Commit 4b1fe8e492

Andrew Kelley <andrew@ziglang.org>
2021-02-28 08:53:05
glibc: clang 12 assembler regression workaround
Our glibc stub assembly file looked something like this: ``` .globl _Exit_2_2_5 .type _Exit_2_2_5, %function; .symver _Exit_2_2_5, _Exit@@GLIBC_2.2.5 .hidden _Exit_2_2_5 _Exit_2_2_5: ``` With clang 12, the shared objects this produced stopped having any exported symbols. When I removed the `.hidden` directive, it resolved the issue, however, there are now unwanted exports: ``` $ readelf -W --dyn-syms libc.so.6 | grep sys_errlist 139: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 _sys_errlist_GLIBC_2_3 147: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 _sys_errlist_GLIBC_2_4 395: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 _sys_errlist_GLIBC_2_2_5 487: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 sys_errlist_GLIBC_2_2_5 1266: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 _sys_errlist@@GLIBC_2.12 1267: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 _sys_errlist@GLIBC_2.2.5 1268: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 _sys_errlist@GLIBC_2.3 1269: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 _sys_errlist@GLIBC_2.4 2137: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 sys_errlist@@GLIBC_2.12 2138: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 sys_errlist@GLIBC_2.2.5 2139: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 sys_errlist@GLIBC_2.3 2140: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 sys_errlist@GLIBC_2.4 2156: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 sys_errlist_GLIBC_2_3 2161: 000000000001ee08 0 FUNC GLOBAL DEFAULT 7 sys_errlist_GLIBC_2_4 ``` Every line here without an `@` symbol is an unwanted export. Before, the unwanted ones had LOCAL HIDDEN linkage. As a mitigation, I did two things: * Added `_GLIBC_` to the unwanted exports so that they would not conflict with anything. * Made the default export (the `@@` one) the bare symbol name. This appears to reduce the unwanted exports to only symbols that have more than one symbol (which is still quite many). This will unblock progress on this branch, however, there is now a new issue to solve, that the provided glibc stub .so files have too many symbols exported. We will have to find a way to avoid this.
master
1 parent ab36a16
Changed files (1)
src
glibc.zig
src/glibc.zig
@@ -807,26 +807,26 @@ pub fn buildSharedObjects(comp: *Compilation) !void {
                         // .globl _Exit_2_2_5
                         // .type _Exit_2_2_5, %function;
                         // .symver _Exit_2_2_5, _Exit@@GLIBC_2.2.5
-                        // .hidden _Exit_2_2_5
                         // _Exit_2_2_5:
                         const ver_index = ver_list.versions[ver_i];
                         const ver = metadata.all_versions[ver_index];
                         const sym_name = libc_fn.name;
                         // Default symbol version definition vs normal symbol version definition
-                        const want_two_ats = chosen_def_ver_index != 255 and ver_index == chosen_def_ver_index;
-                        const at_sign_str = "@@"[0 .. @boolToInt(want_two_ats) + @as(usize, 1)];
-
+                        const want_default = chosen_def_ver_index != 255 and ver_index == chosen_def_ver_index;
+                        const at_sign_str: []const u8 = if (want_default) "@@" else "@";
                         if (ver.patch == 0) {
-                            const sym_plus_ver = try std.fmt.allocPrint(
-                                arena,
-                                "{s}_{d}_{d}",
-                                .{ sym_name, ver.major, ver.minor },
-                            );
+                            const sym_plus_ver = if (want_default)
+                                sym_name
+                            else
+                                try std.fmt.allocPrint(
+                                    arena,
+                                    "{s}_GLIBC_{d}_{d}",
+                                    .{ sym_name, ver.major, ver.minor },
+                                );
                             try zig_body.writer().print(
                                 \\.globl {s}
                                 \\.type {s}, %function;
                                 \\.symver {s}, {s}{s}GLIBC_{d}.{d}
-                                \\.hidden {s}
                                 \\{s}:
                                 \\
                             , .{
@@ -838,19 +838,20 @@ pub fn buildSharedObjects(comp: *Compilation) !void {
                                 ver.major,
                                 ver.minor,
                                 sym_plus_ver,
-                                sym_plus_ver,
                             });
                         } else {
-                            const sym_plus_ver = try std.fmt.allocPrint(
-                                arena,
-                                "{s}_{d}_{d}_{d}",
-                                .{ sym_name, ver.major, ver.minor, ver.patch },
-                            );
+                            const sym_plus_ver = if (want_default)
+                                sym_name
+                            else
+                                try std.fmt.allocPrint(
+                                    arena,
+                                    "{s}_GLIBC_{d}_{d}_{d}",
+                                    .{ sym_name, ver.major, ver.minor, ver.patch },
+                                );
                             try zig_body.writer().print(
                                 \\.globl {s}
                                 \\.type {s}, %function;
                                 \\.symver {s}, {s}{s}GLIBC_{d}.{d}.{d}
-                                \\.hidden {s}
                                 \\{s}:
                                 \\
                             , .{
@@ -863,7 +864,6 @@ pub fn buildSharedObjects(comp: *Compilation) !void {
                                 ver.minor,
                                 ver.patch,
                                 sym_plus_ver,
-                                sym_plus_ver,
                             });
                         }
                     }