Re: [PATCH v2 1/2] Unify the handling of stack traces in the consumer

Reviewed-by: Eugene Loh <[email protected]>

On 9/29/25 15:47, Kris Van Hees wrote:
> Distinguishing between kernel stacks and userspace stacks was done
> based on the action id, even when used outside of action context
> (i.e. in aggregation keys).  That is far from ideal.
>
> Encode the stack type along with the nframes and strsize values in
> the  data record description argument for stack() and ustack()
> records.
>
> The macros for managing that argument are moved to dt_impl.h since
> they are internal to the DTrace implementation.
>
> All printing of stack traces is now consolidated in dt_printf.c as
> well.
>
> Signed-off-by: Kris Van Hees <[email protected]>
> ---
>   include/dtrace/actions_defines.h |   5 -
>   libdtrace/dt_cg.c                |   6 +-
>   libdtrace/dt_consume.c           | 256 ++----------------------------
>   libdtrace/dt_impl.h              |  13 ++
>   libdtrace/dt_printf.c            | 263 ++++++++++++++++++++++++++++---
>   libdtrace/dt_printf.h            |  14 +-
>   6 files changed, 272 insertions(+), 285 deletions(-)
>
> diff --git a/include/dtrace/actions_defines.h b/include/dtrace/actions_defines.h
> index 1a9c1a81..7c2f7dda 100644
> --- a/include/dtrace/actions_defines.h
> +++ b/include/dtrace/actions_defines.h
> @@ -156,11 +156,6 @@
>   		(uint16_t)(((x) & DTRACE_LLQUANTIZE_FACTORMASK) >> \
>   			DTRACE_LLQUANTIZE_FACTORSHIFT)
>   
> -#define DTRACE_USTACK_NFRAMES(x)	(uint32_t)((x) & UINT32_MAX)
> -#define DTRACE_USTACK_STRSIZE(x)	(uint32_t)((x) >> 32)
> -#define DTRACE_USTACK_ARG(x, y)		\
> -		((((uint64_t)(y)) << 32) | ((x) & UINT32_MAX))
> -
>   #ifndef _LP64
>   # ifndef _LITTLE_ENDIAN
>   #  define DTRACE_PTR(type, name)	uint32_t name##pad; type *name
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index 6e70331f..51473667 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -2701,7 +2701,7 @@ dt_cg_stack_arg(dtrace_hdl_t *dtp, dt_node_t *dnp, dtrace_actkind_t kind)
>   		strsize = arg1->dn_value;
>   	}
>   
> -	return DTRACE_USTACK_ARG(nframes, strsize);
> +	return DTRACE_STACK_ARG(kind == DTRACEACT_USTACK, nframes, strsize);
>   }
>   
>   /*
> @@ -2738,7 +2738,7 @@ dt_cg_act_stack_sub(dt_pcb_t *pcb, dt_node_t *dnp, int reg, int off, dtrace_actk
>   	/* Get sizing information from dnp->dn_arg. */
>   	arg = dt_cg_stack_arg(dtp, dnp, kind);
>   	prefsz = kind == DTRACEACT_USTACK ? sizeof(uint64_t) : 0;
> -	nframes = DTRACE_USTACK_NFRAMES(arg);
> +	nframes = DTRACE_STACK_NFRAMES(arg);
>   	stacksize = nframes * sizeof(uint64_t);
>   
>   	/* Handle alignment and reserve space in the output buffer. */
> @@ -8700,7 +8700,7 @@ dt_cg_agg(dt_pcb_t *pcb, dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>   				case DT_ACT_USTACK:
>   					arg = dt_cg_stack_arg(dtp, knp, DTRACEACT_USTACK);
>   					kind = DTRACEACT_USTACK;
> -					size = 8 + 8 * DTRACE_USTACK_NFRAMES(arg);
> +					size = 8 + 8 * DTRACE_STACK_NFRAMES(arg);
>   					break;
>   				case DT_ACT_JSTACK:
>   					kind = DTRACEACT_JSTACK;
> diff --git a/libdtrace/dt_consume.c b/libdtrace/dt_consume.c
> index 280ed42a..eca2139f 100644
