[js, ARM] Always check error return from BufferOffset::diffB.

We were missing error checks at two points. In one case an error return
is meaningful; in another case it is not, as the problem should have
been guarded against at a higher level by emitting far jump islands soon
enough during pasteup of compiled code.

2 files changed, 10 insertions, 2 deletions

diff --git a/js/src/jit/arm/Assembler-arm.cpp b/js/src/jit/arm/Assembler-arm.cpp
index 2830f0695..1e20da1c8 100644
--- a/js/src/jit/arm/Assembler-arm.cpp
+++ b/js/src/jit/arm/Assembler-arm.cpp
@@ -2401,7 +2401,12 @@ Assembler::as_b(Label* l, Condition c)
         if (oom())
             return BufferOffset();
 
-        as_b(BufferOffset(l).diffB<BOffImm>(ret), c, ret);
+        BOffImm off = BufferOffset(l).diffB<BOffImm>(ret);
+        if (off.isInvalid()) {
+            m_buffer.fail_bail();
+            return BufferOffset();
+        }
+        as_b(off, c, ret);
 #ifdef JS_DISASM_ARM
         spewBranch(m_buffer.getInstOrNull(ret), l);
 #endif
diff --git a/js/src/jit/arm/MacroAssembler-arm.cpp b/js/src/jit/arm/MacroAssembler-arm.cpp
index d40578514..a4161ab00 100644
--- a/js/src/jit/arm/MacroAssembler-arm.cpp
+++ b/js/src/jit/arm/MacroAssembler-arm.cpp
@@ -5012,7 +5012,10 @@ void
 MacroAssembler::patchCall(uint32_t callerOffset, uint32_t calleeOffset)
 {
     BufferOffset inst(callerOffset - 4);
-    as_bl(BufferOffset(calleeOffset).diffB<BOffImm>(inst), Always, inst);
+    BOffImm off = BufferOffset(calleeOffset).diffB<BOffImm>(inst);
+    MOZ_RELEASE_ASSERT(!off.isInvalid(),
+                       "Failed to insert necessary far jump islands");
+    as_bl(off, Always, inst);
 }
 
 CodeOffset