[Qemu-devel] [Bug 1216845] [NEW] qemu-system-arm semihosting always calls exit(0)

[Qemu-devel] [Bug 1216845] [NEW] qemu-system-arm semihosting always calls exit(0)

[Liviu Ionescu]

Public bug reported:

In my embedded ARM project I have a bunch of unit tests that I run in a
POSIX synthetic environment, and, as usual for POSIX processes, these
tests return 0 for success and !=0 for error.

Now I expanded the testing environment to run some of these tests
compiled for ARM, under QEMU, with the tracing messages forwarded via
the semihosting API.

Up to now everything is fine with the emulation.

However I have a problem with passing the failure code back to the
operating system, to drive the continuous integration framework.

I checked the arm-semi.c code and for SYS_EXIT and I discovered that the
parameter passed is ignored and it always calls exit(0):

    case SYS_EXIT:
        gdb_exit(env, 0);
        exit(0);

To solve my problem I temporarily made a patch, and for cases that
should return non zero codes, I call an unsupported BKPT instruction,
which makes QEMU abort, and pass an non zero code (1) back to the
operating system.

    qemu: Unsupported SemiHosting SWI 0xf1

This kludge is more or less functional, but is quite inconvenient.

After checking the ARM manuals, I discovered that SYS_EXIT is not
standard, and the 0x18 code used for it originally was used for
angel_SWIreason_ReportException, which has a slightly different purpose.

Now the question:

Would it be possible to no longer ignore the code passed to 0x18, and if
it is non zero, to call exit() with a different value?

The suggested rule would be:

if (code ==0 || code == 0x20026)
  exit(0);
elif (code < 256)
  exit(code);
else
  exit(1);

The value 0x20026 means ADP_Stopped_ApplicationExit, and, if I
understood it right, it means that the program terminated successfully.
If this is not true, it can be removed from the first conditional
statement.

What do you think? Can this be added to arm-semi.c?


Regards,

Liviu

** Affects: qemu
     Importance: Undecided
         Status: New

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Title:
  qemu-system-arm semihosting always calls exit(0)

Status in QEMU:
  New

Bug description:
  In my embedded ARM project I have a bunch of unit tests that I run in
  a POSIX synthetic environment, and, as usual for POSIX processes,
  these tests return 0 for success and !=0 for error.

  Now I expanded the testing environment to run some of these tests
  compiled for ARM, under QEMU, with the tracing messages forwarded via
  the semihosting API.

  Up to now everything is fine with the emulation.

  However I have a problem with passing the failure code back to the
  operating system, to drive the continuous integration framework.

  I checked the arm-semi.c code and for SYS_EXIT and I discovered that
  the parameter passed is ignored and it always calls exit(0):

      case SYS_EXIT:
          gdb_exit(env, 0);
          exit(0);

  To solve my problem I temporarily made a patch, and for cases that
  should return non zero codes, I call an unsupported BKPT instruction,
  which makes QEMU abort, and pass an non zero code (1) back to the
  operating system.

      qemu: Unsupported SemiHosting SWI 0xf1

  This kludge is more or less functional, but is quite inconvenient.

  After checking the ARM manuals, I discovered that SYS_EXIT is not
  standard, and the 0x18 code used for it originally was used for
  angel_SWIreason_ReportException, which has a slightly different
  purpose.

  Now the question:

  Would it be possible to no longer ignore the code passed to 0x18, and
  if it is non zero, to call exit() with a different value?

  The suggested rule would be:

  if (code ==0 || code == 0x20026)
    exit(0);
  elif (code < 256)
    exit(code);
  else
    exit(1);

  The value 0x20026 means ADP_Stopped_ApplicationExit, and, if I
  understood it right, it means that the program terminated
  successfully. If this is not true, it can be removed from the first
  conditional statement.

  What do you think? Can this be added to arm-semi.c?

  
  Regards,

  Liviu

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[Qemu-devel] [Bug 1216845] Re: qemu-system-arm semihosting always calls exit(0)

[Karl Zimmerman]

Had a similar problem with my emulation environment.  However, I did
some inspection of the assembly code generated by newlib for ARM semi-
hosting.  While it initially appears that exit() and _exit() discard the
status code, upon careful inspection one finds that it is pushed on the
stack, with the SP pointing right to it at the point at which the SWI is
executed.

