Download raw body.
gprof: Profiling a multi-threaded application (revived)
> Date: Fri, 06 Jun 2025 17:43:10 +0900 (JST)
> From: Yuichiro NAITO <naito.yuichiro@gmail.com>
Hi Yuichiro,
This is changing the interface between libc and libpthread. This is
tricky. Minimally this needs libc and libpthread minor bumps. But it
is more complicated than that and I have trouble wrapping my head
around exactly how that works again. guenther@ should know more.
>
> Small update to my patch.
>
> From: Yuichiro NAITO <naito.yuichiro@gmail.com>
> Subject: Re: gprof: Profiling a multi-threaded application (revived)
> Date: Thu, 05 Jun 2025 18:27:20 +0900 (JST)
>
> > I updated the multi-thread profiling patch through discussion with
> > Theo de Raadt. I'll list the improvements.
> >
> > 1. Allocate kcount buffer memory when a thread starts.
> >
> > The allocation logic becomes simple and also reduces the patch size.
> > This needs the '_gmon_alloc' symbol to be exported for the libpthread.
> >
> > 2. Allocate buffer memory on a single mmap(2) call.
> >
> > This is the same way as Theo's commit.
> > https://github.com/OpenBSD/src/commit/4ea76518007ed1dc99d51b18368b53ba7b11fd17
>
> I misunderstood Theo's intention about pointer calculation. I should
> hold the return value of mmap in a char * variable, so that I don't
> need code-width cast.
>
> > 3. Mark 'static' to '_gmonfree', '_gmoninuse', '_gmonkey' variables.
> >
> > These are used only in the 'gmon.c'.
> >
> > 4. Refactor 'gmonparam' lookup code in the __mcount function.
> >
> > Reduce the patch size.
> >
>
> diff --git a/lib/libc/Symbols.list b/lib/libc/Symbols.list
> index 6eb2cca93e5..d5d5497cf93 100644
> --- a/lib/libc/Symbols.list
> +++ b/lib/libc/Symbols.list
> @@ -880,6 +880,7 @@ _mcleanup
> _monstartup
> moncontrol
> monstartup
> +_gmon_alloc
>
> /* hash */
> MD5Data
> diff --git a/lib/libc/gmon/gmon.c b/lib/libc/gmon/gmon.c
> index 99fd42d7824..93176edd11d 100644
> --- a/lib/libc/gmon/gmon.c
> +++ b/lib/libc/gmon/gmon.c
> @@ -42,12 +42,21 @@
>
> struct gmonparam _gmonparam = { GMON_PROF_OFF };
>
> +#include <pthread.h>
> +#include <thread_private.h>
> +
> +static SLIST_HEAD(, gmonparam) _gmonfree = SLIST_HEAD_INITIALIZER(_gmonfree);
> +static SLIST_HEAD(, gmonparam) _gmoninuse = SLIST_HEAD_INITIALIZER(_gmoninuse);
> +_THREAD_PRIVATE_MUTEX(_gmonlock);
> +static pthread_key_t _gmonkey;
> +
> static int s_scale;
> /* see profil(2) where this is describe (incorrectly) */
> #define SCALE_1_TO_1 0x10000L
>
> #define ERR(s) write(STDERR_FILENO, s, sizeof(s))
>
> +PROTO_NORMAL(_gmon_alloc);
> PROTO_NORMAL(moncontrol);
> PROTO_DEPRECATED(monstartup);
>
> @@ -62,6 +71,19 @@ monstartup(u_long lowpc, u_long highpc)
> #define PAGEMASK (PAGESIZE - 1)
> #define PAGEROUND(x) (((x) + (PAGEMASK)) & ~PAGEMASK)
>
> +static void
> +_gmon_destructor(void *arg)
> +{
> + struct gmonparam *p = arg, *q, **prev;
> +
> + _THREAD_PRIVATE_MUTEX_LOCK(_gmonlock);
