From: Andrew Burgess <andrew.burgess@embecosm.com>
To: Simon Marchi <simon.marchi@polymtl.ca>
Cc: gdb-patches@sourceware.org, koachan+sourceware@protonmail.com
Subject: Re: [PATCH gdb-10-branch candidate] gdb: set current thread in sparc_{fetch,collect}_inferior_registers (PR gdb/27147)
Date: Thu, 4 Mar 2021 10:14:04 +0000 [thread overview]
Message-ID: <20210304101404.GB1720904@embecosm.com> (raw)
In-Reply-To: <20210304004917.1283945-1-simon.marchi@polymtl.ca>
* Simon Marchi <simon.marchi@polymtl.ca> [2021-03-03 19:49:17 -0500]:
> PR 27147 shows that on sparc64, GDB is unable to properly unwind:
>
> Expected result (from GDB 9.2):
>
> #0 0x0000000000108de4 in puts ()
> #1 0x0000000000100950 in hello () at gdb-test.c:4
> #2 0x0000000000100968 in main () at gdb-test.c:8
>
> Actual result (from GDB latest git):
>
> #0 0x0000000000108de4 in puts ()
> #1 0x0000000000100950 in hello () at gdb-test.c:4
> Backtrace stopped: previous frame inner to this frame (corrupt stack?)
>
> The first failing commit is 5b6d1e4fa4fc ("Multi-target support"). The cause
> of the change in behavior is due to (thanks for Andrew Burgess for finding
> this):
>
> - inferior_ptid is no longer set on entry of target_ops::wait, whereas
> it was set to something valid previously
> - deep down in linux_nat_target::wait (see stack trace below), we fetch
> the registers of the event thread
> - on sparc64, fetching registers involves reading memory (in
> sparc_supply_rwindow, see stack trace below)
> - reading memory (target_ops::xfer_partial) relies on inferior_ptid
> being set to the thread from which we want to read memory
>
> This is where things go wrong:
>
> #0 linux_nat_target::xfer_partial (this=0x10000fa2c40 <the_sparc64_linux_nat_target>, object=TARGET_OBJECT_MEMORY, annex=0x0, readbuf=0x7feffe3b000 "", writebuf=0x0, offset=8791798050744, len=8, xfered_len=0x7feffe3ae88) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:3697
> #1 0x00000100007f5b10 in raw_memory_xfer_partial (ops=0x10000fa2c40 <the_sparc64_linux_nat_target>, readbuf=0x7feffe3b000 "", writebuf=0x0, memaddr=8791798050744, len=8, xfered_len=0x7feffe3ae88) at /home/simark/src/binutils-gdb/gdb/target.c:912
> #2 0x00000100007f60e8 in memory_xfer_partial_1 (ops=0x10000fa2c40 <the_sparc64_linux_nat_target>, object=TARGET_OBJECT_MEMORY, readbuf=0x7feffe3b000 "", writebuf=0x0, memaddr=8791798050744, len=8, xfered_len=0x7feffe3ae88) at /home/simark/src/binutils-gdb/gdb/target.c:1043
> #3 0x00000100007f61b4 in memory_xfer_partial (ops=0x10000fa2c40 <the_sparc64_linux_nat_target>, object=TARGET_OBJECT_MEMORY, readbuf=0x7feffe3b000 "", writebuf=0x0, memaddr=8791798050744, len=8, xfered_len=0x7feffe3ae88) at /home/simark/src/binutils-gdb/gdb/target.c:1072
> #4 0x00000100007f6538 in target_xfer_partial (ops=0x10000fa2c40 <the_sparc64_linux_nat_target>, object=TARGET_OBJECT_MEMORY, annex=0x0, readbuf=0x7feffe3b000 "", writebuf=0x0, offset=8791798050744, len=8, xfered_len=0x7feffe3ae88) at /home/simark/src/binutils-gdb/gdb/target.c:1129
> #5 0x00000100007f7094 in target_read_partial (ops=0x10000fa2c40 <the_sparc64_linux_nat_target>, object=TARGET_OBJECT_MEMORY, annex=0x0, buf=0x7feffe3b000 "", offset=8791798050744, len=8, xfered_len=0x7feffe3ae88) at /home/simark/src/binutils-gdb/gdb/target.c:1375
> #6 0x00000100007f721c in target_read (ops=0x10000fa2c40 <the_sparc64_linux_nat_target>, object=TARGET_OBJECT_MEMORY, annex=0x0, buf=0x7feffe3b000 "", offset=8791798050744, len=8) at /home/simark/src/binutils-gdb/gdb/target.c:1415
