Re: [PATCH v3 03/27] util/hexdump: Use a GString for qemu_hexdump_line

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 12/4/24 09:33, Richard Henderson wrote:
> Allocate a new, or append to an existing GString instead of
> using a fixed sized buffer.  Require the caller to determine
> the length of the line -- do not bound len here.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   include/qemu/cutils.h  | 15 ++++++++++-----
>   hw/virtio/vhost-vdpa.c | 14 ++++++++------
>   util/hexdump.c         | 29 +++++++++++++++++------------
>   3 files changed, 35 insertions(+), 23 deletions(-)
> 
> diff --git a/include/qemu/cutils.h b/include/qemu/cutils.h
> index d0c5386e6c..7311fb36ca 100644
> --- a/include/qemu/cutils.h
> +++ b/include/qemu/cutils.h
> @@ -252,12 +252,17 @@ static inline const char *yes_no(bool b)
>    */
>   int parse_debug_env(const char *name, int max, int initial);
>   
> -/*
> - * Hexdump a line of a byte buffer into a hexadecimal/ASCII buffer
> +/**
> + * qemu_hexdump_line:
> + * @str: GString into which to append
> + * @buf: buffer to dump
> + * @len: number of bytes to dump
> + *
> + * Append @len bytes of @buf as hexadecimal into @str.
> + * If @str is NULL, allocate a new string and return it;
> + * otherwise return @str.
>    */
> -#define QEMU_HEXDUMP_LINE_BYTES 16 /* Number of bytes to dump */
> -#define QEMU_HEXDUMP_LINE_LEN 75   /* Number of characters in line */
> -void qemu_hexdump_line(char *line, const void *bufptr, size_t len);
> +GString *qemu_hexdump_line(GString *str, const void *buf, size_t len);


> diff --git a/util/hexdump.c b/util/hexdump.c
> index dbc536fe84..521e346bc6 100644
> --- a/util/hexdump.c
> +++ b/util/hexdump.c
> @@ -16,22 +16,25 @@
>   #include "qemu/osdep.h"
>   #include "qemu/cutils.h"
>   
> -void qemu_hexdump_line(char *line, const void *bufptr, size_t len)
> +GString *qemu_hexdump_line(GString *str, const void *vbuf, size_t len)
>   {
> -    const char *buf = bufptr;
> -    int i, c;
> +    const uint8_t *buf = vbuf;
> +    size_t i;
>   
> -    if (len > QEMU_HEXDUMP_LINE_BYTES) {
> -        len = QEMU_HEXDUMP_LINE_BYTES;
> +    if (str == NULL) {
> +        /* Estimate the length of the output to avoid reallocs. */
> +        i = len * 3 + len / 4;
> +        str = g_string_sized_new(i + 1);
>       }

[*]
          else {
            g_string_truncate(str, 0);
          }

>   
>       for (i = 0; i < len; i++) {
>           if (i != 0 && (i % 4) == 0) {
> -            *line++ = ' ';
> +            g_string_append_c(str, ' ');
>           }
> -        line += sprintf(line, " %02x", (unsigned char)buf[i]);
> +        g_string_append_printf(str, " %02x", buf[i]);
>       }
> -    *line = '\0';
> +
> +    return str;
>   }
>   
>   static void asciidump_line(char *line, const void *bufptr, size_t len)
> @@ -49,24 +52,26 @@ static void asciidump_line(char *line, const void *bufptr, size_t len)
>       *line = '\0';
>   }
>   
> +#define QEMU_HEXDUMP_LINE_BYTES 16
>   #define QEMU_HEXDUMP_LINE_WIDTH \
>       (QEMU_HEXDUMP_LINE_BYTES * 2 + QEMU_HEXDUMP_LINE_BYTES / 4)
>   
>   void qemu_hexdump(FILE *fp, const char *prefix,
>                     const void *bufptr, size_t size)
>   {
> -    char line[QEMU_HEXDUMP_LINE_LEN];
> +    g_autoptr(GString) str = g_string_sized_new(QEMU_HEXDUMP_LINE_WIDTH + 1);
>       char ascii[QEMU_HEXDUMP_LINE_BYTES + 1];
>       size_t b, len;
>   
>       for (b = 0; b < size; b += len) {
>           len = MIN(size - b, QEMU_HEXDUMP_LINE_BYTES);
>   
> -        qemu_hexdump_line(line, bufptr + b, len);
> +        g_string_truncate(str, 0);

Shouldn't we truncate in [*] ?

> +        qemu_hexdump_line(str, bufptr + b, len);
>           asciidump_line(ascii, bufptr + b, len);
>   
> -        fprintf(fp, "%s: %04x: %-*s %s\n",
> -                prefix, b, QEMU_HEXDUMP_LINE_WIDTH, line, ascii);
> +        fprintf(fp, "%s: %04zx: %-*s %s\n",
> +                prefix, b, QEMU_HEXDUMP_LINE_WIDTH, str->str, ascii);
>       }
>   
>   }