Re: [PATCH v13 1/7] tools/lib/subcmd: Don't free the usage string

[Aditya Gupta <adityag@linux.ibm.com>]

Hi Arnaldo,

On 26/07/24 19:53, Arnaldo Carvalho de Melo wrote:
> On Thu, Jul 18, 2024 at 02:29:51PM +0530, Aditya Gupta wrote:
>> Currently, commands which depend on 'parse_options_subcommand()' don't
>> show the usage string, and instead show '(null)'
>>
>>      $ ./perf sched
>> 	Usage: (null)
>>
>>      -D, --dump-raw-trace  dump raw trace in ASCII
>>      -f, --force           don't complain, do it
>>      -i, --input <file>    input file name
>>      -v, --verbose         be more verbose (show symbol address, etc)
>>
>> 'parse_options_subcommand()' is generally expected to initialise the usage
>> string, with information in the passed 'subcommands[]' array
>>
>> This behaviour was changed in:
>>
>>      commit 230a7a71f9221 ("libsubcmd: Fix parse-options memory leak")
>>
>> Where the generated usage string is deallocated, and usage[0] string is
>> reassigned as NULL.
>>
>> As discussed in [1], free the allocated usage string in the main function
>> itself, and don't reset usage string to NULL in parse_options_subcommand
>>
>> With this change, the behaviour is restored.
>>
>>      $ ./perf sched
>>          Usage: perf sched [<options>] {record|latency|map|replay|script|timehist}
>>
>>             -D, --dump-raw-trace  dump raw trace in ASCII
>>             -f, --force           don't complain, do it
>>             -i, --input <file>    input file name
>>             -v, --verbose         be more verbose (show symbol address, etc)
>>
>> [1]: https://lore.kernel.org/linux-perf-users/htq5vhx6piet4nuq2mmhk7fs2bhfykv52dbppwxmo3s7du2odf@styd27tioc6e/
>>
>> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
>> Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
>> Cc: Disha Goel <disgoel@linux.vnet.ibm.com>
>> Cc: Jiri Olsa <jolsa@kernel.org>
>> Cc: Ian Rogers <irogers@google.com>
>> Cc: Kajol Jain <kjain@linux.ibm.com>
>> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
>> Cc: Namhyung Kim <namhyung@kernel.org>
>> Fixes: 230a7a71f922 ("libsubcmd: Fix parse-options memory leak")
>> Acked-by: Namhyung Kim <namhyung@kernel.org>
>> Suggested-by: Namhyung Kim <namhyung@kernel.org>
>> Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
>>
>> ---
>> Note:
>> This patch is independent of the series.
>>
>> But I kept it along with the series, since the rest of the patches should
>> be applied only after this patch is applied (else the 'free' in
>> builtin-check.c will crash)
>> ---
>> ---
>>   tools/lib/subcmd/parse-options.c | 8 +++-----
>>   tools/perf/builtin-kmem.c        | 2 ++
>>   tools/perf/builtin-kvm.c         | 3 +++
>>   tools/perf/builtin-kwork.c       | 3 +++
>>   tools/perf/builtin-lock.c        | 3 +++
>>   tools/perf/builtin-mem.c         | 3 +++
>>   tools/perf/builtin-sched.c       | 3 +++
>>   7 files changed, 20 insertions(+), 5 deletions(-)
>>
>> diff --git a/tools/lib/subcmd/parse-options.c b/tools/lib/subcmd/parse-options.c
>> index 4b60ec03b0bb..eb896d30545b 100644
>> --- a/tools/lib/subcmd/parse-options.c
>> +++ b/tools/lib/subcmd/parse-options.c
>> @@ -633,10 +633,11 @@ int parse_options_subcommand(int argc, const char **argv, const struct option *o
>>   			const char *const subcommands[], const char *usagestr[], int flags)
>>   {
>>   	struct parse_opt_ctx_t ctx;
>> -	char *buf = NULL;
>>   
>>   	/* build usage string if it's not provided */
>>   	if (subcommands && !usagestr[0]) {
>> +		char *buf = NULL;
>> +
>>   		astrcatf(&buf, "%s %s [<options>] {", subcmd_config.exec_name, argv[0]);
>>   
>>   		for (int i = 0; subcommands[i]; i++) {
>> @@ -678,10 +679,7 @@ int parse_options_subcommand(int argc, const char **argv, const struct option *o
>>   			astrcatf(&error_buf, "unknown switch `%c'", *ctx.opt);
>>   		usage_with_options(usagestr, options);
>>   	}
>> -	if (buf) {
>> -		usagestr[0] = NULL;
>> -		free(buf);
>> -	}
>> +
>>   	return parse_options_end(&ctx);
>>   }
>>   
>> diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c
>> index 6fd95be5032b..6b88b8b40784 100644
>> --- a/tools/perf/builtin-kmem.c
>> +++ b/tools/perf/builtin-kmem.c
>> @@ -2058,6 +2058,8 @@ int cmd_kmem(int argc, const char **argv)
>>   
>>   out_delete:
>>   	perf_session__delete(session);
>> +	/* free usage string allocated by parse_options_subcommand */
>> +	free((void *)kmem_usage[0]);
> Can we instead add a parse_options_exit(const char *usagestr[]) that
> does the free?
>
> So that we don't expose these internal details of libsubcmd and if
> something else needs to be done at exit time, thenm that is the place to
> add.