> #7 0x00000100007f69d4 in target_read_memory (memaddr=8791798050744, myaddr=0x7feffe3b000 "", len=8) at /home/simark/src/binutils-gdb/gdb/target.c:1218
> #8 0x0000010000758520 in sparc_supply_rwindow (regcache=0x10000fea4f0, sp=8791798050736, regnum=-1) at /home/simark/src/binutils-gdb/gdb/sparc-tdep.c:1960
> #9 0x000001000076208c in sparc64_supply_gregset (gregmap=0x10000be3190 <sparc64_linux_ptrace_gregmap>, regcache=0x10000fea4f0, regnum=-1, gregs=0x7feffe3b230) at /home/simark/src/binutils-gdb/gdb/sparc64-tdep.c:1974
> #10 0x0000010000751b64 in sparc_fetch_inferior_registers (regcache=0x10000fea4f0, regnum=80) at /home/simark/src/binutils-gdb/gdb/sparc-nat.c:170
> #11 0x0000010000759d68 in sparc64_linux_nat_target::fetch_registers (this=0x10000fa2c40 <the_sparc64_linux_nat_target>, regcache=0x10000fea4f0, regnum=80) at /home/simark/src/binutils-gdb/gdb/sparc64-linux-nat.c:38
> #12 0x00000100008146ec in target_fetch_registers (regcache=0x10000fea4f0, regno=80) at /home/simark/src/binutils-gdb/gdb/target.c:3287
> #13 0x00000100006a8c5c in regcache::raw_update (this=0x10000fea4f0, regnum=80) at /home/simark/src/binutils-gdb/gdb/regcache.c:584
> #14 0x00000100006a8d94 in readable_regcache::raw_read (this=0x10000fea4f0, regnum=80, buf=0x7feffe3b7c0 "") at /home/simark/src/binutils-gdb/gdb/regcache.c:598
> #15 0x00000100006a93b8 in readable_regcache::cooked_read (this=0x10000fea4f0, regnum=80, buf=0x7feffe3b7c0 "") at /home/simark/src/binutils-gdb/gdb/regcache.c:690
> #16 0x00000100006b288c in readable_regcache::cooked_read<unsigned long, void> (this=0x10000fea4f0, regnum=80, val=0x7feffe3b948) at /home/simark/src/binutils-gdb/gdb/regcache.c:777
> #17 0x00000100006a9b44 in regcache_cooked_read_unsigned (regcache=0x10000fea4f0, regnum=80, val=0x7feffe3b948) at /home/simark/src/binutils-gdb/gdb/regcache.c:791
> #18 0x00000100006abf3c in regcache_read_pc (regcache=0x10000fea4f0) at /home/simark/src/binutils-gdb/gdb/regcache.c:1295
> #19 0x0000010000507920 in save_stop_reason (lp=0x10000fc5b10) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:2612
> #20 0x00000100005095a4 in linux_nat_filter_event (lwpid=520983, status=1407) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:3050
> #21 0x0000010000509f9c in linux_nat_wait_1 (ptid=..., ourstatus=0x7feffe3c8f0, target_options=...) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:3194
> #22 0x000001000050b1d0 in linux_nat_target::wait (this=0x10000fa2c40 <the_sparc64_linux_nat_target>, ptid=..., ourstatus=0x7feffe3c8f0, target_options=...) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:3432
> #23 0x00000100007f8ac0 in target_wait (ptid=..., status=0x7feffe3c8f0, options=...) at /home/simark/src/binutils-gdb/gdb/target.c:2000
> #24 0x00000100004ac17c in do_target_wait_1 (inf=0x1000116d280, ptid=..., status=0x7feffe3c8f0, options=...) at /home/simark/src/binutils-gdb/gdb/infrun.c:3464
> #25 0x00000100004ac3b8 in operator() (__closure=0x7feffe3c678, inf=0x1000116d280) at /home/simark/src/binutils-gdb/gdb/infrun.c:3527
> #26 0x00000100004ac7cc in do_target_wait (wait_ptid=..., ecs=0x7feffe3c8c8, options=...) at /home/simark/src/binutils-gdb/gdb/infrun.c:3540
> #27 0x00000100004ad8c4 in fetch_inferior_event () at /home/simark/src/binutils-gdb/gdb/infrun.c:3880
> #28 0x0000010000485568 in inferior_event_handler (event_type=INF_REG_EVENT) at /home/simark/src/binutils-gdb/gdb/inf-loop.c:42
> #29 0x000001000050d394 in handle_target_event (error=0, client_data=0x0) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:4060
