This change allows compilation with...

src/trusted/service_runtime/arch/x86_64/nacl_syscall.S

Index: src/trusted/service_runtime/arch/x86_64/nacl_syscall.S
===================================================================
--- src/trusted/service_runtime/arch/x86_64/nacl_syscall.S	(revision 1067)
+++ src/trusted/service_runtime/arch/x86_64/nacl_syscall.S	(working copy)
@@ -52,7 +52,12 @@
         xor     %eax, %eax
         mov     %gs, %ax
         shr     $3, %eax
+#ifdef __PIC__
+        mov     IDENTIFIER(nacl_user)@GOTPCREL(%rip), %edx

[Mark Seaborn, 2010/02/15 14:45:49]

I'm not sure if this is correct.
It might need an extra dereference to fetch the address from the GOT.
In any case, going via the GOT is not necessary on x86-64, which allows
%rip-relative addressing.

+        lea     0(%edx,%eax,4), %edx
+#else
         lea     IDENTIFIER(nacl_user)(,%eax,4), %edx
+#endif
 
         /* check NaClThreadContext in sel_rt.h for the offsets */
         movl    0(%edx), %edx
@@ -67,7 +72,12 @@
          * any registers having particular values.  we will clear/discard
          * caller-saved registers at system call return.
          */
+#ifdef __PIC__
+        mov     IDENTIFIER(nacl_sys)@GOTPCREL(%rip), %edx
+        lea     0(%edx,%eax,4), %edx
+#else
         lea     IDENTIFIER(nacl_sys)(,%eax,4), %edx
+#endif
         mov     0(%edx), %edx
         /*
          * %cs and %ds already taken care of by NaCl_trampoline_seg_code
@@ -82,7 +92,11 @@
         mov     %ecx, %ss  /* disable intr */
         mov     %rdx, %rsp
         push    %rax
+#ifdef __PIC__
+        call    IDENTIFIER(NaClSyscallCSegHook)@PLT

[Mark Seaborn, 2010/02/15 14:45:49]

Calling via the PLT is not necessary to make this PIC.
CALL instructions are position independent anyway.
Calling via PLT is for cross-library calls.

+#else
         call    IDENTIFIER(NaClSyscallCSegHook)
+#endif
         /*
          * If stack usage in the above code changes, modify initial %esp
          * computation -- see nacl_switch_to_app.c:NaClStartThreadInApp.