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Sundry changes to improve DTrace stability on FreeBSD/arm64, with possibly similar affects for other architectures #1

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Sundry changes to improve DTrace stability on FreeBSD/arm64, with possibly similar affects for other architectures #1

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ec3db25
Don't call instrumentable nanouptime() from within DTrace probes.
rwatson Dec 23, 2020
4de37d6
On FreeBSD/amd64, don't allow instrumentation of handle_el1h_sync.
rwatson Dec 23, 2020
e14fc5f
Don't allow FBT to instrument DDB, which makes debugging FBT quite hard.
rwatson Dec 23, 2020
e73f2bb
Blacklist one more exception-handling related function from being
rwatson Dec 23, 2020
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3 changes: 2 additions & 1 deletion sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@ __FBSDID("$FreeBSD$");
extern dtrace_id_t dtrace_probeid_error;
extern int (*dtrace_invop_jump_addr)(struct trapframe *);
extern void dtrace_getnanotime(struct timespec *tsp);
extern void dtrace_getnanouptime(struct timespec *tsp);

int dtrace_invop(uintptr_t, struct trapframe *, uintptr_t);
void dtrace_invop_init(void);
Expand Down Expand Up @@ -163,7 +164,7 @@ dtrace_gethrtime()
{
struct timespec curtime;

nanouptime(&curtime);
dtrace_getnanouptime(&curtime);

return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);

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3 changes: 2 additions & 1 deletion sys/cddl/dev/dtrace/arm/dtrace_subr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,7 @@ __FBSDID("$FreeBSD$");
extern dtrace_id_t dtrace_probeid_error;
extern int (*dtrace_invop_jump_addr)(struct trapframe *);
extern void dtrace_getnanotime(struct timespec *tsp);
extern void dtrace_getnanouptime(struct timespec *tsp);

int dtrace_invop(uintptr_t, struct trapframe *, uintptr_t);
void dtrace_invop_init(void);
Expand Down Expand Up @@ -174,7 +175,7 @@ dtrace_gethrtime()
{
struct timespec curtime;

nanouptime(&curtime);
dtrace_getnanouptime(&curtime);

return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);

Expand Down
3 changes: 2 additions & 1 deletion sys/cddl/dev/dtrace/riscv/dtrace_subr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,7 @@ __FBSDID("$FreeBSD$");
extern dtrace_id_t dtrace_probeid_error;
extern int (*dtrace_invop_jump_addr)(struct trapframe *);
extern void dtrace_getnanotime(struct timespec *tsp);
extern void dtrace_getnanouptime(struct timespec *tsp);

int dtrace_invop(uintptr_t, struct trapframe *);
void dtrace_invop_init(void);
Expand Down Expand Up @@ -165,7 +166,7 @@ dtrace_gethrtime()
{
struct timespec curtime;

nanouptime(&curtime);
dtrace_getnanouptime(&curtime);

return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);

Expand Down
26 changes: 26 additions & 0 deletions sys/cddl/dev/fbt/fbt.c
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Expand Up @@ -127,6 +127,13 @@ fbt_excluded(const char *name)
return (1);
}

/*
* Omit instrumentation of functions that are probably in DDB. It
* makes it too hard to debug broken FBT.
*/
if (strncmp(name, "db_", 3) == 0)
return (1);

/*
* Lock owner methods may be called from probe context.
*/
Expand All @@ -136,6 +143,15 @@ fbt_excluded(const char *name)
strcmp(name, "owner_sx") == 0)
return (1);

/*
* The compiler will sometimes replace memcpy()-like code with calls
* to memcpy() (or similar), which can occur in the DTrace code
* itself. For now, rather than prevent that in the build, just don't
* instrument at run time.
*/
if (strcmp(name, "memcpy") == 0)
return (1);

/*
* Stack unwinders may be called from probe context on some
* platforms.
Expand All @@ -145,6 +161,16 @@ fbt_excluded(const char *name)
return (1);
#endif

/*
* Some assembly-language exception handlers are not suitable for
* instrumentation.
*/
#if defined(__aarch64__)
if (strcmp(name, "handle_el1h_sync") == 0 ||
strcmp(name, "do_el1h_sync") == 0)
return (1);
#endif

/*
* When DTrace is built into the kernel we need to exclude
* the FBT functions from instrumentation.
Expand Down
15 changes: 15 additions & 0 deletions sys/kern/kern_tc.c
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Expand Up @@ -146,6 +146,7 @@ static void tc_windup(struct bintime *new_boottimebin);
static void cpu_tick_calibrate(int);

void dtrace_getnanotime(struct timespec *tsp);
void dtrace_getnanouptime(struct timespec *tsp);

static int
sysctl_kern_boottime(SYSCTL_HANDLER_ARGS)
Expand Down Expand Up @@ -997,6 +998,20 @@ dtrace_getnanotime(struct timespec *tsp)
GETTHMEMBER(tsp, th_nanotime);
}

/*
* This is a clone of getnanouptime used for time since boot.
* The dtrace_ prefix prevents fbt from creating probes for
* it so an uptime that can be safely used in all fbt probes.
*/
void
dtrace_getnanouptime(struct timespec *tsp)
{
struct bintime bt;

GETTHMEMBER(&bt, th_offset);
bintime2timespec(&bt, tsp);
}

/*
* System clock currently providing time to the system. Modifiable via sysctl
* when the FFCLOCK option is defined.
Expand Down