[Qemu-arm] [PATCH v2 00/15] target/arm: Implement semihosting v2.0

[Peter Maydell]

This patchset implements support in QEMU for v2.0 of the
Arm semihosting specification:
 https://developer.arm.com/docs/100863/latest/preface

Specifically, v2.0 has:
 * a mechanism for detection of optional extra features,
   which works by allowing the guest to open a magic file
   named ":semihosting-features" and read some feature
   flags from it
 * two defined extensions:
  - STDOUT_STDERR lets the guest separately open stdout and
    stderr via the ":tt" magic filename (v1.0 only allowed
    access to stdout)
  - EXIT_EXTENDED lets A32/T32 guests exit with a specified
    exit status (otherwise only available to A64 guests).
    This is something that people have been complaining
    about for a long time.

(Technically some of the things we already support, like
having an A64 semihosting interface at all, are also part of
the v2.0 spec.)

This patchset:
 * fixes some bugs relating to errnos in some cases
 * makes semihosting hand out its own filedescriptors rather
   than just passing out host fd numbers
 * abstracts out the fd-related semihosting calls so they
   indirect via a function table based on the type of the fd
 * adds a new type of fd representing the magic file
   ":semihosting-features" which is used for feature-detection
 * implements both of the extensions defined by the v2.0 spec

I've tested this by improving my semihosting test suite:
 https://git.linaro.org/people/peter.maydell/semihosting-tests.git/
(if people have other guest binaries that make much use of
semihosting then testing would certainly be welcome.)

Changes v1->v2:
 * Added a patch which corrects misunderstanding in a FIXME
   comment about the when the callback function is called
   for arm_gdb_syscall()
 * in patch 4, if the SYS_open is going via the gdbstub, we
   must do the associate_guestfd() work in the gdbstub callback
   function. This is because in softmmu mode the callback will
   not be called until after do_arm_semihosting() returns.
   (The v1 series effectively broke SYS_open in the gdbstub
   + softmmu config)
 * Pass CPUARMState* to set_swi_errno(), rather than creating
   an odd local-to-this-file typedef of TaskState for the
   softmmu compilation
 * New patch: avoid ifdeffery in gdb callback fns by
   using set_swi_errno() rather than doing it by-hand
 * The various 'factor out SYS_foo' patches are basically
   unchanged, but all the functions no longer need to take
   a TaskState*. This seemed kind of borderline as to whether
   to retain Alex's reviewed-by tags, so I dropped them.
 * Since we need 'env' for set_swi_errno(), we don't need
   to put the variable declaration inside ifdefs any more
   in the host_readfn() etc.

I do plan to have a go at fixing the odd FIXME surrounding
arm_gdb_syscall() which patch 3 clarifies/states in a comment.
But I thought it better to not tangle that up with this
patchset, which is already pretty long.

thanks
-- PMM


Peter Maydell (15):
  target/arm/arm-semi: Capture errno in softmmu version of
    set_swi_errno()
  target/arm/arm-semi: Always set some kind of errno for failed calls
  target/arm/arm-semi: Correct comment about gdb syscall races
  target/arm/arm-semi: Make semihosting code hand out its own file
    descriptors
  target/arm/arm-semi: Restrict use of TaskState*
  target/arm/arm-semi: Use set_swi_errno() in gdbstub callback functions
  target/arm/arm-semi: Factor out implementation of SYS_CLOSE
  target/arm/arm-semi: Factor out implementation of SYS_WRITE
  target/arm/arm-semi: Factor out implementation of SYS_READ
  target/arm/arm-semi: Factor out implementation of SYS_ISTTY
  target/arm/arm-semi: Factor out implementation of SYS_SEEK
  target/arm/arm-semi: Factor out implementation of SYS_FLEN
  target/arm/arm-semi: Implement support for semihosting feature
    detection
  target/arm/arm-semi: Implement SH_EXT_EXIT_EXTENDED extension
  target/arm/arm-semi: Implement SH_EXT_STDOUT_STDERR extension

 target/arm/arm-semi.c | 707 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 577 insertions(+), 130 deletions(-)

-- 
2.20.1