From 2f50fef095298706e7dbe1f47b7d9421c74a790b Mon Sep 17 00:00:00 2001
From: Petr Hosek <phosek@chromium.org>
Date: Wed, 7 Dec 2016 02:26:16 +0000
Subject: [PATCH] [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

llvm-svn: 288878
---
 lld/ELF/Config.h                             |  1 +
 lld/ELF/Driver.cpp                           |  4 ++--
 lld/ELF/Writer.cpp                           | 10 ++++++----
 lld/test/ELF/gc-sections-keep-shared-start.s | 29 ++++++++++++++++++++++++++++
 4 files changed, 38 insertions(+), 6 deletions(-)
 create mode 100644 lld/test/ELF/gc-sections-keep-shared-start.s

diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index 31ecd26..874c5c4 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -107,6 +107,7 @@ struct Configuration {
   bool GcSections;
   bool GdbIndex;
   bool GnuHash = false;
+  bool HasEntry = false;
   bool ICF;
   bool Mips64EL = false;
   bool MipsN32Abi = false;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index cb27adc..9774c7c 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -521,6 +521,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   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::link(opt::InputArgList &Args) {
     // 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";
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 98b335e..555fe78 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -1410,14 +1410,16 @@ template <class ELFT> typename ELFT::uint Writer<ELFT>::getEntryAddr() {
 
   // 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;
 }
 
diff --git a/lld/test/ELF/gc-sections-keep-shared-start.s b/lld/test/ELF/gc-sections-keep-shared-start.s
new file mode 100644
index 0000000..53b3358
--- /dev/null
+++ b/lld/test/ELF/gc-sections-keep-shared-start.s
@@ -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
-- 
2.7.4