Thus, if the code passed to 0x18 is 0x20026, you can fetch the status
code passed to exit() from the stack.

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Title:
  qemu-system-arm semihosting always calls exit(0)

Status in QEMU:
  New

Bug description:
  In my embedded ARM project I have a bunch of unit tests that I run in
  a POSIX synthetic environment, and, as usual for POSIX processes,
  these tests return 0 for success and !=0 for error.

  Now I expanded the testing environment to run some of these tests
  compiled for ARM, under QEMU, with the tracing messages forwarded via
  the semihosting API.

  Up to now everything is fine with the emulation.

  However I have a problem with passing the failure code back to the
  operating system, to drive the continuous integration framework.

  I checked the arm-semi.c code and for SYS_EXIT and I discovered that
  the parameter passed is ignored and it always calls exit(0):

      case SYS_EXIT:
          gdb_exit(env, 0);
          exit(0);

  To solve my problem I temporarily made a patch, and for cases that
  should return non zero codes, I call an unsupported BKPT instruction,
  which makes QEMU abort, and pass an non zero code (1) back to the
  operating system.

      qemu: Unsupported SemiHosting SWI 0xf1

  This kludge is more or less functional, but is quite inconvenient.

  After checking the ARM manuals, I discovered that SYS_EXIT is not
  standard, and the 0x18 code used for it originally was used for
  angel_SWIreason_ReportException, which has a slightly different
  purpose.

  Now the question:

  Would it be possible to no longer ignore the code passed to 0x18, and
  if it is non zero, to call exit() with a different value?

  The suggested rule would be:

  if (code ==0 || code == 0x20026)
    exit(0);
  elif (code < 256)
    exit(code);
  else
    exit(1);

  The value 0x20026 means ADP_Stopped_ApplicationExit, and, if I
  understood it right, it means that the program terminated
  successfully. If this is not true, it can be removed from the first
  conditional statement.

  What do you think? Can this be added to arm-semi.c?

  
  Regards,

  Liviu

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[Qemu-devel] [Bug 1216845] Re: qemu-system-arm semihosting always calls exit(0)

[Liviu Ionescu]

thank you for your suggestion.

as semihosting servers I use the j-link gdb server, openocd and qemu. if
I got it right, you suggest to modify all these servers to retrieve the
exit code from a specific location. as long as this is not documented in
the ARM manuals, I cannot recommend such a solution.

in the GNU ARM Eclipse project templates I  fixed the problem by using
my own semihosting routines, where exit returns different values for 0
and non zero, so I no longer depend on the newlib support for
semihosting.

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Title:
  qemu-system-arm semihosting always calls exit(0)

Status in QEMU:
  New

Bug description:
  In my embedded ARM project I have a bunch of unit tests that I run in
  a POSIX synthetic environment, and, as usual for POSIX processes,
  these tests return 0 for success and !=0 for error.

  Now I expanded the testing environment to run some of these tests
  compiled for ARM, under QEMU, with the tracing messages forwarded via
  the semihosting API.

  Up to now everything is fine with the emulation.

  However I have a problem with passing the failure code back to the
  operating system, to drive the continuous integration framework.

  I checked the arm-semi.c code and for SYS_EXIT and I discovered that
  the parameter passed is ignored and it always calls exit(0):

      case SYS_EXIT:
          gdb_exit(env, 0);
          exit(0);

  To solve my problem I temporarily made a patch, and for cases that
  should return non zero codes, I call an unsupported BKPT instruction,
  which makes QEMU abort, and pass an non zero code (1) back to the
  operating system.

      qemu: Unsupported SemiHosting SWI 0xf1

  This kludge is more or less functional, but is quite inconvenient.

  After checking the ARM manuals, I discovered that SYS_EXIT is not
  standard, and the 0x18 code used for it originally was used for
  angel_SWIreason_ReportException, which has a slightly different
  purpose.

  Now the question:

  Would it be possible to no longer ignore the code passed to 0x18, and
  if it is non zero, to call exit() with a different value?

