Fix for building ARM/linux using clang.

src/trusted/service_runtime/linux/nacl_bootstrap_munge_phdr.py

Index: src/trusted/service_runtime/linux/nacl_bootstrap_munge_phdr.py
diff --git a/src/trusted/service_runtime/linux/nacl_bootstrap_munge_phdr.py b/src/trusted/service_runtime/linux/nacl_bootstrap_munge_phdr.py
index b3a0e1ae627df92db526ab41c071c6da28c67c0a..03188b9677ad522c13f925014fba37aff58be40b 100644
--- a/src/trusted/service_runtime/linux/nacl_bootstrap_munge_phdr.py
+++ b/src/trusted/service_runtime/linux/nacl_bootstrap_munge_phdr.py
@@ -29,8 +29,12 @@ def Main(argv):
   [prog, munger, infile, outfile] = argv
   tmpfile = outfile + '.tmp'
   shutil.copy(infile, tmpfile)
-  segment_num = '2'
-  subprocess.check_call([munger, tmpfile, segment_num])
+  segment_num = '3'

[Mark Seaborn, 2014/07/24 21:17:24]

I investigated this.

I was able to reproduce the problem, and I got the following ELF headers:

$ readelf -a
scons-out/dbg-linux-arm/obj/src/trusted/service_runtime/nacl_bootstrap_raw
...
Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  EXIDX          0x0029e8 0x000129e8 0x000129e8 0x00008 0x00008 R   0x4
  LOAD           0x000000 0x00010000 0x00010000 0x029f0 0x029f0 R E 0x1000
  LOAD           0x0029f0 0x000139f0 0x000139f0 0x00000 0x01005 RW  0x1000
  LOAD           0x003000 0x00015000 0x00015000 0x00000 0x3ffed000     0x1000
  LOAD           0x003000 0x40002000 0x40002000 0x00014 0x00014 RW  0x1000
  NOTE           0x000114 0x00010114 0x00010114 0x00024 0x00024 R   0x4
  GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x4

 Section to Segment mapping:
  Segment Sections...
   00     .ARM.exidx 
   01     .note.gnu.build-id .text .rodata .ARM.exidx 
   02     .bss 
   03     .reserve 
   04     .r_debug 
   05     .note.gnu.build-id 
   06     
...

ARM.exidx is unwind info in an ARM-specific format.

It seems Clang generates this even if we compile with -fno-exceptions (the
default for C anyway) and -fno-unwind-tables.

A simple fix is just to change the "DISCARD" list in the linker script:

--- a/src/trusted/service_runtime/linux/nacl_bootstrap.x
+++ b/src/trusted/service_runtime/linux/nacl_bootstrap.x
@@ -131,5 +131,6 @@ SECTIONS {
     *(.reginfo)
     *(.rel*)
     *(.igot.plt)
+    *(.ARM.exidx)
   }
 }

+  cmd = [munger, tmpfile, segment_num]
+  rtn = subprocess.call(cmd)
+  if rtn != 0:
+    print 'Command failed with %d: %s' % (rtn, cmd)
+    return rtn
   shutil.move(tmpfile, outfile)
   return 0