Error: matching constraint not valid in output operand

-1

I'm having trouble getting GCC inline assembler to accept some inline assembly for Power9.

The regular assembly I am trying to get GCC to accept is darn 3, 1, where 3 is r3 and 1 is parameter called L in the docs. It disassembles to this on big-endian:

0:   e6 05 61 7c    darn    r3,1

And on little-endian:

0:   7c 61 05 e6    darn    r3,1

Due to various reasons and problems, including old compilers and compilers that pretend to be other compilers, I want to issue byte codes for the instruction. My test program:

gcc112:~$ cat test.c

#include <stdint.h>



void random()

{

  volatile uint64_t x = __builtin_darn();



  __asm__ __volatile__ ("darn 3, 1");



  uint64_t y;

  __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

}

Compiling it results in:

$ /opt/cfarm/gcc-latest/bin/gcc -mcpu=power9 -c test.c

test.c: In function 'random':

test.c:10:3: error: matching constraint not valid in output operand

   __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

   ^~~~~~~

test.c:10:3: error: matching constraint not valid in output operand

test.c:10:3: error: invalid lvalue in asm output 0

Here's the section of the GCC inline assembly manual that should cover it, but I don't see it expalined: 6.45.2.3 Output Operands. I also checked simple and machine constraints but did not see it.

How do I tell GCC to execute the instruction, and then move r3 into y?

We do the same thing on x86 with rdrand. It works without problems on all version of GCC going back to 2.9:

uint64_t temp;

__asm__ __volatile__

(

    // radrand rax with retry

    "1:n"

    ".byte 0x48, 0x0f, 0xc7, 0xf0;n"

    "jnc 1b;n"

    : "=a" (temp)

    : : "cc"

);

edited Nov 26 '18 at 11:22

asked Nov 26 '18 at 11:04

jww

54.1k41234513

3

I'm not familiar with r3 as an output constraint. I'm guessing this is intended to indicated that the output will be in the 'r3' register, but I don't think you can do it this way (although I'm no expert on powerpc's machine constraints). Perhaps you could try register uint64_t y asm("r3"); (ie a local register variable) and then just use =r as the constraint?

– David Wohlferd
Nov 27 '18 at 3:01

Possible duplicate of How to have GCC combine "move r10, r3; store r10" into a "store r3"?, where I posted basically the same register-asm local variable answer as @David.

– Peter Cordes
Nov 30 '18 at 4:24

add a comment |

-1

I'm having trouble getting GCC inline assembler to accept some inline assembly for Power9.

The regular assembly I am trying to get GCC to accept is darn 3, 1, where 3 is r3 and 1 is parameter called L in the docs. It disassembles to this on big-endian:

0:   e6 05 61 7c    darn    r3,1

And on little-endian:

0:   7c 61 05 e6    darn    r3,1

Due to various reasons and problems, including old compilers and compilers that pretend to be other compilers, I want to issue byte codes for the instruction. My test program:

gcc112:~$ cat test.c

#include <stdint.h>



void random()

{

  volatile uint64_t x = __builtin_darn();



  __asm__ __volatile__ ("darn 3, 1");



  uint64_t y;

  __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

}

Compiling it results in:

$ /opt/cfarm/gcc-latest/bin/gcc -mcpu=power9 -c test.c

test.c: In function 'random':

test.c:10:3: error: matching constraint not valid in output operand

   __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

   ^~~~~~~

test.c:10:3: error: matching constraint not valid in output operand

test.c:10:3: error: invalid lvalue in asm output 0

Here's the section of the GCC inline assembly manual that should cover it, but I don't see it expalined: 6.45.2.3 Output Operands. I also checked simple and machine constraints but did not see it.

How do I tell GCC to execute the instruction, and then move r3 into y?

