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Subject[PATCH 4.14 14/71] ARM: net: bpf: avoid bx instruction on non-Thumb capable CPUs
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Russell King <rmk+kernel@armlinux.org.uk>

commit e9062481824384f00299971f923fecf6b3668001 upstream.

Avoid the 'bx' instruction on CPUs that have no support for Thumb and
thus do not implement this instruction by moving the generation of this
opcode to a separate function that selects between:

bx reg

and

mov pc, reg

according to the capabilities of the CPU.

Fixes: 39c13c204bb1 ("arm: eBPF JIT compiler")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/net/bpf_jit_32.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -285,16 +285,20 @@ static inline void emit_mov_i(const u8 r
emit_mov_i_no8m(rd, val, ctx);
}

-static inline void emit_blx_r(u8 tgt_reg, struct jit_ctx *ctx)
+static void emit_bx_r(u8 tgt_reg, struct jit_ctx *ctx)
{
- ctx->seen |= SEEN_CALL;
-#if __LINUX_ARM_ARCH__ < 5
- emit(ARM_MOV_R(ARM_LR, ARM_PC), ctx);
-
if (elf_hwcap & HWCAP_THUMB)
emit(ARM_BX(tgt_reg), ctx);
else
emit(ARM_MOV_R(ARM_PC, tgt_reg), ctx);
+}
+
+static inline void emit_blx_r(u8 tgt_reg, struct jit_ctx *ctx)
+{
+ ctx->seen |= SEEN_CALL;
+#if __LINUX_ARM_ARCH__ < 5
+ emit(ARM_MOV_R(ARM_LR, ARM_PC), ctx);
+ emit_bx_r(tgt_reg, ctx);
#else
emit(ARM_BLX_R(tgt_reg), ctx);
#endif
@@ -997,7 +1001,7 @@ static int emit_bpf_tail_call(struct jit
emit_a32_mov_i(tmp2[1], off, false, ctx);
emit(ARM_LDR_R(tmp[1], tmp[1], tmp2[1]), ctx);
emit(ARM_ADD_I(tmp[1], tmp[1], ctx->prologue_bytes), ctx);
- emit(ARM_BX(tmp[1]), ctx);
+ emit_bx_r(tmp[1], ctx);

/* out: */
if (out_offset == -1)
@@ -1166,7 +1170,7 @@ static void build_epilogue(struct jit_ct
emit(ARM_POP(reg_set), ctx);
/* Return back to the callee function */
if (!(ctx->seen & SEEN_CALL))
- emit(ARM_BX(ARM_LR), ctx);
+ emit_bx_r(ARM_LR, ctx);
#endif
}


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