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From: Jiri Olsa <jolsa@redhat.com>
To: Yonghong Song <yhs@fb.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>, Daniel Xu <dxu@dxuuu.xyz>,
	Viktor Malik <vmalik@redhat.com>
Subject: Re: [PATCH 10/19] bpf: Allow to store caller's ip as argument
Date: Mon, 7 Jun 2021 20:15:33 +0200	[thread overview]
Message-ID: <YL5iRT59TpOiUWe3@krava> (raw)
In-Reply-To: <03777e58-a2b0-83b5-959f-3ae4afadb191@fb.com>

On Sun, Jun 06, 2021 at 08:21:51PM -0700, Yonghong Song wrote:
> 
> 
> On 6/5/21 4:10 AM, Jiri Olsa wrote:
> > When we will have multiple functions attached to trampoline
> > we need to propagate the function's address to the bpf program.
> > 
> > Adding new BPF_TRAMP_F_IP_ARG flag to arch_prepare_bpf_trampoline
> > function that will store origin caller's address before function's
> > arguments.
> > 
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >   arch/x86/net/bpf_jit_comp.c | 18 ++++++++++++++----
> >   include/linux/bpf.h         |  5 +++++
> >   2 files changed, 19 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index b77e6bd78354..d2425c18272a 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -1951,7 +1951,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> >   				void *orig_call)
> >   {
> >   	int ret, i, cnt = 0, nr_args = m->nr_args;
> > -	int stack_size = nr_args * 8;
> > +	int stack_size = nr_args * 8, ip_arg = 0;
> >   	struct bpf_tramp_progs *fentry = &tprogs[BPF_TRAMP_FENTRY];
> >   	struct bpf_tramp_progs *fexit = &tprogs[BPF_TRAMP_FEXIT];
> >   	struct bpf_tramp_progs *fmod_ret = &tprogs[BPF_TRAMP_MODIFY_RETURN];
> > @@ -1975,6 +1975,9 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> >   		 */
> >   		orig_call += X86_PATCH_SIZE;
> > +	if (flags & BPF_TRAMP_F_IP_ARG)
> > +		stack_size += 8;
> > +
> >   	prog = image;
> >   	EMIT1(0x55);		 /* push rbp */
> > @@ -1982,7 +1985,14 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> >   	EMIT4(0x48, 0x83, 0xEC, stack_size); /* sub rsp, stack_size */
> >   	EMIT1(0x53);		 /* push rbx */
> > -	save_regs(m, &prog, nr_args, stack_size);
> > +	if (flags & BPF_TRAMP_F_IP_ARG) {
> > +		emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
> > +		EMIT4(0x48, 0x83, 0xe8, X86_PATCH_SIZE); /* sub $X86_PATCH_SIZE,%rax*/
> 
> Could you explain what the above EMIT4 is for? I am not quite familiar with
> this piece of code and hence the question. Some comments here
> should help too.

it's there to generate the 'sub $X86_PATCH_SIZE,%rax' instruction
to get the real IP address of the traced function, and it's stored
to stack on the next line

I'll put more comments in there

jirka

> 
> > +		emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -stack_size);
> > +		ip_arg = 8;
> > +	}
> > +
> > +	save_regs(m, &prog, nr_args, stack_size - ip_arg);
> >   	if (flags & BPF_TRAMP_F_CALL_ORIG) {
> >   		/* arg1: mov rdi, im */
> > @@ -2011,7 +2021,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> >   	}
> >   	if (flags & BPF_TRAMP_F_CALL_ORIG) {
> > -		restore_regs(m, &prog, nr_args, stack_size);
> > +		restore_regs(m, &prog, nr_args, stack_size - ip_arg);
> >   		if (flags & BPF_TRAMP_F_ORIG_STACK) {
> >   			emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
> > @@ -2052,7 +2062,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> >   		}
> >   	if (flags & BPF_TRAMP_F_RESTORE_REGS)
> > -		restore_regs(m, &prog, nr_args, stack_size);
> > +		restore_regs(m, &prog, nr_args, stack_size - ip_arg);
> >   	/* This needs to be done regardless. If there were fmod_ret programs,
> >   	 * the return value is only updated on the stack and still needs to be
> [...]
> 


  reply	other threads:[~2021-06-07 18:15 UTC|newest]

