[PATCH] D53515: Don't mess up RelIplt symbols during relocatable processing

[Dimitry Andric via Phabricator via llvm-commits]

dim created this revision.
dim added reviewers: grimar, ruiu, emaste.
Herald added subscribers: krytarowski, arichardson.
Herald added a reviewer: espindola.

During upgrading of the FreeBSD source tree with lld 7.0.0, I noticed
that it started complaining about `crt1.o` having an "index past the
end of the symbol table".

Such a symbol table looks approximately like this, viewed with `readelf
-s` (note the `Ndx` field being messed up):

  Symbol table '.symtab' contains 4 entries:
     Num:    Value  Size Type    Bind   Vis      Ndx Name
       0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND
       1: 00000000     0 SECTION LOCAL  DEFAULT    1
       2: 00000000     0 NOTYPE  WEAK   HIDDEN  RSV[0xffff] __rel_iplt_end
       3: 00000000     0 NOTYPE  WEAK   HIDDEN  RSV[0xffff] __rel_iplt_start

At first, it seemed that recent ifunc relocation work had caused this:
https://reviews.freebsd.org/rS339351, but it turned out that it was
due to incorrect processing of the object files by lld, when using `-r`
(a.k.a. --relocatable).

Bisecting showed that https://reviews.llvm.org/rL324421 ("Convert a use of Config->Static") was
the commit where this new behavior began.  Simply reverting it solved
the issue, and the `__rel_iplt` symbols had an index of `UND` again.

Looking at Rafael's commit message, I think he simply missed the
possibility of `--relocatable` being in effect, so I have added an
additional check for it.

I also added a simple regression test case.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D53515

Files:
  ELF/Writer.cpp
  test/ELF/relocatable-rel-iplt.s


Index: test/ELF/relocatable-rel-iplt.s
===================================================================
--- /dev/null
+++ test/ELF/relocatable-rel-iplt.s
@@ -0,0 +1,56 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=i686-- %s -o %t1.o
+# RUN: ld.lld -r %t1.o -o %t2.o
+# RUN: llvm-readobj -t %t2.o | FileCheck %s
+
+// CHECK:      Symbols [
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name:  (0)
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Local (0x0)
+// CHECK-NEXT:     Type: None (0x0)
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: Undefined (0x0)
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name:  (0)
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Local (0x0)
+// CHECK-NEXT:     Type: Section (0x3)
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: .text (0x1)
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: __rel_iplt_end (1)
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Weak (0x2)
+// CHECK-NEXT:     Type: None (0x0)
+// CHECK-NEXT:     Other [ (0x2)
+// CHECK-NEXT:       STV_HIDDEN (0x2)
+// CHECK-NEXT:     ]
+// CHECK-NEXT:     Section: Undefined (0x0)
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: __rel_iplt_start (16)
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Weak (0x2)
+// CHECK-NEXT:     Type: None (0x0)
+// CHECK-NEXT:     Other [ (0x2)
+// CHECK-NEXT:       STV_HIDDEN (0x2)
+// CHECK-NEXT:     ]
+// CHECK-NEXT:     Section: Undefined (0x0)
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+
+	movl	__rel_iplt_start, %eax
+	movl	__rel_iplt_end, %eax
+	ret
+
+	.hidden	__rel_iplt_start
+	.hidden	__rel_iplt_end
+	.weak	__rel_iplt_start
+	.weak	__rel_iplt_end
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -880,7 +880,7 @@
 // need these symbols, since IRELATIVE relocs are resolved through GOT
 // and PLT. For details, see http://www.airs.com/blog/archives/403.
 template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
-  if (needsInterpSection())
+  if (Config->Relocatable || needsInterpSection())
     return;
   StringRef S = Config->IsRela ? "__rela_iplt_start" : "__rel_iplt_start";
   addOptionalRegular(S, In.RelaIplt, 0, STV_HIDDEN, STB_WEAK);


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