Re: [Qemu-devel] [RFC PATCH 06/11] target/arm: use the common interface for WRITE0/WRITEC in arm-semi

[Miroslav Rezanina <mrezanin@redhat.com>]

----- Original Message -----
> From: "Alex Bennée" <alex.bennee@linaro.org>
> To: "Miroslav Rezanina" <mrezanin@redhat.com>
> Cc: qemu-devel@nongnu.org, "Peter Maydell" <peter.maydell@linaro.org>, "Riku Voipio" <riku.voipio@iki.fi>,
> qemu-arm@nongnu.org, "Laurent Vivier" <laurent@vivier.eu>
> Sent: Friday, May 31, 2019 1:08:06 PM
> Subject: Re: [Qemu-devel] [RFC PATCH 06/11] target/arm: use the common interface for WRITE0/WRITEC in arm-semi
> 
> 
> Miroslav Rezanina <mrezanin@redhat.com> writes:
> 
> > On Tue, May 14, 2019 at 04:52:56PM +0100, Alex Bennée wrote:
> >> Now we have a common semihosting console interface use that for our
> >> string output. However ARM is currently unique in also supporting
> >> semihosting for linux-user so we need to replicate the API in
> >> linux-user. If other architectures gain this support we can move the
> >> file later.
> >>
> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> >> ---
> >>  linux-user/Makefile.objs  |  2 ++
> >>  linux-user/arm/semihost.c | 24 ++++++++++++++++++++++++
> >>  target/arm/arm-semi.c     | 31 ++++++-------------------------
> >>  3 files changed, 32 insertions(+), 25 deletions(-)
> >>  create mode 100644 linux-user/arm/semihost.c
> >>
> >> diff --git a/linux-user/Makefile.objs b/linux-user/Makefile.objs
> >> index 769b8d83362..285c5dfa17a 100644
> >> --- a/linux-user/Makefile.objs
> >> +++ b/linux-user/Makefile.objs
> >> @@ -6,4 +6,6 @@ obj-y = main.o syscall.o strace.o mmap.o signal.o \
> >>  obj-$(TARGET_HAS_BFLT) += flatload.o
> >>  obj-$(TARGET_I386) += vm86.o
> >>  obj-$(TARGET_ARM) += arm/nwfpe/
> >> +obj-$(TARGET_ARM) += arm/semihost.o
> >> +obj-$(TARGET_AARCH64) += arm/semihost.o
> >>  obj-$(TARGET_M68K) += m68k-sim.o
> >> diff --git a/linux-user/arm/semihost.c b/linux-user/arm/semihost.c
> >> new file mode 100644
> >> index 00000000000..9554102a855
> >> --- /dev/null
> >> +++ b/linux-user/arm/semihost.c
> >> @@ -0,0 +1,24 @@
> >> +/*
> >> + * ARM Semihosting Console Support
> >> + *
> >> + * Copyright (c) 2019 Linaro Ltd
> >> + *
> >> + * Currently ARM is unique in having support for semihosting support
> >> + * in linux-user. So for now we implement the common console API but
> >> + * just for arm linux-user.
> >> + *
> >> + * SPDX-License-Identifier: GPL-2.0-or-later
> >> + */
> >> +
> >> +#include "qemu/osdep.h"
> >> +#include "cpu.h"
> >> +#include "hw/semihosting/console.h"
> >> +#include "qemu.h"
> >> +
> >> +int qemu_semihosting_console_out(CPUArchState *env, target_ulong addr,
> >> int len)
> >> +{
> >> +    void *s = lock_user_string(addr);
> >> +    len = write(STDERR_FILENO, s, len ? len : strlen(s));
> >> +    unlock_user(s, addr, 0);
> >> +    return len;
> >> +}
> >> diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c
> >> index 9e5a414dd89..253c66b172a 100644
> >> --- a/target/arm/arm-semi.c
> >> +++ b/target/arm/arm-semi.c
> >> @@ -27,6 +27,7 @@
> >>
> >>  #include "cpu.h"
> >>  #include "hw/semihosting/semihost.h"
> >> +#include "hw/semihosting/console.h"
> >>  #ifdef CONFIG_USER_ONLY
> >>  #include "qemu.h"
> >>
> >> @@ -314,32 +315,12 @@ target_ulong do_arm_semihosting(CPUARMState *env)
> >>              return set_swi_errno(ts, close(arg0));
> >>          }
> >>      case TARGET_SYS_WRITEC:
> >> -        {
> >> -          char c;
> >> -
> >> -          if (get_user_u8(c, args))
> >> -              /* FIXME - should this error code be -TARGET_EFAULT ? */
> >> -              return (uint32_t)-1;
> >> -          /* Write to debug console.  stderr is near enough.  */
> >> -          if (use_gdb_syscalls()) {
> >> -                return arm_gdb_syscall(cpu, arm_semi_cb, "write,2,%x,1",
> >> args);
> >> -          } else {
> >> -                return write(STDERR_FILENO, &c, 1);
> >> -          }
> >> -        }
> >> +    {
> >> +        qemu_semihosting_console_out(env, args, 1);
> >> +        return 0xdeadbeef;
> >> +    }
> >>      case TARGET_SYS_WRITE0:
> >> -        if (!(s = lock_user_string(args)))
> >> -            /* FIXME - should this error code be -TARGET_EFAULT ? */
> >> -            return (uint32_t)-1;
> >> -        len = strlen(s);
> >> -        if (use_gdb_syscalls()) {
> >> -            return arm_gdb_syscall(cpu, arm_semi_cb, "write,2,%x,%x",
> >> -                                   args, len);
> >> -        } else {
> >> -            ret = write(STDERR_FILENO, s, len);
> >> -        }
> >> -        unlock_user(s, args, 0);
> >> -        return ret;
> >> +        return qemu_semihosting_console_out(env, args, 0);
> >>      case TARGET_SYS_WRITE:
> >>          GET_ARG(0);
> >>          GET_ARG(1);
> >> --
> >> 2.20.1
> >>
> >>
> >
> > Hi Alex,
> >
> > this patch breaks build for softmmu target when CONFIG_SEMIHOSTING is not
> > enabled as qemu_semihosting_console_out
> > is not defined in such case - neither linux-user/arm/semihost.c nor
> > hw/semihosting/console.c compiled and function
> > is not in stubs/semihost.c
> 
> How do you do that? I tried ../../configure --without-default-devices
> and that still builds for me.

It's usual RHEL way - use --without-default-devices and use specific
list of enabled devices (this mean disable CONFIG_SEMIHOSTING in
default_config/* file).

> 
> But I suspect what's needed is to change:
> 
> #ifndef CONFIG_USER_ONLY
> 
> to
> 
> #ifdef CONFIG_SEMIHOSTING
> 
> to the relevant headers and helper bits.

Yeah, have to find out what are relevant pieces.

Mirek

> 
> >
> > Mirek
> 
> 
> --
> Alex Bennée
> 

-- 
Miroslav Rezanina
Software Engineer - Virtualization Team Maintainer