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Per-thread FPE pointer not being initialized
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Per-thread FPE pointer not being initialized
by David Reiss-3
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The per-thread last floating point exception pointer is not initialized to
NULL when it is allocated. As a result, spurious floating point exceptions are reported. This is 100% reproducible for me on CentOS 5.1 for x86-64, with Erlang/OTP R13B built from source with gcc 2.5 and gcc 4.1.2. It doesn't happen with R13B01, but, based on the nature of the bug, I think that is most likely due to chance. Steps to reproduce: 1/ Start up a node with dreiss@dev016:~$ erl -noshell -name bob@`hostname` 2/ Build and compile test program dreiss@dev016:~$ cat test.erl -module(test). -export([start/1]). start([Remote]) -> rpc:call(Remote, erlang, is_float, [750.0]). dreiss@dev016:~$ erlc test.erl 3/ Run test program dreiss@dev016:~$ erl -noshell -name alice@`hostname` -pz . -s test start bob@`hostname` -s init stop The "alice" node exits with no output. After running the "alice" command, the "bob" node prints the following ERTS_FP_CHECK_INIT at 0x4aaded: detected unhandled FPE at 0x2 Patch: diff otp_src_R13B/erts/emulator/sys/unix/sys_float.c otp_src_R13B/sys/unix/sys_float.c/sys/unix/sys_float.c --- otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 17:53:31.000000000 -0700 +++ otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 17:53:31.000000000 -0700 @@ -57,7 +57,8 @@ void erts_thread_init_fp_exception(void) { unsigned long *fpe = erts_alloc(ERTS_ALC_T_FP_EXCEPTION, sizeof(*fpe)); + *fpe = 0; erts_tsd_set(fpe_key, fpe); } --David ________________________________________________________________ erlang-patches mailing list. See http://www.erlang.org/faq.html erlang-patches (at) erlang.org |
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Re: Per-thread FPE pointer not being initialized
by Raimo Niskanen-5
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I can not reproduce it - that would need exact match
of floating point exception vs signals i guess. I see no harm ininitializing an allocated buffer (except for performance) but suspect the bug might be elswhere. The patch is scheduled for R13B02 and I will check with the guys that know better if the fix should be somewhere else... On Tue, Jun 30, 2009 at 07:34:39PM -0700, David Reiss wrote: > The per-thread last floating point exception pointer is not initialized to > NULL when it is allocated. As a result, spurious floating point > exceptions are reported. > > This is 100% reproducible for me on CentOS 5.1 for x86-64, with Erlang/OTP > R13B built from source with gcc 2.5 and gcc 4.1.2. It doesn't happen with > R13B01, but, based on the nature of the bug, I think that is most likely > due to chance. > > Steps to reproduce: > > 1/ Start up a node with > dreiss@dev016:~$ erl -noshell -name bob@`hostname` > > 2/ Build and compile test program > dreiss@dev016:~$ cat test.erl > -module(test). > -export([start/1]). > start([Remote]) -> > rpc:call(Remote, erlang, is_float, [750.0]). > dreiss@dev016:~$ erlc test.erl > > 3/ Run test program > dreiss@dev016:~$ erl -noshell -name alice@`hostname` -pz . -s test > start bob@`hostname` -s init stop > > The "alice" node exits with no output. After running the "alice" command, > the "bob" node prints the following > > ERTS_FP_CHECK_INIT at 0x4aaded: detected unhandled FPE at 0x2 > > Patch: > > diff otp_src_R13B/erts/emulator/sys/unix/sys_float.c > otp_src_R13B/sys/unix/sys_float.c/sys/unix/sys_float.c > --- otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > 17:53:31.000000000 -0700 > +++ otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > 17:53:31.000000000 -0700 > @@ -57,7 +57,8 @@ > void erts_thread_init_fp_exception(void) > { > unsigned long *fpe = erts_alloc(ERTS_ALC_T_FP_EXCEPTION, sizeof(*fpe)); > + *fpe = 0; > erts_tsd_set(fpe_key, fpe); > } > > > > --David > > ________________________________________________________________ > erlang-patches mailing list. See http://www.erlang.org/faq.html > erlang-patches (at) erlang.org -- / Raimo Niskanen, Erlang/OTP, Ericsson AB ________________________________________________________________ erlang-patches mailing list. See http://www.erlang.org/faq.html erlang-patches (at) erlang.org |