> --- a/libdtrace/dt_consume.c
> +++ b/libdtrace/dt_consume.c
> @@ -1079,232 +1079,6 @@ dt_print_tracemem(dtrace_hdl_t *dtp, FILE *fp, const dtrace_recdesc_t *rec,
>   	return nconsumed;
>   }
>   
> -int
> -dt_print_stack(dtrace_hdl_t *dtp, FILE *fp, const char *format,
> -    caddr_t addr, int depth, int size)
> -{
> -	dtrace_syminfo_t dts;
> -	GElf_Sym sym;
> -	int i, indent;
> -	char c[PATH_MAX * 2];
> -	uint64_t pc;
> -
> -	if (dt_printf(dtp, fp, "\n") < 0)
> -		return -1;
> -
> -	if (format == NULL)
> -		format = "%s";
> -
> -	if (dtp->dt_options[DTRACEOPT_STACKINDENT] != DTRACEOPT_UNSET)
> -		indent = (int)dtp->dt_options[DTRACEOPT_STACKINDENT];
> -	else
> -		indent = _dtrace_stkindent;
> -
> -	for (i = 0; i < depth; i++) {
> -		switch (size) {
> -		case sizeof(uint32_t):
> -			/* LINTED - alignment */
> -			pc = *((uint32_t *)addr);
> -			break;
> -
> -		case sizeof(uint64_t):
> -			/* LINTED - alignment */
> -			pc = *((uint64_t *)addr);
> -			break;
> -
> -		default:
> -			return dt_set_errno(dtp, EDT_BADSTACKPC);
> -		}
> -
> -		if (pc == 0)
> -			break;
> -
> -		addr += size;
> -
> -		if (dt_printf(dtp, fp, "%*s", indent, "") < 0)
> -			return -1;
> -
> -		if (dtrace_lookup_by_addr(dtp, pc, &sym, &dts) == 0) {
> -			if (pc > sym.st_value)
> -				snprintf(c, sizeof(c), "%s`%s+0x%llx",
> -					 dts.object, dts.name,
> -					 (long long unsigned)pc - sym.st_value);
> -			else
> -				snprintf(c, sizeof(c), "%s`%s",
> -					 dts.object, dts.name);
> -		} else {
> -			/*
> -			 * We'll repeat the lookup, but this time we'll specify
> -			 * a NULL GElf_Sym -- indicating that we're only
> -			 * interested in the containing module.
> -			 */
> -			if (dtrace_lookup_by_addr(dtp, pc, NULL, &dts) == 0)
> -				snprintf(c, sizeof(c), "%s`0x%llx",
> -					 dts.object, (long long unsigned)pc);
> -			else
> -				snprintf(c, sizeof(c), "0x%llx",
> -				    (long long unsigned)pc);
> -		}
> -
> -		if (dt_printf(dtp, fp, format, c) < 0)
> -			return -1;
> -
> -		if (dt_printf(dtp, fp, "\n") < 0)
> -			return -1;
> -	}
> -
> -	return 0;
> -}
> -
> -int
> -dt_print_ustack(dtrace_hdl_t *dtp, FILE *fp, const char *format,
> -    caddr_t addr, uint64_t arg)
> -{
> -	/* LINTED - alignment */
> -	uint64_t *pc = ((uint64_t *)addr);
> -	uint32_t depth = DTRACE_USTACK_NFRAMES(arg);
> -	uint32_t strsize = DTRACE_USTACK_STRSIZE(arg);
> -	const char *strbase = addr + (depth + 1) * sizeof(uint64_t);
> -	const char *str = strsize ? strbase : NULL;
> -	int err = 0;
> -
> -	const char *name;
> -	char objname[PATH_MAX], c[PATH_MAX * 2];
> -	GElf_Sym sym;
> -	int i, indent;
> -	pid_t pid = -1, tgid;
> -
> -	if (depth == 0)
> -		return 0;
> -
> -	tgid = (pid_t)*pc++;
> -
> -	if (dt_printf(dtp, fp, "\n") < 0)
> -		return -1;
> -
> -	if (format == NULL)
> -		format = "%s";
> -
> -	if (dtp->dt_options[DTRACEOPT_STACKINDENT] != DTRACEOPT_UNSET)
> -		indent = (int)dtp->dt_options[DTRACEOPT_STACKINDENT];
> -	else
> -		indent = _dtrace_stkindent;
> -
> -	/*
> -	 * Ultimately, we need to add an entry point in the library vector for
> -	 * determining <symbol, offset> from <tgid, address>.  For now, if
> -	 * this is a vector open, we just print the raw address or string.
