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sdt: Support fetching the probe sixth argument with MI machinery

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SDT calls dtrace_probe() directly, and this can be used to pass up to
five probe arguments directly.  To pass the sixth argument (SDT
currently doesn't support more than this), we use a hack: just add
additional parameters to the call and cast dtrace_probe accordingly.
This happens to work on amd64, but doesn't work in general.

Modify SDT to call dtrace_probe() after storing arguments beyond the
first five in thread-local storage.  Implement sdt_getargval() to fetch
extra argument values this way.  An alternative would be to use invop
handlers instead and make sdt_probe_func point to a breakpoint
instruction, so that one can extract arguments using the breakpoint
exception trapframe, but this makes the providers more expensive when
enabled and doesn't seem justified.  This approach works well unless we
want to add more than one or two more parameters to SDT probes, which
seems unlikely at present.

In particular, this fixes fetching the last argument of most ip and tcp
probes on arm64.

Reported by:	rwatson
Reviewed by:	Domagoj Stolfa
MFC after:	1 month
Sponsored by:	Innovate UK
Differential Revision:	https://reviews.freebsd.org/D45648
This commit is contained in:
Mark Johnston 2024-06-20 12:40:25 -04:00
parent 0667538b88
commit 70c712a86d
4 changed files with 38 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
sys/cddl/dev/dtrace/dtrace_cddl.h
View File

@ -79,7 +79,7 @@ typedef struct kdtrace_thread {
#ifdef __amd64__
uintptr_t td_dtrace_regv;
#endif
uint64_t td_hrtime; /* Last time on cpu. */
uintptr_t td_dtrace_sdt_arg[1]; /* Space for extra SDT args */
void *td_dtrace_sscr; /* Saved scratch space location. */
void *td_systrace_args; /* syscall probe arguments. */
uint64_t td_fasttrap_tp_gen; /* Tracepoint hash table gen. */
@ -110,6 +110,7 @@ typedef struct kdtrace_thread {
#define t_dtrace_scrpc td_dtrace->td_dtrace_scrpc
#define t_dtrace_astpc td_dtrace->td_dtrace_astpc
#define t_dtrace_regv td_dtrace->td_dtrace_regv
#define t_dtrace_sdt_arg td_dtrace->td_dtrace_sdt_arg
#define t_dtrace_sscr td_dtrace->td_dtrace_sscr
#define t_dtrace_systrace_args td_dtrace->td_systrace_args
#define t_fasttrap_tp_gen td_dtrace->td_fasttrap_tp_gen

35
sys/cddl/dev/sdt/sdt.c
View File

@ -58,8 +58,11 @@
#include <sys/dtrace.h>
#include <sys/dtrace_bsd.h>
#include <cddl/dev/dtrace/dtrace_cddl.h>
/* DTrace methods. */
static void sdt_getargdesc(void *, dtrace_id_t, void *, dtrace_argdesc_t *);
static uint64_t sdt_getargval(void *, dtrace_id_t, void *, int, int);
static void sdt_provide_probes(void *, dtrace_probedesc_t *);
static void sdt_destroy(void *, dtrace_id_t, void *);
static void sdt_enable(void *, dtrace_id_t, void *);
@ -93,7 +96,7 @@ static dtrace_pops_t sdt_pops = {
.dtps_suspend = NULL,
.dtps_resume = NULL,
.dtps_getargdesc = sdt_getargdesc,
.dtps_getargval = NULL,
.dtps_getargval = sdt_getargval,
.dtps_usermode = NULL,
.dtps_destroy = sdt_destroy,
};
@ -321,6 +324,23 @@ sdt_getargdesc(void *arg, dtrace_id_t id, void *parg, dtrace_argdesc_t *desc)
}
}
/*
* Fetch arguments beyond the first five passed directly to dtrace_probe().
* FreeBSD's SDT implement currently only supports up to 6 arguments, so we just
* need to handle arg5 here.
*/
static uint64_t
sdt_getargval(void *arg __unused, dtrace_id_t id __unused,
void *parg __unused, int argno, int aframes __unused)
{
if (argno != 5) {
DTRACE_CPUFLAG_SET(CPU_DTRACE_ILLOP);
return (0);
} else {
return (curthread->t_dtrace_sdt_arg[argno - 5]);
}
}
static void
sdt_destroy(void *arg, dtrace_id_t id, void *parg)
{
@ -449,14 +469,21 @@ sdt_load_probes_cb(linker_file_t lf, void *arg __unused)
return (0);
}
static void
sdt_dtrace_probe(dtrace_id_t id, uintptr_t arg0, uintptr_t arg1,
uintptr_t arg2, uintptr_t arg3, uintptr_t arg4, uintptr_t arg5)
{
curthread->t_dtrace_sdt_arg[0] = arg5;
dtrace_probe(id, arg0, arg1, arg2, arg3, arg4);
}
static void
sdt_load(void)
{
TAILQ_INIT(&sdt_prov_list);
sdt_probe_func = dtrace_probe;
sdt_probe6_func = (sdt_probe6_func_t)dtrace_probe;
sdt_probe_func = sdt_dtrace_probe;
sdt_kld_load_tag = EVENTHANDLER_REGISTER(kld_load, sdt_kld_load, NULL,
EVENTHANDLER_PRI_ANY);
@ -482,7 +509,6 @@ sdt_unload(void)
EVENTHANDLER_DEREGISTER(kld_unload_try, sdt_kld_unload_try_tag);
sdt_probe_func = sdt_probe_stub;
sdt_probe6_func = (sdt_probe6_func_t)sdt_probe_stub;
TAILQ_FOREACH_SAFE(prov, &sdt_prov_list, prov_entry, tmp) {
ret = dtrace_unregister(prov->id);
@ -515,3 +541,4 @@ SYSUNINIT(sdt_unload, SI_SUB_DTRACE_PROVIDER, SI_ORDER_ANY, sdt_unload, NULL);
DEV_MODULE(sdt, sdt_modevent, NULL);
MODULE_VERSION(sdt, 1);
MODULE_DEPEND(sdt, dtrace, 1, 1, 1);
MODULE_DEPEND(sdt, opensolaris, 1, 1, 1);

