[ELF] - Properly handle R_386_GOTPC relocation.

[grimar]

Summary

This is PR33243. R_GOTONLY_PC_FROM_END was not in a list of link time constant
expressions and that was a result of confusiing messages like PR shows:

/usr/bin/ld.lld: error: /usr/lib/go/src/runtime/alg.go:47:
can't create dynamic relocation R_386_GOTPC against local symbol in readonly segment defined in /tmp/nice/go-link-597453838/go.o

Though in reality we just should not have try to create a dynamic relocation for this case at all.

Patch fixes the issue.

lld/trunk/ELF/Relocations.cpp

 // dynamic relocation so that the relocation will be fixed at load-time.
 template <class ELFT>
 static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
                                      const SymbolBody &Body,
                                      InputSectionBase &S, uint64_t RelOff) {
   // These expressions always compute a constant
   if (isRelExprOneOf<R_SIZE, R_GOT_FROM_END, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE,
                      R_MIPS_GOT_OFF, R_MIPS_GOT_OFF32, R_MIPS_GOT_GP_PC,
-                     R_MIPS_TLSGD, R_GOT_PAGE_PC, R_GOT_PC, R_PLT_PC,
-                     R_TLSGD_PC, R_TLSGD, R_PPC_PLT_OPD, R_TLSDESC_CALL,
-                     R_TLSDESC_PAGE, R_HINT>(E))
+                     R_MIPS_TLSGD, R_GOT_PAGE_PC, R_GOT_PC,
+                     R_GOTONLY_PC_FROM_END, R_PLT_PC, R_TLSGD_PC, R_TLSGD,
+                     R_PPC_PLT_OPD, R_TLSDESC_CALL, R_TLSDESC_PAGE, R_HINT>(E))
     return true;
 
   // These never do, except if the entire file is position dependent or if
   // only the low bits are used.
   if (E == R_GOT || E == R_PLT || E == R_TLSDESC)
     return Target->usesOnlyLowPageBits(Type) || !Config->Pic;
 
   if (isPreemptible(Body, Type))

lld/trunk/test/ELF/i386-gotpc-dynamic.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=i686-pc-linux %s -o %t.o
+# RUN: ld.lld %t.o -o %t.so -shared
+# RUN: llvm-readobj -s %t.so | FileCheck %s
+# RUN: llvm-objdump -d %t.so | FileCheck --check-prefix=DISASM %s
+
+# CHECK:       Section {
+# CHECK:        Index: 7
+# CHECK-NEXT:   Name: .got
+# CHECK-NEXT:   Type: SHT_PROGBITS
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:     SHF_ALLOC
+# CHECK-NEXT:     SHF_WRITE
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Address: 0x2030
+# CHECK-NEXT:   Offset:
+# CHECK-NEXT:   Size:
+# CHECK-NEXT:   Link:
+# CHECK-NEXT:   Info:
+# CHECK-NEXT:   AddressAlignment:
+# CHECK-NEXT:   EntrySize:
+# CHECK-NEXT: }
+
+## 0x1000 + 4144 = 0x2030
+# DISASM: 1000: {{.*}} movl $4144, %eax
+
+.section .foo,"ax",@progbits
+foo:
+ movl $bar@got-., %eax # R_386_GOTPC
+
+.local bar
+bar: