Re: [PATCH bpf-next 2/2] perf: stop using deprecated bpf__object_next() API

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Wed, Jan 05, 2022 at 02:49:03PM +0100, Jiri Olsa escreveu:
> On Tue, Jan 04, 2022 at 03:40:49PM +0100, Jiri Olsa wrote:
> > On Wed, Dec 29, 2021 at 11:01:35AM -0800, Christy Lee wrote:
> > 
> > SNIP
> > 
> > > > >
> > > > > I don't use it, I just know it's there.. that's why I asked ;-)
> > > > >
> > > > > it's possible to specify bpf program on the perf command line
> > > > > to be attached to event, like:
> > > > >
> > > > >       # cat tools/perf/examples/bpf/hello.c
> > > > >       #include <stdio.h>
> > > > >
> > > > >       int syscall_enter(openat)(void *args)
> > > > >       {
> > > > >               puts("Hello, world\n");
> > > > >               return 0;
> > > > >       }
> > > > >
> > > > >       license(GPL);
> > > > >       #
> > > > >       # perf trace -e openat,tools/perf/examples/bpf/hello.c cat /etc/passwd > /dev/null
> > > > >          0.016 (         ): __bpf_stdout__:Hello, world
> > > > >          0.018 ( 0.010 ms): cat/9079 openat(dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC) = 3
> > > > >          0.057 (         ): __bpf_stdout__:Hello, world
> > > > >          0.059 ( 0.011 ms): cat/9079 openat(dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC) = 3
> > > > >          0.417 (         ): __bpf_stdout__:Hello, world
> > > > >          0.419 ( 0.009 ms): cat/9079 openat(dfd: CWD, filename: /etc/passwd) = 3
> > > > >       #
> > > > >
> > > > > I took that example from commit message
> > > [...]
> > > 
> > > I found the original commit aa3abf30bb28addcf593578d37447d42e3f65fc3
> > > that included a test case, but I'm having trouble reproducing it due to syntax
> > > error. I am running this on bpf-next master without my patches.
> > > 
> > > I ran 'perf test -v LLVM' and used it's output to generate a script for
> > > compiling the perf test object:
> > > 
> > > --------------------------------------------------
> > > $ cat ~/bin/hello-ebpf
> > > INPUT_FILE=/tmp/test.c
> > > OUTPUT_FILE=/tmp/test.o
> > > 
> > > export KBUILD_DIR=/lib/modules/5.12.0-0_fbk2_3390_g7ecb4ac46d7f/build
> > > export NR_CPUS=56
> > > export LINUX_VERSION_CODE=0x50c00
> > > export CLANG_EXEC=/data/users/christylee/devtools/llvm/latest/bin/clang
> > > export CLANG_OPTIONS=-xc
> > > export KERNEL_INC_OPTIONS="-nostdinc -isystem
> > > /data/users/christylee/devtools/gcc/10.3.0/lib/gcc/x86_64-pc-linux-gnu/10.3.0/include
> > > -I./arch/\
> > > x86/include -I./arch/x86/include/generated  -I./include
> > > -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi
> > > -I./include/uapi -I./in\
> > > clude/generated/uapi -include ./include/linux/compiler-version.h
> > > -include ./include/linux/kconfig.h"
> > > export PERF_BPF_INC_OPTIONS=-I/home/christylee/lib/perf/include/bpf
> > > export WORKING_DIR=/lib/modules/5.12.0-0_fbk2_3390_g7ecb4ac46d7f/build
> > > export CLANG_SOURCE=-
> > > 
> > > rm -f $OUTPUT_FILE
> > > cat $INPUT_FILE |
> > > /data/users/christylee/devtools/llvm/latest/bin/clang -D__KERNEL__
> > > -D__NR_CPUS__=56 -DLINUX_VERSION_CODE=0x50c00 -xc  -I/ho\
> > > me/christylee/lib/perf/include/bpf  -nostdinc -isystem
> > > /data/users/christylee/devtools/gcc/10.3.0/lib/gcc/x86_64-pc-linux-gnu/10.3.0/include
> > > \
> > > -I./arch/x86/include -I./arch/x86/include/generated  -I./include
> > > -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi
> > > -I./include/ua\
> > > pi -I./include/generated/uapi -include
> > > ./include/linux/compiler-version.h -include ./include/linux/kconfig.h
> > > -Wno-unused-value -Wno-pointer-\
> > > sign -working-directory
> > > /lib/modules/5.12.0-0_fbk2_3390_g7ecb4ac46d7f/build -c - -target bpf
> > > -O2 -o $OUTPUT_FILE
> > > --------------------------------------------------
> > > 
> > > I then wrote and compiled a script that ask to get asks to put a probe
> > > at a function that
> > > does not exists in the kernel, it errors out as expected:
> > > 
> > > $ cat /tmp/test.c
> > > __attribute__((section("fork=does_not_exist"), used)) int fork(void *ctx) {
> > >     return 0;
> > > }
> > > 
> > > char _license[] __attribute__((section("license"), used)) = "GPL";
> > > int _version __attribute__((section("version"), used)) = 0x40100;
> > > $ cd ~/bin && ./hello-ebpf
> > > $ perf record --event /tmp/test.o sleep 1
> > > Using perf wrapper that supports hot-text. Try perf.real if you
> > > encounter any issues.
> > > Probe point 'does_not_exist' not found.
> > > event syntax error: '/tmp/test.o'
> > >                      \___ You need to check probing points in BPF file
> > > 
> > > (add -v to see detail)
> > > Run 'perf list' for a list of valid events
> > > 
> > >  Usage: perf record [<options>] [<command>]
> > >     or: perf record [<options>] -- <command> [<options>]
> > > 
> > >     -e, --event <event>   event selector. use 'perf list' to list
> > > available events
> > > 
> > > ---------------------------------------------------
> > > 
> > > Next I changed the attribute to something that exists in the kernel.
> > > As expected, it errors out
> > > with permission problem:
> > > $ cat /tmp/test.c
> > > __attribute__((section("fork=fork_init"), used)) int fork(void *ctx) {
> > >     return 0;
> > > }
> > > char _license[] __attribute__((section("license"), used)) = "GPL";
> > > int _version __attribute__((section("version"), used)) = 0x40100;
> > > $ grep fork_init /proc/kallsyms
> > > ffffffff8146e250 T xfs_ifork_init_cow
> > > ffffffff83980481 T fork_init
> > > $ cd ~/bin && ./hello-ebpf
> > > $ perf record --event /tmp/test.o sleep 1
> > > Using perf wrapper that supports hot-text. Try perf.real if you
> > > encounter any issues.
> > > Failed to open kprobe_events: Permission denied
> > > event syntax error: '/tmp/test.o'
> > >                      \___ You need to be root
> > > 
> > > (add -v to see detail)
> > > Run 'perf list' for a list of valid events
> > > 
> > >  Usage: perf record [<options>] [<command>]
> > >     or: perf record [<options>] -- <command> [<options>]
> > > 
> > >     -e, --event <event>   event selector. use 'perf list' to list
> > > available events
> > > 
> > > ---------------------------------------------------
> > > 
> > > So I reran as root, but this time I get an invalid syntax error:
> > > 
> > > # perf record --event /tmp/test.o -v sleep 1
> > > Using perf wrapper that supports hot-text. Try perf.real if you
> > > encounter any issues.
> > > Failed to write event: Invalid argument
> > > event syntax error: '/tmp/test.o'
> > >                      \___ Invalid argument
> > > 
> > > (add -v to see detail)
> > > Run 'perf list' for a list of valid events
> > > 
> > >  Usage: perf record [<options>] [<command>]
> > >     or: perf record [<options>] -- <command> [<options>]
> > > 
> > >     -e, --event <event>   event selector. use 'perf list' to list
> > > available events
> > > ---------------------------------------------------
> > > 
> > > Is there a different way to attach a custom event probe point?
> > > 
> > 
> > nice, good question ;-)
> > 
> > looks like there are no volunteers from original authors,
> > I'll check on that
> 
> there's small bug in perf trace that makes it to die early,
> (fix below) but other than that it works.. I'll send full
> patch later