8
sys/kern/kern_sdt.c
View File

@ -28,6 +28,7 @@
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kdb.h>
#include <sys/proc.h>
#include <sys/sdt.h>
SDT_PROVIDER_DEFINE(sdt);
@ -37,7 +38,6 @@ SDT_PROVIDER_DEFINE(sdt);
* dtrace_probe() when it loads.
*/
sdt_probe_func_t sdt_probe_func = sdt_probe_stub;
sdt_probe6_func_t sdt_probe6_func = (sdt_probe6_func_t)sdt_probe_stub;
volatile bool __read_frequently sdt_probes_enabled;
/*
@ -48,7 +48,7 @@ volatile bool __read_frequently sdt_probes_enabled;
void
sdt_probe_stub(uint32_t id __unused, uintptr_t arg0 __unused,
uintptr_t arg1 __unused, uintptr_t arg2 __unused, uintptr_t arg3 __unused,
uintptr_t arg4 __unused)
uintptr_t arg4 __unused, uintptr_t arg5 __unused)
{
printf("sdt_probe_stub: unexpectedly called\n");
kdb_backtrace();
@ -58,12 +58,12 @@ void
sdt_probe(uint32_t id, uintptr_t arg0, uintptr_t arg1,
uintptr_t arg2, uintptr_t arg3, uintptr_t arg4)
{
sdt_probe_func(id, arg0, arg1, arg2, arg3, arg4);
sdt_probe_func(id, arg0, arg1, arg2, arg3, arg4, 0);
}
void
sdt_probe6(uint32_t id, uintptr_t arg0, uintptr_t arg1,
uintptr_t arg2, uintptr_t arg3, uintptr_t arg4, uintptr_t arg5)
{
sdt_probe6_func(id, arg0, arg1, arg2, arg3, arg4, arg5);
sdt_probe_func(id, arg0, arg1, arg2, arg3, arg4, arg5);
}

5
sys/sys/sdt.h
View File

@ -419,15 +419,12 @@ __sdt_probe##uniq:; \
* way to avoid having to rely on CDDL code.
*/
typedef void (*sdt_probe_func_t)(uint32_t, uintptr_t arg0, uintptr_t arg1,
uintptr_t arg2, uintptr_t arg3, uintptr_t arg4);
typedef void (*sdt_probe6_func_t)(uint32_t, uintptr_t arg0, uintptr_t arg1,
uintptr_t arg2, uintptr_t arg3, uintptr_t arg4, uintptr_t arg5);
/*
* The 'sdt' provider will set it to dtrace_probe when it loads.
*/
extern sdt_probe_func_t sdt_probe_func;
extern sdt_probe6_func_t sdt_probe6_func;
struct sdt_probe;
struct sdt_provider;
@ -466,7 +463,7 @@ struct sdt_provider {
};
void sdt_probe_stub(uint32_t, uintptr_t, uintptr_t, uintptr_t, uintptr_t,
uintptr_t);
uintptr_t, uintptr_t);
SDT_PROVIDER_DECLARE(sdt);