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cmd/link: don't use label symbol for absolute address relocations on ARM64 PE
On ARM64 PE, when external linking, the PE relocation does not have an explicit addend, and instead has the addend encoded in the instruction or data. An instruction (e.g. ADRP, ADD) has limited width for the addend, so when the addend is large we use a label symbol, which points to the middle of the original target symbol, and a smaller addend. But for an absolute address relocation in the data section, we have the full width to encode the addend and we should not use the label symbol. Also, since we do not adjust the addend in the data, using the label symbol will actually make it point to the wrong address. E.g for an R_ADDR relocation targeting x+0x123456, we should emit 0x123456 in the data with an IMAGE_REL_ARM64_ADDR64 relocation pointing to x, whereas the current code emits 0x123456 in the data with an IMAGE_REL_ARM64_ADDR64 relocation pointing to the label symbol x+1MB, so it will actually be resolved to x+0x223456. This CL fixes this. Fixes #47557. Change-Id: I64e02b56f1d792f8c20ca61b78623ef5c3e34d7e Reviewed-on: https://go-review.googlesource.com/c/go/+/360895 Trust: Cherry Mui <cherryyz@google.com> Run-TryBot: Cherry Mui <cherryyz@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>
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@ -602,7 +602,7 @@ func pereloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym,
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rs := r.Xsym
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rt := r.Type
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if r.Xadd != signext21(r.Xadd) {
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if rt == objabi.R_ADDRARM64 && r.Xadd != signext21(r.Xadd) {
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// If the relocation target would overflow the addend, then target
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// a linker-manufactured label symbol with a smaller addend instead.
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label := ldr.Lookup(offsetLabelName(ldr, rs, r.Xadd/peRelocLimit*peRelocLimit), ldr.SymVersion(rs))
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@ -997,13 +997,31 @@ package main
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var x = [1<<25]byte{1<<23: 23, 1<<24: 24}
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var addr = [...]*byte{
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&x[1<<23-1],
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&x[1<<23],
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&x[1<<23+1],
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&x[1<<24-1],
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&x[1<<24],
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&x[1<<24+1],
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}
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func main() {
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// check relocations in instructions
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check(x[1<<23-1], 0)
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check(x[1<<23], 23)
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check(x[1<<23+1], 0)
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check(x[1<<24-1], 0)
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check(x[1<<24], 24)
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check(x[1<<24+1], 0)
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// check absolute address relocations in data
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check(*addr[0], 0)
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check(*addr[1], 23)
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check(*addr[2], 0)
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check(*addr[3], 0)
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check(*addr[4], 24)
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check(*addr[5], 0)
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}
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func check(x, y byte) {
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