Re: [Qemu-devel] [RFC PATCH] target/arm: semihosting docs, formatting and return clean-ups

[Philippe Mathieu-Daudé]

Hi Alex,

On 5/10/19 9:10 PM, Alex Bennée wrote:
> This is a clean-up of the semihosting calls after reading ver 2.0 of
> the specification. There are a number of small fixes that seemed too
> insignificant to split into smaller patches:
> 

Can you split at least this one of:

>   - fixup block comments as per standard

The rest is probably acceptable as an unique patch:

>   - add reference to the ARM semihosting spec
>   - add some additional commentary on return values
>   - audit return values, return 0xdeadbeef for corrupted values
>   - fix up leaks from early returns with lock_user_string
>   - return bytes not written/read instead of -1
>   - add LOG_UNIMP for missing functionality

Thanks!

Phil.

> 
> This is very much a Friday patch. It might be worth splitting up if
> coming back for a more concerted clean-up series for semihosting as
> the asynchronous gdb calls probably need more attention.
> 
> Signed-off-by: Alex Bennée <address@hidden>
> ---
>  target/arm/arm-semi.c | 180 +++++++++++++++++++++++++-----------------
>  1 file changed, 109 insertions(+), 71 deletions(-)
> 
> diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c
> index 4c326fdc2fb..8deaed2807c 100644
> --- a/target/arm/arm-semi.c
> +++ b/target/arm/arm-semi.c
> @@ -2,6 +2,7 @@
>   *  Arm "Angel" semihosting syscalls
>   *
>   *  Copyright (c) 2005, 2007 CodeSourcery.
> + *  Copyright (c) 2019 Linaro
>   *  Written by Paul Brook.
>   *
>   *  This program is free software; you can redistribute it and/or modify
> @@ -15,13 +16,19 @@
>   *  GNU General Public License for more details.
>   *
>   *  You should have received a copy of the GNU General Public License
> - *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> + *  along with this program; if not, see
> + *  <http://www.gnu.org/licenses/>.
> + *
> + *  ARM Semihosting is documented in:
> + *     Semihosting for AArch32 and AArch64 Release 2.0
> + *     https://static.docs.arm.com/100863/0200/semihosting.pdf
>   */
>  
>  #include "qemu/osdep.h"
>  
>  #include "cpu.h"
>  #include "exec/semihost.h"
> +#include "exec/log.h"
>  #ifdef CONFIG_USER_ONLY
>  #include "qemu.h"
>  
> @@ -241,13 +248,18 @@ static target_ulong arm_gdb_syscall(ARMCPU *cpu, 
> gdb_syscall_complete_cb cb,
>       put_user_u64(val, args + (n) * 8) :                \
>       put_user_u32(val, args + (n) * 4))
>  
> +/*
> + * Do a semihosting call. Returns the "RETURN REGISTER" which is
> + * documented as corrupted for some calls. In this case we use the
> + * venerable 0xdeadbeef.
> + */
>  target_ulong do_arm_semihosting(CPUARMState *env)
>  {
>      ARMCPU *cpu = arm_env_get_cpu(env);
>      CPUState *cs = CPU(cpu);
>      target_ulong args;
>      target_ulong arg0, arg1, arg2, arg3;
> -    char * s;
> +    char *s;
>      int nr;
>      uint32_t ret;
>      uint32_t len;
> @@ -273,9 +285,9 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          GET_ARG(2);
>          s = lock_user_string(arg0);
>          if (!s) {
> -            /* FIXME - should this error code be -TARGET_EFAULT ? */
>              return (uint32_t)-1;
>          }
> +        /* check for invalid open mode */
>          if (arg1 >= 12) {
>              unlock_user(s, arg0, 0);
>              return (uint32_t)-1;
> @@ -287,7 +299,7 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          }
>          if (use_gdb_syscalls()) {
>              ret = arm_gdb_syscall(cpu, arm_semi_cb, "open,%s,%x,1a4", arg0,
> -                                  (int)arg2+1, gdb_open_modeflags[arg1]);
> +                                  (int) arg2 + 1, gdb_open_modeflags[arg1]);
>          } else {
>              ret = set_swi_errno(ts, open(s, open_modeflags[arg1], 0644));
>          }
> @@ -301,48 +313,51 @@ 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()) {
> +    {
> +        char c;
> +        if (!get_user_u8(c, args)) {
> +            /* 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 {
> +            } else {
>  #ifdef CONFIG_SOFTMMU
> -              Chardev *chardev = semihosting_get_chardev();
> -              if (chardev) {
> -                  return qemu_chr_write_all(chardev, (uint8_t *) &c, 1);
> -              } else
> +                Chardev *chardev = semihosting_get_chardev();
> +                if (chardev) {
> +                    return qemu_chr_write_all(chardev, (uint8_t *) &c, 1);
> +                }
>  #endif
> -              {
> -                  return write(STDERR_FILENO, &c, 1);
> -              }
> -          }
> +                return write(STDERR_FILENO, &c, 1);
> +            }
> +        } else {
> +            /* return register is corrupted */