> -	 */
> -	if (dtp->dt_vector == NULL)
> -		pid = dt_proc_grab_lock(dtp, tgid, DTRACE_PROC_WAITING |
> -		    DTRACE_PROC_SHORTLIVED);
> -
> -	for (i = 0; i < depth && pc[i] != 0; i++) {
> -		const prmap_t *map;
> -
> -		if ((err = dt_printf(dtp, fp, "%*s", indent, "")) < 0)
> -			break;
> -		if (dtp->dt_options[DTRACEOPT_NORESOLVE] != DTRACEOPT_UNSET
> -		    && pid >= 0) {
> -			if (dt_Pobjname(dtp, pid, pc[i], objname,
> -			    sizeof(objname)) != NULL) {
> -				const prmap_t *pmap = NULL;
> -				uint64_t offset = pc[i];
> -
> -				pmap = dt_Paddr_to_map(dtp, pid, pc[i]);
> -
> -				if (pmap)
> -					offset = pc[i] - pmap->pr_vaddr;
> -
> -				snprintf(c, sizeof(c), "%s:0x%llx",
> -				    dt_basename(objname), (unsigned long long)offset);
> -
> -			} else
> -				snprintf(c, sizeof(c), "0x%llx",
> -				    (unsigned long long)pc[i]);
> -
> -		} else if (pid >= 0 && dt_Plookup_by_addr(dtp, pid, pc[i],
> -							  &name, &sym) == 0) {
> -			if (dt_Pobjname(dtp, pid, pc[i], objname,
> -					sizeof(objname)) != NULL) {
> -				if (pc[i] > sym.st_value)
> -					snprintf(c, sizeof(c), "%s`%s+0x%llx",
> -						 dt_basename(objname), name,
> -						 (unsigned long long)(pc[i] - sym.st_value));
> -				else
> -					snprintf(c, sizeof(c), "%s`%s",
> -						 dt_basename(objname), name);
> -			} else
> -				snprintf(c, sizeof(c), "0x%llx",
> -				    (unsigned long long)pc[i]);
> -			/* Allocated by Plookup_by_addr. */
> -			free((char *)name);
> -		} else if (str != NULL && str[0] != '\0' && str[0] != '@' &&
> -		    (pid >= 0 &&
> -			((map = dt_Paddr_to_map(dtp, pid, pc[i])) == NULL ||
> -			    (map->pr_mflags & MA_WRITE)))) {
> -			/*
> -			 * If the current string pointer in the string table
> -			 * does not point to an empty string _and_ the program
> -			 * counter falls in a writable region, we'll use the
> -			 * string from the string table instead of the raw
> -			 * address.  This last condition is necessary because
> -			 * some (broken) ustack helpers will return a string
> -			 * even for a program counter that they can't
> -			 * identify.  If we have a string for a program
> -			 * counter that falls in a segment that isn't
> -			 * writable, we assume that we have fallen into this
> -			 * case and we refuse to use the string.
> -			 */
> -			snprintf(c, sizeof(c), "%s", str);
> -		} else {
> -			if (pid >= 0 && dt_Pobjname(dtp, pid, pc[i], objname,
> -			    sizeof(objname)) != NULL)
> -				snprintf(c, sizeof(c), "%s`0x%llx",
> -				    dt_basename(objname), (unsigned long long)pc[i]);
> -			else
> -				snprintf(c, sizeof(c), "0x%llx",
> -				    (unsigned long long)pc[i]);
> -		}
> -
> -		if ((err = dt_printf(dtp, fp, format, c)) < 0)
> -			break;
> -
> -		if ((err = dt_printf(dtp, fp, "\n")) < 0)
> -			break;
> -
> -		if (str != NULL && str[0] == '@') {
> -			/*
> -			 * If the first character of the string is an "at" sign,
> -			 * then the string is inferred to be an annotation --
> -			 * and it is printed out beneath the frame and offset
> -			 * with brackets.