  The suggested rule would be:

  if (code ==0 || code == 0x20026)
    exit(0);
  elif (code < 256)
    exit(code);
  else
    exit(1);

  The value 0x20026 means ADP_Stopped_ApplicationExit, and, if I
  understood it right, it means that the program terminated
  successfully. If this is not true, it can be removed from the first
  conditional statement.

  What do you think? Can this be added to arm-semi.c?

  
  Regards,

  Liviu

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Re: [Qemu-devel] [Bug 1216845] Re: qemu-system-arm semihosting always calls exit(0)

[Peter Maydell]

On 4 February 2015 at 15:56, Karl Zimmerman
<karl.erik.zimmerman@gmail.com> wrote:
> Had a similar problem with my emulation environment.  However, I did
> some inspection of the assembly code generated by newlib for ARM semi-
> hosting.  While it initially appears that exit() and _exit() discard the
> status code, upon careful inspection one finds that it is pushed on the
> stack, with the SP pointing right to it at the point at which the SWI is
> executed.
>
> Thus, if the code passed to 0x18 is 0x20026, you can fetch the status
> code passed to exit() from the stack.

Yes, but this is an internal implementation detail of newlib,
not a part of the semihosting ABI. It might well change
in different versions of newlib and we can't rely on it.

-- PMM

[Qemu-devel] [Bug 1216845] Re: qemu-system-arm semihosting always calls exit(0)

[Peter Maydell]

With the new 2.0 ARM semihosting ABI, there is an optional extension
SYS_EXIT_EXTENDED which can be used to implement returning a non-zero
exit code for 32-bit ARM programs:

https://developer.arm.com/docs/100863/latest/semihosting-operations
/sys_exit_extended-0x20#sh-ext-exit-extended

QEMU should implement this.


** Changed in: qemu
       Status: New => Confirmed

** Tags added: arm

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1216845

Title:
  qemu-system-arm semihosting always calls exit(0)

Status in QEMU:
  Confirmed

Bug description:
  In my embedded ARM project I have a bunch of unit tests that I run in
  a POSIX synthetic environment, and, as usual for POSIX processes,
  these tests return 0 for success and !=0 for error.

  Now I expanded the testing environment to run some of these tests
  compiled for ARM, under QEMU, with the tracing messages forwarded via
  the semihosting API.

  Up to now everything is fine with the emulation.

  However I have a problem with passing the failure code back to the
  operating system, to drive the continuous integration framework.

  I checked the arm-semi.c code and for SYS_EXIT and I discovered that
  the parameter passed is ignored and it always calls exit(0):

      case SYS_EXIT:
          gdb_exit(env, 0);
          exit(0);

  To solve my problem I temporarily made a patch, and for cases that
  should return non zero codes, I call an unsupported BKPT instruction,
  which makes QEMU abort, and pass an non zero code (1) back to the
  operating system.

      qemu: Unsupported SemiHosting SWI 0xf1

  This kludge is more or less functional, but is quite inconvenient.

  After checking the ARM manuals, I discovered that SYS_EXIT is not
  standard, and the 0x18 code used for it originally was used for
  angel_SWIreason_ReportException, which has a slightly different
  purpose.

  Now the question:

  Would it be possible to no longer ignore the code passed to 0x18, and
  if it is non zero, to call exit() with a different value?

  The suggested rule would be:

  if (code ==0 || code == 0x20026)
    exit(0);
  elif (code < 256)
    exit(code);
  else
    exit(1);

  The value 0x20026 means ADP_Stopped_ApplicationExit, and, if I
  understood it right, it means that the program terminated
  successfully. If this is not true, it can be removed from the first
  conditional statement.

  What do you think? Can this be added to arm-semi.c?

  
  Regards,

  Liviu

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[Bug 1216845] Re: qemu-system-arm semihosting always calls exit(0)

[Peter Maydell]

https://patchew.org/QEMU/20190916141544.17540-1-peter.maydell@linaro.org/
is a patchset which adds semihosting v2 support to QEMU. With those
patches and a guest binary which understands semihosting v2 and knows
how to probe for the existence of the EXIT_EXTENDED extension, arm guest
binaries will be able to pass a non-zero exit status.


