Optimize __memset_chk, __memcpy_chk. DO NOT MERGE.

This change creates assembler versions of __memcpy_chk/__memset_chk
that is implemented in the memcpy/memset assembler code. This change
avoids an extra call to memcpy/memset, instead allowing a simple fall
through to occur from the chk code into the body of the real
implementation.

Testing:

- Ran the libc_test on __memcpy_chk/__memset_chk on all nexus devices.
- Wrote a small test executable that has three calls to __memcpy_chk and
  three calls to __memset_chk. First call dest_len is length + 1. Second
  call dest_len is length. Third call dest_len is length - 1.
  Verified that the first two calls pass, and the third fails. Examined
  the logcat output on all nexus devices to verify that the fortify
  error message was sent properly.
- I benchmarked the new __memcpy_chk and __memset_chk on all systems. For
  __memcpy_chk and large copies, the savings is relatively small (about 1%).
  For small copies, the savings is large on cortex-a15/krait devices
  (between 5% to 30%).
  For cortex-a9 and small copies, the speed up is present, but relatively
  small (about 3% to 5%).
  For __memset_chk and large copies, the savings is also small (about 1%).
  However, all processors show larger speed-ups on small copies (about 30% to
  100%).

Bug: 9293744

Merge from internal master.

(cherry-picked from 7c860db0747f6276a6e43984d43f8fa5181ea936)

Change-Id: I916ad305e4001269460ca6ebd38aaa0be8ac7f52

1 files changed, 24 insertions, 0 deletions

diff --git a/libc/arch-arm/krait/bionic/memset.S b/libc/arch-arm/krait/bionic/memset.S
index a2e2d80..4e4788b 100644
--- a/libc/arch-arm/krait/bionic/memset.S
+++ b/libc/arch-arm/krait/bionic/memset.S
@@ -28,6 +28,7 @@
 
 #include <machine/cpu-features.h>
 #include <machine/asm.h>
+#include "libc_events.h"
 
 /*
  * This code assumes it is running on a processor that supports all arm v7
@@ -37,9 +38,28 @@
 
     .fpu    neon
 
+ENTRY(__memset_chk)
+        cmp         r2, r3
+        bls         done
+
+        ldr         r0, error_message
+        ldr         r1, error_code
+1:
+        add         r0, pc
+        bl          __fortify_chk_fail
+error_code:
+        .word       BIONIC_EVENT_MEMSET_BUFFER_OVERFLOW
+error_message:
+        .word       error_string-(1b+8)
+
+END(__memset_chk)
+
 ENTRY(bzero)
         mov     r2, r1
         mov     r1, #0
+
+done:
+        // Fall through to memset...
 END(bzero)
 
 /* memset() returns its first argument.  */
@@ -79,3 +99,7 @@ ENTRY(memset)
         ldmfd       sp!, {r0}
         bx          lr
 END(memset)
+
+        .data
+error_string:
+        .string     "memset buffer overflow"