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Diffstat (limited to 'arch/powerpc/net/bpf_jit_comp.c')
-rw-r--r--arch/powerpc/net/bpf_jit_comp.c701
1 files changed, 701 insertions, 0 deletions
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
new file mode 100644
index 00000000000..82e82cadcde
--- /dev/null
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -0,0 +1,701 @@
+/* bpf_jit_comp.c: BPF JIT compiler for PPC64
+ *
+ * Copyright 2011 Matt Evans <matt@ozlabs.org>, IBM Corporation
+ *
+ * Based on the x86 BPF compiler, by Eric Dumazet (eric.dumazet@gmail.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+#include <linux/moduleloader.h>
+#include <asm/cacheflush.h>
+#include <linux/netdevice.h>
+#include <linux/filter.h>
+#include <linux/if_vlan.h>
+
+#include "bpf_jit.h"
+
+int bpf_jit_enable __read_mostly;
+
+static inline void bpf_flush_icache(void *start, void *end)
+{
+ smp_wmb();
+ flush_icache_range((unsigned long)start, (unsigned long)end);
+}
+
+static void bpf_jit_build_prologue(struct sk_filter *fp, u32 *image,
+ struct codegen_context *ctx)
+{
+ int i;
+ const struct sock_filter *filter = fp->insns;
+
+ if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
+ /* Make stackframe */
+ if (ctx->seen & SEEN_DATAREF) {
+ /* If we call any helpers (for loads), save LR */
+ EMIT(PPC_INST_MFLR | __PPC_RT(R0));
+ PPC_STD(0, 1, 16);
+
+ /* Back up non-volatile regs. */
+ PPC_STD(r_D, 1, -(8*(32-r_D)));
+ PPC_STD(r_HL, 1, -(8*(32-r_HL)));
+ }
+ if (ctx->seen & SEEN_MEM) {
+ /*
+ * Conditionally save regs r15-r31 as some will be used
+ * for M[] data.
+ */
+ for (i = r_M; i < (r_M+16); i++) {
+ if (ctx->seen & (1 << (i-r_M)))
+ PPC_STD(i, 1, -(8*(32-i)));
+ }
+ }
+ EMIT(PPC_INST_STDU | __PPC_RS(R1) | __PPC_RA(R1) |
+ (-BPF_PPC_STACKFRAME & 0xfffc));
+ }
+
+ if (ctx->seen & SEEN_DATAREF) {
+ /*
+ * If this filter needs to access skb data,
+ * prepare r_D and r_HL:
+ * r_HL = skb->len - skb->data_len
+ * r_D = skb->data
+ */
+ PPC_LWZ_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
+ data_len));
+ PPC_LWZ_OFFS(r_HL, r_skb, offsetof(struct sk_buff, len));
+ PPC_SUB(r_HL, r_HL, r_scratch1);
+ PPC_LD_OFFS(r_D, r_skb, offsetof(struct sk_buff, data));
+ }
+
+ if (ctx->seen & SEEN_XREG) {
+ /*
+ * TODO: Could also detect whether first instr. sets X and
+ * avoid this (as below, with A).
+ */
+ PPC_LI(r_X, 0);
+ }
+
+ switch (filter[0].code) {
+ case BPF_RET | BPF_K:
+ case BPF_LD | BPF_W | BPF_LEN:
+ case BPF_LD | BPF_W | BPF_ABS:
+ case BPF_LD | BPF_H | BPF_ABS:
+ case BPF_LD | BPF_B | BPF_ABS:
+ /* first instruction sets A register (or is RET 'constant') */
+ break;
+ default:
+ /* make sure we dont leak kernel information to user */
+ PPC_LI(r_A, 0);
+ }
+}
+
+static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
+{
+ int i;
+
+ if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
+ PPC_ADDI(1, 1, BPF_PPC_STACKFRAME);
+ if (ctx->seen & SEEN_DATAREF) {
+ PPC_LD(0, 1, 16);
+ PPC_MTLR(0);
+ PPC_LD(r_D, 1, -(8*(32-r_D)));
+ PPC_LD(r_HL, 1, -(8*(32-r_HL)));
+ }
+ if (ctx->seen & SEEN_MEM) {
+ /* Restore any saved non-vol registers */
+ for (i = r_M; i < (r_M+16); i++) {
+ if (ctx->seen & (1 << (i-r_M)))
+ PPC_LD(i, 1, -(8*(32-i)));
+ }
+ }
+ }
+ /* The RETs have left a return value in R3. */
+
+ PPC_BLR();
+}
+
+#define CHOOSE_LOAD_FUNC(K, func) \
+ ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
+
+/* Assemble the body code between the prologue & epilogue. */
+static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
+ struct codegen_context *ctx,
+ unsigned int *addrs)
+{
+ const struct sock_filter *filter = fp->insns;
+ int flen = fp->len;
+ u8 *func;
+ unsigned int true_cond;
+ int i;
+
+ /* Start of epilogue code */
+ unsigned int exit_addr = addrs[flen];
+
+ for (i = 0; i < flen; i++) {
+ unsigned int K = filter[i].k;
+ u16 code = bpf_anc_helper(&filter[i]);
+
+ /*
+ * addrs[] maps a BPF bytecode address into a real offset from
+ * the start of the body code.