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-05 11:10 [RFCv3 00/19] x86/ftrace/bpf: Add batch support for direct/tracing attach Jiri Olsa
2021-06-05 11:10 ` [PATCH 01/19] x86/ftrace: Remove extra orig rax move Jiri Olsa
2021-06-05 11:10 ` [PATCH 02/19] x86/ftrace: Remove fault protection code in prepare_ftrace_return Jiri Olsa
2021-06-05 11:10 ` [PATCH 03/19] x86/ftrace: Make function graph use ftrace directly Jiri Olsa
2021-06-08 18:35   ` Andrii Nakryiko
2021-06-08 18:51     ` Jiri Olsa
2021-06-08 19:11       ` Steven Rostedt
2021-06-05 11:10 ` [PATCH 04/19] tracing: Add trampoline/graph selftest Jiri Olsa
2021-06-05 11:10 ` [PATCH 05/19] ftrace: Add ftrace_add_rec_direct function Jiri Olsa
2021-06-05 11:10 ` [PATCH 06/19] ftrace: Add multi direct register/unregister interface Jiri Olsa
2021-06-05 11:10 ` [PATCH 07/19] ftrace: Add multi direct modify interface Jiri Olsa
2021-06-05 11:10 ` [PATCH 08/19] ftrace/samples: Add multi direct interface test module Jiri Olsa
2021-06-05 11:10 ` [PATCH 09/19] bpf, x64: Allow to use caller address from stack Jiri Olsa
2021-06-07  3:07   ` Yonghong Song
2021-06-07 18:13     ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 10/19] bpf: Allow to store caller's ip as argument Jiri Olsa
2021-06-07  3:21   ` Yonghong Song
2021-06-07 18:15     ` Jiri Olsa [this message]
2021-06-08 18:49   ` Andrii Nakryiko
2021-06-08 20:58     ` Jiri Olsa
2021-06-08 21:02       ` Andrii Nakryiko
2021-06-08 21:11         ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 11/19] bpf: Add support to load multi func tracing program Jiri Olsa
2021-06-07  3:56   ` Yonghong Song
2021-06-07 18:18     ` Jiri Olsa
2021-06-07 19:35       ` Yonghong Song
2021-06-05 11:10 ` [PATCH 12/19] bpf: Add bpf_trampoline_alloc function Jiri Olsa
2021-06-05 11:10 ` [PATCH 13/19] bpf: Add support to link multi func tracing program Jiri Olsa
2021-06-07  5:36   ` Yonghong Song
2021-06-07 18:25     ` Jiri Olsa
2021-06-07 19:39       ` Yonghong Song
2021-06-08 15:42   ` Alexei Starovoitov
2021-06-08 18:17     ` Jiri Olsa
2021-06-08 18:49       ` Alexei Starovoitov
2021-06-08 21:07         ` Jiri Olsa
2021-06-08 23:05           ` Alexei Starovoitov
2021-06-09  5:08             ` Andrii Nakryiko
2021-06-09 13:42               ` Jiri Olsa
2021-06-09 13:33             ` Jiri Olsa
2021-06-09  5:18   ` Andrii Nakryiko
2021-06-09 13:53     ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 14/19] libbpf: Add btf__find_by_pattern_kind function Jiri Olsa
2021-06-09  5:29   ` Andrii Nakryiko
2021-06-09 13:59     ` Jiri Olsa
2021-06-09 14:19       ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 15/19] libbpf: Add support to link multi func tracing program Jiri Olsa
2021-06-07  5:49   ` Yonghong Song
2021-06-07 18:28     ` Jiri Olsa
2021-06-07 19:42       ` Yonghong Song
2021-06-07 20:11         ` Jiri Olsa
2021-06-09  5:34   ` Andrii Nakryiko
2021-06-09 14:17     ` Jiri Olsa
2021-06-10 17:05       ` Andrii Nakryiko
2021-06-10 20:35         ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 16/19] selftests/bpf: Add fentry multi func test Jiri Olsa
2021-06-07  6:06   ` Yonghong Song
2021-06-07 18:42     ` Jiri Olsa
2021-06-09  5:40   ` Andrii Nakryiko
2021-06-09 14:29     ` Jiri Olsa
2021-06-10 17:00       ` Andrii Nakryiko
2021-06-10 20:28         ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 17/19] selftests/bpf: Add fexit " Jiri Olsa
2021-06-05 11:10 ` [PATCH 18/19] selftests/bpf: Add fentry/fexit " Jiri Olsa
2021-06-09  5:41   ` Andrii Nakryiko
2021-06-09 14:29     ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 19/19] selftests/bpf: Temporary fix for fentry_fexit_multi_test Jiri Olsa
2021-06-17 20:29 ` [RFCv3 00/19] x86/ftrace/bpf: Add batch support for direct/tracing attach Andrii Nakryiko
2021-06-19  8:33   ` Jiri Olsa
2021-06-19 16:19     ` Yonghong Song
2021-06-19 17:09       ` Jiri Olsa
2021-06-20 16:56         ` Yonghong Song
2021-06-20 17:47           ` Alexei Starovoitov
2021-06-21  6:46             ` Andrii Nakryiko
2021-06-21  6:50     ` Andrii Nakryiko
2021-07-06 20:26       ` Andrii Nakryiko
2021-07-07 15:19         ` Jiri Olsa

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