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

[Alex Bennée]

Miroslav Rezanina <address@hidden> writes:

> ----- Original Message -----
>> From: "Alex Bennée" <address@hidden>
>> To: "Miroslav Rezanina" <address@hidden>
>> Cc: address@hidden, "Peter Maydell" <address@hidden>, "Riku Voipio" 
>> <address@hidden>,
>> address@hidden, "Laurent Vivier" <address@hidden>
>> 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 <address@hidden> 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 <address@hidden>
>> >> ---
>> >>  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).

OK - so from the upstream source tree CONFIG_SEMIHOSTING is still =y
(but I can see most of them are now =n). Isn't the simplest solution to
fix-up your version of the default_config file to include SEMIHOSTING?

Is this an out-of-tree RHEL addition?

>>
>> 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
>>


--
Alex Bennée