+ */
+ addrs[i] = ctx->idx * 4;
+
+ switch (code) {
+ /*** ALU ops ***/
+ case BPF_ALU | BPF_ADD | BPF_X: /* A += X; */
+ ctx->seen |= SEEN_XREG;
+ PPC_ADD(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_ADD | BPF_K: /* A += K; */
+ if (!K)
+ break;
+ PPC_ADDI(r_A, r_A, IMM_L(K));
+ if (K >= 32768)
+ PPC_ADDIS(r_A, r_A, IMM_HA(K));
+ break;
+ case BPF_ALU | BPF_SUB | BPF_X: /* A -= X; */
+ ctx->seen |= SEEN_XREG;
+ PPC_SUB(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_SUB | BPF_K: /* A -= K */
+ if (!K)
+ break;
+ PPC_ADDI(r_A, r_A, IMM_L(-K));
+ if (K >= 32768)
+ PPC_ADDIS(r_A, r_A, IMM_HA(-K));
+ break;
+ case BPF_ALU | BPF_MUL | BPF_X: /* A *= X; */
+ ctx->seen |= SEEN_XREG;
+ PPC_MUL(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_MUL | BPF_K: /* A *= K */
+ if (K < 32768)
+ PPC_MULI(r_A, r_A, K);
+ else {
+ PPC_LI32(r_scratch1, K);
+ PPC_MUL(r_A, r_A, r_scratch1);
+ }
+ break;
+ case BPF_ALU | BPF_MOD | BPF_X: /* A %= X; */
+ ctx->seen |= SEEN_XREG;
+ PPC_CMPWI(r_X, 0);
+ if (ctx->pc_ret0 != -1) {
+ PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
+ } else {
+ PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
+ PPC_LI(r_ret, 0);
+ PPC_JMP(exit_addr);
+ }
+ PPC_DIVWU(r_scratch1, r_A, r_X);
+ PPC_MUL(r_scratch1, r_X, r_scratch1);
+ PPC_SUB(r_A, r_A, r_scratch1);
+ break;
+ case BPF_ALU | BPF_MOD | BPF_K: /* A %= K; */
+ PPC_LI32(r_scratch2, K);
+ PPC_DIVWU(r_scratch1, r_A, r_scratch2);
+ PPC_MUL(r_scratch1, r_scratch2, r_scratch1);
+ PPC_SUB(r_A, r_A, r_scratch1);
+ break;
+ case BPF_ALU | BPF_DIV | BPF_X: /* A /= X; */
+ ctx->seen |= SEEN_XREG;
+ PPC_CMPWI(r_X, 0);
+ if (ctx->pc_ret0 != -1) {
+ PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
+ } else {
+ /*
+ * Exit, returning 0; first pass hits here
+ * (longer worst-case code size).
