From 57df0e138a0e7eec78b74ca2aee8f0a87bf339f0 Mon Sep 17 00:00:00 2001
From: Vladimir Vukicevic <vladimir@pobox.com>
Date: Wed, 22 Oct 2008 11:02:24 -0700
Subject: [PATCH] [arm] Use real B/BX instead of BL for side exit jumps; no
 need to update lr

---
 js/src/nanojit/NativeARM.cpp | 39 +++++++++++++++++++++++++++---------
 js/src/nanojit/NativeARM.h   |  1 +
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/js/src/nanojit/NativeARM.cpp b/js/src/nanojit/NativeARM.cpp
index a783ea9dfd55..450bc4700345 100644
--- a/js/src/nanojit/NativeARM.cpp
+++ b/js/src/nanojit/NativeARM.cpp
@@ -119,7 +119,7 @@ Assembler::nFragExit(LInsp guard)
 
         // we need to know that there's an extra immediate value available
         // for us; always force a far jump here.
-        BL_far(_epilogue);
+        JMP_far(_epilogue);
 
         // stick the jmp pointer to the start of the sequence
         lr->jmp = _nIns;
@@ -706,27 +706,27 @@ Assembler::nativePageSetup()
 NIns*
 Assembler::asm_adjustBranch(NIns* at, NIns* target)
 {
-    // This always got emitted as a BL_far sequence; at points
-    // to the first of 4 instructions.  Ensure that we're where
+    // This always got emitted as a JMP_far sequence; at points
+    // to the first of 3 instructions.  Ensure that we're where
     // we think we were..
-    NanoAssert(at[1] == (NIns)( COND_AL | OP_IMM | (1<<23) | (PC<<16) | (LR<<12) | (4) ));
-    NanoAssert(at[2] == (NIns)( COND_AL | (0x9<<21) | (0xFFF<<8) | (1<<4) | (IP) ));
+    NanoAssert(at[0] == (NIns)( COND_AL | (0x59<<20) | (PC<<16) | (IP<<12) | (0) ));
+    NanoAssert(at[1] == (NIns)( COND_AL | (0x9<<21) | (0xFFF<<8) | (1<<4) | (IP) ));
 
-    NIns* was = (NIns*) at[3];
+    NIns* was = (NIns*) at[2];
 
     //fprintf (stderr, "Adjusting branch @ 0x%8x: 0x%x -> 0x%x\n", at+3, at[3], target);
 
-    at[3] = (NIns)target;
+    at[2] = (NIns)target;
 
 #if defined(UNDER_CE)
     // we changed the code, so we need to do this (sadly)
     FlushInstructionCache(GetCurrentProcess(), NULL, NULL);
 #elif defined(AVMPLUS_LINUX)
-    __clear_cache((char*)at, (char*)(at+4));
+    __clear_cache((char*)at, (char*)(at+3));
 #endif
 
 #ifdef AVMPLUS_PORTING_API
-    NanoJIT_PortAPI_FlushInstructionCache(at, at+4);
+    NanoJIT_PortAPI_FlushInstructionCache(at, at+3);
 #endif
 
     return was;
@@ -767,6 +767,27 @@ Assembler::underrunProtect(int bytes)
     }
 }
 
+void
+Assembler::JMP_far(NIns* addr)
+{
+    // we have to stick an immediate into the stream
+    underrunProtect(12);
+
+    // TODO use a slot in const pool for address, but emit single insn
+    // for branch if offset fits
+
+    // the address
+    *(--_nIns) = (NIns)((addr));
+    // bx ip             // branch to the address we loaded earlier
+    *(--_nIns) = (NIns)( COND_AL | (0x9<<21) | (0xFFF<<8) | (1<<4) | (IP) );
+    // ldr ip, [pc + #0] // load the address into ip, reading it from [pc]
+    *(--_nIns) = (NIns)( COND_AL | (0x59<<20) | (PC<<16) | (IP<<12) | (0));
+
+    //fprintf (stderr, "JMP_far sequence @ 0x%08x\n", _nIns);
+
+    asm_output1("b %p (32-bit)", addr);
+}
+
 void
 Assembler::BL_far(NIns* addr)
 {
diff --git a/js/src/nanojit/NativeARM.h b/js/src/nanojit/NativeARM.h
index e57947c48cf1..792880fd56ad 100644
--- a/js/src/nanojit/NativeARM.h
+++ b/js/src/nanojit/NativeARM.h
@@ -199,6 +199,7 @@ verbose_only( extern const char* regNames[]; )
     void LD32_nochk(Register r, int32_t imm);                           \
     void BL(NIns*);                                                     \
     void BL_far(NIns*);                                                 \
+    void JMP_far(NIns*);                                                \
     void B_cond_chk(ConditionCode, NIns*, bool);                        \
     void underrunProtect(int bytes);                                    \
     void nativePageReset();                                             \