> -			 */
> -			if ((err = dt_printf(dtp, fp, "%*s", indent, "")) < 0)
> -				break;
> -
> -			snprintf(c, sizeof(c), "  [ %s ]", &str[1]);
> -
> -			if ((err = dt_printf(dtp, fp, format, c)) < 0)
> -				break;
> -
> -			if ((err = dt_printf(dtp, fp, "\n")) < 0)
> -				break;
> -		}
> -
> -		if (str != NULL) {
> -			str += strlen(str) + 1;
> -			if (str - strbase >= strsize)
> -				str = NULL;
> -		}
> -	}
> -
> -	if (pid >= 0)
> -		dt_proc_release_unlock(dtp, pid);
> -
> -	return err;
> -}
> -
>   static int
>   dt_print_usym(dtrace_hdl_t *dtp, FILE *fp, caddr_t addr, dtrace_actkind_t act)
>   {
> @@ -1355,7 +1129,7 @@ dt_print_umod(dtrace_hdl_t *dtp, FILE *fp, const char *format, caddr_t addr)
>   		format = "  %-50s";
>   
>   	/*
> -	 * See the comment in dt_print_ustack() for the rationale for
> +	 * See the comment in dt_print_stack_user() for the rationale for
>   	 * printing raw addresses in the vectored case.
>   	 */
>   	if (dtp->dt_vector == NULL)
> @@ -1660,12 +1434,15 @@ dt_print_datum(dtrace_hdl_t *dtp, FILE *fp, dtrace_recdesc_t *rec,
>   
>   	switch (act) {
>   	case DTRACEACT_STACK:
> -		return dt_print_stack(dtp, fp, NULL, addr, rec->dtrd_arg,
> -				      rec->dtrd_size / rec->dtrd_arg);
> +	case DTRACEACT_USTACK: {
> +		dtrace_probedata_t	pdat;
>   
> -	case DTRACEACT_USTACK:
> -	case DTRACEACT_JSTACK:
> -		return dt_print_ustack(dtp, fp, NULL, addr, rec->dtrd_arg);
> +		/* dt_print_stack() uses dtpda_data only */
> +		memset(&pdat, 0, sizeof(pdat));
> +		pdat.dtpda_data = addr;
> +
> +		return dt_print_stack(dtp, fp, NULL, &pdat, rec, 1, NULL, 0);
> +	}
>   
>   	case DTRACEACT_USYM:
>   	case DTRACEACT_UADDR:
> @@ -2467,14 +2244,6 @@ dt_consume_one_probe(dtrace_hdl_t *dtp, FILE *fp, char *data, uint32_t size,
>   			return dt_set_errno(dtp, EDT_BADRVAL);
>   
>   		switch (act) {
> -		case DTRACEACT_STACK: {
> -			int depth = rec->dtrd_arg;
> -
> -			if (dt_print_stack(dtp, fp, NULL, recdata,
> -					   depth, rec->dtrd_size / depth) < 0)
> -				return -1;
> -			continue;
> -		}
>   		case DTRACEACT_SYM:
>   			if (dt_print_sym(dtp, fp, NULL, recdata) < 0)
>   				return -1;
> @@ -2483,11 +2252,10 @@ dt_consume_one_probe(dtrace_hdl_t *dtp, FILE *fp, char *data, uint32_t size,
>   			if (dt_print_mod(dtp, fp, NULL, recdata) < 0)
>   				return -1;
>   			continue;
> +		case DTRACEACT_STACK:
>   		case DTRACEACT_USTACK:
> -			if (dt_print_ustack(dtp, fp, NULL,
> -					    recdata, rec->dtrd_arg) < 0)
> -				return -1;
> -			continue;
> +			func = dt_print_stack;
> +			break;