> #30 0x0000010000ab5c8c in handle_file_event (file_ptr=0x10001207270, ready_mask=1) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:575
> #31 0x0000010000ab6334 in gdb_wait_for_event (block=0) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:701
> #32 0x0000010000ab487c in gdb_do_one_event () at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:212
> #33 0x0000010000542668 in start_event_loop () at /home/simark/src/binutils-gdb/gdb/main.c:348
> #34 0x000001000054287c in captured_command_loop () at /home/simark/src/binutils-gdb/gdb/main.c:408
> #35 0x0000010000544e84 in captured_main (data=0x7feffe3d188) at /home/simark/src/binutils-gdb/gdb/main.c:1242
> #36 0x0000010000544f2c in gdb_main (args=0x7feffe3d188) at /home/simark/src/binutils-gdb/gdb/main.c:1257
> #37 0x00000100000c1f14 in main (argc=4, argv=0x7feffe3d548) at /home/simark/src/binutils-gdb/gdb/gdb.c:32
>
> There is a target_read_memory call in sparc_supply_rwindow, whose return
> value is not checked. That call fails, because inferior_ptid does not
> contain a valid ptid, and uninitialized buffer contents is used.
> Ultimately it results in a corrupt stop_pc.
>
> target_ops::fetch_registers can be (and should remain, in my opinion)
> independent of inferior_ptid, because the ptid of the thread from which
> to fetch registers can be obtained from the regcache. In other words,
> implementations of target_ops::fetch_registers should not rely on
> inferior_ptid having a sensible value on entry.
>
> The sparc64_linux_nat_target::fetch_registers case is special, because it calls
> a target method that is dependent on the inferior_ptid value
> (target_read_inferior, and ultimately target_ops::xfer_partial). So I would
> say it's the responsibility of sparc64_linux_nat_target::fetch_registers to set
> up inferior_ptid correctly prior to calling target_read_inferior.
>
> This patch makes sparc64_linux_nat_target::fetch_registers (and
> store_registers, since it works the same) temporarily set inferior_ptid. If we
> ever make target_ops::xfer_partial independent of inferior_ptid, setting
> inferior_ptid won't be necessary, we'll simply pass down the ptid as a
> parameter in some way.
>
> I chose to set/restore inferior_ptid in sparc_fetch_inferior_registers, because
> I am not convinced that doing so in an inner location (in sparc_supply_rwindow
> for instance) would always be correct. We have access to the ptid in
> sparc_supply_rwindow (from the regcache), so we _could_ set inferior_ptid
> there. However, I don't want to just set inferior_ptid, as that would make it
> not desync'ed with `current_thread ()` and `current_inferior ()`. It's
> preferable to use switch_to_thread instead, as that switches all the global
> "current" stuff in a coherent way. But doing so requires a `thread_info *`,
> and getting a `thread_info *` from a ptid requires a `process_stratum_target
> *`. We could use `current_inferior()->process_target()` in
> sparc_supply_rwindow for this (using target_read_memory uses the current
> inferior's target stack anyway). However, sparc_supply_rwindow is also used in
> the context of BSD uthreads, where a thread stratum target defines threads. I
> presume the ptid in the regcache would be the ptid of the uthread, defined by
> the thread stratum target (bsd_uthread_target). Using
> `current_inferior()->process_target()` would look up a ptid defined by the
> thread stratum target using the process stratum target. I don't think it would
> give good results. So I prefer playing it safe and looking up the thread
> earlier, in sparc_fetch_inferior_registers.
