mirror of
https://sourceware.org/git/binutils-gdb.git
synced 2024-11-27 12:03:41 +08:00
2009-06-19 Tristan Gingold <gingold@adacore.com>
* machoread.c (macho_symtab_read): Adjust for bfd changes. * darwin-nat.h (struct darwin_exception_msg): New type to describe a mach exception. (struct private_thread_info): New type to describe the state of the thread. (DEF_VEC_I thread_t): Removed, replaced by ... (DEF_VEC_O darwin_thread_t): ... this new type. (struct darwin_inferior): Renamed to ... (struct private_inferior): ... this type. Fields added. (darwin_not_port): Moved into the private inferior structure. * darwin-nat.c: Add includes, improve comments. Rewrite to handle multiple threads and processes. (darwin_resume_to): New function and protype. (darwin_resume, darwin_wait_to, darwin_wait): Ditto. (darwin_kill_inferior): Add ops argument. (darwin_pid_to_str): New function. (darwin_thread_alive): Ditto. (darwin_inf, darwin_not_port): Removed. (darwin_inf_fake_stop): New variable. (msgin, msgout, msg_state, exc_msg): Removed. (mach_check_error): Use warning instead of error. (darwin_ptrace): Adjust debug level. (cmp_thread_t): Fix names (typo). (darwin_check_new_threads): Argument is now an inferior, adjust for new structures, add no change check, ignore dead ports, handle first thread case. (find_inferior_task_it): New function. (find_inferior_notify_it): Ditto. (darwin_find_inferior_by_task): Ditto. (darwin_find_inferior_by_notify): Ditto. (darwin_find_thread): Ditto. (darwin_suspend_inferior): Ditto. (darwin_resume_inferior): Ditto. (catch_exception_raise_state): Removed. (catch_exception_raise_state_identity): Removed. (darwin_suspend_inferior_it): New function. (darwin_resume_inferior_it): Ditto. (darwin_dump_message): New function, extracted from darwin_wait. (darwin_decode_exception_message): New function. (darwin_encode_reply): New function. (catch_exception_raise): Removed. (darwin_send_reply): New function, extracted from darwin_resume. (darwin_resume_thread): New function, extracted from darwin_resume. (struct resume_inferior_threads_param): New type. (darwin_resume_inferior_threads_it): New function. (darwin_resume_inferior_threads): New function. (darwin_suspend_inferior_threads): New function. (darwin_resume): Mostly rewritten to handle multiple threads and some corner cases. (darwin_decode_message): New function extracted from darwin_wait. (cancel_breakpoint): New function. (darwin_wait): Mostly rewritten. Handle multiple threads. (darwin_mourn_inferior): Adjust for per process structures. (darwin_reply_to_all_pending_messages): New function. (darwin_stop_inferior): Adjust for per inferior structures. (darwin_attach_pid): Ditto. (darwin_init_thread_list): Ditto. (darwin_attach): Ditto. (darwin_detach): Ditto. (darwin_files_info): Now empty. (darwin_pid_to_str): Adjust returns string to match one expected by the testsuite. (darwin_read_write_inferior): Rename err variable to match other uses. Adjust debug message. Handle submaps. (darwin_xfer_memory): Adjust for per inferior structures. (set_enable_mach_exceptions): Ditto. (darwin_pid_to_exec_file): New function. (darwin_get_ada_task_ptid): Ditto. (darwin_supports_multi_process): Ditto. (_initialize_darwin_inferior): Remove useless assertion, adjust for per inferior structures. Add new target operations.
This commit is contained in:
parent
cf8fd78b38
commit
bb00b29d78
@ -1,3 +1,77 @@
|
||||
2009-06-19 Tristan Gingold <gingold@adacore.com>
|
||||
|
||||
* machoread.c (macho_symtab_read): Adjust for bfd changes.
|
||||
* darwin-nat.h (struct darwin_exception_msg): New type to describe
|
||||
a mach exception.
|
||||
(struct private_thread_info): New type to describe the state of the
|
||||
thread.
|
||||
(DEF_VEC_I thread_t): Removed, replaced by ...
|
||||
(DEF_VEC_O darwin_thread_t): ... this new type.
|
||||
(struct darwin_inferior): Renamed to ...
|
||||
(struct private_inferior): ... this type. Fields added.
