Re: [PATCH 2/3] bsps/i386: use Pentimum instructions for pc586 and pc686 builds.

[Sebastian Huber]

This looks like a compiler or libatomic configuration bug. I currently 
have no time to investigate this further.


On 12/10/16 15:36, Pavel Pisa wrote:

Hello Sebastian,

On Wednesday 12 of October 2016 10:35:55 Sebastian Huber wrote:

On 12/10/16 10:26, p...@cmp.felk.cvut.cz wrote:

SMP build is broken with i386 set because libatomic and GCC
generate infinite loop for __atomic_fetch_add_4 used
in rtems_interrupt_lock_acquire

__atomic_fetch_add_4:
  push   %ebp
  mov%esp,%ebp
  movl   $0x5,0x10(%ebp)
  pop%ebp
  jmp__atomic_fetch_add_4

Do you have a test case for this compiler/RTEMS bug?  The use of
libatomic is inefficient, but it should work.

may be it is problem of my i386 toolchain build, I have not
updated it from April.

The next is a simple test


#include 

atomic_uint atvar1;

volatile unsigned int res1;
volatile unsigned int  res2;

int main(void)
{

   res1 = atomic_fetch_or(, 0x55);

   res2 = atomic_fetch_add(, 0xaa);

   return 0;
}


The next build commands are used

i386-rtems4.12-gcc --pipe -B/opt/rtems4.12/i386-rtems4.12/pc686/lib/ -specs
bsp_specs -qrtems-I /opt/rtems4.12/i386-rtems4.12/pc686/lib/include 
-march=i386 -Wall  -O2 -g -ffunction-sections -fdata-sections -o
libatomic-add-test.o -c libatomic-add-test.c

i386-rtems4.12-gcc --pipe -B/opt/rtems4.12/i386-rtems4.12/pc686/lib/ -specs
bsp_specs -qrtems -mtune=pentiumpro -march=pentium -Wall -O2 -g 
-ffunction-sections -fdata-sections   -Wl,--gc-sections -Wl,-Ttext,0x0010
libatomic-add-test.o -o libatomic-test-add

problem appears with and without -march=i386, when -march is something
newer (pentium) then all is OK.


Disassembly looks like



00120a76 <__atomic_fetch_add_4>:
   120a76:   55  push   %ebp
   120a77:   89 e5   mov%esp,%ebp
   120a79:   c7 45 10 05 00 00 00movl   $0x5,0x10(%ebp)
   120a80:   5d  pop%ebp
   120a81:   eb f3   jmp120a76 <__atomic_fetch_add_4>

00120a83 <__atomic_add_fetch_4>:
   120a83:   55  push   %ebp
   120a84:   89 e5   mov%esp,%ebp
   120a86:   c7 45 10 05 00 00 00movl   $0x5,0x10(%ebp)
   120a8d:   5d  pop%ebp
   120a8e:   eb e6   jmp120a76 <__atomic_fetch_add_4>

00120a90 <__atomic_fetch_or_4>:
   120a90:   55  push   %ebp
   120a91:   89 e5   mov%esp,%ebp
   120a93:   56  push   %esi
   120a94:   53  push   %ebx
   120a95:   83 ec 0csub$0xc,%esp
   120a98:   8b 5d 08mov0x8(%ebp),%ebx
   120a9b:   53  push   %ebx
   120a9c:   e8 df 66 00 00  call   127180 
<_Libatomic_Protect_start>
   120aa1:   8b 33   mov(%ebx),%esi
   120aa3:   8b 55 0cmov0xc(%ebp),%edx
   120aa6:   09 f2   or %esi,%edx
   120aa8:   89 13   mov%edx,(%ebx)
   120aaa:   5a  pop%edx
   120aab:   59  pop%ecx
   120aac:   50  push   %eax
   120aad:   53  push   %ebx
   120aae:   e8 ed 66 00 00  call   1271a0 <_Libatomic_Protect_end>
   120ab3:   8d 65 f8lea-0x8(%ebp),%esp
   120ab6:   89 f0   mov%esi,%eax
   120ab8:   5b  pop%ebx
   120ab9:   5e  pop%esi
   120aba:   5d  pop%ebp
   120abb:   c3  ret




_Libatomic_Protect_start is provided by RTEMS.


