cmd/link: use R12 as trampoline scratch register on ARM

The external linker uses R12. Do the same. We previously use R11,
the temp register in Go ABI. This does not really matter if the
caller is Go code, because all registers are clobbered at call.
But it the caller is C code, it may assume R11 live across a call.
Using R11 may clobber live value. On the callee side, R12 is not
an argument register in both Go and C calling convention.

Change-Id: I958c5dad52aa51bb282a7ad420f5423863e69c14
Reviewed-on: https://go-review.googlesource.com/c/go/+/314454
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

diff --git a/src/cmd/link/internal/arm/asm.go b/src/cmd/link/internal/arm/asm.go
index efdaff198dd8be68287aee3f37292f28707cb69b..33b20febd7780434c36b7879c0eafbd38c2f9224 100644 (file)
--- a/src/cmd/link/internal/arm/asm.go
+++ b/src/cmd/link/internal/arm/asm.go
@@ -443,8 +443,8 @@ func gentramp(arch *sys.Arch, linkmode ld.LinkMode, ldr *loader.Loader, tramp *l
        tramp.SetSize(12) // 3 instructions
        P := make([]byte, tramp.Size())
        t := ldr.SymValue(target) + offset
-       o1 := uint32(0xe5900000 | 11<<12 | 15<<16) // MOVW (R15), R11 // R15 is actual pc + 8
-       o2 := uint32(0xe12fff10 | 11)              // JMP  (R11)
+       o1 := uint32(0xe5900000 | 12<<12 | 15<<16) // MOVW (R15), R12 // R15 is actual pc + 8
+       o2 := uint32(0xe12fff10 | 12)              // JMP  (R12)
        o3 := uint32(t)                            // WORD $target
        arch.ByteOrder.PutUint32(P, o1)
        arch.ByteOrder.PutUint32(P[4:], o2)
@@ -464,9 +464,9 @@ func gentramp(arch *sys.Arch, linkmode ld.LinkMode, ldr *loader.Loader, tramp *l
 func gentramppic(arch *sys.Arch, tramp *loader.SymbolBuilder, target loader.Sym, offset int64) {
        tramp.SetSize(16) // 4 instructions
        P := make([]byte, tramp.Size())
-       o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 4)  // MOVW 4(R15), R11 // R15 is actual pc + 8
-       o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
-       o3 := uint32(0xe12fff10 | 11)                   // JMP  (R11)
+       o1 := uint32(0xe5900000 | 12<<12 | 15<<16 | 4)  // MOVW 4(R15), R12 // R15 is actual pc + 8
+       o2 := uint32(0xe0800000 | 12<<12 | 15<<16 | 12) // ADD R15, R12, R12
+       o3 := uint32(0xe12fff10 | 12)                   // JMP  (R12)
        o4 := uint32(0)                                 // WORD $(target-pc) // filled in with relocation
        arch.ByteOrder.PutUint32(P, o1)
        arch.ByteOrder.PutUint32(P[4:], o2)
@@ -484,10 +484,10 @@ func gentramppic(arch *sys.Arch, tramp *loader.SymbolBuilder, target loader.Sym,
 // generate a trampoline to target+offset in dynlink mode (using GOT)
 func gentrampdyn(arch *sys.Arch, tramp *loader.SymbolBuilder, target loader.Sym, offset int64) {
        tramp.SetSize(20)                               // 5 instructions
-       o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 8)  // MOVW 8(R15), R11 // R15 is actual pc + 8
-       o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
-       o3 := uint32(0xe5900000 | 11<<12 | 11<<16)      // MOVW (R11), R11
-       o4 := uint32(0xe12fff10 | 11)                   // JMP  (R11)
+       o1 := uint32(0xe5900000 | 12<<12 | 15<<16 | 8)  // MOVW 8(R15), R12 // R15 is actual pc + 8
+       o2 := uint32(0xe0800000 | 12<<12 | 15<<16 | 12) // ADD R15, R12, R12
+       o3 := uint32(0xe5900000 | 12<<12 | 12<<16)      // MOVW (R12), R12
+       o4 := uint32(0xe12fff10 | 12)                   // JMP  (R12)
        o5 := uint32(0)                                 // WORD $target@GOT // filled in with relocation
        o6 := uint32(0)
        if offset != 0 {
@@ -495,8 +495,8 @@ func gentrampdyn(arch *sys.Arch, tramp *loader.SymbolBuilder, target loader.Sym,
                tramp.SetSize(24) // 6 instructions
                o6 = o5
                o5 = o4
-               o4 = 0xe2800000 | 11<<12 | 11<<16 | immrot(uint32(offset)) // ADD $offset, R11, R11
-               o1 = uint32(0xe5900000 | 11<<12 | 15<<16 | 12)             // MOVW 12(R15), R11
+               o4 = 0xe2800000 | 12<<12 | 12<<16 | immrot(uint32(offset)) // ADD $offset, R12, R12
+               o1 = uint32(0xe5900000 | 12<<12 | 15<<16 | 12)             // MOVW 12(R15), R12
        }
        P := make([]byte, tramp.Size())
        arch.ByteOrder.PutUint32(P, o1)