|
||||
(darwin_not_port): Moved into the private inferior structure.
|
||||
* darwin-nat.c: Add includes, improve comments.
|
||||
Rewrite to handle multiple threads and processes.
|
||||
(darwin_resume_to): New function and protype.
|
||||
(darwin_resume, darwin_wait_to, darwin_wait): Ditto.
|
||||
(darwin_kill_inferior): Add ops argument.
|
||||
(darwin_pid_to_str): New function.
|
||||
(darwin_thread_alive): Ditto.
|
||||
(darwin_inf, darwin_not_port): Removed.
|
||||
(darwin_inf_fake_stop): New variable.
|
||||
(msgin, msgout, msg_state, exc_msg): Removed.
|
||||
(mach_check_error): Use warning instead of error.
|
||||
(darwin_ptrace): Adjust debug level.
|
||||
(cmp_thread_t): Fix names (typo).
|
||||
(darwin_check_new_threads): Argument is now an inferior,
|
||||
adjust for new structures, add no change check, ignore dead ports,
|
||||
handle first thread case.
|
||||
(find_inferior_task_it): New function.
|
||||
(find_inferior_notify_it): Ditto.
|
||||
(darwin_find_inferior_by_task): Ditto.
|
||||
(darwin_find_inferior_by_notify): Ditto.
|
||||
(darwin_find_thread): Ditto.
|
||||
(darwin_suspend_inferior): Ditto.
|
||||
(darwin_resume_inferior): Ditto.
|
||||
(catch_exception_raise_state): Removed.
|
||||
(catch_exception_raise_state_identity): Removed.
|
||||
(darwin_suspend_inferior_it): New function.
|
||||
(darwin_resume_inferior_it): Ditto.
|
||||
(darwin_dump_message): New function, extracted from darwin_wait.
|
||||
(darwin_decode_exception_message): New function.
|
||||
(darwin_encode_reply): New function.
|
||||
(catch_exception_raise): Removed.
|
||||
(darwin_send_reply): New function, extracted from darwin_resume.
|
||||
(darwin_resume_thread): New function, extracted from darwin_resume.
|
||||
(struct resume_inferior_threads_param): New type.
|
||||
(darwin_resume_inferior_threads_it): New function.
|
||||
(darwin_resume_inferior_threads): New function.
|
||||
(darwin_suspend_inferior_threads): New function.
|
||||
(darwin_resume): Mostly rewritten to handle multiple threads and
|
||||
some corner cases.
|
||||
(darwin_decode_message): New function extracted from darwin_wait.
|
||||
(cancel_breakpoint): New function.
|
||||
(darwin_wait): Mostly rewritten. Handle multiple threads.
|
||||
(darwin_mourn_inferior): Adjust for per process structures.
|
||||
(darwin_reply_to_all_pending_messages): New function.
|
||||
(darwin_stop_inferior): Adjust for per inferior structures.
|
||||
(darwin_attach_pid): Ditto.
|
||||
(darwin_init_thread_list): Ditto.
|
||||
(darwin_attach): Ditto.
|
||||
(darwin_detach): Ditto.
|
||||
(darwin_files_info): Now empty.
|
||||
(darwin_pid_to_str): Adjust returns string to match one expected by
|
||||
the testsuite.
|
||||
(darwin_read_write_inferior): Rename err variable to match other uses.
|
||||
Adjust debug message. Handle submaps.
|
||||
(darwin_xfer_memory): Adjust for per inferior structures.
|
||||
(set_enable_mach_exceptions): Ditto.
|
||||
(darwin_pid_to_exec_file): New function.
|
||||
(darwin_get_ada_task_ptid): Ditto.
|
||||
(darwin_supports_multi_process): Ditto.
|
||||
(_initialize_darwin_inferior): Remove useless assertion, adjust for
|
||||
per inferior structures. Add new target operations.
|
||||
|
||||
2009-06-18 Hui Zhu <teawater@gmail.com>
|
||||
Michael Snyder <msnyder@vmware.com>
|
||||
|
||||
|
@ -1,5 +1,5 @@
|
||||
/* Darwin support for GDB, the GNU debugger.
|
||||
Copyright 1997, 1998, 1999, 2000, 2001, 2002, 2008, 2009
|
||||
Copyright 1997, 1998, 1999, 2000, 2001, 2002, 2008
|
||||
Free Software Foundation, Inc.