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Re: Per-thread FPE pointer not being initialized
by Mikael Pettersson-3
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David Reiss writes:
> The per-thread last floating point exception pointer is not initialized to > NULL when it is allocated. As a result, spurious floating point > exceptions are reported. > > This is 100% reproducible for me on CentOS 5.1 for x86-64, with Erlang/OTP > R13B built from source with gcc 2.5 and gcc 4.1.2. It doesn't happen with > R13B01, but, based on the nature of the bug, I think that is most likely > due to chance. > > Steps to reproduce: > > 1/ Start up a node with > dreiss@dev016:~$ erl -noshell -name bob@`hostname` > > 2/ Build and compile test program > dreiss@dev016:~$ cat test.erl > -module(test). > -export([start/1]). > start([Remote]) -> > rpc:call(Remote, erlang, is_float, [750.0]). > dreiss@dev016:~$ erlc test.erl > > 3/ Run test program > dreiss@dev016:~$ erl -noshell -name alice@`hostname` -pz . -s test > start bob@`hostname` -s init stop > > The "alice" node exits with no output. After running the "alice" command, > the "bob" node prints the following > > ERTS_FP_CHECK_INIT at 0x4aaded: detected unhandled FPE at 0x2 > > Patch: > > diff otp_src_R13B/erts/emulator/sys/unix/sys_float.c > otp_src_R13B/sys/unix/sys_float.c/sys/unix/sys_float.c > --- otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > 17:53:31.000000000 -0700 > +++ otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > 17:53:31.000000000 -0700 > @@ -57,7 +57,8 @@ > void erts_thread_init_fp_exception(void) > { > unsigned long *fpe = erts_alloc(ERTS_ALC_T_FP_EXCEPTION, sizeof(*fpe)); > + *fpe = 0; > erts_tsd_set(fpe_key, fpe); > } Thanks, that bug was mine :-( Your fix is correct. I believe the initialisation here wasn't needed originally, but became necessary as a side effect of some FP exn machinery redesign I did late last year. Where did the spurious FP exception get detected, i.e., what runtime system procedure does 0x4aaded correspond to? /Mikael ________________________________________________________________ erlang-patches mailing list. See http://www.erlang.org/faq.html erlang-patches (at) erlang.org |
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Re: Per-thread FPE pointer not being initialized
by Raimo Niskanen-5
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On Wed, Jul 01, 2009 at 12:03:04PM +0200, Mikael Pettersson wrote:
> David Reiss writes: > > The per-thread last floating point exception pointer is not initialized to > > NULL when it is allocated. As a result, spurious floating point > > exceptions are reported. > > > > This is 100% reproducible for me on CentOS 5.1 for x86-64, with Erlang/OTP > > R13B built from source with gcc 2.5 and gcc 4.1.2. It doesn't happen with > > R13B01, but, based on the nature of the bug, I think that is most likely > > due to chance. > > > > Steps to reproduce: > > > > 1/ Start up a node with > > dreiss@dev016:~$ erl -noshell -name bob@`hostname` > > > > 2/ Build and compile test program > > dreiss@dev016:~$ cat test.erl > > -module(test). > > -export([start/1]). > > start([Remote]) -> > > rpc:call(Remote, erlang, is_float, [750.0]). > > dreiss@dev016:~$ erlc test.erl > > > > 3/ Run test program > > dreiss@dev016:~$ erl -noshell -name alice@`hostname` -pz . -s test > > start bob@`hostname` -s init stop > > > > The "alice" node exits with no output. After running the "alice" command, > > the "bob" node prints the following > > > > ERTS_FP_CHECK_INIT at 0x4aaded: detected unhandled FPE at 0x2 > > > > Patch: > > > > diff otp_src_R13B/erts/emulator/sys/unix/sys_float.c > > otp_src_R13B/sys/unix/sys_float.c/sys/unix/sys_float.c > > --- otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > > 17:53:31.000000000 -0700 > > +++ otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > > 17:53:31.000000000 -0700 > > @@ -57,7 +57,8 @@ > > void erts_thread_init_fp_exception(void) > > { > > unsigned long *fpe = erts_alloc(ERTS_ALC_T_FP_EXCEPTION, sizeof(*fpe)); > > + *fpe = 0; > > erts_tsd_set(fpe_key, fpe); > > } > > Thanks, that bug was mine :-( Your fix is correct. Would your patch in http://www.erlang.org/cgi-bin/ezmlm-cgi/2/1380 also solve this problem? Or are both needed? --- otp-0622/erts/emulator/sys/unix/sys_float.c.