bpf: Use given function address for trampoline ip arg

Using function address given at the generation time as the trampoline
ip argument. This way we get directly the function address that we
need, so we don't need to:
  - read the ip from the stack
  - subtract X86_PATCH_SIZE
  - subtract ENDBR_INSN_SIZE if CONFIG_X86_KERNEL_IBT is enabled
    which is not even implemented yet ;-)
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220926153340.1621984-4-jolsa@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

arch/x86/net/bpf_jit_comp.c

@@ -662,7 +662,7 @@ static void emit_mov_imm64(u8 **pprog, u32 dst_reg,
 		 */
 		emit_mov_imm32(&prog, false, dst_reg, imm32_lo);
 	} else {
-		/* movabsq %rax, imm64 */
+		/* movabsq rax, imm64 */
 		EMIT2(add_1mod(0x48, dst_reg), add_1reg(0xB8, dst_reg));
 		EMIT(imm32_lo, 4);
 		EMIT(imm32_hi, 4);
@@ -2039,13 +2039,14 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
 int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image_end,
 				const struct btf_func_model *m, u32 flags,
 				struct bpf_tramp_links *tlinks,
-				void *orig_call)
+				void *func_addr)
 {
 	int ret, i, nr_args = m->nr_args, extra_nregs = 0;
 	int regs_off, ip_off, args_off, stack_size = nr_args * 8, run_ctx_off;
 	struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
 	struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT];
 	struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
+	void *orig_call = func_addr;
 	u8 **branches = NULL;
 	u8 *prog;
 	bool save_ret;
@@ -2126,12 +2127,10 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
 
 	if (flags & BPF_TRAMP_F_IP_ARG) {
 		/* Store IP address of the traced function:
-		 * mov rax, QWORD PTR [rbp + 8]
-		 * sub rax, X86_PATCH_SIZE
+		 * movabsq rax, func_addr
 		 * mov QWORD PTR [rbp - ip_off], rax
 		 */
-		emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
-		EMIT4(0x48, 0x83, 0xe8, X86_PATCH_SIZE);
+		emit_mov_imm64(&prog, BPF_REG_0, (long) func_addr >> 32, (u32) (long) func_addr);
 		emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -ip_off);
 	}