>   		case DTRACEACT_USYM:
>   		case DTRACEACT_UADDR:
>   			if (dt_print_usym(dtp, fp, recdata, act) < 0)
> diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
> index 7d8e4432..4dc4c9a7 100644
> --- a/libdtrace/dt_impl.h
> +++ b/libdtrace/dt_impl.h
> @@ -236,6 +236,19 @@ typedef struct dt_tstring {
>   	int		in_use;			/* In use (1) or not (0) */
>   } dt_tstring_t;
>   
> +/*
> + * The stack()/ustack() data record argument encodes:
> + *  - the stack type (kernel or userspace)
> + *  - the number of frames in the stack trace
> + *  - the size of the optional string area for ustack()
> + */
> +#define DTRACE_STACK_IS_USER(x)		((x) & (1 << 31))
> +#define DTRACE_STACK_NFRAMES(x)		(uint32_t)((x) & INT32_MAX)
> +#define DTRACE_STACK_STRSIZE(x)		(uint32_t)((x) >> 32)
> +#define DTRACE_STACK_ARG(t, x, y)	((((uint64_t)(y)) << 32) | \
> +					 ((t) ? (1UL << 31) : 0) | \
> +					 ((x) & INT32_MAX))
> +
>   typedef struct dt_dirpath {
>   	dt_list_t dir_list;		/* linked-list forward/back pointers */
>   	char *dir_path;			/* directory pathname */
> diff --git a/libdtrace/dt_printf.c b/libdtrace/dt_printf.c
> index 1e01d468..0d7c0bb4 100644
> --- a/libdtrace/dt_printf.c
> +++ b/libdtrace/dt_printf.c
> @@ -1,6 +1,6 @@
>   /*
>    * Oracle Linux DTrace.
> - * Copyright (c) 2009, 2024, Oracle and/or its affiliates. All rights reserved.
> + * Copyright (c) 2009, 2025, 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.
>    */
> @@ -374,6 +374,200 @@ pfprint_uaddr(dtrace_hdl_t *dtp, FILE *fp, const char *format,
>   	return dt_printf(dtp, fp, format, s);
>   }
>   
> +static int
> +dt_print_stack_kernel(dtrace_hdl_t *dtp, FILE *fp, const char *format,
> +		      caddr_t addr, int indent, uint32_t depth)
> +{
> +	dtrace_syminfo_t dts;
> +	GElf_Sym sym;
> +	int i;
> +	char c[PATH_MAX * 2];
> +	uint64_t pc;
> +
> +	if (format == NULL)
> +		format = "%s";
> +
> +	for (i = 0; i < depth; i++) {
> +		pc = *((uint64_t *)addr);
> +		if (pc == 0)
> +			break;
> +
> +		addr += sizeof(pc);
> +
> +		if (dt_printf(dtp, fp, "%*s", indent, "") < 0)
> +			return -1;
> +
> +		if (dtrace_lookup_by_addr(dtp, pc, &sym, &dts) == 0) {
> +			if (pc > sym.st_value)
> +				snprintf(c, sizeof(c), "%s`%s+0x%llx",
> +					 dts.object, dts.name,
> +					 (long long unsigned)pc - sym.st_value);
> +			else
> +				snprintf(c, sizeof(c), "%s`%s",
> +					 dts.object, dts.name);
> +		} else {
> +			/*
> +			 * We'll repeat the lookup, but this time we'll specify
> +			 * a NULL GElf_Sym -- indicating that we're only
> +			 * interested in the containing module.