00127180 <_Libatomic_Protect_start>:
__uint32_t _Libatomic_Protect_start( void *ptr )
{
   ISR_Level isr_level;

   (void) ptr;
   _ISR_Local_disable( isr_level );
   127180:   9c  pushf
   127181:   fa  cli
   127182:   58  pop%eax
static inline bool _CPU_atomic_Flag_test_and_set( CPU_atomic_Flag *obj, 
CPU_atomic_Order order )
{
#if defined(_RTEMS_SCORE_CPUSTDATOMIC_USE_ATOMIC)
   return obj->test_and_set( order );
#elif defined(_RTEMS_SCORE_CPUSTDATOMIC_USE_STDATOMIC)
   return atomic_flag_test_and_set_explicit( obj, order );
   127183:   b1 01   mov$0x1,%cl
   127185:   8d 74 26 00 lea0x0(%esi,%eiz,1),%esi
   127189:   8d bc 27 00 00 00 00lea0x0(%edi,%eiz,1),%edi
   127190:   88 ca   mov%cl,%dl
   127192:   86 15 8c 85 13 00   xchg   %dl,0x13858c

#if defined(RTEMS_SMP)
   while (
   127198:

Re: [PATCH 2/3] bsps/i386: use Pentimum instructions for pc586 and pc686 builds.

[Pavel Pisa]

Hello Sebastian,

On Wednesday 12 of October 2016 10:35:55 Sebastian Huber wrote:
> On 12/10/16 10:26, p...@cmp.felk.cvut.cz wrote:
> > SMP build is broken with i386 set because libatomic and GCC
> > generate infinite loop for __atomic_fetch_add_4 used
> > in rtems_interrupt_lock_acquire
> >
> > __atomic_fetch_add_4:
> >  push   %ebp
> >  mov%esp,%ebp
> >  movl   $0x5,0x10(%ebp)
> >  pop%ebp
> >  jmp__atomic_fetch_add_4
>
> Do you have a test case for this compiler/RTEMS bug?  The use of
> libatomic is inefficient, but it should work.

may be it is problem of my i386 toolchain build, I have not
updated it from April.

The next is a simple test


#include 

atomic_uint atvar1;

volatile unsigned int res1;
volatile unsigned int  res2;

int main(void)
{

  res1 = atomic_fetch_or(, 0x55);

  res2 = atomic_fetch_add(, 0xaa);

  return 0;
}


The next build commands are used

i386-rtems4.12-gcc --pipe -B/opt/rtems4.12/i386-rtems4.12/pc686/lib/ -specs 
bsp_specs -qrtems-I /opt/rtems4.12/i386-rtems4.12/pc686/lib/include 
-march=i386 -Wall  -O2 -g -ffunction-sections -fdata-sections -o 
libatomic-add-test.o -c libatomic-add-test.c

i386-rtems4.12-gcc --pipe -B/opt/rtems4.12/i386-rtems4.12/pc686/lib/ -specs 
bsp_specs -qrtems -mtune=pentiumpro -march=pentium -Wall -O2 -g 
-ffunction-sections -fdata-sections   -Wl,--gc-sections -Wl,-Ttext,0x0010  
libatomic-add-test.o -o libatomic-test-add

problem appears with and without -march=i386, when -march is something
newer (pentium) then all is OK.


Disassembly looks like



00120a76 <__atomic_fetch_add_4>:
  120a76:   55  push   %ebp
  120a77:   89 e5   mov%esp,%ebp
  120a79:   c7 45 10 05 00 00 00movl   $0x5,0x10(%ebp)
  120a80:   5d  pop%ebp
  120a81:   eb f3   jmp120a76 <__atomic_fetch_add_4>

00120a83 <__atomic_add_fetch_4>:
  120a83:   55  push   %ebp
  120a84:   89 e5   mov%esp,%ebp
  120a86:   c7 45 10 05 00 00 00movl   $0x5,0x10(%ebp)
  120a8d:   5d  pop%ebp
  120a8e:   eb e6   jmp120a76 <__atomic_fetch_add_4>

00120a90 <__atomic_fetch_or_4>:
  120a90:   55  push   %ebp
  120a91:   89 e5   mov%esp,%ebp
  120a93:   56  push   %esi
  120a94:   53  push   %ebx
  120a95:   83 ec 0csub$0xc,%esp
  120a98:   8b 5d 08mov0x8(%ebp),%ebx
  120a9b:   53  push   %ebx
  120a9c:   e8 df 66 00 00  call   127180 <_Libatomic_Protect_start>
  120aa1:   8b 33   mov(%ebx),%esi
  120aa3:   8b 55 0cmov0xc(%ebp),%edx
  120aa6:   09 f2   or %esi,%edx
  120aa8:   89 13   mov%edx,(%ebx)
  120aaa:   5a  pop%edx
  120aab:   59  pop%ecx
  120aac:   50  push   %eax
  120aad:   53  push   %ebx
  120aae:   e8 ed 66 00 00  call   1271a0 <_Libatomic_Protect_end>
  120ab3:   8d 65 f8lea-0x8(%ebp),%esp
  120ab6:   89 f0   mov%esi,%eax
  120ab8:   5b  pop%ebx
  120ab9:   5e  pop%esi
  120aba:   5d  pop%ebp
  120abb:   c3  ret




_Libatomic_Protect_start is provided by RTEMS.