|
||||
|
||||
Contributed by Apple Computer, Inc.
|
||||
@ -8,7 +8,7 @@
|
||||
|
||||
This program is free software; you can redistribute it and/or modify
|
||||
it under the terms of the GNU General Public License as published by
|
||||
the Free Software Foundation; either version 3 of the License, or
|
||||
the Free Software Foundation; either version 2 of the License, or
|
||||
(at your option) any later version.
|
||||
|
||||
This program is distributed in the hope that it will be useful,
|
||||
@ -17,7 +17,9 @@
|
||||
GNU General Public License for more details.
|
||||
|
||||
You should have received a copy of the GNU General Public License
|
||||
along with this program. If not, see <http://www.gnu.org/licenses/>. */
|
||||
along with this program; if not, write to the Free Software
|
||||
Foundation, Inc., 59 Temple Place - Suite 330,
|
||||
Boston, MA 02111-1307, USA. */
|
||||
|
||||
/* The name of the ppc_thread_state structure, and the names of its
|
||||
members, have been changed for Unix conformance reasons. The easiest
|
||||
@ -118,9 +120,9 @@ get_task_from_args (char *args)
|
||||
|
||||
if (args == NULL || *args == 0)
|
||||
{
|
||||
if (darwin_inf->task == TASK_NULL)
|
||||
if (ptid_equal (inferior_ptid, null_ptid))
|
||||
printf_unfiltered (_("No inferior running\n"));
|
||||
return darwin_inf->task;
|
||||
return current_inferior ()->private->task;
|
||||
}
|
||||
if (strcmp (args, "gdb") == 0)
|
||||
return mach_task_self ();
|
||||
@ -252,27 +254,46 @@ info_mach_ports_command (char *args, int from_tty)
|
||||
printf_unfiltered (_(" gdb-task"));
|
||||
else if (port == darwin_host_self)
|
||||
printf_unfiltered (_(" host-self"));
|
||||
else if (port == darwin_not_port)
|
||||
printf_unfiltered (_(" gdb-notifier"));
|
||||
else if (port == darwin_ex_port)
|
||||
printf_unfiltered (_(" gdb-exception"));
|
||||
else if (port == darwin_port_set)
|
||||
printf_unfiltered (_(" gdb-port_set"));
|
||||
else if (darwin_inf && port == darwin_inf->task)
|
||||
else if (!ptid_equal (inferior_ptid, null_ptid))
|
||||
{
|
||||
struct inferior *inf = current_inferior ();
|
||||
|
||||
if (port == inf->private->task)
|
||||
printf_unfiltered (_(" inferior-task"));
|
||||
else if (darwin_inf && darwin_inf->threads)
|
||||
else if (port == inf->private->notify_port)
|
||||
printf_unfiltered (_(" inferior-notify"));
|
||||
else
|
||||
{
|
||||
int k;
|
||||
thread_t t;
|
||||
for (k = 0; VEC_iterate(thread_t, darwin_inf->threads, k, t); k++)
|
||||
if (port == t)
|
||||
darwin_thread_t *t;
|
||||
|
||||
for (k = 0; k < inf->private->exception_info.count; k++)
|
||||
if (port == inf->private->exception_info.ports[k])
|
||||
{
|
||||
printf_unfiltered (_(" inferior-excp-port"));
|
||||
break;
|
||||
}
|
||||
|
||||
if (inf->private->threads)
|
||||
{
|
||||
for (k = 0;
|
||||
VEC_iterate(darwin_thread_t,
|
||||
inf->private->threads, k, t);
|
||||
k++)
|
||||
if (port == t->gdb_port)
|
||||
{
|
||||
printf_unfiltered (_(" inferior-thread for 0x%x"),
|
||||
darwin_inf->task);
|
||||
inf->private->task);
|
||||
break;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
printf_unfiltered (_("\n"));
|
||||
}
|
||||
|
||||
@ -600,12 +621,36 @@ darwin_debug_regions_recurse (task_t task)
|
||||
vm_region_submap_short_info_data_64_t r_info;
|
||||
kern_return_t kret;
|
||||
int ret;
|
||||
struct cleanup *table_chain;
|
||||
|
||||