~1~ 2009-02-26 11:45:48.000000000 +0100 +++ otp-0622/erts/emulator/sys/unix/sys_float.c 2009-06-26 11:14:15.000000000 +0200 @@ -792,6 +792,8 @@ sys_chars_to_double(char* buf, double* f int matherr(struct exception *exc) { +#if !defined(NO_FPE_SIGNALS) set_current_fp_exception((unsigned long)__builtin_return_address(0)); +#endif return 1; } > > I believe the initialisation here wasn't needed originally, > but became necessary as a side effect of some FP exn machinery > redesign I did late last year. > > Where did the spurious FP exception get detected, i.e., > what runtime system procedure does 0x4aaded correspond to? > > /Mikael > > ________________________________________________________________ > erlang-patches mailing list. See http://www.erlang.org/faq.html > erlang-patches (at) erlang.org -- / Raimo Niskanen, Erlang/OTP, Ericsson AB ________________________________________________________________ erlang-patches mailing list. See http://www.erlang.org/faq.html erlang-patches (at) erlang.org |
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Re: Per-thread FPE pointer not being initialized
by Mikael Pettersson-3
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Raimo Niskanen writes:
> On Wed, Jul 01, 2009 at 12:03:04PM +0200, Mikael Pettersson wrote: > > David Reiss writes: > > > The per-thread last floating point exception pointer is not initialized to > > > NULL when it is allocated. As a result, spurious floating point > > > exceptions are reported. > > > > > > This is 100% reproducible for me on CentOS 5.1 for x86-64, with Erlang/OTP > > > R13B built from source with gcc 2.5 and gcc 4.1.2. It doesn't happen with > > > R13B01, but, based on the nature of the bug, I think that is most likely > > > due to chance. > > > > > > Steps to reproduce: > > > > > > 1/ Start up a node with > > > dreiss@dev016:~$ erl -noshell -name bob@`hostname` > > > > > > 2/ Build and compile test program > > > dreiss@dev016:~$ cat test.erl > > > -module(test). > > > -export([start/1]). > > > start([Remote]) -> > > > rpc:call(Remote, erlang, is_float, [750.0]). > > > dreiss@dev016:~$ erlc test.erl > > > > > > 3/ Run test program > > > dreiss@dev016:~$ erl -noshell -name alice@`hostname` -pz . -s test > > > start bob@`hostname` -s init stop > > > > > > The "alice" node exits with no output. After running the "alice" command, > > > the "bob" node prints the following > > > > > > ERTS_FP_CHECK_INIT at 0x4aaded: detected unhandled FPE at 0x2 > > > > > > Patch: > > > > > > diff otp_src_R13B/erts/emulator/sys/unix/sys_float.c > > > otp_src_R13B/sys/unix/sys_float.c/sys/unix/sys_float.c > > > --- otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > > > 17:53:31.000000000 -0700 > > > +++ otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > > > 17:53:31.000000000 -0700 > > > @@ -57,7 +57,8 @@ > > > void erts_thread_init_fp_exception(void) > > > { > > > unsigned long *fpe = erts_alloc(ERTS_ALC_T_FP_EXCEPTION, sizeof(*fpe)); > > > + *fpe = 0; > > > erts_tsd_set(fpe_key, fpe); > > > } > > > > Thanks, that bug was mine :-( Your fix is correct. > > Would your patch in http://www.erlang.org/cgi-bin/ezmlm-cgi/2/1380 > also solve this problem? Or are both needed? > > --- otp-0622/erts/emulator/sys/unix/sys_float.c.~1~ 2009-02-26 11:45:48.000000000 +0100 > +++ otp-0622/erts/emulator/sys/unix/sys_float.c 2009-06-26 11:14:15.000000000 +0200 > @@ -792,6 +792,8 @@ sys_chars_to_double(char* buf, double* f > int > matherr(struct exception *exc) > { > +#if !defined(NO_FPE_SIGNALS) > set_current_fp_exception((unsigned long)__builtin_return_address(0)); > +#endif > return 1; > } The two patches fix independent issues. The #if !defined change in sys_chars_to_double() fixes a compile/link error with !gcc. /Mikael ________________________________________________________________ erlang-patches mailing list. See http://www.erlang.org/faq.html erlang-patches (at) erlang.org |