> + SLIST_REMOVE(&_gmoninuse, p, gmonparam, list);
> + SLIST_INSERT_HEAD(&_gmonfree, p, list);
> + _THREAD_PRIVATE_MUTEX_UNLOCK(_gmonlock);
> +
> + pthread_setspecific(_gmonkey, NULL);
> +}
> +
> void
> _monstartup(u_long lowpc, u_long highpc)
> {
> @@ -130,12 +152,166 @@ _monstartup(u_long lowpc, u_long highpc)
> else
> p->dirfd = -1;
>
> + pthread_key_create(&_gmonkey, _gmon_destructor);
> +
> moncontrol(1);
>
> if (p->dirfd != -1)
> close(p->dirfd);
> }
>
> +struct gmonparam *
> +_gmon_alloc(void)
> +{
> + struct gmonparam *p;
> + char *a;
> +
> + if (_gmonparam.state == GMON_PROF_OFF)
> + return NULL;
> +
> + _THREAD_PRIVATE_MUTEX_LOCK(_gmonlock);
> + p = SLIST_FIRST(&_gmonfree);
> + if (p != NULL) {
> + SLIST_REMOVE_HEAD(&_gmonfree, list);
> + SLIST_INSERT_HEAD(&_gmoninuse, p, list);
> + } else {
> + _THREAD_PRIVATE_MUTEX_UNLOCK(_gmonlock);
> + a = mmap(NULL,
> + _ALIGN(sizeof(*p)) + _ALIGN(_gmonparam.fromssize) +
> + _ALIGN(_gmonparam.tossize),
> + PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
> + if (a == MAP_FAILED) {
> + pthread_setspecific(_gmonkey, NULL);
> + ERR("_gmon_alloc: out of memory\n");
> + return NULL;
> + }
> + p = (struct gmonparam *)a;
> + *p = _gmonparam;
> + p->kcount = NULL;
> + p->kcountsize = 0;
> + p->froms = (void *)(a + _ALIGN(sizeof(*p)));
> + p->tos = (void *)(a + _ALIGN(sizeof(*p)) +
> + _ALIGN(_gmonparam.fromssize));
> + _THREAD_PRIVATE_MUTEX_LOCK(_gmonlock);
> + SLIST_INSERT_HEAD(&_gmoninuse, p, list);
> + }
> + _THREAD_PRIVATE_MUTEX_UNLOCK(_gmonlock);
> + pthread_setspecific(_gmonkey, p);
> +
> + return p;
> +}
> +DEF_WEAK(_gmon_alloc);
> +
> +static void
> +_gmon_merge_two(struct gmonparam *p, struct gmonparam *q)
> +{
> + u_long fromindex, selfpc, endfrom;
> + u_short *frompcindex, qtoindex, toindex;
> + long count;
> + struct tostruct *top;
> +
> + endfrom = (q->fromssize / sizeof(*q->froms));
> + for (fromindex = 0; fromindex < endfrom; fromindex++) {
> + if (q->froms[fromindex] == 0)
> + continue;
> + for (qtoindex = q->froms[fromindex]; qtoindex != 0;
> + qtoindex = q->tos[qtoindex].link) {
> + selfpc = q->tos[qtoindex].selfpc;
> + count = q->tos[qtoindex].count;
> + /* cribbed from mcount */
> + frompcindex = &p->froms[fromindex];
> + toindex = *frompcindex;
> + if (toindex == 0) {
> + /*
> + * first time traversing this arc
> + */
> + toindex = ++p->tos[0].link;
> + if (toindex >= p->tolimit)
> + /* halt further profiling */
> + goto overflow;
> +
> + *frompcindex = (u_short)toindex;
> + top = &p->tos[(size_t)toindex];
> + top->selfpc = selfpc;
> + top->count = count;
> + top->link = 0;
> + goto done;
> + }
> + top = &p->tos[(size_t)toindex];
> + if (top->selfpc == selfpc) {
> + /*
> + * arc at front of chain; usual case.
> + */
> + top->count+= count;
> + goto done;
> + }
> + /*
> + * have to go looking down chain for it.
> + * top points to what we are looking at,
> + * we know it is not at the head of the chain.
