Subject: Re: [PATCH v1 1/2] perf probe: Fixup Arm64 SDT arguments

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Thu, 24 Dec 2020 10:51:39 -0300

Em Wed, Dec 23, 2020 at 02:39:04PM +0800, Leo Yan escreveu:
> Arm64 ELF section '.note.stapsdt' uses string format "-4@[sp, NUM]" if
> the probe is to access data in stack, e.g. below is an example for
> dumping Arm64 ELF file and shows the argument format:
> 
>   Arguments: -4@[sp, 12] -4@[sp, 8] -4@[sp, 4]
> 
> Comparing against other archs' argument format, Arm64's argument
> introduces an extra space character in the middle of square brackets,
> due to argv_split() uses space as splitter, the argument is wrongly
> divided into two items.
> 
> To support Arm64 SDT, this patch fixes up for this case, if any item
> contains sub string "[sp", concatenates the two continuous items.  And
> adds the detailed explaination in comment.
> 
> Signed-off-by: Leo Yan <[email-masked]>
> ---
>  tools/perf/util/probe-file.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> index 064b63a6a3f3..60878c859e60 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -794,6 +794,8 @@ static char *synthesize_sdt_probe_command(struct sdt_note *note,
>  	char *ret = NULL, **args;
>  	int i, args_count, err;
>  	unsigned long long ref_ctr_offset;
> +	char *arg;
> +	int arg_idx = 0;
>  
>  	if (strbuf_init(&buf, 32) < 0)
>  		return NULL;
> @@ -815,8 +817,34 @@ static char *synthesize_sdt_probe_command(struct sdt_note *note,
>  	if (note->args) {
>  		args = argv_split(note->args, &args_count);
>  
> -		for (i = 0; i < args_count; ++i) {
> -			if (synthesize_sdt_probe_arg(&buf, i, args[i]) < 0)
> +		for (i = 0; i < args_count; ) {
> +			/*
> +			 * FIXUP: Arm64 ELF section '.note.stapsdt' uses string
> +			 * format "-4@[sp, NUM]" if a probe is to access data in
> +			 * the stack, e.g. below is an example for the SDT
> +			 * Arguments:
> +			 *
> +			 *   Arguments: -4@[sp, 12] -4@[sp, 8] -4@[sp, 4]
> +			 *
> +			 * Since the string introduces an extra space character
> +			 * in the middle of square brackets, the argument is
> +			 * divided into two items.  Fixup for this case, if an
> +			 * item contains sub string "[sp,", need to concatenate
> +			 * the two items.
> +			 */
> +			if (strstr(args[i], "[sp,") && (i+1) < args_count) {
> +				arg = strcat(args[i], args[i+1]);
> +				i += 2;
> +			} else {
> +				arg = strdup(args[i]);
> +				i += 1;
> +			}
> +
> +			err = synthesize_sdt_probe_arg(&buf, arg_idx, arg);
> +			free(arg);

So you free here unconditionally because either you used something you
got from argv_split() that strdup'ed all the entries in the array it
returns, or that you strdup'ed in the else branch.

But then you may not free all the things argv_split() returned, right?
Also, that strcat(args[i], args[i+1]), are you sure that is safe? strcat
expects dest to have enough space for the concatenation, I don't see
argv_split[] adding extra bytes, just a strdup().

So probably you need asprintf() where you use strcat() and then, at the
end of the loop, you need to free what argv_split() returned, using
argv_free(), no?

Also please check strdup() (and then asprintf) managed to allocate, else
synthesize_sdt_probe_arg() will receive its 'desc' argument as NULL, do
_another_ strdup on it and boom.

Or am I missing something? :)

I just looked ant synthesize_sdt_probe_command() is leaking the args it
gets from argv_split()

So this patch is needed, ack?

diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
index 064b63a6a3f311cd..bbecb449ea944395 100644
--- a/tools/perf/util/probe-file.c
+++ b/tools/perf/util/probe-file.c
@@ -791,7 +791,7 @@ static char *synthesize_sdt_probe_command(struct sdt_note *note,
 					const char *sdtgrp)
 {
 	struct strbuf buf;
-	char *ret = NULL, **args;
+	char *ret = NULL;
 	int i, args_count, err;
 	unsigned long long ref_ctr_offset;
 
@@ -813,12 +813,19 @@ static char *synthesize_sdt_probe_command(struct sdt_note *note,
 		goto out;
 
 	if (note->args) {
-		args = argv_split(note->args, &args_count);
+		char **args = argv_split(note->args, &args_count);
+
+		if (args == NULL)
+			goto error;
 
 		for (i = 0; i < args_count; ++i) {
-			if (synthesize_sdt_probe_arg(&buf, i, args[i]) < 0)
+			if (synthesize_sdt_probe_arg(&buf, i, args[i]) < 0) {
+				argv_free(args);
 				goto error;
+			}
 		}
+
+		argv_free(args);
 	}
 
 out:

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