table_chain = make_cleanup_ui_out_table_begin_end (uiout, 9, -1, "regions");
|
||||
|
||||
if (gdbarch_addr_bit (current_gdbarch) <= 32)
|
||||
{
|
||||
ui_out_table_header (uiout, 10, ui_left, "start", "Start");
|
||||
ui_out_table_header (uiout, 10, ui_left, "end", "End");
|
||||
}
|
||||
else
|
||||
{
|
||||
ui_out_table_header (uiout, 18, ui_left, "start", "Start");
|
||||
ui_out_table_header (uiout, 18, ui_left, "end", "End");
|
||||
}
|
||||
ui_out_table_header (uiout, 3, ui_left, "min-prot", "Min");
|
||||
ui_out_table_header (uiout, 3, ui_left, "max-prot", "Max");
|
||||
ui_out_table_header (uiout, 5, ui_left, "inheritence", "Inh");
|
||||
ui_out_table_header (uiout, 9, ui_left, "share-mode", "Shr");
|
||||
ui_out_table_header (uiout, 1, ui_left, "depth", "D");
|
||||
ui_out_table_header (uiout, 3, ui_left, "submap", "Sm");
|
||||
ui_out_table_header (uiout, 0, ui_noalign, "tag", "Tag");
|
||||
|
||||
ui_out_table_body (uiout);
|
||||
|
||||
r_start = 0;
|
||||
r_depth = 0;
|
||||
while (1)
|
||||
{
|
||||
const char *tag;
|
||||
struct cleanup *row_chain;
|
||||
|
||||
r_info_size = VM_REGION_SUBMAP_SHORT_INFO_COUNT_64;
|
||||
r_size = -1;
|
||||
@ -614,25 +659,39 @@ darwin_debug_regions_recurse (task_t task)
|
||||
&r_info_size);
|
||||
if (kret != KERN_SUCCESS)
|
||||
break;
|
||||
printf_filtered (_("%s-%s %s/%s %-5s %-10s %2d %s"),
|
||||
paddr(r_start),
|
||||
paddr(r_start + r_size),
|
||||
unparse_protection (r_info.protection),
|
||||
unparse_protection (r_info.max_protection),
|
||||
unparse_inheritance (r_info.inheritance),
|
||||
unparse_share_mode (r_info.share_mode),
|
||||
r_depth,
|
||||
row_chain = make_cleanup_ui_out_tuple_begin_end (uiout, "regions-row");
|
||||
|
||||
ui_out_field_core_addr (uiout, "start", r_start);
|
||||
ui_out_field_core_addr (uiout, "end", r_start + r_size);
|
||||
ui_out_field_string (uiout, "min-prot",
|
||||
unparse_protection (r_info.protection));
|
||||
ui_out_field_string (uiout, "max-prot",
|
||||
unparse_protection (r_info.max_protection));
|
||||
ui_out_field_string (uiout, "inheritence",
|
||||
unparse_inheritance (r_info.inheritance));
|
||||
ui_out_field_string (uiout, "share-mode",
|
||||
unparse_share_mode (r_info.share_mode));
|
||||
ui_out_field_int (uiout, "depth", r_depth);
|
||||
ui_out_field_string (uiout, "submap",
|
||||
r_info.is_submap ? _("sm ") : _("obj"));
|
||||
tag = unparse_user_tag (r_info.user_tag);
|
||||
if (tag)
|
||||
printf_unfiltered (_(" %s\n"), tag);
|
||||
ui_out_field_string (uiout, "tag", tag);
|
||||
else
|
||||
printf_unfiltered (_(" %u\n"), r_info.user_tag);
|
||||
ui_out_field_int (uiout, "tag", r_info.user_tag);
|
||||
|
||||
do_cleanups (row_chain);
|
||||
|
||||
if (!ui_out_is_mi_like_p (uiout))
|
||||
ui_out_text (uiout, "\n");
|
||||
|
||||
if (r_info.is_submap)
|
||||
r_depth++;
|
||||
else
|
||||
r_start += r_size;
|
||||
}
|
||||
do_cleanups (table_chain);
|
||||
|
||||
}
|
||||
|
||||
|
||||
@ -672,6 +731,7 @@ info_mach_region_command (char *exp, int from_tty)
|
||||
struct expression *expr;
|
||||
struct value *val;
|
||||
mach_vm_address_t address;
|
||||
struct inferior *inf;
|
||||
|
||||
expr = parse_expression (exp);
|
||||
val = evaluate_expression (expr);
|
||||
@ -679,22 +739,13 @@ info_mach_region_command (char *exp, int from_tty)
|
||||
{
|
||||
val = value_ind (val);
|
||||
}
|
||||
