switch to using a target property to control plt default

Author: durin42

compiler/rustc_session/src/session.rs

@@ -1009,11 +1009,11 @@ impl Session {
         self.edition().rust_2024()
     }
 
-    /// Returns `true` if we cannot skip the PLT for shared library calls.
+    /// Returns `true` if we should use the PLT for shared library calls.
     pub fn needs_plt(&self) -> bool {
-        // Check if the current target usually needs PLT to be enabled.
+        // Check if the current target usually wants PLT to be enabled.
         // The user can use the command line flag to override it.
-        let needs_plt = self.target.arch != "x86_64";
+        let want_plt = self.target.plt_by_default;
 
         let dbg_opts = &self.opts.unstable_opts;
 
@@ -1025,8 +1025,8 @@ impl Session {
         let full_relro = RelroLevel::Full == relro_level;
 
         // If user didn't explicitly forced us to use / skip the PLT,
-        // then try to skip it where possible.
-        dbg_opts.plt.unwrap_or(needs_plt || !full_relro)
+        // then use it unless the target doesn't want it by default or the full relro forces it on.
+        dbg_opts.plt.unwrap_or(want_plt || !full_relro)
     }
 
     /// Checks if LLVM lifetime markers should be emitted.

compiler/rustc_target/src/spec/mod.rs

@@ -1670,7 +1670,7 @@ pub struct TargetOptions {
     pub static_position_independent_executables: bool,
     /// Determines if the target always requires using the PLT for indirect
     /// library calls or not. This controls the default value of the `-Z plt` flag.
-    pub needs_plt: bool,
+    pub plt_by_default: bool,
     /// Either partial, full, or off. Full RELRO makes the dynamic linker
     /// resolve all symbols at startup and marks the GOT read-only before
     /// starting the program, preventing overwriting the GOT.
@@ -1992,7 +1992,7 @@ impl Default for TargetOptions {
             no_default_libraries: true,
             position_independent_executables: false,
             static_position_independent_executables: false,
-            needs_plt: false,
+            plt_by_default: true,
             relro_level: RelroLevel::None,
             pre_link_objects: Default::default(),
             post_link_objects: Default::default(),
@@ -2665,7 +2665,7 @@ impl Target {
         key!(no_default_libraries, bool);
         key!(position_independent_executables, bool);
         key!(static_position_independent_executables, bool);
-        key!(needs_plt, bool);
+        key!(plt_by_default, bool);
         key!(relro_level, RelroLevel)?;
         key!(archive_format);
         key!(allow_asm, bool);
@@ -2921,7 +2921,7 @@ impl ToJson for Target {
         target_option_val!(no_default_libraries);
         target_option_val!(position_independent_executables);
         target_option_val!(static_position_independent_executables);
-        target_option_val!(needs_plt);
+        target_option_val!(plt_by_default);
         target_option_val!(relro_level);
         target_option_val!(archive_format);
         target_option_val!(allow_asm);

compiler/rustc_target/src/spec/x86_64_fortanix_unknown_sgx.rs

@@ -63,6 +63,7 @@ pub fn target() -> Target {
         linker: Some("rust-lld".into()),
         max_atomic_width: Some(64),
         cpu: "x86-64".into(),
+        plt_by_default: false,
         features: "+rdrnd,+rdseed,+lvi-cfi,+lvi-load-hardening".into(),
         llvm_args: cvs!["--x86-experimental-lvi-inline-asm-hardening"],
         position_independent_executables: true,

compiler/rustc_target/src/spec/x86_64_linux_android.rs

@@ -3,6 +3,7 @@ use crate::spec::{Cc, LinkerFlavor, Lld, SanitizerSet, StackProbeType, Target, T
 pub fn target() -> Target {
     let mut base = super::android_base::opts();
     base.cpu = "x86-64".into();
+    base.plt_by_default = false;
     // https://developer.android.com/ndk/guides/abis.html#86-64
     base.features = "+mmx,+sse,+sse2,+sse3,+ssse3,+sse4.1,+sse4.2,+popcnt".into();
     base.max_atomic_width = Some(64);

compiler/rustc_target/src/spec/x86_64_pc_nto_qnx710.rs

@@ -10,6 +10,7 @@ pub fn target() -> Target {
         arch: "x86_64".into(),
         options: TargetOptions {
             cpu: "x86-64".into(),
+            plt_by_default: false,
             max_atomic_width: Some(64),
             pre_link_args: TargetOptions::link_args(
                 LinkerFlavor::Gnu(Cc::Yes, Lld::No),

compiler/rustc_target/src/spec/x86_64_pc_solaris.rs

@@ -4,6 +4,7 @@ pub fn target() -> Target {
     let mut base = super::solaris_base::opts();
     base.add_pre_link_args(LinkerFlavor::Unix(Cc::Yes), &["-m64"]);
     base.cpu = "x86-64".into();
+    base.plt_by_default = false;
     base.vendor = "pc".into();
     base.max_atomic_width = Some(64);
     base.stack_probes = StackProbeType::X86;

compiler/rustc_target/src/spec/x86_64_pc_windows_gnu.rs

@@ -3,6 +3,7 @@ use crate::spec::{Cc, LinkerFlavor, Lld, Target};
 pub fn target() -> Target {
     let mut base = super::windows_gnu_base::opts();
     base.cpu = "x86-64".into();
+    base.plt_by_default = false;
     // Use high-entropy 64 bit address space for ASLR
     base.add_pre_link_args(
         LinkerFlavor::Gnu(Cc::No, Lld::No),

compiler/rustc_target/src/spec/x86_64_pc_windows_gnullvm.rs

@@ -3,6 +3,7 @@ use crate::spec::{Cc, LinkerFlavor, Lld, Target};
 pub fn target() -> Target {
     let mut base = super::windows_gnullvm_base::opts();
     base.cpu = "x86-64".into();
+    base.plt_by_default = false;
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
     base.max_atomic_width = Some(64);
     base.linker = Some("x86_64-w64-mingw32-clang".into());

compiler/rustc_target/src/spec/x86_64_pc_windows_msvc.rs

@@ -3,6 +3,7 @@ use crate::spec::Target;
 pub fn target() -> Target {
     let mut base = super::windows_msvc_base::opts();
     base.cpu = "x86-64".into();
+    base.plt_by_default = false;
     base.max_atomic_width = Some(64);
 
     Target {

compiler/rustc_target/src/spec/x86_64_sun_solaris.rs

@@ -4,6 +4,7 @@ pub fn target() -> Target {
     let mut base = super::solaris_base::opts();
     base.add_pre_link_args(LinkerFlavor::Unix(Cc::Yes), &["-m64"]);
     base.cpu = "x86-64".into();
+    base.plt_by_default = false;
     base.vendor = "sun".into();
     base.max_atomic_width = Some(64);
     base.stack_probes = StackProbeType::X86;