> +			 */
> +			if (dtrace_lookup_by_addr(dtp, pc, NULL, &dts) == 0)
> +				snprintf(c, sizeof(c), "%s`0x%llx",
> +					 dts.object, (long long unsigned)pc);
> +			else
> +				snprintf(c, sizeof(c), "0x%llx",
> +				    (long long unsigned)pc);
> +		}
> +
> +		if (dt_printf(dtp, fp, format, c) < 0)
> +			return -1;
> +
> +		if (dt_printf(dtp, fp, "\n") < 0)
> +			return -1;
> +	}
> +
> +	return 0;
> +}
> +
> +static int
> +dt_print_stack_user(dtrace_hdl_t *dtp, FILE *fp, const char *format,
> +		    caddr_t addr, int indent, uint32_t depth, uint32_t strsize)
> +{
> +	/* LINTED - alignment */
> +	uint64_t *pc = ((uint64_t *)addr);
> +	const char *strbase = addr + (depth + 1) * sizeof(uint64_t);
> +	const char *str = strsize ? strbase : NULL;
> +	int err = 0;
> +
> +	const char *name;
> +	char objname[PATH_MAX], c[PATH_MAX * 2];
> +	GElf_Sym sym;
> +	int i;
> +	pid_t pid = -1, tgid;
> +
> +	if (depth == 0)
> +		return 0;
> +
> +	tgid = (pid_t)*pc++;
> +
> +	if (format == NULL)
> +		format = "%s";
> +
> +	/*
> +	 * Ultimately, we need to add an entry point in the library vector for
> +	 * determining <symbol, offset> from <tgid, address>.  For now, if
> +	 * this is a vector open, we just print the raw address or string.
> +	 */
> +	if (dtp->dt_vector == NULL)
> +		pid = dt_proc_grab_lock(dtp, tgid, DTRACE_PROC_WAITING |
> +		    DTRACE_PROC_SHORTLIVED);
> +
> +	for (i = 0; i < depth && pc[i] != 0; i++) {
> +		const prmap_t *map;
> +
> +		if ((err = dt_printf(dtp, fp, "%*s", indent, "")) < 0)
> +			break;
> +		if (dtp->dt_options[DTRACEOPT_NORESOLVE] != DTRACEOPT_UNSET
> +		    && pid >= 0) {
> +			if (dt_Pobjname(dtp, pid, pc[i], objname,
> +			    sizeof(objname)) != NULL) {
> +				const prmap_t *pmap = NULL;
> +				uint64_t offset = pc[i];
> +
> +				pmap = dt_Paddr_to_map(dtp, pid, pc[i]);
> +
> +				if (pmap)
> +					offset = pc[i] - pmap->pr_vaddr;
> +
> +				snprintf(c, sizeof(c), "%s:0x%llx",
> +				    dt_basename(objname), (unsigned long long)offset);
> +
> +			} else
> +				snprintf(c, sizeof(c), "0x%llx",
> +				    (unsigned long long)pc[i]);
> +
> +		} else if (pid >= 0 && dt_Plookup_by_addr(dtp, pid, pc[i],
> +							  &name, &sym) == 0) {
> +			if (dt_Pobjname(dtp, pid, pc[i], objname,
> +					sizeof(objname)) != NULL) {
> +				if (pc[i] > sym.st_value)
> +					snprintf(c, sizeof(c), "%s`%s+0x%llx",
> +						 dt_basename(objname), name,
> +						 (unsigned long long)(pc[i] - sym.st_value));
> +				else
> +					snprintf(c, sizeof(c), "%s`%s",
> +						 dt_basename(objname), name);
> +			} else
> +				snprintf(c, sizeof(c), "0x%llx",
> +				    (unsigned long long)pc[i]);
> +			/* Allocated by Plookup_by_addr. */
> +			free((char *)name);
> +		} else if (str != NULL && str[0] != '\0' && str[0] != '@' &&
> +		    (pid >= 0 &&
> +			((map = dt_Paddr_to_map(dtp, pid, pc[i])) == NULL ||
> +			    (map->pr_mflags & MA_WRITE)))) {
> +			/*
> +			 * If the current string pointer in the string table
> +			 * does not point to an empty string _and_ the program
> +			 * counter falls in a writable region, we'll use the
> +			 * string from the string table instead of the raw
> +			 * address.  This last condition is necessary because
> +			 * some (broken) ustack helpers will return a string
> +			 * even for a program counter that they can't
> +			 * identify.  If we have a string for a program
> +			 * counter that falls in a segment that isn't
> +			 * writable, we assume that we have fallen into this
> +			 * case and we refuse to use the string.