** Changed in: qemu
       Status: Confirmed => In Progress

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Title:
  qemu-system-arm semihosting always calls exit(0)

Status in QEMU:
  In Progress

Bug description:
  In my embedded ARM project I have a bunch of unit tests that I run in
  a POSIX synthetic environment, and, as usual for POSIX processes,
  these tests return 0 for success and !=0 for error.

  Now I expanded the testing environment to run some of these tests
  compiled for ARM, under QEMU, with the tracing messages forwarded via
  the semihosting API.

  Up to now everything is fine with the emulation.

  However I have a problem with passing the failure code back to the
  operating system, to drive the continuous integration framework.

  I checked the arm-semi.c code and for SYS_EXIT and I discovered that
  the parameter passed is ignored and it always calls exit(0):

      case SYS_EXIT:
          gdb_exit(env, 0);
          exit(0);

  To solve my problem I temporarily made a patch, and for cases that
  should return non zero codes, I call an unsupported BKPT instruction,
  which makes QEMU abort, and pass an non zero code (1) back to the
  operating system.

      qemu: Unsupported SemiHosting SWI 0xf1

  This kludge is more or less functional, but is quite inconvenient.

  After checking the ARM manuals, I discovered that SYS_EXIT is not
  standard, and the 0x18 code used for it originally was used for
  angel_SWIreason_ReportException, which has a slightly different
  purpose.

  Now the question:

  Would it be possible to no longer ignore the code passed to 0x18, and
  if it is non zero, to call exit() with a different value?

  The suggested rule would be:

  if (code ==0 || code == 0x20026)
    exit(0);
  elif (code < 256)
    exit(code);
  else
    exit(1);

  The value 0x20026 means ADP_Stopped_ApplicationExit, and, if I
  understood it right, it means that the program terminated
  successfully. If this is not true, it can be removed from the first
  conditional statement.

  What do you think? Can this be added to arm-semi.c?

  
  Regards,

  Liviu

To manage notifications about this bug go to:
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[Bug 1216845] Re: qemu-system-arm semihosting always calls exit(0)

[Peter Maydell]

The semihosting v2 support went into QEMU in the 4.2 release, but I
forgot to close this bug...


** Changed in: qemu
       Status: In Progress => Fix Released

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Title:
  qemu-system-arm semihosting always calls exit(0)

Status in QEMU:
  Fix Released

Bug description:
  In my embedded ARM project I have a bunch of unit tests that I run in
  a POSIX synthetic environment, and, as usual for POSIX processes,
  these tests return 0 for success and !=0 for error.

  Now I expanded the testing environment to run some of these tests
  compiled for ARM, under QEMU, with the tracing messages forwarded via
  the semihosting API.

  Up to now everything is fine with the emulation.

  However I have a problem with passing the failure code back to the
  operating system, to drive the continuous integration framework.

  I checked the arm-semi.c code and for SYS_EXIT and I discovered that
  the parameter passed is ignored and it always calls exit(0):

      case SYS_EXIT:
          gdb_exit(env, 0);
          exit(0);

  To solve my problem I temporarily made a patch, and for cases that
  should return non zero codes, I call an unsupported BKPT instruction,
  which makes QEMU abort, and pass an non zero code (1) back to the
  operating system.

      qemu: Unsupported SemiHosting SWI 0xf1

  This kludge is more or less functional, but is quite inconvenient.

  After checking the ARM manuals, I discovered that SYS_EXIT is not
  standard, and the 0x18 code used for it originally was used for
  angel_SWIreason_ReportException, which has a slightly different
  purpose.

  Now the question:

  Would it be possible to no longer ignore the code passed to 0x18, and
  if it is non zero, to call exit() with a different value?

  The suggested rule would be:

  if (code ==0 || code == 0x20026)
    exit(0);
  elif (code < 256)
    exit(code);
  else
    exit(1);

  The value 0x20026 means ADP_Stopped_ApplicationExit, and, if I
  understood it right, it means that the program terminated
  successfully. If this is not true, it can be removed from the first
  conditional statement.

  What do you think? Can this be added to arm-semi.c?

  
  Regards,

  Liviu

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