>
> I added some assertions (in sparc_supply_rwindow and others) to verify
> that the regcache's ptid matches inferior_ptid. That verifies that the
> caller has properly set the correct global context. This would have
> caught (though a failed assertion) the current problem.
>
> gdb/ChangeLog:
>
> PR gdb/27147
> * sparc-nat.h (sparc_fetch_inferior_registers): Add
> process_stratum_target parameter,
> sparc_store_inferior_registers): update callers.
> * sparc-nat.c (sparc_fetch_inferior_registers,
> sparc_store_inferior_registers): Add process_stratum_target
> parameter. Switch current thread before calling
> sparc_supply_gregset / sparc_collect_rwindow.
> (sparc_store_inferior_registers): Likewise.
> * sparc-obsd-tdep.c (sparc32obsd_supply_uthread): Add assertion.
> (sparc32obsd_collect_uthread): Likewise.
> * sparc-tdep.c (sparc_supply_rwindow, sparc_collect_rwindow):
> Add assertion.
> * sparc64-obsd-tdep.c (sparc64obsd_collect_uthread,
> sparc64obsd_supply_uthread): Add assertion.
LGTM.
Thanks,
Andrew
>
> Change-Id: I16c658cd70896cea604516714f7e2428fbaf4301
> ---
> gdb/sparc-nat.c | 19 +++++++++++++++++--
> gdb/sparc-nat.h | 10 ++++++----
> gdb/sparc-obsd-tdep.c | 7 +++++++
> gdb/sparc-tdep.c | 6 ++++++
> gdb/sparc64-linux-nat.c | 4 ++--
> gdb/sparc64-obsd-tdep.c | 7 +++++++
> 6 files changed, 45 insertions(+), 8 deletions(-)
>
> diff --git a/gdb/sparc-nat.c b/gdb/sparc-nat.c
> index bc3afce20277..fa3b32cee184 100644
> --- a/gdb/sparc-nat.c
> +++ b/gdb/sparc-nat.c
> @@ -147,7 +147,8 @@ sparc32_fpregset_supplies_p (struct gdbarch *gdbarch, int regnum)
> for all registers (including the floating-point registers). */
>
> void
> -sparc_fetch_inferior_registers (struct regcache *regcache, int regnum)
> +sparc_fetch_inferior_registers (process_stratum_target *proc_target,
> + regcache *regcache, int regnum)
> {
> struct gdbarch *gdbarch = regcache->arch ();
> ptid_t ptid = regcache->ptid ();
> @@ -167,6 +168,12 @@ sparc_fetch_inferior_registers (struct regcache *regcache, int regnum)
> if (gdb_ptrace (PTRACE_GETREGS, ptid, (PTRACE_TYPE_ARG3) ®s) == -1)
> perror_with_name (_("Couldn't get registers"));
>
> + /* Deep down, sparc_supply_rwindow reads memory, so needs the global
> + thread context to be set. */
> + thread_info *thread = find_thread_ptid (proc_target, ptid);
> + scoped_restore_current_thread restore_thread;
> + switch_to_thread (thread);
> +
> sparc_supply_gregset (sparc_gregmap, regcache, -1, ®s);
> if (regnum != -1)
> return;
> @@ -184,7 +191,8 @@ sparc_fetch_inferior_registers (struct regcache *regcache, int regnum)
> }
>
> void
> -sparc_store_inferior_registers (struct regcache *regcache, int regnum)
> +sparc_store_inferior_registers (process_stratum_target *proc_target,
> + regcache *regcache, int regnum)
> {
> struct gdbarch *gdbarch = regcache->arch ();
> ptid_t ptid = regcache->ptid ();
> @@ -208,6 +216,13 @@ sparc_store_inferior_registers (struct regcache *regcache, int regnum)
> ULONGEST sp;
>
> regcache_cooked_read_unsigned (regcache, SPARC_SP_REGNUM, &sp);
> +