> +			 */
> +			snprintf(c, sizeof(c), "%s", str);
> +		} else {
> +			if (pid >= 0 && dt_Pobjname(dtp, pid, pc[i], objname,
> +			    sizeof(objname)) != NULL)
> +				snprintf(c, sizeof(c), "%s`0x%llx",
> +				    dt_basename(objname), (unsigned long long)pc[i]);
> +			else
> +				snprintf(c, sizeof(c), "0x%llx",
> +				    (unsigned long long)pc[i]);
> +		}
> +
> +		if ((err = dt_printf(dtp, fp, format, c)) < 0)
> +			break;
> +
> +		if ((err = dt_printf(dtp, fp, "\n")) < 0)
> +			break;
> +
> +		if (str != NULL && str[0] == '@') {
> +			/*
> +			 * If the first character of the string is an "at" sign,
> +			 * then the string is inferred to be an annotation --
> +			 * and it is printed out beneath the frame and offset
> +			 * with brackets.
> +			 */
> +			if ((err = dt_printf(dtp, fp, "%*s", indent, "")) < 0)
> +				break;
> +
> +			snprintf(c, sizeof(c), "  [ %s ]", &str[1]);
> +
> +			if ((err = dt_printf(dtp, fp, format, c)) < 0)
> +				break;
> +
> +			if ((err = dt_printf(dtp, fp, "\n")) < 0)
> +				break;
> +		}
> +
> +		if (str != NULL) {
> +			str += strlen(str) + 1;
> +			if (str - strbase >= strsize)
> +				str = NULL;
> +		}
> +	}
> +
> +	if (pid >= 0)
> +		dt_proc_release_unlock(dtp, pid);
> +
> +	return err;
> +}
> +
>   /*ARGSUSED*/
>   static int
>   pfprint_stack(dtrace_hdl_t *dtp, FILE *fp, const char *format,
> @@ -381,19 +575,20 @@ pfprint_stack(dtrace_hdl_t *dtp, FILE *fp, const char *format,
>   	      uint64_t normal, uint64_t sig)
>   {
>   	int width;
> -	dtrace_optval_t saved = dtp->dt_options[DTRACEOPT_STACKINDENT];
>   	const dtrace_recdesc_t *rec = pfd->pfd_rec;
>   	caddr_t addr = (caddr_t)vaddr;
> +	uint32_t depth = DTRACE_STACK_NFRAMES(rec->dtrd_arg);
>   	int err = 0;
>   
> +	if (depth == 0)
> +		return 0;
> +
>   	/*
> -	 * We have stashed the value of the STACKINDENT option, and we will
> -	 * now override it for the purposes of formatting the stack.  If the
> -	 * field has been specified as left-aligned (i.e. (%-#), we set the
> -	 * indentation to be the width.  This is a slightly odd semantic, but
> -	 * it's useful functionality -- and it's slightly odd to begin with to
> -	 * be using a single format specifier to be formatting multiple lines
> -	 * of text...
> +	 * If the field has been specified as left-aligned (i.e. (%-#), we use
> +	 * the field width as indentation.  This is a slightly odd semantic
> +	 * but it's useful functionality -- and it's slightly odd to begin with
> +	 * to be using a single format specifier to be formatting multiple
> +	 * lines of text...