Ok, waiting then.

- Arnaldo
 
> you need to specify full path for bpf object, not like in the
> example I pasted above.. I recall fixing that in code because
> it clashed with pmu syntax
> 
> so on fedora 35 I can run following with the change below:
> 
> 	# ./perf trace -e openat,/home/jolsa/linux-qemu/tools/perf/examples/bpf/hello.c  
> 	/home/jolsa/linux-qemu/tools/perf/examples/bpf/hello.c:5:2: warning: variable length array folded to constant array as an extension [-Wgnu-folding-constant]
> 		puts("Hello, world\n");
> 		^
> 	/home/jolsa/lib/perf/include/bpf/stdio.h:14:10: note: expanded from macro 'puts'
> 		   char __from[__len] = from; \
> 			^
> 	1 warning generated.
> 	     0.000 (         ): systemd-resolv/1142 __bpf_stdout__(Hello, world)
> 	     0.016 ( 0.031 ms): systemd-resolv/1142 openat(dfd: CWD, filename: 0x6b1c4a70, flags: RDONLY|CLOEXEC)         = -1 ENOENT (No such file or directory)
> 	     0.070 (         ): systemd-resolv/1142 __bpf_stdout__(Hello, world)
> 	     0.074 ( 0.011 ms): systemd-resolv/1142 openat(dfd: CWD, filename: 0x6b1c4a70, flags: RDONLY|CLOEXEC)         = -1 ENOENT (No such file or directory)
> 	     0.097 (         ): systemd-resolv/1142 __bpf_stdout__(Hello, world)
> 	     0.101 ( 0.010 ms): systemd-resolv/1142 openat(dfd: CWD, filename: 0x6b1c4a70, flags: RDONLY|CLOEXEC)         = -1 ENOENT (No such file or directory)
> 	     0.123 (         ): systemd-resolv/1142 __bpf_stdout__(Hello, world)
> 	     0.127 ( 0.010 ms): systemd-resolv/1142 openat(dfd: CWD, filename: 0x6b1c4a70, flags: RDONLY|CLOEXEC)         = -1 ENOENT (No such file or directory)
> 	     0.148 (         ): systemd-resolv/1142 __bpf_stdout__(Hello, world)
> 	     0.152 ( 0.010 ms): systemd-resolv/1142 openat(dfd: CWD, filename: 0x6b1c4a70, flags: RDONLY|CLOEXEC)         = -1 ENOENT (No such file or directory)
> 	     0.219 (         ): systemd-resolv/1142 __bpf_stdout__(Hello, world)
> 	...
> 
> 
> jirka
> 
> 
> ---
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 97121fb45842..df9fc00b4cd6 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -3936,6 +3936,7 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
>  	bool draining = false;
>  
>  	trace->live = true;
> +	signal(SIGCHLD, sig_handler);
>  
>  	if (!trace->raw_augmented_syscalls) {
>  		if (trace->trace_syscalls && trace__add_syscall_newtp(trace))
> @@ -4884,7 +4885,6 @@ int cmd_trace(int argc, const char **argv)
>  
>  	signal(SIGSEGV, sighandler_dump_stack);
>  	signal(SIGFPE, sighandler_dump_stack);
> -	signal(SIGCHLD, sig_handler);
>  	signal(SIGINT, sig_handler);
>  
>  	trace.evlist = evlist__new();

-- 

- Arnaldo