> + /* Deep down, sparc_collect_rwindow writes memory, so needs the global
> + thread context to be set. */
> + thread_info *thread = find_thread_ptid (proc_target, ptid);
> + scoped_restore_current_thread restore_thread;
> + switch_to_thread (thread);
> +
> sparc_collect_rwindow (regcache, sp, regnum);
> }
>
> diff --git a/gdb/sparc-nat.h b/gdb/sparc-nat.h
> index 196bf1f2307e..9d0c24f731f6 100644
> --- a/gdb/sparc-nat.h
> +++ b/gdb/sparc-nat.h
> @@ -41,8 +41,10 @@ extern int (*sparc_fpregset_supplies_p) (struct gdbarch *gdbarch, int);
> extern int sparc32_gregset_supplies_p (struct gdbarch *gdbarch, int regnum);
> extern int sparc32_fpregset_supplies_p (struct gdbarch *gdbarch, int regnum);
>
> -extern void sparc_fetch_inferior_registers (struct regcache *, int);
> -extern void sparc_store_inferior_registers (struct regcache *, int);
> +extern void sparc_fetch_inferior_registers (process_stratum_target *proc_target,
> + regcache *, int);
> +extern void sparc_store_inferior_registers (process_stratum_target *proc_target,
> + regcache *, int);
>
> extern target_xfer_status sparc_xfer_wcookie (enum target_object object,
> const char *annex,
> @@ -59,10 +61,10 @@ template<typename BaseTarget>
> struct sparc_target : public BaseTarget
> {
> void fetch_registers (struct regcache *regcache, int regnum) override
> - { sparc_fetch_inferior_registers (regcache, regnum); }
> + { sparc_fetch_inferior_registers (this, regcache, regnum); }
>
> void store_registers (struct regcache *regcache, int regnum) override
> - { sparc_store_inferior_registers (regcache, regnum); }
> + { sparc_store_inferior_registers (this, regcache, regnum); }
>
> enum target_xfer_status xfer_partial (enum target_object object,
> const char *annex,
> diff --git a/gdb/sparc-obsd-tdep.c b/gdb/sparc-obsd-tdep.c
> index 6cd9227f8aed..e198e9702cdb 100644
> --- a/gdb/sparc-obsd-tdep.c
> +++ b/gdb/sparc-obsd-tdep.c
> @@ -25,6 +25,7 @@
> #include "regcache.h"
> #include "symtab.h"
> #include "trad-frame.h"
> +#include "inferior.h"
>
> #include "obsd-tdep.h"
> #include "sparc-tdep.h"
> @@ -158,6 +159,9 @@ sparc32obsd_supply_uthread (struct regcache *regcache,
> CORE_ADDR fp, fp_addr = addr + SPARC32OBSD_UTHREAD_FP_OFFSET;
> gdb_byte buf[4];
>
> + /* This function calls functions that depend on the global current thread. */
> + gdb_assert (regcache->ptid () == inferior_ptid);
> +
> gdb_assert (regnum >= -1);
>
> fp = read_memory_unsigned_integer (fp_addr, 4, byte_order);
> @@ -203,6 +207,9 @@ sparc32obsd_collect_uthread(const struct regcache *regcache,
> CORE_ADDR sp;
> gdb_byte buf[4];
>
> + /* This function calls functions that depend on the global current thread. */
> + gdb_assert (regcache->ptid () == inferior_ptid);
> +
> gdb_assert (regnum >= -1);
>
> if (regnum == SPARC_SP_REGNUM || regnum == -1)
> diff --git a/gdb/sparc-tdep.c b/gdb/sparc-tdep.c
> index 4f9c679b55cd..34f22879737a 100644
> --- a/gdb/sparc-tdep.c
> +++ b/gdb/sparc-tdep.c
> @@ -1948,6 +1948,9 @@ sparc_supply_rwindow (struct regcache *regcache, CORE_ADDR sp, int regnum)
