[DTrace-devel] [PATCH 2/2] Use asprintf() to allocate strings

[Kris Van Hees]

On Fri, Jan 16, 2026 at 01:55:29PM -0500, eugene.loh at oracle.com wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> Earlier patches have slowly replaced constructs like:
>     int len;
>     len = snprintf(NULL, 0, format, args) + 1;
>     buf = malloc(len);
>     snprintf(buf, len, format, args);
> with the more compact:
>     asprintf(&buf, format, args);
> 
> Replace the remaining instances of the bulkier construct.
> 
> Note that dt_conf_init() continues to compute a buffer length and
> allocate a buffer, since that buffer will be reused multiple times.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
> ---
>  libdtrace/dt_link.c        | 17 +++++++----------
>  libdtrace/dt_probe.c       | 11 +++--------
>  libdtrace/dt_prov_dtrace.c | 12 +++---------
>  3 files changed, 13 insertions(+), 27 deletions(-)
> 
> diff --git a/libdtrace/dt_link.c b/libdtrace/dt_link.c
> index c9e0ea5fe..ffa16d9a4 100644
> --- a/libdtrace/dt_link.c
> +++ b/libdtrace/dt_link.c
> @@ -1,6 +1,6 @@
>  /*
>   * Oracle Linux DTrace.
> - * Copyright (c) 2008, 2025, Oracle and/or its affiliates. All rights reserved.
> + * Copyright (c) 2008, 2026, Oracle and/or its affiliates. All rights reserved.
>   * Licensed under the Universal Permissive License v 1.0 as shown at
>   * http://oss.oracle.com/licenses/upl.
>   */
> @@ -416,7 +416,6 @@ dtrace_program_link(dtrace_hdl_t *dtp, dtrace_prog_t *pgp, uint_t dflags,
>  	char drti[PATH_MAX], symvers[PATH_MAX];
>  	int fd, i, cur;
>  	char *cmd;
> -	size_t len;
>  	int ret = 0, status = 0;
>  
>  	/*
> @@ -426,6 +425,7 @@ dtrace_program_link(dtrace_hdl_t *dtp, dtrace_prog_t *pgp, uint_t dflags,
>  	 */
>  	if (pgp == NULL) {
>  		const char *fmt = "%s -o %s -r";
> +		size_t len;
>  
>  		len = snprintf(NULL, 0, fmt, dtp->dt_ld_path, file) + 1;
>  
> @@ -521,15 +521,12 @@ dtrace_program_link(dtrace_hdl_t *dtp, dtrace_prog_t *pgp, uint_t dflags,
>  		}
>  		snprintf(symvers, sizeof (symvers), "%s/drti/drti-vers", libdir->dir_path);
>  
> -		len = snprintf(NULL, 0, fmt, dtp->dt_ld_path, emu, file,
> -			       symvers, fd, drti) + 1;
> +		asprintf(&cmd, fmt, dtp->dt_ld_path, emu, file, symvers, fd,
> +			 drti);
> +		status = system(cmd);
> +		free(cmd);
>  
> -		cmd = alloca(len);
> -
> -		(void) snprintf(cmd, len, fmt, dtp->dt_ld_path, emu, file,
> -				symvers, fd, drti);
> -
> -		if ((status = system(cmd)) == -1) {
> +		if (status == -1) {
>  			ret = dt_link_error(dtp, NULL, -1,
>  			    "failed to run %s: %s", dtp->dt_ld_path,
>  			    strerror(errno));
> diff --git a/libdtrace/dt_probe.c b/libdtrace/dt_probe.c
> index 65316f515..86353893f 100644
> --- a/libdtrace/dt_probe.c
> +++ b/libdtrace/dt_probe.c
> @@ -1,6 +1,6 @@
>  /*
>   * Oracle Linux DTrace.
> - * Copyright (c) 2006, 2025, Oracle and/or its affiliates. All rights reserved.
> + * Copyright (c) 2006, 2026, Oracle and/or its affiliates. All rights reserved.
>   * Licensed under the Universal Permissive License v 1.0 as shown at
>   * http://oss.oracle.com/licenses/upl.
>   */
> @@ -475,15 +475,9 @@ dt_probe_tag(dt_probe_t *prp, uint_t argn, dt_node_t *dnp)
>  {
>  	dtrace_hdl_t *dtp = prp->prov->pv_hdl;
>  	dtrace_typeinfo_t dtt;
> -	size_t len;
>  	char *tag;
>  
> -	len = snprintf(NULL, 0, "__dtrace_%s___%s_arg%u",
> -	    prp->prov->desc.dtvd_name, prp->pr_name, argn);
> -
> -	tag = alloca(len + 1);
> -
> -	snprintf(tag, len + 1, "__dtrace_%s___%s_arg%u",
> +	asprintf(&tag, "__dtrace_%s___%s_arg%u",
>  	    prp->prov->desc.dtvd_name, prp->pr_name, argn);

This one should not be replaced, because if the ctf_add_typedef fails, 'tag'
will never be freed and thus becomes a memory leak.  Granted, in that case
dtrace will end with an error message anyway, but still, it is a bit sloppy.

This is why the original code here is using an alloca()... that goes away at
the end of the function scope.

>  
>  	if (dtrace_lookup_by_type(dtp, DTRACE_OBJ_DDEFS, tag, &dtt) != 0) {
> @@ -498,6 +492,7 @@ dt_probe_tag(dt_probe_t *prp, uint_t argn, dt_node_t *dnp)
>  			    tag, ctf_errmsg(ctf_errno(dtt.dtt_ctfp)));
>  		}
>  	}
> +	free(tag);
>  
>  	memset(dnp, 0, sizeof(dt_node_t));
>  	dnp->dn_kind = DT_NODE_TYPE;
> diff --git a/libdtrace/dt_prov_dtrace.c b/libdtrace/dt_prov_dtrace.c
> index 102afd84e..d417a864b 100644
> --- a/libdtrace/dt_prov_dtrace.c
> +++ b/libdtrace/dt_prov_dtrace.c
> @@ -232,7 +232,6 @@ static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)
>  		char	*spec;
>  		char	*fn;
>  		FILE	*f;
> -		size_t	len;
>  		int	fd, rc = -1;
>  
>  		/* get a uprobe specification for this probe */
> @@ -252,16 +251,11 @@ static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)
>  			return -ENOENT;
>  
>  		/* open format file */
> -		len = snprintf(NULL, 0, "%s" PROBE_FMT "/format",
> -			       EVENTSFS, PROBE_DATA) + 1;
> -		fn = dt_alloc(dtp, len);
> -		if (fn == NULL)
> +		if (asprintf(&fn, "%s" PROBE_FMT "/format", EVENTSFS,
> +			     PROBE_DATA) < 0)
>  			return -ENOENT;
> -
> -		snprintf(fn, len, "%s" PROBE_FMT "/format",
> -			 EVENTSFS, PROBE_DATA);
>  		f = fopen(fn, "r");
> -		dt_free(dtp, fn);
> +		free(fn);
>  		if (f == NULL)
>  			return -ENOENT;
>  
> -- 
> 2.47.3
>