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Re: Per-thread FPE pointer not being initialized
by Raimo Niskanen-5
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On Wed, Jul 01, 2009 at 01:55:39PM +0200, Mikael Pettersson wrote:
> Raimo Niskanen writes: > > On Wed, Jul 01, 2009 at 12:03:04PM +0200, Mikael Pettersson wrote: > > > David Reiss writes: > > > > The per-thread last floating point exception pointer is not initialized to > > > > NULL when it is allocated. As a result, spurious floating point > > > > exceptions are reported. > > > > > > > > This is 100% reproducible for me on CentOS 5.1 for x86-64, with Erlang/OTP > > > > R13B built from source with gcc 2.5 and gcc 4.1.2. It doesn't happen with > > > > R13B01, but, based on the nature of the bug, I think that is most likely > > > > due to chance. > > > > > > > > Steps to reproduce: > > > > > > > > 1/ Start up a node with > > > > dreiss@dev016:~$ erl -noshell -name bob@`hostname` > > > > > > > > 2/ Build and compile test program > > > > dreiss@dev016:~$ cat test.erl > > > > -module(test). > > > > -export([start/1]). > > > > start([Remote]) -> > > > > rpc:call(Remote, erlang, is_float, [750.0]). > > > > dreiss@dev016:~$ erlc test.erl > > > > > > > > 3/ Run test program > > > > dreiss@dev016:~$ erl -noshell -name alice@`hostname` -pz . -s test > > > > start bob@`hostname` -s init stop > > > > > > > > The "alice" node exits with no output. After running the "alice" command, > > > > the "bob" node prints the following > > > > > > > > ERTS_FP_CHECK_INIT at 0x4aaded: detected unhandled FPE at 0x2 > > > > > > > > Patch: > > > > > > > > diff otp_src_R13B/erts/emulator/sys/unix/sys_float.c > > > > otp_src_R13B/sys/unix/sys_float.c/sys/unix/sys_float.c > > > > --- otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > > > > 17:53:31.000000000 -0700 > > > > +++ otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 > > > > 17:53:31.000000000 -0700 > > > > @@ -57,7 +57,8 @@ > > > > void erts_thread_init_fp_exception(void) > > > > { > > > > unsigned long *fpe = erts_alloc(ERTS_ALC_T_FP_EXCEPTION, sizeof(*fpe)); > > > > + *fpe = 0; > > > > erts_tsd_set(fpe_key, fpe); > > > > } > > > > > > Thanks, that bug was mine :-( Your fix is correct. > > > > Would your patch in http://www.erlang.org/cgi-bin/ezmlm-cgi/2/1380 > > also solve this problem? Or are both needed? > > > > --- otp-0622/erts/emulator/sys/unix/sys_float.c.~1~ 2009-02-26 11:45:48.000000000 +0100 > > +++ otp-0622/erts/emulator/sys/unix/sys_float.c 2009-06-26 11:14:15.000000000 +0200 > > @@ -792,6 +792,8 @@ sys_chars_to_double(char* buf, double* f > > int > > matherr(struct exception *exc) > > { > > +#if !defined(NO_FPE_SIGNALS) > > set_current_fp_exception((unsigned long)__builtin_return_address(0)); > > +#endif > > return 1; > > } > > The two patches fix independent issues. The #if !defined change in > sys_chars_to_double() fixes a compile/link error with !gcc. Sorry I misread the patch. I accidentally saw it add set_current_fp_exception(0) to matherr(exc) but it only added preprocessor directives... > > /Mikael > > ________________________________________________________________ > erlang-patches mailing list. See http://www.erlang.org/faq.html > erlang-patches (at) erlang.org -- / Raimo Niskanen, Erlang/OTP, Ericsson AB ________________________________________________________________ erlang-patches mailing list. See http://www.erlang.org/faq.html erlang-patches (at) erlang.org |
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Re: Per-thread FPE pointer not being initialized
by David Reiss-3
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> Where did the spurious FP exception get detected, i.e.,