+ */
+ PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
+ PPC_LI(r_ret, 0);
+ PPC_JMP(exit_addr);
+ }
+ PPC_DIVWU(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_DIV | BPF_K: /* A /= K */
+ if (K == 1)
+ break;
+ PPC_LI32(r_scratch1, K);
+ PPC_DIVWU(r_A, r_A, r_scratch1);
+ break;
+ case BPF_ALU | BPF_AND | BPF_X:
+ ctx->seen |= SEEN_XREG;
+ PPC_AND(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_AND | BPF_K:
+ if (!IMM_H(K))
+ PPC_ANDI(r_A, r_A, K);
+ else {
+ PPC_LI32(r_scratch1, K);
+ PPC_AND(r_A, r_A, r_scratch1);
+ }
+ break;
+ case BPF_ALU | BPF_OR | BPF_X:
+ ctx->seen |= SEEN_XREG;
+ PPC_OR(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_OR | BPF_K:
+ if (IMM_L(K))
+ PPC_ORI(r_A, r_A, IMM_L(K));
+ if (K >= 65536)
+ PPC_ORIS(r_A, r_A, IMM_H(K));
+ break;
+ case BPF_ANC | SKF_AD_ALU_XOR_X:
+ case BPF_ALU | BPF_XOR | BPF_X: /* A ^= X */
+ ctx->seen |= SEEN_XREG;
+ PPC_XOR(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_XOR | BPF_K: /* A ^= K */
+ if (IMM_L(K))
+ PPC_XORI(r_A, r_A, IMM_L(K));
+ if (K >= 65536)
+ PPC_XORIS(r_A, r_A, IMM_H(K));
+ break;
+ case BPF_ALU | BPF_LSH | BPF_X: /* A <<= X; */
+ ctx->seen |= SEEN_XREG;
+ PPC_SLW(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_LSH | BPF_K:
+ if (K == 0)
+ break;
+ else
+ PPC_SLWI(r_A, r_A, K);
+ break;
+ case BPF_ALU | BPF_RSH | BPF_X: /* A >>= X; */
+ ctx->seen |= SEEN_XREG;
+ PPC_SRW(r_A, r_A, r_X);
+ break;
+ case BPF_ALU | BPF_RSH | BPF_K: /* A >>= K; */
+ if (K == 0)
+ break;
+ else
+ PPC_SRWI(r_A, r_A, K);
+ break;
+ case BPF_ALU | BPF_NEG:
+ PPC_NEG(r_A, r_A);
+ break;
+ case BPF_RET | BPF_K:
+ PPC_LI32(r_ret, K);
+ if (!K) {
+ if (ctx->pc_ret0 == -1)
+ ctx->pc_ret0 = i;
+ }
+ /*
+ * If this isn't the very last instruction, branch to
+ * the epilogue if we've stuff to clean up. Otherwise,
+ * if there's nothing to tidy, just return. If we /are/
+ * the last instruction, we're about to fall through to
+ * the epilogue to return.
+ */
+ if (i != flen - 1) {
+ /*
+ * Note: 'seen' is properly valid only on pass
+ * #2. Both parts of this conditional are the
+ * same instruction size though, meaning the
+ * first pass will still correctly determine the
+ * code size/addresses.
+ */
+ if (ctx->seen)
+ PPC_JMP(exit_addr);
+ else
+ PPC_BLR();
+ }
+ break;
+ case BPF_RET | BPF_A:
+ PPC_MR(r_ret, r_A);
+ if (i != flen - 1) {
+ if (ctx->seen)
+ PPC_JMP(exit_addr);
+ else
+ PPC_BLR();
+ }
+ break;
+ case BPF_MISC | BPF_TAX: /* X = A */
+ PPC_MR(r_X, r_A);
+ break;
+ case BPF_MISC | BPF_TXA: /* A = X */
+ ctx->seen |= SEEN_XREG;
+ PPC_MR(r_A, r_X);
+ break;
+
+ /*** Constant loads/M[] access ***/
+ case BPF_LD | BPF_IMM: /* A = K */
+ PPC_LI32(r_A, K);
+ break;
+ case BPF_LDX | BPF_IMM: /* X = K */
+ PPC_LI32(r_X, K);
+ break;
+ case BPF_LD | BPF_MEM: /* A = mem[K] */
+ PPC_MR(r_A, r_M + (K & 0xf));
+ ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
+ break;
+ case BPF_LDX | BPF_MEM: /* X = mem[K] */
+ PPC_MR(r_X, r_M + (K & 0xf));
+ ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
+ break;
+ case BPF_ST: /* mem[K] = A */
+ PPC_MR(r_M + (K & 0xf), r_A);
+ ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
+ break;
+ case BPF_STX: /* mem[K] = X */
+ PPC_MR(r_M + (K & 0xf), r_X);
+ ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf));
+ break;
+ case BPF_LD | BPF_W | BPF_LEN: /* A = skb->len; */
