Align and pad code segments to 64k

nacl/dyn-link/ldscripts/elf_nacl.xs

 /* Script for ld --shared: link shared library */
 OUTPUT_FORMAT("elf32-nacl", "elf32-nacl",
               "elf32-nacl")
 OUTPUT_ARCH(i386)
 ENTRY(_start)
 SEARCH_DIR("=/usr/local/lib32"); SEARCH_DIR("=/lib32"); SEARCH_DIR("=/usr/lib32");
 SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib");
 PHDRS
 {
   seg_code     PT_LOAD FLAGS(5) ;       /* read + execute */
   seg_rodata   PT_LOAD FLAGS(4) ;       /* read */
   seg_rwdata   PT_LOAD FLAGS(6) ;       /* read + write */
   seg_bss      PT_LOAD FLAGS(6) ;       /* read + write */
   seg_dynamic  PT_DYNAMIC FLAGS(6) ;
   seg_stack    PT_GNU_STACK FLAGS(6) ;
   seg_tls      PT_TLS FLAGS(4) ;
 }
 SECTIONS
 {
-  /* NaCl runtime treats ld.so as an executable.  NaCl executables must have
-     page-aligned code and data segments, so linker script for ld.so is patched
-     to remove SIZEOF_HEADERS below and make code segment aligned to page
-     boundary. */
-  . = SEGMENT_START("text", 0) + SIZEOF_HEADERS;
+  . = SEGMENT_START("text", 0);
   _begin = .;
+
   /* The ALIGN(32) instructions below are workarounds.
      TODO(mseaborn): Get the object files to include the correct
      alignments and padding themselves.
      See http://code.google.com/p/nativeclient/issues/detail?id=499. */
   .init           : SUBALIGN(32)
   {
     KEEP (*(.init))
     . = ALIGN(32); /* ensure nop padding */
   } :seg_code =0x90909090
   .plt            : { *(.plt) }
   .text           : SUBALIGN(32)
   {
     *(.text .stub .text.* .gnu.linkonce.t.*)
     KEEP (*(.text.*personality*))
     /* .gnu.warning sections are handled specially by elf32.em.  */
     *(.gnu.warning)
     /* Putting .fini here makes the align pad correctly when .fini is empty.
        Listing the __libc* sections is also necessary to make padding work. */
     KEEP (*(.fini))
     *(__libc_freeres_fn)
     *(__libc_thread_freeres_fn)
-    . = ALIGN(32); /* ensure nop padding */
+    . = ALIGN(CONSTANT (MAXPAGESIZE)); /* ensures NOP fill */
   } =0x90909090
   PROVIDE (__etext = .);
   PROVIDE (_etext = .);
   PROVIDE (etext = .);
 
-  /* Adjust data segment so that is has the same position within the page as
-     the end of code segment.  In this case linker can store them without any
-     zeros in between.
-     
-     NaCl runtime treats ld.so as an executable which must have page-aligned
-     read-only data segment.  So the last term is replaced with 0 while patching
-     linker script for ld.so. */
-  . = SEGMENT_START("text", 0) + 0x10000000 +
-      (. & (CONSTANT (MAXPAGESIZE) - 1));
+  . = ALIGN(SEGMENT_START("text", 0) + 0x10000000, CONSTANT (MAXPAGESIZE));
   .note.gnu.build-id : { *(.note.gnu.build-id) } :seg_rodata
   .hash           : { *(.hash) }
   .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }
   .dynstr         : { *(.dynstr) }
   .gnu.version    : { *(.gnu.version) }
   .gnu.version_d  : { *(.gnu.version_d) }
   .gnu.version_r  : { *(.gnu.version_r) }
   .rel.init       : { *(.rel.init) }
   .rela.init      : { *(.rela.init) }
@@ skipping 17 matching lines @@
   .rela.dtors     : { *(.rela.dtors) }
   .rel.got        : { *(.rel.got) }
   .rela.got       : { *(.rela.got) }
   .rel.bss        : { *(.rel.bss .rel.bss.* .rel.gnu.linkonce.b.*) }
   .rela.bss       : { *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*) }
   .rel.plt        : { *(.rel.plt) }
   .rela.plt       : { *(.rela.plt) }
   .rodata         : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
   .rodata1        : { *(.rodata1) }
   .eh_frame_hdr : { *(.eh_frame_hdr) }
-  .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) } 
+  .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) }
   .gcc_except_table   : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }
   /* Adjust the address for the data segment.  We want to adjust up to
      the same address within the page on the next page up.  */
   . = ALIGN (CONSTANT (MAXPAGESIZE)) - ((CONSTANT (MAXPAGESIZE) - .) & (CONSTANT (MAXPAGESIZE) - 1)); . = DATA_SEGMENT_ALIGN (CONSTANT (MAXPAGESIZE), CONSTANT (COMMONPAGESIZE));
   /* Executables loaded by sel_ldr are not required to have seg_rwdata aligned
      to page boundary.  So we can omit alignment here both for ld.so and normal
      libraries. */
   /* Exception handling  */
   .eh_frame       : ONLY_IF_RW { KEEP (*(.eh_frame)) } :seg_rwdata
   .gcc_except_table   : ONLY_IF_RW { *(.gcc_except_table .gcc_except_table.*) }
@@ skipping 126 matching lines @@
   .debug_funcnames 0 : { *(.debug_funcnames) }
   .debug_typenames 0 : { *(.debug_typenames) }
   .debug_varnames  0 : { *(.debug_varnames) }
   /* DWARF 3 */
   .debug_pubtypes 0 : { *(.debug_pubtypes) }
   .debug_ranges   0 : { *(.debug_ranges) }
   .gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
   /DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) }
   /DISCARD/ : { *(.note.ABI-tag) }
 }