> + */
> + for (; /* goto done */; ) {
> + if (top->link == 0) {
> + /*
> + * top is end of the chain and
> + * none of the chain had
> + * top->selfpc == selfpc. so
> + * we allocate a new tostruct
> + * and link it to the head of
> + * the chain.
> + */
> + toindex = ++p->tos[0].link;
> + if (toindex >= p->tolimit)
> + goto overflow;
> + top = &p->tos[(size_t)toindex];
> + top->selfpc = selfpc;
> + top->count = count;
> + top->link = *frompcindex;
> + *frompcindex = (u_short)toindex;
> + goto done;
> + }
> + /*
> + * otherwise, check the next arc on the chain.
> + */
> + top = &p->tos[top->link];
> + if (top->selfpc == selfpc) {
> + /*
> + * there it is.
> + * add to its count.
> + */
> + top->count += count;
> + goto done;
> + }
> +
> + }
> +
> + done: ;
> + }
> +
> + }
> +overflow: ;
> +
> +}
> +
> +static void
> +_gmon_merge(void)
> +{
> + struct gmonparam *q;
> +
> + _THREAD_PRIVATE_MUTEX_LOCK(_gmonlock);
> +
> + SLIST_FOREACH(q, &_gmonfree, list)
> + _gmon_merge_two(&_gmonparam, q);
> +
> + SLIST_FOREACH(q, &_gmoninuse, list) {
> + q->state = GMON_PROF_OFF;
> + _gmon_merge_two(&_gmonparam, q);
> + }
> +
> + _THREAD_PRIVATE_MUTEX_UNLOCK(_gmonlock);
> +}
> +
> +
> void
> _mcleanup(void)
> {
> @@ -179,6 +355,9 @@ _mcleanup(void)
> p->kcount, p->kcountsize);
> write(log, dbuf, strlen(dbuf));
> #endif
> +
> + _gmon_merge();
> +
> hdr = (struct gmonhdr *)p->outbuf;
> hdr->lpc = p->lowpc;
> hdr->hpc = p->highpc;
> diff --git a/lib/libc/gmon/mcount.c b/lib/libc/gmon/mcount.c
> index 6846c10c857..f5ecb3f7cdc 100644
> --- a/lib/libc/gmon/mcount.c
> +++ b/lib/libc/gmon/mcount.c
> @@ -31,6 +31,11 @@
> #include <sys/types.h>
> #include <sys/gmon.h>
>
> +#ifndef _KERNEL
> +#include <thread_private.h>
> +#include <tib.h>
> +#endif
> +
> /*
> * mcount is called on entry to each function compiled with the profiling
> * switch set. _mcount(), which is declared in a machine-dependent way
> @@ -65,13 +70,14 @@ _MCOUNT_DECL(u_long frompc, u_long selfpc)
> if ((p = curcpu()->ci_gmon) == NULL)
> return;
> #else
> - p = &_gmonparam;
> + p = (__isthreaded) ?
> + ((pthread_t)TIB_GET()->tib_thread)->gmonparam : &_gmonparam;
> #endif
> /*
> * check that we are profiling
> * and that we aren't recursively invoked.
