Remove nacl_user[] array lookup from syscall code path on x86-64 and MIPS

Remove nacl_user[] array lookup from syscall code path on x86-64 and MIPS

Replace the nacl_thread_index/gNaClThreadIdx TLS variable with a TLS
variable that points to the NaClThreadContext directly.

This saves a memory access in the syscall code path.

This also reduces the number of cases in which we rely on thread
indexes.

Replace NaCl{Get,Set}TlsIdx() with NaCl{Get,Set}CurrentThread().

Add a cleanup step in NaClAppThreadTeardown() to unset the TLS
variable.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3280
TEST=run_hello_world_test

Committed: https://src.chromium.org/viewvc/native_client?view=rev&revision=10849

[bsy, 2013-02-19 19:03:08]

naming nit.  feel free to ignore.

lgtm

https://codereview.chromium.org/12218089/diff/1/src/trusted/service_runtime/a...
File src/trusted/service_runtime/arch/mips/nacl_tls.c (right):

https://codereview.chromium.org/12218089/diff/1/src/trusted/service_runtime/a...
src/trusted/service_runtime/arch/mips/nacl_tls.c:23: THREAD struct
NaClThreadContext *nacl_current_thread;
maybe nacl_current_thread_context?

[Mark Seaborn, 2013-03-27 00:29:07]

Old review.  For the record...

https://codereview.chromium.org/12218089/diff/1/src/trusted/service_runtime/a...
File src/trusted/service_runtime/arch/mips/nacl_tls.c (right):

https://codereview.chromium.org/12218089/diff/1/src/trusted/service_runtime/a...
src/trusted/service_runtime/arch/mips/nacl_tls.c:23: THREAD struct
NaClThreadContext *nacl_current_thread;
On 2013/02/19 19:03:08, bsy wrote:
> maybe nacl_current_thread_context?

I opted to leave this as "nacl_current_thread" because NaClAppThread and
NaClThreadContext are effectively interchangeable and I'd like to rename
NaClThreadContext to something like NaClAppThreadArch at some point.