[PATCHv4 bpf-next 3/6] bpf: Use given function address for trampoline ip arg

[Jiri Olsa <jolsa@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 arch/x86/net/bpf_jit_comp.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index ae89f4143eb4..d4a6183197e9 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/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);
 	}
 
-- 
2.37.3