> +            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 {
> +    {
> +        s = lock_user_string(args);
> +        if (s) {
> +            len = strlen(s);
> +            if (use_gdb_syscalls()) {
> +                arm_gdb_syscall(cpu, arm_semi_cb, "write,2,%x,%x",
> +                                args, len);
> +            } else {
>  #ifdef CONFIG_SOFTMMU
> -            Chardev *chardev = semihosting_get_chardev();
> -            if (chardev) {
> -                ret = qemu_chr_write_all(chardev, (uint8_t *) s, len);
> -            } else
> +                Chardev *chardev = semihosting_get_chardev();
> +                if (chardev) {
> +                    qemu_chr_write_all(chardev, (uint8_t *) s, len);
> +                } else
>  #endif
> -            {
> -                ret = write(STDERR_FILENO, s, len);
> +                {
> +                    /* result ignored */
> +                    ret = write(STDERR_FILENO, s, len);
> +                }
>              }
>          }
>          unlock_user(s, args, 0);
> -        return ret;
> +        /* return register is corrupted */
> +        return 0xdeadbeef;
> +    }
>      case TARGET_SYS_WRITE:
>          GET_ARG(0);
>          GET_ARG(1);
> @@ -355,13 +370,15 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          } else {
>              s = lock_user(VERIFY_READ, arg1, len, 1);
>              if (!s) {
> -                /* FIXME - should this error code be -TARGET_EFAULT ? */
> -                return (uint32_t)-1;
> +                /* Return bytes not written on error */
> +                return len;
>              }
>              ret = set_swi_errno(ts, write(arg0, s, len));
>              unlock_user(s, arg1, 0);
> -            if (ret == (uint32_t)-1)
> -                return -1;
> +            if (ret == (uint32_t)-1) {
> +                ret = 0;
> +            }
> +            /* Return bytes not written */
>              return len - ret;
>          }
>      case TARGET_SYS_READ:
> @@ -376,26 +393,33 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          } else {
>              s = lock_user(VERIFY_WRITE, arg1, len, 0);
>              if (!s) {
> -                /* FIXME - should this error code be -TARGET_EFAULT ? */
> -                return (uint32_t)-1;
> +                /* return bytes not read */
> +                return len;
>              }
>              do {
>                  ret = set_swi_errno(ts, read(arg0, s, len));
>              } while (ret == -1 && errno == EINTR);
>              unlock_user(s, arg1, len);
> -            if (ret == (uint32_t)-1)
> -                return -1;
> +            if (ret == (uint32_t)-1) {
> +                ret = 0;
> +            }
> +            /* Return bytes not read */
>              return len - ret;
>          }
>      case TARGET_SYS_READC:
> -       /* XXX: Read from debug console. Not implemented.  */
> +        qemu_log_mask(LOG_UNIMP, "%s: TARGET_SYS_READC not implemented",
> +                      __func__);
>          return 0;
>      case TARGET_SYS_ISTTY:
>          GET_ARG(0);
>          if (use_gdb_syscalls()) {
>              return arm_gdb_syscall(cpu, arm_semi_cb, "isatty,%x", arg0);
>          } else {
> -            return isatty(arg0);
> +            if (isatty(arg0)) {
> +                return 1;
> +            } else {
> +                return (errno == EBADF ? -1 : 0);
> +            }
>          }
>      case TARGET_SYS_SEEK:
>          GET_ARG(0);
> @@ -405,8 +429,9 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>                                     arg0, arg1);
>          } else {
>              ret = set_swi_errno(ts, lseek(arg0, arg1, SEEK_SET));
> -            if (ret == (uint32_t)-1)
> -              return -1;
> +            if (ret == (uint32_t)-1) {
> +                return -1;
> +            }
>              return 0;
>          }
>      case TARGET_SYS_FLEN:
> @@ -417,28 +442,30 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          } else {
>              struct stat buf;
>              ret = set_swi_errno(ts, fstat(arg0, &buf));
> -            if (ret == (uint32_t)-1)
> +            if (ret == (uint32_t)-1) {
>                  return -1;
> +            }
>              return buf.st_size;
>          }
>      case TARGET_SYS_TMPNAM:
> -        /* XXX: Not implemented.  */
> +        qemu_log_mask(LOG_UNIMP, "%s: TARGET_SYS_TMPNAM not implemented",
> +                      __func__);
>          return -1;
>      case TARGET_SYS_REMOVE:
>          GET_ARG(0);
>          GET_ARG(1);
>          if (use_gdb_syscalls()) {
>              ret = arm_gdb_syscall(cpu, arm_semi_cb, "unlink,%s",
> -                                  arg0, (int)arg1+1);
> +                                  arg0, (int)arg1 + 1);
>          } else {
