[lld] r304803 - Define __executable_start.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Tue Jun  6 11:18:48 2017
New Revision: 304803

URL: http://llvm.org/viewvc/llvm-project?rev=304803&view=rev
Log:
Define __executable_start.

This is defined by both bfd and gold and used by the android libc.

Modified:
    lld/trunk/ELF/Writer.cpp
    lld/trunk/test/ELF/ehdr_start.s

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=304803&r1=304802&r2=304803&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Tue Jun  6 11:18:48 2017
@@ -901,16 +901,18 @@ template <class ELFT> void Writer<ELFT>:
   if (!InX::DynSymTab)
     Symtab<ELFT>::X->addIgnored("__tls_get_addr");
 
-  // __dso_handle symbol is passed to cxa_finalize as a marker to identify
-  // each DSO. The address of the symbol doesn't matter as long as they are
-  // different in different DSOs, so we chose the start address of the DSO.
-  addOptionalRegular<ELFT>("__dso_handle", Out::ElfHeader, 0, STV_HIDDEN);
-
   // __ehdr_start is the location of ELF file headers. Note that we define
   // this symbol unconditionally even when using a linker script, which
   // differs from the behavior implemented by GNU linker which only define
   // this symbol if ELF headers are in the memory mapped segment.
-  addOptionalRegular<ELFT>("__ehdr_start", Out::ElfHeader, 0, STV_HIDDEN);
+  // __executable_start is not documented, but the expectation of at
+  // least the android libc is that it points to the elf header too.
+  // __dso_handle symbol is passed to cxa_finalize as a marker to identify
+  // each DSO. The address of the symbol doesn't matter as long as they are
+  // different in different DSOs, so we chose the start address of the DSO.
+  for (const char *Name :
+       {"__ehdr_start", "__executable_start", "__dso_handle"})
+    addOptionalRegular<ELFT>(Name, Out::ElfHeader, 0, STV_HIDDEN);
 
   // If linker script do layout we do not need to create any standart symbols.
   if (Script->Opt.HasSections)

Modified: lld/trunk/test/ELF/ehdr_start.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/ehdr_start.s?rev=304803&r1=304802&r2=304803&view=diff
==============================================================================
--- lld/trunk/test/ELF/ehdr_start.s (original)
+++ lld/trunk/test/ELF/ehdr_start.s Tue Jun  6 11:18:48 2017
@@ -13,10 +13,21 @@
 # CHECK-NEXT:    ]
 # CHECK-NEXT:    Section: .text (0x1)
 
+# CHECK:    Name: __executable_start
+# CHECK-NEXT:    Value: 0x200000
+# CHECK-NEXT:    Size: 0
+# CHECK-NEXT:    Binding: Local
+# CHECK-NEXT:    Type: None
+# CHECK-NEXT:    Other [
+# CHECK-NEXT:      STV_HIDDEN
+# CHECK-NEXT:    ]
+# CHECK-NEXT:    Section: .text
+
 .text
 .global _start, __ehdr_start
 _start:
   .quad __ehdr_start
+  .quad __executable_start
 
 # RUN: ld.lld -r %t.o -o %t.r
 # RUN: llvm-readobj -symbols %t.r | FileCheck %s --check-prefix=RELOCATABLE