[lld] r288878 - [ELF] Shared libraries should have entry point

[Petr Hosek via llvm-commits]

Author: phosek
Date: Tue Dec  6 20:26:16 2016
New Revision: 288878

URL: http://llvm.org/viewvc/llvm-project?rev=288878&view=rev
Log:
[ELF] Shared libraries should have entry point

Shared libraries should have entry set following the same rules as for
regular binaries. The only difference is that in case the default entry
point (_start or __start) isn't found (unless it was set explicitly), we
shouldn't give a warning as in case of regular binaries.

Differential Revision: https://reviews.llvm.org/D27497

Added:
    lld/trunk/test/ELF/gc-sections-keep-shared-start.s
Modified:
    lld/trunk/ELF/Config.h
    lld/trunk/ELF/Driver.cpp
    lld/trunk/ELF/Writer.cpp

Modified: lld/trunk/ELF/Config.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Config.h?rev=288878&r1=288877&r2=288878&view=diff
==============================================================================
--- lld/trunk/ELF/Config.h (original)
+++ lld/trunk/ELF/Config.h Tue Dec  6 20:26:16 2016
@@ -107,6 +107,7 @@ struct Configuration {
   bool GcSections;
   bool GdbIndex;
   bool GnuHash = false;
+  bool HasEntry = false;
   bool ICF;
   bool Mips64EL = false;
   bool MipsN32Abi = false;

Modified: lld/trunk/ELF/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Driver.cpp?rev=288878&r1=288877&r2=288878&view=diff
==============================================================================
--- lld/trunk/ELF/Driver.cpp (original)
+++ lld/trunk/ELF/Driver.cpp Tue Dec  6 20:26:16 2016
@@ -521,6 +521,7 @@ void LinkerDriver::readConfigs(opt::Inpu
   Config->EnableNewDtags = !Args.hasArg(OPT_disable_new_dtags);
   Config->ExportDynamic = Args.hasArg(OPT_export_dynamic);
   Config->FatalWarnings = Args.hasArg(OPT_fatal_warnings);
+  Config->HasEntry = Args.hasArg(OPT_entry);
   Config->GcSections = getArg(Args, OPT_gc_sections, OPT_no_gc_sections, false);
   Config->GdbIndex = Args.hasArg(OPT_gdb_index);
   Config->ICF = Args.hasArg(OPT_icf);
@@ -786,8 +787,7 @@ template <class ELFT> void LinkerDriver:
     // It is either "-e <addr>" or "-e <symbol>".
     if (!Config->Entry.getAsInteger(0, Config->EntryAddr))
       Config->Entry = "";
-  } else if (!Config->Shared && !Config->Relocatable &&
-             Config->EMachine != EM_AMDGPU) {
+  } else if (!Config->Relocatable && Config->EMachine != EM_AMDGPU) {
     // -e was not specified. Use the default start symbol name
     // if it is resolvable.
     Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=288878&r1=288877&r2=288878&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Tue Dec  6 20:26:16 2016
@@ -1410,14 +1410,16 @@ template <class ELFT> typename ELFT::uin
 
   // Case 4
   if (OutputSectionBase *Sec = findSection(".text")) {
-    warn("cannot find entry symbol " + Config->Entry + "; defaulting to 0x" +
-         utohexstr(Sec->Addr));
+    if (!Config->Shared || Config->HasEntry)
+      warn("cannot find entry symbol " + Config->Entry + "; defaulting to 0x" +
+           utohexstr(Sec->Addr));
     return Sec->Addr;
   }
 
   // Case 5
-  warn("cannot find entry symbol " + Config->Entry +
-       "; not setting start address");
+  if (!Config->Shared || Config->HasEntry)
+    warn("cannot find entry symbol " + Config->Entry +
+         "; not setting start address");
   return 0;
 }
 

Added: lld/trunk/test/ELF/gc-sections-keep-shared-start.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/gc-sections-keep-shared-start.s?rev=288878&view=auto
==============================================================================
--- lld/trunk/test/ELF/gc-sections-keep-shared-start.s (added)
+++ lld/trunk/test/ELF/gc-sections-keep-shared-start.s Tue Dec  6 20:26:16 2016
@@ -0,0 +1,29 @@
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: ld.lld -shared --gc-sections -o %t1 %t
+# RUN: llvm-readobj --elf-output-style=GNU --file-headers --symbols %t1
+#   | FileCheck %s
+# CHECK: Entry point address:               0x1000
+# CHECK: 0000000000001000     0 FUNC    LOCAL  HIDDEN     4 _start
+# CHECK: 0000000000001006     0 FUNC    LOCAL  HIDDEN     4 internal
+# CHECK: 0000000000001005     0 FUNC    GLOBAL DEFAULT    4 foobar
+
+.section .text.start,"ax"
+.globl _start
+.type _start,%function
+.hidden _start
+_start:
+  jmp internal
+
+.section .text.foobar,"ax"
+.globl foobar
+.type foobar,%function
+foobar:
+  ret
+
+.section .text.internal,"ax"
+.globl internal
+.hidden internal
+.type internal,%function
+internal:
+	ret