Sure that would be better, but might require a flag somewhere, to know 
that `usagestr` was allocated by 'parse_options_subcommand', and not 
statically present. (so that we don't run free on a statically allocated 
string).

Currently i don't see where we can keep such thing in subcmd, will try 
to see how I can know this, or maybe some magic inside 
'parse_options_exit' to check if string is NOT NULL, AND, dynamically 
allocated, then only we free it ?


Thanks,

Aditya Gupta

> Thanks,
>
> - Arnaldo
>    
>>   	return ret;
>>   }
>> diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
>> index 71165036e4ca..988bef73bd09 100644
>> --- a/tools/perf/builtin-kvm.c
>> +++ b/tools/perf/builtin-kvm.c
>> @@ -2187,5 +2187,8 @@ int cmd_kvm(int argc, const char **argv)
>>   	else
>>   		usage_with_options(kvm_usage, kvm_options);
>>   
>> +	/* free usage string allocated by parse_options_subcommand */
>> +	free((void *)kvm_usage[0]);
>> +
>>   	return 0;
>>   }
>> diff --git a/tools/perf/builtin-kwork.c b/tools/perf/builtin-kwork.c
>> index 56e3f3a5e03a..fd53838b5a78 100644
>> --- a/tools/perf/builtin-kwork.c
>> +++ b/tools/perf/builtin-kwork.c
>> @@ -2520,5 +2520,8 @@ int cmd_kwork(int argc, const char **argv)
>>   	} else
>>   		usage_with_options(kwork_usage, kwork_options);
>>   
>> +	/* free usage string allocated by parse_options_subcommand */
>> +	free((void *)kwork_usage[0]);
>> +
>>   	return 0;
>>   }
>> diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
>> index 0253184b3b58..b25d50716e63 100644
>> --- a/tools/perf/builtin-lock.c
>> +++ b/tools/perf/builtin-lock.c
>> @@ -2713,6 +2713,9 @@ int cmd_lock(int argc, const char **argv)
>>   		usage_with_options(lock_usage, lock_options);
>>   	}
>>   
>> +	/* free usage string allocated by parse_options_subcommand */
>> +	free((void *)lock_usage[0]);
>> +
>>   	zfree(&lockhash_table);
>>   	return rc;
>>   }
>> diff --git a/tools/perf/builtin-mem.c b/tools/perf/builtin-mem.c
>> index 863fcd735dae..b7c1cf6d0e5a 100644
>> --- a/tools/perf/builtin-mem.c
>> +++ b/tools/perf/builtin-mem.c
>> @@ -517,5 +517,8 @@ int cmd_mem(int argc, const char **argv)
>>   	else
>>   		usage_with_options(mem_usage, mem_options);
>>   
>> +	/* free usage string allocated by parse_options_subcommand */
>> +	free((void *)mem_usage[0]);
>> +
>>   	return 0;
>>   }
>> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
>> index 8750b5f2d49b..d6acc53ae89e 100644
>> --- a/tools/perf/builtin-sched.c
>> +++ b/tools/perf/builtin-sched.c
>> @@ -3805,5 +3805,8 @@ int cmd_sched(int argc, const char **argv)
>>   		usage_with_options(sched_usage, sched_options);
>>   	}
>>   
>> +	/* free usage string allocated by parse_options_subcommand */
>> +	free((void *)sched_usage[0]);
>> +
>>   	return 0;
>>   }
>> -- 
>> 2.45.2