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
+ PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len));
+ break;
+ case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */
+ PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len));
+ break;
+
+ /*** Ancillary info loads ***/
+ case BPF_ANC | SKF_AD_PROTOCOL: /* A = ntohs(skb->protocol); */
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
+ protocol) != 2);
+ PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff,
+ protocol));
+ break;
+ case BPF_ANC | SKF_AD_IFINDEX:
+ PPC_LD_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
+ dev));
+ PPC_CMPDI(r_scratch1, 0);
+ if (ctx->pc_ret0 != -1) {
+ PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
+ } else {
+ /* Exit, returning 0; first pass hits here. */
+ PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
+ PPC_LI(r_ret, 0);
+ PPC_JMP(exit_addr);
+ }
+ BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
+ ifindex) != 4);
+ PPC_LWZ_OFFS(r_A, r_scratch1,
+ offsetof(struct net_device, ifindex));
+ break;
+ case BPF_ANC | SKF_AD_MARK:
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
+ PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
+ mark));
+ break;
+ case BPF_ANC | SKF_AD_RXHASH:
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4);
+ PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
+ hash));
+ break;
+ case BPF_ANC | SKF_AD_VLAN_TAG:
+ case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT:
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2);
+ BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000);
+
+ PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
+ vlan_tci));
+ if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) {
+ PPC_ANDI(r_A, r_A, ~VLAN_TAG_PRESENT);
+ } else {
+ PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT);
+ PPC_SRWI(r_A, r_A, 12);
+ }
+ break;
+ case BPF_ANC | SKF_AD_QUEUE:
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
+ queue_mapping) != 2);
+ PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
+ queue_mapping));
+ break;
+ case BPF_ANC | SKF_AD_CPU:
+#ifdef CONFIG_SMP
+ /*
+ * PACA ptr is r13:
+ * raw_smp_processor_id() = local_paca->paca_index
+ */
+ BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct,
+ paca_index) != 2);
+ PPC_LHZ_OFFS(r_A, 13,
+ offsetof(struct paca_struct, paca_index));
+#else
+ PPC_LI(r_A, 0);
+#endif
+ break;
+
+ /*** Absolute loads from packet header/data ***/
+ case BPF_LD | BPF_W | BPF_ABS:
+ func = CHOOSE_LOAD_FUNC(K, sk_load_word);
+ goto common_load;
+ case BPF_LD | BPF_H | BPF_ABS:
+ func = CHOOSE_LOAD_FUNC(K, sk_load_half);
+ goto common_load;
+ case BPF_LD | BPF_B | BPF_ABS:
+ func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
+ common_load:
+ /* Load from [K]. */
+ ctx->seen |= SEEN_DATAREF;
+ PPC_LI64(r_scratch1, func);
+ PPC_MTLR(r_scratch1);
+ PPC_LI32(r_addr, K);
+ PPC_BLRL();
+ /*
+ * Helper returns 'lt' condition on error, and an
+ * appropriate return value in r3
+ */
+ PPC_BCC(COND_LT, exit_addr);
+ break;
+
+ /*** Indirect loads from packet header/data ***/
+ case BPF_LD | BPF_W | BPF_IND:
+ func = sk_load_word;
+ goto common_load_ind;
+ case BPF_LD | BPF_H | BPF_IND:
+ func = sk_load_half;
+ goto common_load_ind;
+ case BPF_LD | BPF_B | BPF_IND:
+ func = sk_load_byte;
+ common_load_ind:
+ /*
+ * Load from [X + K]. Negative offsets are tested for
+ * in the helper functions.
