Merge pull request #7204 from LemonBoy/piecrash

Fix logic for detecting _DYNAMIC symbol

lib/std/dynamic_library.zig

@@ -59,24 +59,12 @@ const RDebug = extern struct {
     r_ldbase: usize,
 };
 
-// TODO: This should be weak (#1917)
-extern var _DYNAMIC: [128]elf.Dyn;
-
-comptime {
-    if (std.Target.current.os.tag == .linux) {
-        asm (
-            \\ .weak _DYNAMIC
-            \\ .hidden _DYNAMIC
-        );
-    }
-}
-
 pub fn linkmap_iterator(phdrs: []elf.Phdr) !LinkMap.Iterator {
-    if (@ptrToInt(&_DYNAMIC[0]) == 0) {
+    const _DYNAMIC = @extern([*]elf.Dyn, .{ .name = "_DYNAMIC", .linkage = .Weak }) orelse {
         // No PT_DYNAMIC means this is either a statically-linked program or a
-        // badly corrupted one
+        // badly corrupted dynamically-linked one.
         return LinkMap.Iterator{ .current = null };
-    }
+    };
 
     const link_map_ptr = init: {
         var i: usize = 0;

lib/std/os.zig

@@ -4340,7 +4340,7 @@ pub fn dl_iterate_phdr(
 
     const elf_base = std.process.getBaseAddress();
     const ehdr = @intToPtr(*elf.Ehdr, elf_base);
-    // Make sure the base address points to an ELF image
+    // Make sure the base address points to an ELF image.
     assert(mem.eql(u8, ehdr.e_ident[0..4], "\x7fELF"));
     const n_phdr = ehdr.e_phnum;
     const phdrs = (@intToPtr([*]elf.Phdr, elf_base + ehdr.e_phoff))[0..n_phdr];
@@ -4348,10 +4348,21 @@ pub fn dl_iterate_phdr(
     var it = dl.linkmap_iterator(phdrs) catch unreachable;
 
     // The executable has no dynamic link segment, create a single entry for
-    // the whole ELF image
+    // the whole ELF image.
     if (it.end()) {
+        // Find the base address for the ELF image, if this is a PIE the value
+        // is non-zero.
+        const base_address = for (phdrs) |*phdr| {
+            if (phdr.p_type == elf.PT_PHDR) {
+                break @ptrToInt(phdrs.ptr) - phdr.p_vaddr;
+                // We could try computing the difference between _DYNAMIC and
+                // the p_vaddr of the PT_DYNAMIC section, but using the phdr is
+                // good enough (Is it?).
+            }
+        } else unreachable;
+
         var info = dl_phdr_info{
-            .dlpi_addr = 0,
+            .dlpi_addr = base_address,
             .dlpi_name = "/proc/self/exe",
             .dlpi_phdr = phdrs.ptr,
             .dlpi_phnum = ehdr.e_phnum,
@@ -4360,7 +4371,7 @@ pub fn dl_iterate_phdr(
         return callback(&info, @sizeOf(dl_phdr_info), context);
     }
 
-    // Last return value from the callback function
+    // Last return value from the callback function.
     while (it.next()) |entry| {
         var dlpi_phdr: [*]elf.Phdr = undefined;
         var dlpi_phnum: u16 = undefined;

lib/std/os/linux/start_pie.zig

@@ -56,12 +56,13 @@ fn getDynamicSymbol() [*]elf.Dyn {
             : [ret] "=r" (-> usize)
         ),
         .riscv64 => asm volatile (
+            \\ .weak _DYNAMIC
+            \\ .hidden _DYNAMIC
             \\ lla %[ret], _DYNAMIC
             : [ret] "=r" (-> usize)
         ),
         else => @compileError("???"),
     };
-    if (addr == 0) unreachable;
     return @intToPtr([*]elf.Dyn, addr);
 }
 

lib/std/os/test.zig

@@ -386,8 +386,6 @@ fn iter_fn(info: *dl_phdr_info, size: usize, counter: *usize) IterFnError!void {
 test "dl_iterate_phdr" {
     if (builtin.os.tag == .windows or builtin.os.tag == .wasi or builtin.os.tag == .macos)
         return error.SkipZigTest;
-    if (builtin.position_independent_executable)
-        return error.SkipZigTest;
 
     var counter: usize = 0;
     try os.dl_iterate_phdr(&counter, IterFnError, iter_fn);

test/stack_traces.zig

@@ -282,7 +282,7 @@ pub fn addCases(cases: *tests.StackTracesContext) void {
                     \\source.zig:10:8: [address] in main (test)
                     \\    foo();
                     \\       ^
-                    \\start.zig:331:29: [address] in std.start.posixCallMainAndExit (test)
+                    \\start.zig:337:29: [address] in std.start.posixCallMainAndExit (test)
                     \\            return root.main();
                     \\                            ^
                     \\start.zig:162:5: [address] in std.start._start (test)