[glibc] stdio: Remove __libc_message alloca usage

[glibc] stdio: Remove __libc_message alloca usage

[Joe Simmons-Talbott]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5f798d38e967c62cca40c99bfc3e9c5ca0f37540

commit 5f798d38e967c62cca40c99bfc3e9c5ca0f37540
Author: Joe Simmons-Talbott <josimmon@redhat.com>
Date:   Mon Sep 11 16:16:49 2023 +0000

    stdio: Remove __libc_message alloca usage
    
    Use a fixed size array instead.  The maximum number of arguments
    is set by macro tricks.
    
    Co-authored-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Diff:
---
 include/stdio.h            | 29 +++++++++++++++++++++++++++-
 sysdeps/posix/libc_fatal.c | 47 +++++++++++++---------------------------------
 2 files changed, 41 insertions(+), 35 deletions(-)

diff --git a/include/stdio.h b/include/stdio.h
index 6755877911..7e70f95c6d 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -172,10 +172,37 @@ extern int __gen_tempname (char *__tmpl, int __suffixlen, int __flags,
    and abort.  */
 extern void __libc_fatal (const char *__message)
      __attribute__ ((__noreturn__));
-_Noreturn void __libc_message (const char *__fnt, ...) attribute_hidden;
 extern void __fortify_fail (const char *msg) __attribute__ ((__noreturn__));
 libc_hidden_proto (__fortify_fail)
 
+/* The maximum number of varargs allowed in a __libc_message format string */
+#define LIBC_MESSAGE_MAX_ARGS 4
+
+_Noreturn void __libc_message_impl (const char *__fnt, ...) attribute_hidden
+     __attribute__ ((__format__ (__printf__, 1, 2)));
+
+#define __libc_message0(fmt) \
+   __libc_message_impl (fmt)
+#define __libc_message1(fmt, a1) \
+   __libc_message_impl (fmt, a1)
+#define __libc_message2(fmt, a1, a2) \
+   __libc_message_impl (fmt, a1, a2)
+#define __libc_message3(fmt, a1, a2, a3) \
+   __libc_message_impl (fmt, a1, a2, a3)
+#define __libc_message4(fmt, a1, a2, a3, a4) \
+   __libc_message_impl (fmt, a1, a2, a3, a4)
+
+#define __libc_message_concat_x(a,b)  a##b
+#define __libc_message_concat(a,b)    __libc_message_concat_x (a, b)
+
+#define __libc_message_nargs_x(a0,a1,a2,a3,a4,a5,a6,...) a6
+#define __libc_message_nargs(b, ...) \
+   __libc_message_nargs_x (__VA_ARGS__,6,5,4,3,2,1,0,)
+#define __libc_message_disp(b, ...) \
+   __libc_message_concat (b, __libc_message_nargs (__VA_ARGS__))(__VA_ARGS__)
+#define __libc_message(...) \
+   __libc_message_disp (__libc_message, __VA_ARGS__)
+
 /* Acquire ownership of STREAM.  */
 extern void __flockfile (FILE *__stream) attribute_hidden;
 
diff --git a/sysdeps/posix/libc_fatal.c b/sysdeps/posix/libc_fatal.c
index 70edcc10c1..cf28387ee6 100644
--- a/sysdeps/posix/libc_fatal.c
+++ b/sysdeps/posix/libc_fatal.c
@@ -45,22 +45,13 @@ writev_for_fatal (int fd, const struct iovec *iov, size_t niov, size_t total)
 }
 #endif
 
-struct str_list
-{
-  const char *str;
-  size_t len;
-  struct str_list *next;
-};
-
 /* Abort with an error message.  */
 void
-__libc_message (const char *fmt, ...)
+__libc_message_impl (const char *fmt, ...)
 {
   va_list ap;
   int fd = -1;
 
-  va_start (ap, fmt);
-
 #ifdef FATAL_PREPARE
   FATAL_PREPARE;
 #endif
@@ -68,9 +59,11 @@ __libc_message (const char *fmt, ...)
   if (fd == -1)
     fd = STDERR_FILENO;
 
-  struct str_list *list = NULL;
-  int nlist = 0;
+  struct iovec iov[LIBC_MESSAGE_MAX_ARGS * 2 - 1];
+  int iovcnt = 0;
+  ssize_t total = 0;
 
+  va_start (ap, fmt);
   const char *cp = fmt;
   while (*cp != '\0')
     {
@@ -100,28 +93,16 @@ __libc_message (const char *fmt, ...)
 	  cp = next;
 	}
 
-      struct str_list *newp = alloca (sizeof (struct str_list));
-      newp->str = str;
-      newp->len = len;
-      newp->next = list;
-      list = newp;
-      ++nlist;
+      iov[iovcnt].iov_base = (char *) str;
+      iov[iovcnt].iov_len = len;
+      total += len;
+      iovcnt++;
     }
+  va_end (ap);
 
-  if (nlist > 0)
+  if (iovcnt > 0)
     {
-      struct iovec *iov = alloca (nlist * sizeof (struct iovec));
-      ssize_t total = 0;
-
-      for (int cnt = nlist - 1; cnt >= 0; --cnt)
-	{
-	  iov[cnt].iov_base = (char *) list->str;
-	  iov[cnt].iov_len = list->len;
-	  total += list->len;
-	  list = list->next;
-	}
-
-      WRITEV_FOR_FATAL (fd, iov, nlist, total);
+      WRITEV_FOR_FATAL (fd, iov, iovcnt, total);
 
       total = (total + 1 + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
       struct abort_msg_s *buf = __mmap (NULL, total,
@@ -131,7 +112,7 @@ __libc_message (const char *fmt, ...)
 	{
 	  buf->size = total;
 	  char *wp = buf->msg;
-	  for (int cnt = 0; cnt < nlist; ++cnt)
+	  for (int cnt = 0; cnt < iovcnt; ++cnt)
 	    wp = mempcpy (wp, iov[cnt].iov_base, iov[cnt].iov_len);
 	  *wp = '\0';
 
@@ -144,8 +125,6 @@ __libc_message (const char *fmt, ...)
 	}
     }
 
-  va_end (ap);
-
   /* Kill the application.  */
   abort ();
 }