[PATCH] D43351: Relax relocation type checking in a non-ALLOC section.

[Rui Ueyama via Phabricator via llvm-commits]

ruiu updated this revision to Diff 134531.
ruiu added a comment.

- keep reporting errors if not R_ABS nor R_PC
- restore the original test for an unknown relocation type


https://reviews.llvm.org/D43351

Files:
  lld/ELF/InputSection.cpp
  lld/test/ELF/i386-debug-noabs.test
  lld/test/ELF/non-abs-reloc.s


Index: lld/test/ELF/non-abs-reloc.s
===================================================================
--- lld/test/ELF/non-abs-reloc.s
+++ lld/test/ELF/non-abs-reloc.s
@@ -1,11 +1,19 @@
 // REQUIRES: x86
 // RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
-// RUN: not ld.lld %t.o -o %t.so -shared 2>&1 | FileCheck %s
-// CHECK: {{.*}}:(.dummy+0x0): has non-ABS relocation R_X86_64_GOTPCREL against symbol 'foo'
+// RUN: ld.lld %t.o -o %t 2>&1 | FileCheck %s
+// CHECK: (.nonalloc+0x1): has non-ABS relocation R_X86_64_PC32 against symbol '_start'
+// CHECK: (.nonalloc+0x6): has non-ABS relocation R_X86_64_PC32 against symbol '_start'
+
+// RUN: llvm-objdump -D %t | FileCheck --check-prefix=DISASM %s
+// DISASM:      Disassembly of section .nonalloc:
+// DISASM-NEXT: .nonalloc:
+// DISASM-NEXT: 0: {{.*}}  callq {{.*}} <_start>
+// DISASM-NEXT: 5: {{.*}}  callq {{.*}} <_start>
 
 .globl _start
 _start:
   nop
 
-.section .dummy
-  .long foo at gotpcrel
+.section .nonalloc
+  call _start
+  call _start
Index: lld/test/ELF/i386-debug-noabs.test
===================================================================
--- lld/test/ELF/i386-debug-noabs.test
+++ lld/test/ELF/i386-debug-noabs.test
@@ -1,7 +1,7 @@
 # REQUIRES: x86
 
 # RUN: yaml2obj %s -o %t.o
-# RUN: ld.lld %t.o -o %t.exe
+# RUN: ld.lld %t.o -o %t.exe --entry 0 --fatal-warnings
 
 ## This is for https://bugs.llvm.org//show_bug.cgi?id=34852. GCC 8.0 or
 ## earlier have a bug which creates non-absolute R_386_GOTPC relocations
Index: lld/ELF/InputSection.cpp
===================================================================
--- lld/ELF/InputSection.cpp
+++ lld/ELF/InputSection.cpp
@@ -641,6 +641,14 @@
 
   for (const RelTy &Rel : Rels) {
     RelType Type = Rel.getType(Config->IsMips64EL);
+
+    // GCC 8.0 or earlier have a bug that they emit R_386_GOTPC relocations
+    // against _GLOBAL_OFFSET_TABLE_ for .debug_info. The bug has been fixed
+    // in 2017 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82630), but we
+    // need to keep this bug-compatible code for a while.
+    if (Config->EMachine == EM_386 && Type == R_386_GOTPC)
+      continue;
+
     uint64_t Offset = getOffset(Rel.r_offset);
     uint8_t *BufLoc = Buf + Offset;
     int64_t Addend = getAddend<ELFT>(Rel);
@@ -651,17 +659,27 @@
     RelExpr Expr = Target->getRelExpr(Type, Sym, BufLoc);
     if (Expr == R_NONE)
       continue;
+
     if (Expr != R_ABS) {
-      // GCC 8.0 or earlier have a bug that it emits R_386_GOTPC relocations
-      // against _GLOBAL_OFFSET_TABLE for .debug_info. The bug seems to have
-      // been fixed in 2017: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82630,
-      // but we need to keep this bug-compatible code for a while.
-      if (Config->EMachine == EM_386 && Type == R_386_GOTPC)
-        continue;
+      std::string Msg = getLocation<ELFT>(Offset) +
+                        ": has non-ABS relocation " + toString(Type) +
+                        " against symbol '" + toString(Sym) + "'";
+      if (Expr != R_PC) {
+        error(Msg);
+        return;
+      }
 
-      error(getLocation<ELFT>(Offset) + ": has non-ABS relocation " +
-            toString(Type) + " against symbol '" + toString(Sym) + "'");
-      return;
+      // If the control reaches here, we found a PC-relative relocation in a
+      // non-ALLOC section. Since non-ALLOC section is not loaded into memory
+      // at runtime, the notion of PC-relative doesn't make sense here. So,
+      // this is a usage error. However, GNU linkers historically accept such
+      // relocations without any errors and relocate them as if they were at
+      // address 0. For bug-compatibilty, we accepts them with warnings. We
+      // know Steel Bank Common Lisp as of 2018 have this bug.
+      warn(Msg);
+      Target->relocateOne(BufLoc, Type,
+                          SignExtend64<Bits>(Sym.getVA(Addend - Offset)));
+      continue;
     }
 
     if (Sym.isTls() && !Out::TlsPhdr)


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