Re: [PATCH 1/3] perf/bpf: Remove prologue generation

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Feb 10, 2022 at 04:18:10PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sun, Jan 23, 2022 at 11:19:30PM +0100, Jiri Olsa escreveu:
> > Removing code for ebpf program prologue generation.
> > 
> > The prologue code was used to get data for extra arguments specified
> > in program section name, like:
> > 
> >   SEC("lock_page=__lock_page page->flags")
> >   int lock_page(struct pt_regs *ctx, int err, unsigned long flags)
> >   {
> >          return 1;
> >   }
> > 
> > This code is using deprecated libbpf API and blocks its removal.
> > 
> > This feature was not documented and broken for some time without
> > anyone complaining, also original authors are not responding,
> > so I'm removing it.
> 
> So, the example below breaks, how hard would be to move the deprecated
> APIs to perf like was done in some other cases?
> 
> - Arnaldo
> 
> Before:
> 
> [root@quaco perf]# cat tools/perf/examples/bpf/5sec.c 
> // SPDX-License-Identifier: GPL-2.0
> /*
>     Description:
> 
>     . Disable strace like syscall tracing (--no-syscalls), or try tracing
>       just some (-e *sleep).
> 
>     . Attach a filter function to a kernel function, returning when it should
>       be considered, i.e. appear on the output.
> 
>     . Run it system wide, so that any sleep of >= 5 seconds and < than 6
>       seconds gets caught.
> 
>     . Ask for callgraphs using DWARF info, so that userspace can be unwound
> 
>     . While this is running, run something like "sleep 5s".
> 
>     . If we decide to add tv_nsec as well, then it becomes:
> 
>       int probe(hrtimer_nanosleep, rqtp->tv_sec rqtp->tv_nsec)(void *ctx, int err, long sec, long nsec)
> 
>       I.e. add where it comes from (rqtp->tv_nsec) and where it will be
>       accessible in the function body (nsec)
> 
>     # perf trace --no-syscalls -e tools/perf/examples/bpf/5sec.c/call-graph=dwarf/
>          0.000 perf_bpf_probe:func:(ffffffff9811b5f0) tv_sec=5
>                                            hrtimer_nanosleep ([kernel.kallsyms])
>                                            __x64_sys_nanosleep ([kernel.kallsyms])
>                                            do_syscall_64 ([kernel.kallsyms])
>                                            entry_SYSCALL_64 ([kernel.kallsyms])
>                                            __GI___nanosleep (/usr/lib64/libc-2.26.so)
>                                            rpl_nanosleep (/usr/bin/sleep)
>                                            xnanosleep (/usr/bin/sleep)
>                                            main (/usr/bin/sleep)
>                                            __libc_start_main (/usr/lib64/libc-2.26.so)
>                                            _start (/usr/bin/sleep)
>     ^C#
> 
>    Copyright (C) 2018 Red Hat, Inc., Arnaldo Carvalho de Melo <acme@redhat.com>
> */
> 
> #include <bpf.h>
> 
> #define NSEC_PER_SEC	1000000000L
> 
> int probe(hrtimer_nanosleep, rqtp)(void *ctx, int err, long long sec)
> {
> 	return sec / NSEC_PER_SEC == 5ULL;
> }

that sucks ;-) I'll check if we can re-implement as we discussed earlier,
however below is workaround how to do it without the prologue support

jirka


---
diff --git a/tools/perf/examples/bpf/5sec.c b/tools/perf/examples/bpf/5sec.c
index e6b6181c6dc6..734d39debdb8 100644
--- a/tools/perf/examples/bpf/5sec.c
+++ b/tools/perf/examples/bpf/5sec.c
@@ -43,9 +43,17 @@
 
 #define NSEC_PER_SEC	1000000000L
 
-int probe(hrtimer_nanosleep, rqtp)(void *ctx, int err, long long sec)
+struct pt_regs {
+        long di;
+};
+
+SEC("function=hrtimer_nanosleep")
+int krava(struct pt_regs *ctx)
 {
-	return sec / NSEC_PER_SEC == 5ULL;
+	unsigned long arg;
+
+	probe_read_kernel(&arg, sizeof(arg), __builtin_preserve_access_index(&ctx->di));
+	return arg / NSEC_PER_SEC == 5ULL;
 }
 
 license(GPL);
diff --git a/tools/perf/include/bpf/bpf.h b/tools/perf/include/bpf/bpf.h
index b422aeef5339..b7d6d2fc8342 100644
--- a/tools/perf/include/bpf/bpf.h
+++ b/tools/perf/include/bpf/bpf.h
@@ -64,6 +64,7 @@ int _version SEC("version") = LINUX_VERSION_CODE;
 
 static int (*probe_read)(void *dst, int size, const void *unsafe_addr) = (void *)BPF_FUNC_probe_read;
 static int (*probe_read_str)(void *dst, int size, const void *unsafe_addr) = (void *)BPF_FUNC_probe_read_str;
+static long (*probe_read_kernel)(void *dst, __u32 size, const void *unsafe_ptr) = (void *) BPF_FUNC_probe_read_kernel;
 
 static int (*perf_event_output)(void *, struct bpf_map *, int, void *, unsigned long) = (void *)BPF_FUNC_perf_event_output;
 
diff --git a/tools/perf/util/llvm-utils.c b/tools/perf/util/llvm-utils.c
index 96c8ef60f4f8..9274a3373847 100644
--- a/tools/perf/util/llvm-utils.c
+++ b/tools/perf/util/llvm-utils.c
@@ -25,7 +25,7 @@
 		"$CLANG_OPTIONS $PERF_BPF_INC_OPTIONS $KERNEL_INC_OPTIONS " \
 		"-Wno-unused-value -Wno-pointer-sign "		\
 		"-working-directory $WORKING_DIR "		\
-		"-c \"$CLANG_SOURCE\" -target bpf $CLANG_EMIT_LLVM -O2 -o - $LLVM_OPTIONS_PIPE"
+		"-g -c \"$CLANG_SOURCE\" -target bpf $CLANG_EMIT_LLVM -O2 -o - $LLVM_OPTIONS_PIPE"
 
 struct llvm_param llvm_param = {
 	.clang_path = "clang",