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arm32, bpf: add support for sign-extension mov instruction 

The cpuv4 added a new BPF_MOVSX instruction that sign extends the src
before moving it to the destination.

BPF_ALU | BPF_MOVSX sign extends 8-bit and 16-bit operands into 32-bit
operands, and zeroes the remaining upper 32 bits.

BPF_ALU64 | BPF_MOVSX sign extends 8-bit, 16-bit, and 32-bit  operands
into 64-bit operands.

The offset field of the instruction is used to tell the number of bit to
use for sign-extension. BPF_MOV and BPF_MOVSX have the same code but the
former sets offset to 0 and the later one sets the offset to 8, 16 or 32

The behaviour of this instruction is dst = (s8,s16,s32)src

On ARM32 the implementation uses LSH and ARSH to extend the 8/16 bits to
a 32-bit register and then it is sign extended to the upper 32-bit
register using ARSH. For 32-bit we just move it to the destination
register and use ARSH to extend it to the upper 32-bit register.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20230907230550.1417590-4-puranjay12@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Puranjay Mohan 2023-09-07 23:05:44 +00:00 committed by Alexei Starovoitov
parent f9e6981b1f
commit fc832653fa
1 changed files with 30 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
arch/arm/net/bpf_jit_32.c
View File

@ -747,12 +747,16 @@ static inline void emit_a32_alu_r64(const bool is64, const s8 dst[],
}
/* dst = src (4 bytes)*/
static inline void emit_a32_mov_r(const s8 dst, const s8 src,
static inline void emit_a32_mov_r(const s8 dst, const s8 src, const u8 off,
struct jit_ctx *ctx) {
const s8 *tmp = bpf2a32[TMP_REG_1];
s8 rt;
rt = arm_bpf_get_reg32(src, tmp[0], ctx);
if (off && off != 32) {
emit(ARM_LSL_I(rt, rt, 32 - off), ctx);
emit(ARM_ASR_I(rt, rt, 32 - off), ctx);
}
arm_bpf_put_reg32(dst, rt, ctx);
}
@ -761,15 +765,15 @@ static inline void emit_a32_mov_r64(const bool is64, const s8 dst[],
const s8 src[],
struct jit_ctx *ctx) {
if (!is64) {
emit_a32_mov_r(dst_lo, src_lo, ctx);
emit_a32_mov_r(dst_lo, src_lo, 0, ctx);
if (!ctx->prog->aux->verifier_zext)
/* Zero out high 4 bytes */
emit_a32_mov_i(dst_hi, 0, ctx);
} else if (__LINUX_ARM_ARCH__ < 6 &&
ctx->cpu_architecture < CPU_ARCH_ARMv5TE) {
/* complete 8 byte move */
emit_a32_mov_r(dst_lo, src_lo, ctx);
emit_a32_mov_r(dst_hi, src_hi, ctx);
emit_a32_mov_r(dst_lo, src_lo, 0, ctx);
emit_a32_mov_r(dst_hi, src_hi, 0, ctx);
} else if (is_stacked(src_lo) && is_stacked(dst_lo)) {
const u8 *tmp = bpf2a32[TMP_REG_1];
@ -785,6 +789,24 @@ static inline void emit_a32_mov_r64(const bool is64, const s8 dst[],
}
}
/* dst = (signed)src */
static inline void emit_a32_movsx_r64(const bool is64, const u8 off, const s8 dst[], const s8 src[],
struct jit_ctx *ctx) {
const s8 *tmp = bpf2a32[TMP_REG_1];
const s8 *rt;
rt = arm_bpf_get_reg64(dst, tmp, ctx);
emit_a32_mov_r(dst_lo, src_lo, off, ctx);
if (!is64) {
if (!ctx->prog->aux->verifier_zext)
/* Zero out high 4 bytes */
emit_a32_mov_i(dst_hi, 0, ctx);
} else {
emit(ARM_ASR_I(rt[0], rt[1], 31), ctx);
}
}
/* Shift operations */
static inline void emit_a32_alu_i(const s8 dst, const u32 val,
struct jit_ctx *ctx, const u8 op) {
@ -1450,7 +1472,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
emit_a32_mov_i(dst_hi, 0, ctx);
break;
}
emit_a32_mov_r64(is64, dst, src, ctx);
if (insn->off)
emit_a32_movsx_r64(is64, insn->off, dst, src, ctx);
else
emit_a32_mov_r64(is64, dst, src, ctx);
break;
case BPF_K:
/* Sign-extend immediate value to destination reg */