We do the same thing on x86 with rdrand. It works without problems on all version of GCC going back to 2.9:

uint64_t temp;

__asm__ __volatile__

(

    // radrand rax with retry

    "1:n"

    ".byte 0x48, 0x0f, 0xc7, 0xf0;n"

    "jnc 1b;n"

    : "=a" (temp)

    : : "cc"

);

edited Nov 26 '18 at 11:22

asked Nov 26 '18 at 11:04

jww

54.1k41234513

3

I'm not familiar with r3 as an output constraint. I'm guessing this is intended to indicated that the output will be in the 'r3' register, but I don't think you can do it this way (although I'm no expert on powerpc's machine constraints). Perhaps you could try register uint64_t y asm("r3"); (ie a local register variable) and then just use =r as the constraint?

– David Wohlferd
Nov 27 '18 at 3:01

Possible duplicate of How to have GCC combine "move r10, r3; store r10" into a "store r3"?, where I posted basically the same register-asm local variable answer as @David.

– Peter Cordes
Nov 30 '18 at 4:24

add a comment |

-1

I'm having trouble getting GCC inline assembler to accept some inline assembly for Power9.

The regular assembly I am trying to get GCC to accept is darn 3, 1, where 3 is r3 and 1 is parameter called L in the docs. It disassembles to this on big-endian:

0:   e6 05 61 7c    darn    r3,1

And on little-endian:

0:   7c 61 05 e6    darn    r3,1

Due to various reasons and problems, including old compilers and compilers that pretend to be other compilers, I want to issue byte codes for the instruction. My test program:

gcc112:~$ cat test.c

#include <stdint.h>



void random()

{

  volatile uint64_t x = __builtin_darn();



  __asm__ __volatile__ ("darn 3, 1");



  uint64_t y;

  __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

}

Compiling it results in:

$ /opt/cfarm/gcc-latest/bin/gcc -mcpu=power9 -c test.c

test.c: In function 'random':

test.c:10:3: error: matching constraint not valid in output operand

   __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

   ^~~~~~~

test.c:10:3: error: matching constraint not valid in output operand

test.c:10:3: error: invalid lvalue in asm output 0

Here's the section of the GCC inline assembly manual that should cover it, but I don't see it expalined: 6.45.2.3 Output Operands. I also checked simple and machine constraints but did not see it.

How do I tell GCC to execute the instruction, and then move r3 into y?

We do the same thing on x86 with rdrand. It works without problems on all version of GCC going back to 2.9:

uint64_t temp;

__asm__ __volatile__

(

    // radrand rax with retry

    "1:n"

    ".byte 0x48, 0x0f, 0xc7, 0xf0;n"

    "jnc 1b;n"

    : "=a" (temp)

    : : "cc"

);

edited Nov 26 '18 at 11:22

asked Nov 26 '18 at 11:04

jww

54.1k41234513

I'm having trouble getting GCC inline assembler to accept some inline assembly for Power9.

The regular assembly I am trying to get GCC to accept is darn 3, 1, where 3 is r3 and 1 is parameter called L in the docs. It disassembles to this on big-endian:

0:   e6 05 61 7c    darn    r3,1

And on little-endian:

0:   7c 61 05 e6    darn    r3,1

Due to various reasons and problems, including old compilers and compilers that pretend to be other compilers, I want to issue byte codes for the instruction. My test program:

gcc112:~$ cat test.c

#include <stdint.h>



void random()

{

  volatile uint64_t x = __builtin_darn();



  __asm__ __volatile__ ("darn 3, 1");



  uint64_t y;

  __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

}

Compiling it results in:

$ /opt/cfarm/gcc-latest/bin/gcc -mcpu=power9 -c test.c

test.c: In function 'random':

test.c:10:3: error: matching constraint not valid in output operand

   __asm__ __volatile__ (".byte 0x7c, 0x61, 0x05, 0xe6  n" : "=r3" (y));

   ^~~~~~~

test.c:10:3: error: matching constraint not valid in output operand

test.c:10:3: error: invalid lvalue in asm output 0

Here's the section of the GCC inline assembly manual that should cover it, but I don't see it expalined: 6.45.2.3 Output Operands. I also checked simple and machine constraints but did not see it.