>              s = lock_user_string(arg0);
>              if (!s) {
> -                /* FIXME - should this error code be -TARGET_EFAULT ? */
> -                return (uint32_t)-1;
> +                return -EIO;
>              }
> -            ret =  set_swi_errno(ts, remove(s));
> +            ret = set_swi_errno(ts, remove(s));
>              unlock_user(s, arg0, 0);
>          }
> +        /* 0 on success or host-specific error code */
>          return ret;
>      case TARGET_SYS_RENAME:
>          GET_ARG(0);
> @@ -447,20 +474,23 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          GET_ARG(3);
>          if (use_gdb_syscalls()) {
>              return arm_gdb_syscall(cpu, arm_semi_cb, "rename,%s,%s",
> -                                   arg0, (int)arg1+1, arg2, (int)arg3+1);
> +                                   arg0, (int)arg1 + 1, arg2, (int)arg3 + 1);
>          } else {
>              char *s2;
>              s = lock_user_string(arg0);
>              s2 = lock_user_string(arg2);
> -            if (!s || !s2)
> -                /* FIXME - should this error code be -TARGET_EFAULT ? */
> -                ret = (uint32_t)-1;
> -            else
> +            if (s && s2) {
>                  ret = set_swi_errno(ts, rename(s, s2));
> -            if (s2)
> +            } else {
> +                ret = -EIO;
> +            }
> +            if (s2) {
>                  unlock_user(s2, arg2, 0);
> -            if (s)
> +            }
> +            if (s) {
>                  unlock_user(s, arg0, 0);
> +            }
> +            /* 0 on success or host-specific error code */
>              return ret;
>          }
>      case TARGET_SYS_CLOCK:
> @@ -472,7 +502,7 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          GET_ARG(1);
>          if (use_gdb_syscalls()) {
>              return arm_gdb_syscall(cpu, arm_semi_cb, "system,%s",
> -                                   arg0, (int)arg1+1);
> +                                   arg0, (int)arg1 + 1);
>          } else {
>              s = lock_user_string(arg0);
>              if (!s) {
> @@ -527,14 +557,16 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>  
>              output_size = ts->info->arg_end - ts->info->arg_start;
>              if (!output_size) {
> -                /* We special-case the "empty command line" case (argc==0).
> -                   Just provide the terminating 0. */
> +                /*
> +                 * We special-case the "empty command line" case (argc==0).
> +                 * Just provide the terminating 0.
> +                 */
>                  output_size = 1;
>              }
>  #endif
>  
>              if (output_size > input_size) {
> -                 /* Not enough space to store command-line arguments.  */
> +                /* Not enough space to store command-line arguments.  */
>                  return -1;
>              }
>  
> @@ -588,8 +620,10 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>              GET_ARG(0);
>  
>  #ifdef CONFIG_USER_ONLY
> -            /* Some C libraries assume the heap immediately follows .bss, so
> -               allocate it using sbrk.  */
> +            /*
> +             * Some C libraries assume the heap immediately follows .bss, so
> +             * allocate it using sbrk.
> +             */
>              if (!ts->heap_limit) {
>                  abi_ulong ret;
>  
> @@ -637,7 +671,8 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>          }
>      case TARGET_SYS_EXIT:
>          if (is_a64(env)) {
> -            /* The A64 version of this call takes a parameter block,
> +            /*
> +             * The A64 version of this call takes a parameter block,
>               * so the application-exit type can return a subcode which
>               * is the exit status code from the application.
>               */
> @@ -650,14 +685,17 @@ target_ulong do_arm_semihosting(CPUARMState *env)
>                  ret = 1;
>              }
>          } else {
> -            /* ARM specifies only Stopped_ApplicationExit as normal
> -             * exit, everything else is considered an error */
> +            /*
> +             * ARM specifies only Stopped_ApplicationExit as normal
> +             * exit, everything else is considered an error
> +             */
>              ret = (args == ADP_Stopped_ApplicationExit) ? 0 : 1;
>          }
>          gdb_exit(env, ret);
>          exit(ret);
>      case TARGET_SYS_SYNCCACHE:
> -        /* Clean the D-cache and invalidate the I-cache for the specified
> +        /*
> +         * Clean the D-cache and invalidate the I-cache for the specified
>           * virtual address range. This is a nop for us since we don't
>           * implement caches. This is only present on A64.
>           */
>