/* In rvalue contexts, such as this, functions are coerced into
|
||||
pointers to functions. */
|
||||
if (TYPE_CODE (value_type (val)) == TYPE_CODE_FUNC
|
||||
&& VALUE_LVAL (val) == lval_memory)
|
||||
{
|
||||
address = value_address (val);
|
||||
}
|
||||
else
|
||||
{
|
||||
address = value_as_address (val);
|
||||
}
|
||||
|
||||
if ((!darwin_inf) || (darwin_inf->task == TASK_NULL))
|
||||
if (ptid_equal (inferior_ptid, null_ptid))
|
||||
error (_("Inferior not available"));
|
||||
|
||||
darwin_debug_region (darwin_inf->task, address);
|
||||
inf = current_inferior ();
|
||||
darwin_debug_region (inf->private->task, address);
|
||||
}
|
||||
|
||||
static void
|
||||
@ -761,9 +812,9 @@ info_mach_exceptions_command (char *args, int from_tty)
|
||||
{
|
||||
if (strcmp (args, "saved") == 0)
|
||||
{
|
||||
if (darwin_inf->task == TASK_NULL)
|
||||
error (_("No inferior running\n"));
|
||||
disp_exception (&darwin_inf->exception_info);
|
||||
if (ptid_equal (inferior_ptid, null_ptid))
|
||||
printf_unfiltered (_("No inferior running\n"));
|
||||
disp_exception (¤t_inferior ()->private->exception_info);
|
||||
return;
|
||||
}
|
||||
else if (strcmp (args, "host") == 0)
|
||||
@ -780,11 +831,14 @@ info_mach_exceptions_command (char *args, int from_tty)
|
||||
}
|
||||
else
|
||||
{
|
||||
if (darwin_inf->task == TASK_NULL)
|
||||
error (_("No inferior running\n"));
|
||||
struct inferior *inf;
|
||||
|
||||
if (ptid_equal (inferior_ptid, null_ptid))
|
||||
printf_unfiltered (_("No inferior running\n"));
|
||||
inf = current_inferior ();
|
||||
|
||||
kret = task_get_exception_ports
|
||||
(darwin_inf->task, EXC_MASK_ALL, info.masks,
|
||||
(inf->private->task, EXC_MASK_ALL, info.masks,
|
||||
&info.count, info.ports, info.behaviors, info.flavors);
|
||||
MACH_CHECK_ERROR (kret);
|
||||
disp_exception (&info);
|
||||
|
1711
gdb/darwin-nat.c
1711
gdb/darwin-nat.c
File diff suppressed because it is too large
Load Diff
@ -22,9 +22,6 @@
|
||||
#include <mach/mach.h>
|
||||
#include "gdb_assert.h"
|
||||
|
||||
/* Define the threads vector type. */
|
||||
DEF_VEC_I (thread_t);
|
||||
|
||||
/* Describe the mach exception handling state for a task. This state is saved
|
||||
before being changed and restored when a process is detached.
|
||||
For more information on these fields see task_get_exception_ports manual
|
||||
@ -48,35 +45,83 @@ struct darwin_exception_info
|
||||
};
|
||||
typedef struct darwin_exception_info darwin_exception_info;
|
||||
|
||||
/* Describe an inferior. */
|
||||
struct darwin_inferior
|
||||
struct darwin_exception_msg
|
||||
{
|
||||
/* Inferior PID. */
|
||||
int pid;
|
||||
mach_msg_header_t header;
|
||||
|
||||
/* Thread and task taking the exception. */
|
||||
mach_port_t thread_port;
|
||||
mach_port_t task_port;
|
||||
|
||||
/* Type of the exception. */
|
||||
exception_type_t ex_type;
|
||||
|
||||
/* Machine dependent details. */
|
||||
mach_msg_type_number_t data_count;
|
||||
integer_t ex_data[2];
|
||||
};
|
||||
|
||||
enum darwin_msg_state { DARWIN_RUNNING, DARWIN_STOPPED, DARWIN_MESSAGE };
|
||||
|
||||
struct private_thread_info
|
||||
{
|
||||
/* The thread port from a GDB point of view. */
|
||||
thread_t gdb_port;
|
||||
|
||||
/* The thread port from the inferior point of view. Not to be used inside
|
||||
gdb except for get_ada_task_ptid. */
|
||||
thread_t inf_port;
|
||||
|
||||
/* Current message state.
