LoongArch: BPF: Inline bpf_get_current_task/_btf() helpers

The pointer to task_struct is always available in the $tp register, so
the calls to bpf_get_current_task() and bpf_get_current_task_btf() can
be inlined into a single move instruction.

(1) Here is the sample test.c:

  #include <linux/bpf.h>
  #include <bpf/bpf_helpers.h>

  SEC("raw_tp/sys_enter")
  long test_task(void *ctx)
  {
	  return (long)bpf_get_current_task();
  }
  char _license[] SEC("license") = "GPL";

(2) Here are the test steps:

  sudo yum install libbpf-devel kernel-devel bpftool
  clang -target bpf -O2 -c test.c -o test.o
  sudo sysctl -w net.core.bpf_jit_enable=1
  sudo bpftool prog show name test_task
  sudo rm -f /sys/fs/bpf/test_task
  sudo bpftool prog load test.o /sys/fs/bpf/test_task
  ID=$(sudo bpftool prog show pinned /sys/fs/bpf/test_task | grep -oE '^[0-9]+')
  sudo bpftool prog dump jited id $ID

(3) Here are the test results:

Before: 6 instructions

  ...
  64:	lu12i.w	$t1, 1093
  68:	ori	$t1, $t1, 3320
  6c:	lu32i.d	$t1, 0
  70:	lu52i.d	$t1, $t1, -1792
  74:	jirl	$ra, $t1, 0
  78:	move	$a5, $a0
  ...

After: 1 instruction

  ...
  64:	move	$a5, $tp
  ...

This is similar with commit 2bb138cb20a6 ("bpf, arm64: Inline
bpf_get_current_task/_btf() helpers").

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 99294f93091489d67657b212f03b444282a206a3..66e8c1d2d5cb5c5e7bf259ea6ca318a8a646e1c7 100644 (file)
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1161,6 +1161,13 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
 
        /* function call */
        case BPF_JMP | BPF_CALL:
+               /* Implement helper call to bpf_get_current_task/_btf() inline */
+               if (insn->src_reg == 0 && (insn->imm == BPF_FUNC_get_current_task ||
+                                          insn->imm == BPF_FUNC_get_current_task_btf)) {
+                       move_reg(ctx, regmap[BPF_REG_0], LOONGARCH_GPR_TP);
+                       break;
+               }
+
                ret = bpf_jit_get_func_addr(ctx->prog, insn, extra_pass,
                                            &func_addr, &func_addr_fixed);
                if (ret < 0)
@@ -2381,3 +2388,14 @@ bool bpf_jit_supports_subprog_tailcalls(void)
 {
        return true;
 }
+
+bool bpf_jit_inlines_helper_call(s32 imm)
+{
+       switch (imm) {
+       case BPF_FUNC_get_current_task:
+       case BPF_FUNC_get_current_task_btf:
+               return true;
+       default:
+               return false;
+       }
+}