How do I tell GCC to execute the instruction, and then move r3 into y?

We do the same thing on x86 with rdrand. It works without problems on all version of GCC going back to 2.9:

uint64_t temp;

__asm__ __volatile__

(

    // radrand rax with retry

    "1:n"

    ".byte 0x48, 0x0f, 0xc7, 0xf0;n"

    "jnc 1b;n"

    : "=a" (temp)

    : : "cc"

);

gcc inline-assembly powerpc altivec

edited Nov 26 '18 at 11:22

asked Nov 26 '18 at 11:04

jww

54.1k41234513

edited Nov 26 '18 at 11:22

asked Nov 26 '18 at 11:04

jww

54.1k41234513

edited Nov 26 '18 at 11:22

asked Nov 26 '18 at 11:04

jww

54.1k41234513

asked Nov 26 '18 at 11:04

jww

54.1k41234513

asked Nov 26 '18 at 11:04

jww

54.1k41234513

3

I'm not familiar with r3 as an output constraint. I'm guessing this is intended to indicated that the output will be in the 'r3' register, but I don't think you can do it this way (although I'm no expert on powerpc's machine constraints). Perhaps you could try register uint64_t y asm("r3"); (ie a local register variable) and then just use =r as the constraint?

– David Wohlferd
Nov 27 '18 at 3:01

Possible duplicate of How to have GCC combine "move r10, r3; store r10" into a "store r3"?, where I posted basically the same register-asm local variable answer as @David.

– Peter Cordes
Nov 30 '18 at 4:24

add a comment |

3

I'm not familiar with r3 as an output constraint. I'm guessing this is intended to indicated that the output will be in the 'r3' register, but I don't think you can do it this way (although I'm no expert on powerpc's machine constraints). Perhaps you could try register uint64_t y asm("r3"); (ie a local register variable) and then just use =r as the constraint?

– David Wohlferd
Nov 27 '18 at 3:01

Possible duplicate of How to have GCC combine "move r10, r3; store r10" into a "store r3"?, where I posted basically the same register-asm local variable answer as @David.

– Peter Cordes
Nov 30 '18 at 4:24

I'm not familiar with r3 as an output constraint. I'm guessing this is intended to indicated that the output will be in the 'r3' register, but I don't think you can do it this way (although I'm no expert on powerpc's machine constraints). Perhaps you could try register uint64_t y asm("r3"); (ie a local register variable) and then just use =r as the constraint?

– David Wohlferd
Nov 27 '18 at 3:01

Possible duplicate of How to have GCC combine "move r10, r3; store r10" into a "store r3"?, where I posted basically the same register-asm local variable answer as @David.

– Peter Cordes
Nov 30 '18 at 4:24

add a comment |

1 Answer
1

active

oldest

votes

Moving my (untested) comment to an answer to attempt to close this out

I'm not familiar with r3 as an output constraint. I'm guessing this is intended to indicate that the output will be in the 'r3' register, but I don't think you can do it this way (although I'm no expert on powerpc's machine constraints). Instead, perhaps you could try:

register uint64_t y asm("r3");

(ie make y a local register variable) and then just use "=r" as the constraint?

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

Thanks David. I tried both the register local and pointer to register local but neither worked. Both resulted in a wild write that segfault'd the program. The disassembly showed two stores occurring. That's why I want to get =r3 working as expected (which I don't think is possible).

– jww
Nov 30 '18 at 9:35

1

Looking at the output from godbolt, I'm seeing the same results for __builtin_darn that I see for using a local register. If there's a wild pointer, I'm not convinced it's coming from this code. Did you remove the 'extra' __asm__ __volatile__ ("darn 3, 1");? That code is invalid as it overwrites r3 without informing the compiler.

