[PATCH] D27497: [ELF] Shared libraries should have entry point

[Petr Hosek via Phabricator via llvm-commits]

phosek created this revision.
phosek added a reviewer: ruiu.
phosek added a subscriber: llvm-commits.
phosek set the repository for this revision to rL LLVM.
phosek added a project: lld.

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.


Repository:
  rL LLVM

https://reviews.llvm.org/D27497

Files:
  ELF/Config.h
  ELF/Driver.cpp
  ELF/Writer.cpp
  test/ELF/gc-sections-keep-shared-start.s


Index: test/ELF/gc-sections-keep-shared-start.s
===================================================================
--- /dev/null
+++ 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
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1410,14 +1410,16 @@
 
   // 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;
 }
 
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -521,6 +521,7 @@
   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 @@
     // 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";
Index: ELF/Config.h
===================================================================
--- ELF/Config.h
+++ ELF/Config.h
@@ -107,6 +107,7 @@
   bool GcSections;
   bool GdbIndex;
   bool GnuHash = false;
+  bool HasEntry = false;
   bool ICF;
   bool Mips64EL = false;
   bool MipsN32Abi = false;


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