|
||||
If the kernel has sent a message it expects a reply and the inferior
|
||||
can't be killed before. */
|
||||
enum darwin_msg_state msg_state;
|
||||
|
||||
/* True if this thread is single-stepped. */
|
||||
unsigned char single_step;
|
||||
|
||||
/* True if a signal was manually sent to the thread. */
|
||||
unsigned char signaled;
|
||||
|
||||
/* The last exception received. */
|
||||
struct darwin_exception_msg event;
|
||||
};
|
||||
typedef struct private_thread_info darwin_thread_t;
|
||||
|
||||
/* Define the threads vector type. */
|
||||
DEF_VEC_O (darwin_thread_t);
|
||||
|
||||
|
||||
/* Describe an inferior. */
|
||||
struct private_inferior
|
||||
{
|
||||
/* Corresponding task port. */
|
||||
task_t task;
|
||||
|
||||
/* Previous port for request notification on task. */
|
||||
mach_port_t prev_not_port;
|
||||
/* Port which will receive the dead-name notification for the task port.
|
||||
This is used to detect the death of the task. */
|
||||
mach_port_t notify_port;
|
||||
|
||||
/* Initial exception handling. */
|
||||
darwin_exception_info exception_info;
|
||||
|
||||
/* Sorted vector of known threads. */
|
||||
VEC(thread_t) *threads;
|
||||
};
|
||||
typedef struct darwin_inferior darwin_inferior;
|
||||
/* Number of messages that have been received but not yet replied. */
|
||||
unsigned int pending_messages;
|
||||
|
||||
/* Current inferior. */
|
||||
extern darwin_inferior *darwin_inf;
|
||||
/* Set if inferior is not controlled by ptrace(2) but through Mach. */
|
||||
unsigned char no_ptrace;
|
||||
|
||||
/* True if this task is suspended. */
|
||||
unsigned char suspended;
|
||||
|
||||
/* Sorted vector of known threads. */
|
||||
VEC(darwin_thread_t) *threads;
|
||||
};
|
||||
typedef struct private_inferior darwin_inferior;
|
||||
|
||||
/* Exception port. */
|
||||
extern mach_port_t darwin_ex_port;
|
||||
|
||||
/* Notification port. */
|
||||
extern mach_port_t darwin_not_port;
|
||||
|
||||
/* Port set. */
|
||||
extern mach_port_t darwin_port_set;
|
||||
|
||||
|
@ -103,7 +103,6 @@ macho_symtab_read (struct objfile *objfile,
|
||||
{
|
||||
struct gdbarch *gdbarch = get_objfile_arch (objfile);
|
||||
long storage_needed;
|
||||
asymbol *sym;
|
||||
long i, j;
|
||||
CORE_ADDR offset;
|
||||
enum minimal_symbol_type ms_type;
|
||||
@ -114,15 +113,16 @@ macho_symtab_read (struct objfile *objfile,
|
||||
|
||||
for (i = 0; i < number_of_symbols; i++)
|
||||
{
|
||||
sym = symbol_table[i];
|
||||
asymbol *sym = symbol_table[i];
|
||||
bfd_mach_o_asymbol *mach_o_sym = (bfd_mach_o_asymbol *)sym;
|
||||
|
||||
offset = ANOFFSET (objfile->section_offsets, sym->section->index);
|
||||
|
||||
if (sym->flags & BSF_DEBUGGING)
|
||||
{
|
||||
unsigned char type = BFD_MACH_O_SYM_NTYPE(sym);
|
||||
bfd_vma addr;
|
||||
|
||||
switch (type)
|
||||
switch (mach_o_sym->n_type)
|
||||
{
|
||||
case N_SO:
|
||||
if ((sym->name == NULL || sym->name[0] == 0)
|
||||
|
Loading…
Reference in New Issue
Block a user