+ */
+ ctx->seen |= SEEN_DATAREF | SEEN_XREG;
+ PPC_LI64(r_scratch1, func);
+ PPC_MTLR(r_scratch1);
+ PPC_ADDI(r_addr, r_X, IMM_L(K));
+ if (K >= 32768)
+ PPC_ADDIS(r_addr, r_addr, IMM_HA(K));
+ PPC_BLRL();
+ /* If error, cr0.LT set */
+ PPC_BCC(COND_LT, exit_addr);
+ break;
+
+ case BPF_LDX | BPF_B | BPF_MSH:
+ func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
+ goto common_load;
+ break;
+
+ /*** Jump and branches ***/
+ case BPF_JMP | BPF_JA:
+ if (K != 0)
+ PPC_JMP(addrs[i + 1 + K]);
+ break;
+
+ case BPF_JMP | BPF_JGT | BPF_K:
+ case BPF_JMP | BPF_JGT | BPF_X:
+ true_cond = COND_GT;
+ goto cond_branch;
+ case BPF_JMP | BPF_JGE | BPF_K:
+ case BPF_JMP | BPF_JGE | BPF_X:
+ true_cond = COND_GE;
+ goto cond_branch;
+ case BPF_JMP | BPF_JEQ | BPF_K:
+ case BPF_JMP | BPF_JEQ | BPF_X:
+ true_cond = COND_EQ;
+ goto cond_branch;
+ case BPF_JMP | BPF_JSET | BPF_K:
+ case BPF_JMP | BPF_JSET | BPF_X:
+ true_cond = COND_NE;
+ /* Fall through */
+ cond_branch:
+ /* same targets, can avoid doing the test :) */
+ if (filter[i].jt == filter[i].jf) {
+ if (filter[i].jt > 0)
+ PPC_JMP(addrs[i + 1 + filter[i].jt]);
+ break;
+ }
+
+ switch (code) {
+ case BPF_JMP | BPF_JGT | BPF_X:
+ case BPF_JMP | BPF_JGE | BPF_X:
+ case BPF_JMP | BPF_JEQ | BPF_X:
+ ctx->seen |= SEEN_XREG;
+ PPC_CMPLW(r_A, r_X);
+ break;
+ case BPF_JMP | BPF_JSET | BPF_X:
+ ctx->seen |= SEEN_XREG;
+ PPC_AND_DOT(r_scratch1, r_A, r_X);
+ break;
+ case BPF_JMP | BPF_JEQ | BPF_K:
+ case BPF_JMP | BPF_JGT | BPF_K:
+ case BPF_JMP | BPF_JGE | BPF_K:
+ if (K < 32768)
+ PPC_CMPLWI(r_A, K);
+ else {
+ PPC_LI32(r_scratch1, K);
+ PPC_CMPLW(r_A, r_scratch1);
+ }
+ break;
+ case BPF_JMP | BPF_JSET | BPF_K:
+ if (K < 32768)
+ /* PPC_ANDI is /only/ dot-form */
+ PPC_ANDI(r_scratch1, r_A, K);
+ else {
+ PPC_LI32(r_scratch1, K);
+ PPC_AND_DOT(r_scratch1, r_A,
+ r_scratch1);
+ }
+ break;
+ }
+ /* Sometimes branches are constructed "backward", with
+ * the false path being the branch and true path being
+ * a fallthrough to the next instruction.
+ */
+ if (filter[i].jt == 0)
+ /* Swap the sense of the branch */
+ PPC_BCC(true_cond ^ COND_CMP_TRUE,
+ addrs[i + 1 + filter[i].jf]);
+ else {
+ PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]);
+ if (filter[i].jf != 0)
+ PPC_JMP(addrs[i + 1 + filter[i].jf]);
+ }
+ break;
+ default:
+ /* The filter contains something cruel & unusual.
+ * We don't handle it, but also there shouldn't be
+ * anything missing from our list.
+ */
+ if (printk_ratelimit())
+ pr_err("BPF filter opcode %04x (@%d) unsupported\n",
+ filter[i].code, i);
+ return -ENOTSUPP;
+ }
+
+ }
+ /* Set end-of-body-code address for exit. */
+ addrs[i] = ctx->idx * 4;
+
+ return 0;
+}
+
+void bpf_jit_compile(struct sk_filter *fp)
+{
+ unsigned int proglen;
+ unsigned int alloclen;
+ u32 *image = NULL;
+ u32 *code_base;
+ unsigned int *addrs;
+ struct codegen_context cgctx;
+ int pass;
+ int flen = fp->len;
+
+ if (!bpf_jit_enable)
+ return;
+
+ addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL);
+ if (addrs == NULL)
+ return;
+
+ /*
+ * There are multiple assembly passes as the generated code will change
+ * size as it settles down, figuring out the max branch offsets/exit
+ * paths required.
+ *
+ * The range of standard conditional branches is +/- 32Kbytes. Since
+ * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to
+ * finish with 8 bytes/instruction. Not feasible, so long jumps are
+ * used, distinct from short branches.
