[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Emacs-diffs] master 1242a63: Avoid undefined behavior when printing fun
From: |
Philipp Stephani |
Subject: |
[Emacs-diffs] master 1242a63: Avoid undefined behavior when printing function pointers. |
Date: |
Sat, 4 May 2019 17:10:56 -0400 (EDT) |
branch: master
commit 1242a63671f3fc3d427d9d8061338f826e585031
Author: Philipp Stephani <address@hidden>
Commit: Philipp Stephani <address@hidden>
Avoid undefined behavior when printing function pointers.
* src/print.c (print_vectorlike): Don’t pass a function pointer to
‘snprintf’, as that is undefined behavior. Instead, print the
individual bytes making up the function pointer.
---
src/print.c | 29 ++++++++++++++++++-----------
1 file changed, 18 insertions(+), 11 deletions(-)
diff --git a/src/print.c b/src/print.c
index 68ed678..57aac5f 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1794,17 +1794,24 @@ print_vectorlike (Lisp_Object obj, Lisp_Object
printcharfun, bool escapeflag,
if (symbol == NULL)
{
- print_c_string ("at ", printcharfun);
- enum { pointer_bufsize = sizeof ptr * 16 / CHAR_BIT + 2 + 1 };
- char buffer[pointer_bufsize];
- int needed = snprintf (buffer, sizeof buffer, "%p", ptr);
- const char p0x[] = "0x";
- eassert (needed <= sizeof buffer);
- /* ANSI C doesn't guarantee that %p produces a string that
- begins with a "0x". */
- if (c_strncasecmp (buffer, p0x, sizeof (p0x) - 1) != 0)
- print_c_string (p0x, printcharfun);
- print_c_string (buffer, printcharfun);
+ print_c_string ("at 0x", printcharfun);
+ /* See https://stackoverflow.com/a/2741896 for how to
+ portably print a function pointer. */
+ const unsigned char *p = (const unsigned char *) &ptr;
+ for (size_t i = 0; i < sizeof ptr; ++i)
+ {
+#ifdef WORDS_BIGENDIAN
+ unsigned char b = p[i];
+#else
+ unsigned char b = p[sizeof ptr - i - 1];
+#endif
+ enum { digits = (CHAR_BIT + 4 - 1) / 4 };
+ char buffer[digits + 1];
+ int needed
+ = snprintf (buffer, sizeof buffer, "%0*hhx", digits, b);
+ eassert (needed == digits);
+ print_c_string (buffer, printcharfun);
+ }
}
else
print_c_string (symbol, printcharfun);
[Prev in Thread] |
Current Thread |
[Next in Thread] |
- [Emacs-diffs] master 1242a63: Avoid undefined behavior when printing function pointers.,
Philipp Stephani <=