– David Wohlferd
Nov 30 '18 at 18:36

add a comment |

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Moving my (untested) comment to an answer to attempt to close this out

register uint64_t y asm("r3");

(ie make y a local register variable) and then just use "=r" as the constraint?

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

Thanks David. I tried both the register local and pointer to register local but neither worked. Both resulted in a wild write that segfault'd the program. The disassembly showed two stores occurring. That's why I want to get =r3 working as expected (which I don't think is possible).

– jww
Nov 30 '18 at 9:35

1

Looking at the output from godbolt, I'm seeing the same results for __builtin_darn that I see for using a local register. If there's a wild pointer, I'm not convinced it's coming from this code. Did you remove the 'extra' __asm__ __volatile__ ("darn 3, 1");? That code is invalid as it overwrites r3 without informing the compiler.

– David Wohlferd
Nov 30 '18 at 18:36

add a comment |

Moving my (untested) comment to an answer to attempt to close this out

register uint64_t y asm("r3");

(ie make y a local register variable) and then just use "=r" as the constraint?

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

Thanks David. I tried both the register local and pointer to register local but neither worked. Both resulted in a wild write that segfault'd the program. The disassembly showed two stores occurring. That's why I want to get =r3 working as expected (which I don't think is possible).

– jww
Nov 30 '18 at 9:35

1

Looking at the output from godbolt, I'm seeing the same results for __builtin_darn that I see for using a local register. If there's a wild pointer, I'm not convinced it's coming from this code. Did you remove the 'extra' __asm__ __volatile__ ("darn 3, 1");? That code is invalid as it overwrites r3 without informing the compiler.

– David Wohlferd
Nov 30 '18 at 18:36

add a comment |

Moving my (untested) comment to an answer to attempt to close this out

register uint64_t y asm("r3");

(ie make y a local register variable) and then just use "=r" as the constraint?

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

Moving my (untested) comment to an answer to attempt to close this out

register uint64_t y asm("r3");

(ie make y a local register variable) and then just use "=r" as the constraint?

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

answered Nov 30 '18 at 4:20

David Wohlferd

4,68311434

Thanks David. I tried both the register local and pointer to register local but neither worked. Both resulted in a wild write that segfault'd the program. The disassembly showed two stores occurring. That's why I want to get =r3 working as expected (which I don't think is possible).

– jww
Nov 30 '18 at 9:35

1

Looking at the output from godbolt, I'm seeing the same results for __builtin_darn that I see for using a local register. If there's a wild pointer, I'm not convinced it's coming from this code. Did you remove the 'extra' __asm__ __volatile__ ("darn 3, 1");? That code is invalid as it overwrites r3 without informing the compiler.

– David Wohlferd
Nov 30 '18 at 18:36

add a comment |

Thanks David. I tried both the register local and pointer to register local but neither worked. Both resulted in a wild write that segfault'd the program. The disassembly showed two stores occurring. That's why I want to get =r3 working as expected (which I don't think is possible).

– jww
Nov 30 '18 at 9:35

1

Looking at the output from godbolt, I'm seeing the same results for __builtin_darn that I see for using a local register. If there's a wild pointer, I'm not convinced it's coming from this code. Did you remove the 'extra' __asm__ __volatile__ ("darn 3, 1");? That code is invalid as it overwrites r3 without informing the compiler.

– David Wohlferd
Nov 30 '18 at 18:36

Thanks David. I tried both the register local and pointer to register local but neither worked. Both resulted in a wild write that segfault'd the program. The disassembly showed two stores occurring. That's why I want to get =r3 working as expected (which I don't think is possible).

– jww
Nov 30 '18 at 9:35

Looking at the output from godbolt, I'm seeing the same results for __builtin_darn that I see for using a local register. If there's a wild pointer, I'm not convinced it's coming from this code. Did you remove the 'extra' __asm__ __volatile__ ("darn 3, 1");? That code is invalid as it overwrites r3 without informing the compiler.

– David Wohlferd
Nov 30 '18 at 18:36

add a comment |

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