00127180 <_Libatomic_Protect_start>:
__uint32_t _Libatomic_Protect_start( void *ptr )
{
  ISR_Level isr_level;

  (void) ptr;
  _ISR_Local_disable( isr_level );
  127180:   9c  pushf
  127181:   fa  cli
  127182:   58  pop%eax
static inline bool _CPU_atomic_Flag_test_and_set( CPU_atomic_Flag *obj, 
CPU_atomic_Order order )
{
#if defined(_RTEMS_SCORE_CPUSTDATOMIC_USE_ATOMIC)
  return obj->test_and_set( order );
#elif defined(_RTEMS_SCORE_CPUSTDATOMIC_USE_STDATOMIC)
  return atomic_flag_test_and_set_explicit( obj, order );
  127183:   b1 01   mov$0x1,%cl
  127185:   8d 74 26 00 lea0x0(%esi,%eiz,1),%esi
  127189:   8d bc 27 00 00 00 00lea0x0(%edi,%eiz,1),%edi
  127190:   88 ca   mov%cl,%dl
  127192:   86 15 8c 85 13 00   xchg   %dl,0x13858c

#if defined(RTEMS_SMP)
  while (
  127198:   84 d2   test   %dl,%dl
  12719a:   75 f4   jne127190 
<_Libatomic_Protect_start+0x10>

Re: [PATCH 2/3] bsps/i386: use Pentimum instructions for pc586 and pc686 builds.

[Sebastian Huber]

On 12/10/16 10:26, p...@cmp.felk.cvut.cz wrote:

SMP build is broken with i386 set because libatomic and GCC
generate infinite loop for __atomic_fetch_add_4 used
in rtems_interrupt_lock_acquire

__atomic_fetch_add_4:
 push   %ebp
 mov%esp,%ebp
 movl   $0x5,0x10(%ebp)
 pop%ebp
 jmp__atomic_fetch_add_4


Do you have a test case for this compiler/RTEMS bug?  The use of 
libatomic is inefficient, but it should work.


--
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail  : sebastian.hu...@embedded-brains.de
PGP : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.

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[PATCH 2/3] bsps/i386: use Pentimum instructions for pc586 and pc686 builds.

[pisa]

From: Pavel Pisa 

When GCC option -march is not specifies i386-rtems toolchain
defaults to i386 architecture instruction set. It does not
provide atomic instructions which results in really inefficient
atomic_fetch_or even on UP build.

SMP build is broken with i386 set because libatomic and GCC
generate infinite loop for __atomic_fetch_add_4 used
in rtems_interrupt_lock_acquire

__atomic_fetch_add_4:
push   %ebp
mov%esp,%ebp
movl   $0x5,0x10(%ebp)
pop%ebp
jmp__atomic_fetch_add_4
---
 c/src/lib/libbsp/i386/pc386/make/custom/pc586.cfg | 2 +-
 c/src/lib/libbsp/i386/pc386/make/custom/pc686.cfg | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/c/src/lib/libbsp/i386/pc386/make/custom/pc586.cfg 
b/c/src/lib/libbsp/i386/pc386/make/custom/pc586.cfg
index 73e42cd..6f9cfcb 100644
--- a/c/src/lib/libbsp/i386/pc386/make/custom/pc586.cfg
+++ b/c/src/lib/libbsp/i386/pc386/make/custom/pc586.cfg
@@ -6,7 +6,7 @@ RTEMS_CPU_MODEL=pentium
 
 #  This contains the compiler options necessary to select the CPU model
 #  and (hopefully) optimize for it.
-CPU_CFLAGS = -mtune=pentium
+CPU_CFLAGS = -mtune=pentium -march=pentium
 
 include $(RTEMS_ROOT)/make/custom/pc386.cfg
 
diff --git a/c/src/lib/libbsp/i386/pc386/make/custom/pc686.cfg 
b/c/src/lib/libbsp/i386/pc386/make/custom/pc686.cfg
index 04f001f..b27e8ae 100644
--- a/c/src/lib/libbsp/i386/pc386/make/custom/pc686.cfg
+++ b/c/src/lib/libbsp/i386/pc386/make/custom/pc686.cfg
@@ -6,7 +6,7 @@ RTEMS_CPU_MODEL=pentiumpro
 
 #  This contains the compiler options necessary to select the CPU model
 #  and (hopefully) optimize for it.
-CPU_CFLAGS = -mtune=pentiumpro
+CPU_CFLAGS = -mtune=pentiumpro -march=pentium
 
 include $(RTEMS_ROOT)/make/custom/pc386.cfg
 
-- 
1.9.1

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