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>
Message-Id: <20240412073346.458116-4-richard.henderson@linaro.org>
---
 include/qemu/cutils.h  | 15 ++++++++++-----
 hw/virtio/vhost-vdpa.c | 14 ++++++++------
 util/hexdump.c         | 27 ++++++++++++++++-----------
 3 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/include/qemu/cutils.h b/include/qemu/cutils.h
index c5dea63742..14a3285343 100644
--- a/include/qemu/cutils.h
+++ b/include/qemu/cutils.h
@@ -282,12 +282,17 @@ 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);
 
 /*
  * Hexdump a buffer to a file. An optional string prefix is added to every line
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 7368b71902..419463c154 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -944,13 +944,15 @@ static int vhost_vdpa_set_config_call(struct vhost_dev *dev,
 static void vhost_vdpa_dump_config(struct vhost_dev *dev, const uint8_t *config,
                                    uint32_t config_len)
 {
-    int b, len;
-    char line[QEMU_HEXDUMP_LINE_LEN];
+    g_autoptr(GString) str = g_string_sized_new(4 * 16);
+    size_t b, len;
 
-    for (b = 0; b < config_len; b += 16) {
-        len = config_len - b;
-        qemu_hexdump_line(line, config + b, len);
-        trace_vhost_vdpa_dump_config(dev, b, line);
+    for (b = 0; b < config_len; b += len) {
+        len = MIN(config_len - b, 16);
+
+        g_string_truncate(str, 0);
+        qemu_hexdump_line(str, config + b, len);
+        trace_vhost_vdpa_dump_config(dev, b, str->str);
     }
 }
 
diff --git a/util/hexdump.c b/util/hexdump.c
index 0f943e31e5..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;
+    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);
     }
 
     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);
+        qemu_hexdump_line(str, bufptr + b, len);
         asciidump_line(ascii, bufptr + b, len);
 
         fprintf(fp, "%s: %04zx: %-*s %s\n",
-                prefix, b, QEMU_HEXDUMP_LINE_WIDTH, line, ascii);
+                prefix, b, QEMU_HEXDUMP_LINE_WIDTH, str->str, ascii);
     }
 
 }
-- 
2.34.1