From: Shiz <hi@shiz.me>
Date: Tue, 11 Apr 2017 04:37:00 +0200
Subject: [PATCH] Add support for static PIE executables

Note that static PIE binaries are reported as dynamically linked by file(1):

    $ rustc -C target-feature=+crt-static hello_world.rb
    $ file hello_world
    ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically \
      linked, not stripped, with debug_info

In addition, ldd(1) reports that it's linked with ldd, as it can't find any
dependencies except itself loaded into the process:

    $ ldd hello_world
    ldd (0x237fcc81000)

Static PIE binaries are dynamic binaries without a loader or any DT_NEEDED
entries. The important is that they do not depend on libc or any other system
library, just like static binaries, but more secure.

    $ readelf -d hello_world
    Dynamic section at offset 0x2de40 contains 17 entries:
      Tag        Type                         Name/Value
     0x0000000000000010 (SYMBOLIC)           0x0
     0x000000000000000c (INIT)               0x17a0
     0x000000000000000d (FINI)               0x2003c
     0x000000006ffffef5 (GNU_HASH)           0x1c8
     0x0000000000000005 (STRTAB)             0x278
     0x0000000000000006 (SYMTAB)             0x200
     0x000000000000000a (STRSZ)              60 (bytes)
     0x000000000000000b (SYMENT)             24 (bytes)
     0x0000000000000015 (DEBUG)              0x0
     0x0000000000000003 (PLTGOT)             0x22df90
     0x0000000000000007 (RELA)               0x2b8
     0x0000000000000008 (RELASZ)             5352 (bytes)
     0x0000000000000009 (RELAENT)            24 (bytes)
     0x0000000000000018 (BIND_NOW)
     0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
     0x000000006ffffff9 (RELACOUNT)          223
     0x0000000000000000 (NULL)               0x0

--- a/src/librustc_back/target/linux_musl_base.rs
+++ b/src/librustc_back/target/linux_musl_base.rs
@@ -22,5 +22,8 @@
     // Except for on MIPS, these targets statically link libc by default.
     base.crt_static_default = true;
 
+    // Static position-independent executables are supported.
+    base.static_position_independent_executables = true;
+
     base
 }
--- a/src/librustc_back/target/mod.rs
+++ b/src/librustc_back/target/mod.rs
@@ -350,6 +350,8 @@
     /// the functions in the executable are not randomized and can be used
     /// during an exploit of a vulnerability in any code.
     pub position_independent_executables: bool,
+    /// As above, but also support for static position independent executables.
+    pub static_position_independent_executables: 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.
@@ -434,7 +436,8 @@
             has_rpath: false,
             no_default_libraries: true,
             position_independent_executables: false,
+            static_position_independent_executables: false,
             relro_level: RelroLevel::Off,
             pre_link_objects_exe: Vec::new(),
             pre_link_objects_dll: Vec::new(),
             post_link_objects: Vec::new(),
--- a/src/librustc_trans/back/link.rs
+++ b/src/librustc_trans/back/link.rs
@@ -914,13 +914,9 @@
 
     if crate_type == config::CrateTypeExecutable &&
        t.options.position_independent_executables {
-        let empty_vec = Vec::new();
-        let args = sess.opts.cg.link_args.as_ref().unwrap_or(&empty_vec);
-        let more_args = &sess.opts.cg.link_arg;
-        let mut args = args.iter().chain(more_args.iter()).chain(used_link_args.iter());
-
+        let static_pie = t.options.static_position_independent_executables;
         if get_reloc_model(sess) == llvm::RelocMode::PIC
-            && !sess.crt_static() && !args.any(|x| *x == "-static") {
+            && (!sess.crt_static() || static_pie) {
             cmd.position_independent_executable();
         }
     }
--- a/src/librustc_back/target/mod.rs
+++ b/src/librustc_back/target/mod.rs
@@ -612,7 +612,8 @@
         key!(has_rpath, bool);
         key!(no_default_libraries, bool);
         key!(position_independent_executables, bool);
+        key!(static_position_independent_executables, bool);
         try!(key!(relro_level, RelroLevel));
         key!(archive_format);
         key!(allow_asm, bool);
         key!(custom_unwind_resume, bool);
@@ -776,7 +777,8 @@
         target_option_val!(has_rpath);
         target_option_val!(no_default_libraries);
         target_option_val!(position_independent_executables);
+        target_option_val!(static_position_independent_executables);
         target_option_val!(relro_level);
         target_option_val!(archive_format);
         target_option_val!(allow_asm);
         target_option_val!(custom_unwind_resume);