[ELF][MIPS] Ignore incorrect version definition index for _gp_disp symbol

[atanasyan]

Summary

MIPS BFD linker puts _gp_disp symbol into DSO files and assigns zero version definition index to it. This value means 'unversioned local symbol' while _gp_disp is a section global symbol. We have to handle this bug in the LLD because BFD linker is used for building MIPS toolchain libraries.

[grimar]

ELF/InputFiles.cpp

860 ↗

(On Diff #131276)

I suggest to add "FIXME: " at the begining of comment,
saying that this hack can be removed once fixed in BFD and settle for a while.
It's consistent with other hacks/workarounds we have in code.

[atanasyan]

• Added FIXME tag to the comment

[atanasyan]

Ping?

Here is the bug report and the corresponding patch for GNU BFD: https://sourceware.org/ml/binutils/2018-01/msg00390.html

[atanasyan]

Ping?

lld/trunk/ELF/InputFiles.cpp

for (const Elf_Sym &Sym : Syms) {
     }
 
     if (Sym.getBinding() == STB_LOCAL) {
       warn("found local symbol '" + Name +
            "' in global part of symbol table in file " + toString(this));
       continue;
     }
 
+    if (Config->EMachine == EM_MIPS) {
+      // FIXME: MIPS BFD linker puts _gp_disp symbol into DSO files
+      // and incorrectly assigns VER_NDX_LOCAL to this section global
+      // symbol. Here is a workaround for this bug.
+      if (Versym && VersymIndex == VER_NDX_LOCAL && Name == "_gp_disp")
+        continue;
+    }
+
     const Elf_Verdef *Ver = nullptr;
     if (VersymIndex != VER_NDX_GLOBAL) {
       if (VersymIndex >= Verdefs.size() || VersymIndex == VER_NDX_LOCAL) {
         error("corrupt input file: version definition index " +
               Twine(VersymIndex) + " for symbol " + Name +
               " is out of bounds\n>>> defined in " + toString(this));
         continue;
       }

lld/trunk/test/ELF/Inputs/mips-gp-dips-corrupt-ver.s

+# Source file for mips-gp-dips-corrupt-ver.so
+#
+# % cat gpdisp.ver
+# LLD_1.0.0 { global: foo; };
+#
+# % as mips-gp-dips-corrupt-ver.s -o mips-gp-dips-corrupt-ver.o
+# % ld -shared -o mips-gp-dips-corrupt-ver.so \
+#      --version-script gpdisp.ver mips-gp-dips-corrupt-ver.o
+
+  .global foo
+  .text
+foo:
+  lui    $t0, %hi(_gp_disp)
+  addi   $t0, $t0, %lo(_gp_disp)

lld/trunk/test/ELF/mips-gp-disp-ver.s

+# MIPS BFD linker puts _gp_disp symbol into DSO files and assigns zero
+# version definition index to it. This value means 'unversioned local symbol'
+# while _gp_disp is a section global symbol. We have to handle this bug
+# in the LLD because BFD linker is used for building MIPS toolchain
+# libraries. This test checks such handling.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o %S/Inputs/mips-gp-dips-corrupt-ver.so
+
+  .global __start
+  .text
+__start:
+  lw     $t0, %got(foo)($gp)