Re: [PATCH v3 05/49] semihosting: Add target_strlen for softmmu-uaccess.h

[Richard Henderson]

On 5/20/22 17:03, Richard Henderson wrote:
> Mirror the interface of the user-only function of the same name.
> Use probe_access_flags for the common case of ram, and
> cpu_memory_rw_debug for the uncommon case of mmio.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> v3: Use probe_access_flags (pmm)

Ho hum.  MIPS still selects semihosting without TCG, which means that
probe_access_flags is not present.

At present I'm assuming that semihosting can't work with KVM, and that we should disable 
the feature.


r~

> ---
>   include/semihosting/softmmu-uaccess.h |  3 ++
>   semihosting/uaccess.c                 | 49 +++++++++++++++++++++++++++
>   2 files changed, 52 insertions(+)
>
> diff --git a/include/semihosting/softmmu-uaccess.h 
> b/include/semihosting/softmmu-uaccess.h
> index 03300376d3..4f08dfc098 100644
> --- a/include/semihosting/softmmu-uaccess.h
> +++ b/include/semihosting/softmmu-uaccess.h
> @@ -53,4 +53,7 @@ void softmmu_unlock_user(CPUArchState *env, void *p,
>                            target_ulong addr, target_ulong len);
>   #define unlock_user(s, args, len) softmmu_unlock_user(env, s, args, len)
>   
> +ssize_t softmmu_strlen_user(CPUArchState *env, target_ulong addr);
> +#define target_strlen(p) softmmu_strlen_user(env, p)
> +
>   #endif /* SEMIHOSTING_SOFTMMU_UACCESS_H */
> diff --git a/semihosting/uaccess.c b/semihosting/uaccess.c
> index 0d3b32b75d..51019b79ff 100644
> --- a/semihosting/uaccess.c
> +++ b/semihosting/uaccess.c
> @@ -8,6 +8,7 @@
>    */
>   
>   #include "qemu/osdep.h"
> +#include "exec/exec-all.h"
>   #include "semihosting/softmmu-uaccess.h"
>   
>   void *softmmu_lock_user(CPUArchState *env, target_ulong addr,
> @@ -23,6 +24,54 @@ void *softmmu_lock_user(CPUArchState *env, target_ulong addr,
>       return p;
>   }
>   
> +ssize_t softmmu_strlen_user(CPUArchState *env, target_ulong addr)
> +{
> +    int mmu_idx = cpu_mmu_index(env, false);
> +    size_t len = 0;
> +
> +    while (1) {
> +        size_t left_in_page;
> +        int flags;
> +        void *h;
> +
> +        /* Find the number of bytes remaining in the page. */
> +        left_in_page = -(addr | TARGET_PAGE_MASK);
> +
> +        flags = probe_access_flags(env, addr, MMU_DATA_LOAD,
> +                                   mmu_idx, true, &h, 0);
> +        if (flags & TLB_INVALID_MASK) {
> +            return -1;
> +        }
> +        if (flags & TLB_MMIO) {
> +            do {
> +                uint8_t c;
> +                if (cpu_memory_rw_debug(env_cpu(env), addr, &c, 1, 0)) {
> +                    return -1;
> +                }
> +                if (c == 0) {
> +                    return len;
> +                }
> +                addr++;
> +                len++;
> +                if (len > INT32_MAX) {
> +                    return -1;
> +                }
> +            } while (--left_in_page != 0);
> +        } else {
> +            char *p = memchr(h, 0, left_in_page);
> +            if (p) {
> +                len += p - (char *)h;
> +                return len <= INT32_MAX ? (ssize_t)len : -1;
> +            }
> +            addr += left_in_page;
> +            len += left_in_page;
> +            if (len > INT32_MAX) {
> +                return -1;
> +            }
> +        }
> +    }
> +}
> +
>   char *softmmu_lock_user_string(CPUArchState *env, target_ulong addr)
>   {
>       /* TODO: Make this something that isn't fixed size.  */