nfp: bpf: add helpers for updating immediate instructions

Immediate loads are used to load the return address of a helper.
We need to be able to update those loads for relocations.
Immediate loads can be slightly more complex and spread over
two instructions in general, but here we only care about simple
loads of small (< 65k) constants, so complex cases are not handled.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

drivers/net/ethernet/netronome/nfp/nfp_asm.c

@@ -50,6 +50,11 @@ const struct cmd_tgt_act cmd_tgt_act[__CMD_TGT_MAP_SIZE] = {
 	[CMD_TGT_READ_SWAP_LE] =	{ 0x03, 0x40 },
 };
 
+static bool unreg_is_imm(u16 reg)
+{
+	return (reg & UR_REG_IMM) == UR_REG_IMM;
+}
+
 u16 br_get_offset(u64 instr)
 {
 	u16 addr_lo, addr_hi;
@@ -80,6 +85,59 @@ void br_add_offset(u64 *instr, u16 offset)
 	br_set_offset(instr, addr + offset);
 }
 
+static bool immed_can_modify(u64 instr)
+{
+	if (FIELD_GET(OP_IMMED_INV, instr) ||
+	    FIELD_GET(OP_IMMED_SHIFT, instr) ||
+	    FIELD_GET(OP_IMMED_WIDTH, instr) != IMMED_WIDTH_ALL) {
+		pr_err("Can't decode/encode immed!\n");
+		return false;
+	}
+	return true;
+}
+
+u16 immed_get_value(u64 instr)
+{
+	u16 reg;
+
+	if (!immed_can_modify(instr))
+		return 0;
+
+	reg = FIELD_GET(OP_IMMED_A_SRC, instr);
+	if (!unreg_is_imm(reg))
+		reg = FIELD_GET(OP_IMMED_B_SRC, instr);
+
+	return (reg & 0xff) | FIELD_GET(OP_IMMED_IMM, instr);
+}
+
+void immed_set_value(u64 *instr, u16 immed)
+{
+	if (!immed_can_modify(*instr))
+		return;
+
+	if (unreg_is_imm(FIELD_GET(OP_IMMED_A_SRC, *instr))) {
+		*instr &= ~FIELD_PREP(OP_IMMED_A_SRC, 0xff);
+		*instr |= FIELD_PREP(OP_IMMED_A_SRC, immed & 0xff);
+	} else {
+		*instr &= ~FIELD_PREP(OP_IMMED_B_SRC, 0xff);
+		*instr |= FIELD_PREP(OP_IMMED_B_SRC, immed & 0xff);
+	}
+
+	*instr &= ~OP_IMMED_IMM;
+	*instr |= FIELD_PREP(OP_IMMED_IMM, immed >> 8);
+}
+
+void immed_add_value(u64 *instr, u16 offset)
+{
+	u16 val;
+
+	if (!immed_can_modify(*instr))
+		return;
+
+	val = immed_get_value(*instr);
+	immed_set_value(instr, val + offset);
+}
+
 static u16 nfp_swreg_to_unreg(swreg reg, bool is_dst)
 {
 	bool lm_id, lm_dec = false;

drivers/net/ethernet/netronome/nfp/nfp_asm.h

@@ -138,6 +138,10 @@ enum immed_shift {
 	IMMED_SHIFT_2B = 2,
 };
 
+u16 immed_get_value(u64 instr);
+void immed_set_value(u64 *instr, u16 immed);
+void immed_add_value(u64 *instr, u16 offset);
+
 #define OP_SHF_BASE		0x08000000000ULL
 #define OP_SHF_A_SRC		0x000000000ffULL
 #define OP_SHF_SC		0x00000000300ULL