> */
> - if (p->state != GMON_PROF_ON)
> + if (p == NULL || p->state != GMON_PROF_ON)
> return;
> #ifdef _KERNEL
> MCOUNT_ENTER;
> diff --git a/lib/libc/include/thread_private.h b/lib/libc/include/thread_private.h
> index 1ec10711615..6b8164bab43 100644
> --- a/lib/libc/include/thread_private.h
> +++ b/lib/libc/include/thread_private.h
> @@ -5,6 +5,9 @@
> #ifndef _THREAD_PRIVATE_H_
> #define _THREAD_PRIVATE_H_
>
> +#include <sys/types.h>
> +#include <sys/gmon.h>
> +
> extern int __isthreaded;
>
> #define _MALLOC_MUTEXES 32
> @@ -390,6 +393,7 @@ struct pthread {
>
> /* cancel received in a delayed cancel block? */
> int delayed_cancel;
> + struct gmonparam *gmonparam;
> };
> /* flags in pthread->flags */
> #define THREAD_DONE 0x001
> diff --git a/lib/libc/thread/rthread.c b/lib/libc/thread/rthread.c
> index ae74aceb51b..f8116e8a0e0 100644
> --- a/lib/libc/thread/rthread.c
> +++ b/lib/libc/thread/rthread.c
> @@ -21,6 +21,7 @@
>
> #include <sys/types.h>
> #include <sys/atomic.h>
> +#include <sys/gmon.h>
>
> #include <pthread.h>
> #include <stdlib.h>
> @@ -103,6 +104,9 @@ _rthread_init(void)
> }
>
> _threads_inited = 1;
> +
> + /* Ignore errors. NULL is OK for a non-profiling case. */
> + thread->gmonparam = _gmon_alloc();
> }
>
> /*
> diff --git a/lib/librthread/rthread.c b/lib/librthread/rthread.c
> index 53f1d9ca82b..3389ea6baa9 100644
> --- a/lib/librthread/rthread.c
> +++ b/lib/librthread/rthread.c
> @@ -25,6 +25,7 @@
> #include <elf.h>
> #pragma weak _DYNAMIC
> #endif
> +#include <sys/gmon.h>
>
> #include <stdlib.h>
> #include <unistd.h>
> @@ -393,6 +394,10 @@ pthread_create(pthread_t *threadp, const pthread_attr_t *attr,
>
> /* we're going to be multi-threaded real soon now */
> __isthreaded = 1;
> +
> + /* Ignore errors. NULL is OK for a non-profiling case. */
> + thread->gmonparam = _gmon_alloc();
> +
> rc = __tfork_thread(¶m, sizeof(param), _rthread_start, thread);
> if (rc != -1) {
> /* success */
> diff --git a/sys/lib/libkern/mcount.c b/sys/lib/libkern/mcount.c
> index e020dede07a..59b815a02d5 100644
> --- a/sys/lib/libkern/mcount.c
> +++ b/sys/lib/libkern/mcount.c
> @@ -33,6 +33,11 @@
> #include <sys/param.h>
> #include <sys/gmon.h>
>
> +#ifndef _KERNEL
> +#include <thread_private.h>
> +#include <tib.h>
> +#endif
> +
> /*
> * mcount is called on entry to each function compiled with the profiling
> * switch set. _mcount(), which is declared in a machine-dependent way
> @@ -67,13 +72,14 @@ _MCOUNT_DECL(u_long frompc, u_long selfpc)
> if ((p = curcpu()->ci_gmon) == NULL)
> return;
> #else
> - p = &_gmonparam;
> + p = (__isthreaded) ?
> + ((pthread_t)TIB_GET()->tib_thread)->gmonparam : &_gmonparam;
> #endif
> /*
> * check that we are profiling
> * and that we aren't recursively invoked.
> */
> - if (p->state != GMON_PROF_ON)
> + if (p == NULL || p->state != GMON_PROF_ON)
> return;
> #ifdef _KERNEL
> MCOUNT_ENTER;
> diff --git a/sys/sys/gmon.h b/sys/sys/gmon.h
> index baaf7743be5..a29bfa849d9 100644
> --- a/sys/sys/gmon.h
> +++ b/sys/sys/gmon.h
> @@ -35,6 +35,7 @@
> #ifndef _SYS_GMON_H_
> #define _SYS_GMON_H_
>
> +#include <sys/queue.h>
> #include <machine/profile.h>
>
> /*
> @@ -141,6 +142,7 @@ struct gmonparam {
> size_t outbuflen;
> void *rawarcs;
> int dirfd;
> + SLIST_ENTRY(gmonparam) list;
> };
>
> /*
> @@ -174,6 +176,7 @@ void _monstartup(u_long, u_long);
> void moncontrol(int);
> /* XXX remove end of may 2025 */
> void monstartup(u_long, u_long);
> +struct gmonparam *_gmon_alloc(void);
> __END_DECLS
>
> #endif /* !_KERNEL */
>
> --
> Yuichiro NAITO (naito.yuichiro@gmail.com)
>
>
gprof: Profiling a multi-threaded application (revived)