linux-kernel - Re: [PATCH v2 3/3] perf test: Decompress kernel module before objdump

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Date:   Mon, 5 Jun 2017 14:13:27 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH v2 3/3] perf test: Decompress kernel module before objdump

On 03/06/17 05:00, Namhyung Kim wrote:
> If a kernel modules is compressed, it should be decompressed before
> running objdump to parse binary data correctly.  This fixes a failure of
> object code reading test for me.

Makes sense to me although I have a few small comments below.

> 
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/tests/code-reading.c | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/tests/code-reading.c b/tools/perf/tests/code-reading.c
> index 1f14e7612cbb..fe6bd34d68b1 100644
> --- a/tools/perf/tests/code-reading.c
> +++ b/tools/perf/tests/code-reading.c
> @@ -229,6 +229,7 @@ static int read_object_code(u64 addr, size_t len, u8 cpumode,
>  	unsigned char buf2[BUFSZ];
>  	size_t ret_len;
>  	u64 objdump_addr;
> +	const char *objdump_name;
>  	int ret;
>  
>  	pr_debug("Reading object code for memory address: %#"PRIx64"\n", addr);
> @@ -289,9 +290,32 @@ static int read_object_code(u64 addr, size_t len, u8 cpumode,
>  		state->done[state->done_cnt++] = al.map->start;
>  	}
>  
> +	objdump_name = al.map->dso->long_name;
> +	if (dso__needs_decompress(al.map->dso)) {
> +		char buf[32];  /* for "/tmp/perf-kmod-XXXXXX" */

We should be able to set the temporary file name buffer size without
reference to the format of the name i.e. #define it or use PATH_MAX

> +
> +		if (dso__decompress_kmodule_path(al.map->dso, objdump_name,
> +						 buf, sizeof(buf)) < 0) {

Do we care that it is kmodule i.e. why isn't this function called just
dso__decompress_path().

> +			pr_debug("decompression failed\n");
> +			return -1;
> +		}
> +
> +		objdump_name = strdup(buf);

Why not just put the buf in the outer scope instead of using strdup().

> +		if (objdump_name == NULL) {
> +			pr_debug("memory allocation failed\n");
> +			return -1;
> +		}
> +	}
> +
>  	/* Read the object code using objdump */
>  	objdump_addr = map__rip_2objdump(al.map, al.addr);
> -	ret = read_via_objdump(al.map->dso->long_name, objdump_addr, buf2, len);
> +	ret = read_via_objdump(objdump_name, objdump_addr, buf2, len);
> +
> +	if (objdump_name != al.map->dso->long_name) {
> +		unlink(objdump_name);
> +		free((void *)objdump_name);
> +	}
> +
>  	if (ret > 0) {
>  		/*
>  		 * The kernel maps are inaccurate - assume objdump is right in
>