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

[Philippe Mathieu-Daudé]

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.hender...@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);
      }

}