[PATCH v2] gdb: Fix "target file /proc/.../cmdline contained unexpected null characters"

[Ilya Leoshkevich <iii@linux.ibm.com>]

When using the gcore command, GDB prints the following warning:

    (gdb) gcore
    warning: target file /proc/.../cmdline contained unexpected null characters

The reason is that cmdline is read with target_fileio_read_stralloc(),
which warns on seeing null characters. However, it's perfectly valid
for cmdline to contain \0s, so switch to target_fileio_read_alloc().
---

v1: https://sourceware.org/pipermail/gdb-patches/2023-June/200436.html
    https://sourceware.org/pipermail/gdb-patches/2023-July/200993.html

v1 -> v2: Improve the commit message (Bruno).
          Handle the missing trailing '\0' (Bruno).

 gdb/linux-tdep.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index b5eee5e108c..90ad02310b3 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -1902,15 +1902,23 @@ linux_fill_prpsinfo (struct elf_internal_linux_prpsinfo *p)
   pid = inferior_ptid.pid ();
   xsnprintf (filename, sizeof (filename), "/proc/%d/cmdline", (int) pid);
   /* The full name of the program which generated the corefile.  */
-  gdb::unique_xmalloc_ptr<char> fname
-    = target_fileio_read_stralloc (NULL, filename);
+  gdb_byte *buf = NULL;
+  size_t buf_len = target_fileio_read_alloc (NULL, filename, &buf);
+  gdb::unique_xmalloc_ptr<char> fname ((char *)buf);
 
-  if (fname == NULL || fname.get ()[0] == '\0')
+  if (buf_len < 1 || fname.get ()[0] == '\0')
     {
       /* No program name was read, so we won't be able to retrieve more
 	 information about the process.  */
       return 0;
     }
+  if (fname.get ()[buf_len - 1] != '\0')
+    {
+      warning (_("target file %s "
+		 "does not contain a trailing null character"),
+	       filename);
+      return 0;
+    }
 
   memset (p, 0, sizeof (*p));
 
-- 
2.41.0