "mips5" => elf::EF_MIPS_ARCH_5,
-                s if s.contains("r6") => elf::EF_MIPS_ARCH_32R6,
-                _ => elf::EF_MIPS_ARCH_32R2,
+                "mips32r2" if is_32bit => elf::EF_MIPS_ARCH_32R2,
+                "mips32r6" if is_32bit => elf::EF_MIPS_ARCH_32R6,
+                "mips64r2" if !is_32bit => elf::EF_MIPS_ARCH_64R2,
+                "mips64r6" if !is_32bit => elf::EF_MIPS_ARCH_64R6,
+                s if s.starts_with("mips32") && !is_32bit => {
+                    sess.dcx().fatal(format!("invalid CPU `{}` for 64-bit MIPS target", s))
+                }
+                s if s.starts_with("mips64") && is_32bit => {
+                    sess.dcx().fatal(format!("invalid CPU `{}` for 32-bit MIPS target", s))
+                }
+                _ if is_32bit => elf::EF_MIPS_ARCH_32R2,
+                _ => elf::EF_MIPS_ARCH_64R2,
             };
 
-            let mut e_flags = elf::EF_MIPS_CPIC | arch;
-
-            // If the ABI is explicitly given, use it or default to O32.
-            match sess.target.options.llvm_abiname.to_lowercase().as_str() {
-                "n32" => e_flags |= elf::EF_MIPS_ABI2,
-                "o32" => e_flags |= elf::EF_MIPS_ABI_O32,
-                _ => e_flags |= elf::EF_MIPS_ABI_O32,
+            // If the ABI is explicitly given, use it, or default to O32 on 32-bit MIPS,
+            // which is the only "true" 32-bit option that LLVM supports.
+            match sess.target.options.llvm_abiname.as_ref() {
+                "o32" if is_32bit => e_flags |= elf::EF_MIPS_ABI_O32,
+                "n32" if !is_32bit => e_flags |= elf::EF_MIPS_ABI2,
+                "n64" if !is_32bit => {}
+                "" if is_32bit => e_flags |= elf::EF_MIPS_ABI_O32,
+                "" => sess.dcx().fatal("LLVM ABI must be specifed for 64-bit MIPS targets"),
+                s if is_32bit => {
+                    sess.dcx().fatal(format!("invalid LLVM ABI `{}` for 32-bit MIPS target", s))
+                }
+                s => sess.dcx().fatal(format!("invalid LLVM ABI `{}` for 64-bit MIPS target", s)),
             };
 
             if sess.target.options.relocation_model != RelocModel::Static {
-                e_flags |= elf::EF_MIPS_PIC;
+                // PIC means position-independent code. CPIC means "calls PIC".
+                // CPIC was mutually exclusive with PIC according to
+                // the SVR4 MIPS ABI https://refspecs.linuxfoundation.org/elf/mipsabi.pdf
+                // and should have only appeared on static objects with dynamically calls.
+                // At some point someone (GCC?) decided to set CPIC even for PIC.
+                // Nowadays various things expect both set on the same object file
+                // and may even error if you mix CPIC and non-CPIC object files,
+                // despite that being the entire point of the CPIC ABI extension!
+                // As we are in Rome, we do as the Romans do.
+                e_flags |= elf::EF_MIPS_PIC | elf::EF_MIPS_CPIC;
             }
             if sess.target.options.cpu.contains("r6") {
                 e_flags |= elf::EF_MIPS_NAN2008;
             }
             e_flags
         }
-        Architecture::Mips64 => {
-            // copied from `mips64el-linux-gnuabi64-gcc foo.c -c`
-            let e_flags = elf::EF_MIPS_CPIC
-                | elf::EF_MIPS_PIC
-                | if sess.target.options.cpu.contains("r6") {
-                    elf::EF_MIPS_ARCH_64R6 | elf::EF_MIPS_NAN2008
-                } else {
-                    elf::EF_MIPS_ARCH_64R2
-                };
-            e_flags
-        }
         Architecture::Riscv32 | Architecture::Riscv64 => {
             // Source: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/079772828bd10933d34121117a222b4cc0ee2200/riscv-elf.adoc
             let mut e_flags: u32 = 0x0;