>   	 */
>   	if (pfd->pfd_dynwidth < 0) {
>   		assert(pfd->pfd_flags & DT_PFCONV_DYNWIDTH);
> @@ -404,24 +599,14 @@ pfprint_stack(dtrace_hdl_t *dtp, FILE *fp, const char *format,
>   		width = 0;
>   	}
>   
> -	dtp->dt_options[DTRACEOPT_STACKINDENT] = width;
> -
> -	switch (rec->dtrd_action) {
> -	case DTRACEACT_USTACK:
> -	case DTRACEACT_JSTACK:
> -		err = dt_print_ustack(dtp, fp, format, addr, rec->dtrd_arg);
> -		break;
> -
> -	case DTRACEACT_STACK:
> -		err = dt_print_stack(dtp, fp, format, addr, rec->dtrd_arg,
> -		    rec->dtrd_size / rec->dtrd_arg);
> -		break;
> -
> -	default:
> -		assert(0);
> -	}
> +	if (dt_printf(dtp, fp, "\n") < 0)
> +		return -1;
>   
> -	dtp->dt_options[DTRACEOPT_STACKINDENT] = saved;
> +	if (DTRACE_STACK_IS_USER(rec->dtrd_arg))
> +		err = dt_print_stack_user(dtp, fp, format, addr, width, depth,
> +					  DTRACE_STACK_STRSIZE(rec->dtrd_arg));
> +	else
> +		err = dt_print_stack_kernel(dtp, fp, format, addr, width, depth);
>   
>   	return err;
>   }
> @@ -2287,3 +2472,29 @@ dt_print_type(dtrace_hdl_t *dtp, FILE *fp, void *fmtdata,
>   
>   	return 2;
>   }
> +
> +int
> +dt_print_stack(dtrace_hdl_t *dtp, FILE *fp, void *fmtdata,
> +	       const dtrace_probedata_t *data, const dtrace_recdesc_t *recs,
> +	        uint_t nrecs, const void *buf, size_t len)
> +{
> +	const char	*format;
> +	dt_pfargd_t	pfd;
> +
> +	if (fmtdata == NULL)
> +		format = "%s";
> +	else
> +		format = ((dt_pfargv_t *)fmtdata)->pfv_format;
> +
> +	/* pfprint_stack() uses pfd_rec, pfd_flags, and pfd_width only */
> +	memset(&pfd, 0, sizeof(pfd));
> +	pfd.pfd_rec = recs;
> +	pfd.pfd_flags = DT_PFCONV_LEFT;
> +
> +	if (dtp->dt_options[DTRACEOPT_STACKINDENT] != DTRACEOPT_UNSET)
> +		pfd.pfd_width = (int)dtp->dt_options[DTRACEOPT_STACKINDENT];
> +	else
> +		pfd.pfd_width = _dtrace_stkindent;
> +
> +	return pfprint_stack(dtp, fp, format, &pfd, data->dtpda_data, 0, 0, 0);
> +}
> diff --git a/libdtrace/dt_printf.h b/libdtrace/dt_printf.h
> index f08e48eb..1ebdd8aa 100644
> --- a/libdtrace/dt_printf.h
> +++ b/libdtrace/dt_printf.h
> @@ -1,6 +1,6 @@
>   /*
>    * Oracle Linux DTrace.
> - * Copyright (c) 2005, 2024, Oracle and/or its affiliates. All rights reserved.
> + * Copyright (c) 2005, 2025, 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.
>    */
> @@ -102,16 +102,16 @@ extern void dt_printf_validate(dt_pfargv_t *, uint_t,
>   
>   extern void dt_printa_validate(struct dt_node *, struct dt_node *);
>   
> -extern int dt_print_stack(dtrace_hdl_t *, FILE *,
> -    const char *, caddr_t, int, int);
> -extern int dt_print_ustack(dtrace_hdl_t *, FILE *,
> -    const char *, caddr_t, uint64_t);
>   extern int dt_print_mod(dtrace_hdl_t *, FILE *, const char *, caddr_t);
>   extern int dt_print_umod(dtrace_hdl_t *, FILE *, const char *, caddr_t);
>   extern int dt_print_type(dtrace_hdl_t *dtp, FILE *fp, void *fmtdata,
>   			 const dtrace_probedata_t *data,
> -			 const dtrace_recdesc_t *recs,
> -			 uint_t nrecs, const void *buf, size_t len);
> +			 const dtrace_recdesc_t *recs, uint_t nrecs,
> +			 const void *buf, size_t len);
> +extern int dt_print_stack(dtrace_hdl_t *dtp, FILE *fp, void *fmtdata,
> +			  const dtrace_probedata_t *data,
> +			  const dtrace_recdesc_t *recs, uint_t nrecs,
> +			  const void *buf, size_t len);
>   
>   #ifdef	__cplusplus
>   }