> gdb_byte buf[8];
> int i;
>
> + /* This function calls functions that depend on the global current thread. */
> + gdb_assert (regcache->ptid () == inferior_ptid);
> +
> if (sp & 1)
> {
> /* Registers are 64-bit. */
> @@ -2022,6 +2025,9 @@ sparc_collect_rwindow (const struct regcache *regcache,
> gdb_byte buf[8];
> int i;
>
> + /* This function calls functions that depend on the global current thread. */
> + gdb_assert (regcache->ptid () == inferior_ptid);
> +
> if (sp & 1)
> {
> /* Registers are 64-bit. */
> diff --git a/gdb/sparc64-linux-nat.c b/gdb/sparc64-linux-nat.c
> index ad2cc35bd70f..b741d0216c32 100644
> --- a/gdb/sparc64-linux-nat.c
> +++ b/gdb/sparc64-linux-nat.c
> @@ -35,10 +35,10 @@ class sparc64_linux_nat_target final : public linux_nat_target
> public:
> /* Add our register access methods. */
> void fetch_registers (struct regcache *regcache, int regnum) override
> - { sparc_fetch_inferior_registers (regcache, regnum); }
> + { sparc_fetch_inferior_registers (this, regcache, regnum); }
>
> void store_registers (struct regcache *regcache, int regnum) override
> - { sparc_store_inferior_registers (regcache, regnum); }
> + { sparc_store_inferior_registers (this, regcache, regnum); }
>
> /* Override linux_nat_target low methods. */
>
> diff --git a/gdb/sparc64-obsd-tdep.c b/gdb/sparc64-obsd-tdep.c
> index 9e678d268ad7..cf3138a7ab14 100644
> --- a/gdb/sparc64-obsd-tdep.c
> +++ b/gdb/sparc64-obsd-tdep.c
> @@ -27,6 +27,7 @@
> #include "symtab.h"
> #include "objfiles.h"
> #include "trad-frame.h"
> +#include "inferior.h"
>
> #include "obsd-tdep.h"
> #include "sparc64-tdep.h"
> @@ -328,6 +329,9 @@ sparc64obsd_supply_uthread (struct regcache *regcache,
> CORE_ADDR fp, fp_addr = addr + SPARC64OBSD_UTHREAD_FP_OFFSET;
> gdb_byte buf[8];
>
> + /* This function calls functions that depend on the global current thread. */
> + gdb_assert (regcache->ptid () == inferior_ptid);
> +
> gdb_assert (regnum >= -1);
>
> fp = read_memory_unsigned_integer (fp_addr, 8, byte_order);
> @@ -373,6 +377,9 @@ sparc64obsd_collect_uthread(const struct regcache *regcache,
> CORE_ADDR sp;
> gdb_byte buf[8];
>
> + /* This function calls functions that depend on the global current thread. */
> + gdb_assert (regcache->ptid () == inferior_ptid);
> +
> gdb_assert (regnum >= -1);
>
> if (regnum == SPARC_SP_REGNUM || regnum == -1)
> --
> 2.30.1
>
next prev parent reply other threads:[~2021-03-04 10:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 0:49 [PATCH gdb-10-branch candidate] gdb: set current thread in sparc_{fetch, collect}_inferior_registers " Simon Marchi
2021-03-04 10:14 ` Andrew Burgess [this message]
2021-03-04 17:10 ` [PATCH gdb-10-branch candidate] gdb: set current thread in sparc_{fetch,collect}_inferior_registers " Simon Marchi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210304101404.GB1720904@embecosm.com \
--to=andrew.burgess@embecosm.com \
--cc=gdb-patches@sourceware.org \
--cc=koachan+sourceware@protonmail.com \
--cc=simon.marchi@polymtl.ca \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).