+ *
+ * Current:
+ *
+ * For now, both branch types assemble to 2 words (short branches padded
+ * with a NOP); this is less efficient, but assembly will always complete
+ * after exactly 3 passes:
+ *
+ * First pass: No code buffer; Program is "faux-generated" -- no code
+ * emitted but maximum size of output determined (and addrs[] filled
+ * in). Also, we note whether we use M[], whether we use skb data, etc.
+ * All generation choices assumed to be 'worst-case', e.g. branches all
+ * far (2 instructions), return path code reduction not available, etc.
+ *
+ * Second pass: Code buffer allocated with size determined previously.
+ * Prologue generated to support features we have seen used. Exit paths
+ * determined and addrs[] is filled in again, as code may be slightly
+ * smaller as a result.
+ *
+ * Third pass: Code generated 'for real', and branch destinations
+ * determined from now-accurate addrs[] map.
+ *
+ * Ideal:
+ *
+ * If we optimise this, near branches will be shorter. On the
+ * first assembly pass, we should err on the side of caution and
+ * generate the biggest code. On subsequent passes, branches will be
+ * generated short or long and code size will reduce. With smaller
+ * code, more branches may fall into the short category, and code will
+ * reduce more.
+ *
+ * Finally, if we see one pass generate code the same size as the
+ * previous pass we have converged and should now generate code for
+ * real. Allocating at the end will also save the memory that would
+ * otherwise be wasted by the (small) current code shrinkage.
+ * Preferably, we should do a small number of passes (e.g. 5) and if we
+ * haven't converged by then, get impatient and force code to generate
+ * as-is, even if the odd branch would be left long. The chances of a
+ * long jump are tiny with all but the most enormous of BPF filter
+ * inputs, so we should usually converge on the third pass.
+ */
+
+ cgctx.idx = 0;
+ cgctx.seen = 0;
+ cgctx.pc_ret0 = -1;
+ /* Scouting faux-generate pass 0 */
+ if (bpf_jit_build_body(fp, 0, &cgctx, addrs))
+ /* We hit something illegal or unsupported. */
+ goto out;
+
+ /*
+ * Pretend to build prologue, given the features we've seen. This will
+ * update ctgtx.idx as it pretends to output instructions, then we can
+ * calculate total size from idx.
+ */
+ bpf_jit_build_prologue(fp, 0, &cgctx);
+ bpf_jit_build_epilogue(0, &cgctx);
+
+ proglen = cgctx.idx * 4;
+ alloclen = proglen + FUNCTION_DESCR_SIZE;
+ image = module_alloc(alloclen);
+ if (!image)
+ goto out;
+
+ code_base = image + (FUNCTION_DESCR_SIZE/4);
+
+ /* Code generation passes 1-2 */
+ for (pass = 1; pass < 3; pass++) {
+ /* Now build the prologue, body code & epilogue for real. */
+ cgctx.idx = 0;
+ bpf_jit_build_prologue(fp, code_base, &cgctx);
+ bpf_jit_build_body(fp, code_base, &cgctx, addrs);
+ bpf_jit_build_epilogue(code_base, &cgctx);
+
+ if (bpf_jit_enable > 1)
+ pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass,
+ proglen - (cgctx.idx * 4), cgctx.seen);
+ }
+
+ if (bpf_jit_enable > 1)
+ /* Note that we output the base address of the code_base
+ * rather than image, since opcodes are in code_base.
+ */
+ bpf_jit_dump(flen, proglen, pass, code_base);
+
+ if (image) {
+ bpf_flush_icache(code_base, code_base + (proglen/4));
+ /* Function descriptor nastiness: Address + TOC */
+ ((u64 *)image)[0] = (u64)code_base;
+ ((u64 *)image)[1] = local_paca->kernel_toc;
+ fp->bpf_func = (void *)image;
+ fp->jited = 1;
+ }
+out:
+ kfree(addrs);
+ return;
+}
+
+void bpf_jit_free(struct sk_filter *fp)
+{
+ if (fp->jited)
+ module_free(NULL, fp->bpf_func);
+ kfree(fp);
+}
generated by cgit v1.2.3-70-g09d2 (git 2.46.0) at 2025-11-04 13:06:36 +0000