compiler/rustc_target/src/spec/mod.rs

@@ -3567,7 +3567,19 @@ impl Target {
             "x86" => (Architecture::I386, None),
             "s390x" => (Architecture::S390x, None),
             "mips" | "mips32r6" => (Architecture::Mips, None),
-            "mips64" | "mips64r6" => (Architecture::Mips64, None),
+            "mips64" | "mips64r6" => (
+                // While there are currently no builtin targets
+                // using the N32 ABI, it is possible to specify
+                // it using a custom target specification. N32
+                // is an ILP32 ABI like the Aarch64_Ilp32
+                // and X86_64_X32 cases above and below this one.
+                if self.options.llvm_abiname.as_ref() == "n32" {
+                    Architecture::Mips64_N32
+                } else {
+                    Architecture::Mips64
+                },
+                None,
+            ),
             "x86_64" => (
                 if self.pointer_width == 32 {
                     Architecture::X86_64_X32

compiler/rustc_target/src/spec/targets/mips64_openwrt_linux_musl.rs

@@ -27,6 +27,7 @@ pub(crate) fn target() -> Target {
             abi: "abi64".into(),
             endian: Endian::Big,
             mcount: "_mcount".into(),
+            llvm_abiname: "n64".into(),
             ..base
         },
     }

compiler/rustc_target/src/spec/targets/mips64_unknown_linux_gnuabi64.rs

@@ -22,6 +22,7 @@ pub(crate) fn target() -> Target {
             features: "+mips64r2,+xgot".into(),
             max_atomic_width: Some(64),
             mcount: "_mcount".into(),
+            llvm_abiname: "n64".into(),
 
             ..base::linux_gnu::opts()
         },

compiler/rustc_target/src/spec/targets/mips64_unknown_linux_muslabi64.rs

@@ -25,6 +25,7 @@ pub(crate) fn target() -> Target {
             mcount: "_mcount".into(),
             // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
             crt_static_default: true,
+            llvm_abiname: "n64".into(),
             ..base
         },
     }

compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_gnuabi64.rs

@@ -19,6 +19,7 @@ pub(crate) fn target() -> Target {
             features: "+mips64r2,+xgot".into(),
             max_atomic_width: Some(64),
             mcount: "_mcount".into(),
+            llvm_abiname: "n64".into(),
 
             ..base::linux_gnu::opts()
         },

compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_muslabi64.rs

@@ -19,6 +19,11 @@ pub(crate) fn target() -> Target {
         pointer_width: 64,
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".into(),
         arch: "mips64".into(),
-        options: TargetOptions { abi: "abi64".into(), mcount: "_mcount".into(), ..base },
+        options: TargetOptions {
+            abi: "abi64".into(),
+            mcount: "_mcount".into(),
+            llvm_abiname: "n64".into(),
+            ..base
+        },
     }
 }

compiler/rustc_target/src/spec/targets/mipsisa64r6_unknown_linux_gnuabi64.rs

@@ -22,6 +22,7 @@ pub(crate) fn target() -> Target {
             features: "+mips64r6".into(),
             max_atomic_width: Some(64),
             mcount: "_mcount".into(),
+            llvm_abiname: "n64".into(),
 
             ..base::linux_gnu::opts()
         },

compiler/rustc_target/src/spec/targets/mipsisa64r6el_unknown_linux_gnuabi64.rs

@@ -19,6 +19,7 @@ pub(crate) fn target() -> Target {
             features: "+mips64r6".into(),
             max_atomic_width: Some(64),
             mcount: "_mcount".into(),
+            llvm_abiname: "n64".into(),
 
             ..base::linux_gnu::opts()
         },