[Webkit-unassigned] [Bug 101365] New: Should ARMv7Assembler::replaceWithJump cache-flush the nop on page boundary

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=101365

           Summary: Should ARMv7Assembler::replaceWithJump cache-flush the
                    nop on page boundary
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: yoli at rim.com


ARMv7Assembler::replaceWithJump() contains following code:

if (spansTwo4K) {
   ptr[-2] = OP_NOP_T1;
   ptr++;
}

After that, it calls linkJumpT4(ptr, to) and then cacheFlush(ptr - 2,
sizeof(uint16_t) * 2), so it doesn't cache-flush this instruction.

According to the comments, this seems a work around of a Cortex-A8 bug. 

I'm not sure if we should make sure the nop instruction should also be
cache-flushed, because the instruction was probably nop anyway.

Also, these spansTwo4K are said to workaround a Cortex-A8 issue. Does this also give perf penalty to other cores?

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