> what runtime system procedure does 0x4aaded correspond to? It looks like it is dec_term (and gdb reports it as line 1206 of beam/external.c, which is a call to sys_chars_to_double). When I first detected the problem, it was in the context of a larger application. The reported address was 0x51d507, which is in sys_chars_to_double. The boundaries get a bit blurred in optimized builds. :) --David On Wed, Jul 1, 2009 at 8:16 AM, Raimo Niskanen<raimo+erlang-patches@...> wrote: > On Wed, Jul 01, 2009 at 01:55:39PM +0200, Mikael Pettersson wrote: >> Raimo Niskanen writes: >> > On Wed, Jul 01, 2009 at 12:03:04PM +0200, Mikael Pettersson wrote: >> > > David Reiss writes: >> > > > The per-thread last floating point exception pointer is not initialized to >> > > > NULL when it is allocated. As a result, spurious floating point >> > > > exceptions are reported. >> > > > >> > > > This is 100% reproducible for me on CentOS 5.1 for x86-64, with Erlang/OTP >> > > > R13B built from source with gcc 2.5 and gcc 4.1.2. It doesn't happen with >> > > > R13B01, but, based on the nature of the bug, I think that is most likely >> > > > due to chance. >> > > > >> > > > Steps to reproduce: >> > > > >> > > > 1/ Start up a node with >> > > > dreiss@dev016:~$ erl -noshell -name bob@`hostname` >> > > > >> > > > 2/ Build and compile test program >> > > > dreiss@dev016:~$ cat test.erl >> > > > -module(test). >> > > > -export([start/1]). >> > > > start([Remote]) -> >> > > > rpc:call(Remote, erlang, is_float, [750.0]). >> > > > dreiss@dev016:~$ erlc test.erl >> > > > >> > > > 3/ Run test program >> > > > dreiss@dev016:~$ erl -noshell -name alice@`hostname` -pz . -s test >> > > > start bob@`hostname` -s init stop >> > > > >> > > > The "alice" node exits with no output. After running the "alice" command, >> > > > the "bob" node prints the following >> > > > >> > > > ERTS_FP_CHECK_INIT at 0x4aaded: detected unhandled FPE at 0x2 >> > > > >> > > > Patch: >> > > > >> > > > diff otp_src_R13B/erts/emulator/sys/unix/sys_float.c >> > > > otp_src_R13B/sys/unix/sys_float.c/sys/unix/sys_float.c >> > > > --- otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 >> > > > 17:53:31.000000000 -0700 >> > > > +++ otp_src_R13B/erts/emulator/sys/unix/sys_float.c 2009-06-30 >> > > > 17:53:31.000000000 -0700 >> > > > @@ -57,7 +57,8 @@ >> > > > void erts_thread_init_fp_exception(void) >> > > > { >> > > > unsigned long *fpe = erts_alloc(ERTS_ALC_T_FP_EXCEPTION, sizeof(*fpe)); >> > > > + *fpe = 0; >> > > > erts_tsd_set(fpe_key, fpe); >> > > > } >> > > >> > > Thanks, that bug was mine :-( Your fix is correct. >> > >> > Would your patch in http://www.erlang.org/cgi-bin/ezmlm-cgi/2/1380 >> > also solve this problem? Or are both needed? >> > >> > --- otp-0622/erts/emulator/sys/unix/sys_float.c.~1~ 2009-02-26 11:45:48.000000000 +0100 >> > +++ otp-0622/erts/emulator/sys/unix/sys_float.c 2009-06-26 11:14:15.000000000 +0200 >> > @@ -792,6 +792,8 @@ sys_chars_to_double(char* buf, double* f >> > int >> > matherr(struct exception *exc) >> > { >> > +#if !defined(NO_FPE_SIGNALS) >> > set_current_fp_exception((unsigned long)__builtin_return_address(0)); >> > +#endif >> > return 1; >> > } >> >> The two patches fix independent issues. The #if !defined change in >> sys_chars_to_double() fixes a compile/link error with !gcc. > > Sorry I misread the patch. I accidentally saw it add > set_current_fp_exception(0) to matherr(exc) but it > only added preprocessor directives... > >> >> /Mikael >> >> ________________________________________________________________ >> erlang-patches mailing list. See http://www.erlang.org/faq.html >> erlang-patches (at) erlang.org > > -- > > / Raimo Niskanen, Erlang/OTP, Ericsson AB > > ________________________________________________________________ > erlang-patches mailing list. See http://www.erlang.org/faq.html > erlang-patches (at) erlang.org > > ________________________________________________________________ erlang-patches mailing list. See http://www.erlang.org/faq.html erlang-patches (at) erlang.org |
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