--- Begin Message ---
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Subject: |
29.0.50; generate-new-buffer-name sprintf format overflow warning |
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Date: |
Sun, 14 Aug 2022 19:50:03 +0300 |
|
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) |
Severity: minor
Compiling with gcc (Debian 12.1.0-7) 12.1.0 and -Og, I get the following
-Wformat-overflow warning:
In file included from buffer.c:33:
buffer.c: In function ‘Fgenerate_new_buffer_name’:
buffer.c:1167:46: warning: ‘sprintf’ may write a terminating nul past the end
of the destination [-Wformat-overflow=]
1167 | AUTO_STRING_WITH_LEN (lnumber, number, sprintf (number, "-%d",
i));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~
lisp.h:5493:36: note: in definition of macro ‘AUTO_STRING_WITH_LEN’
5493 | ((&(struct Lisp_String) {{{len, -1, 0, (unsigned char *)
(str)}}}), \
| ^~~
buffer.c:1167:46: note: ‘sprintf’ output between 3 and 9 bytes into a
destination of size 8
1167 | AUTO_STRING_WITH_LEN (lnumber, number, sprintf (number, "-%d",
i));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~
lisp.h:5493:36: note: in definition of macro ‘AUTO_STRING_WITH_LEN’
5493 | ((&(struct Lisp_String) {{{len, -1, 0, (unsigned char *)
(str)}}}), \
| ^~~
Can the upper bound 9 ever be achieved? If so, how? If not, is this a
GCC bug? Either way, is there a way to pacify the warning?
I tried
snprintf (number, sizeof number, ...)
but got the same warning.
BTW, in the preceding
int i = r % 1000000;
can the result of % ever exceed INT_MAX? And do we care either way?
Thanks,
--
Basil
In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version
1.16.0, Xaw3d scroll bars)
of 2022-08-14 built on tia
Repository revision: 1d3fe256907d5e78a4acedd194e55db8ab952952
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Debian GNU/Linux bookworm/sid
Configured using:
'configure CC=gcc-12 'CFLAGS=-Og -ggdb3' --config-cache
--prefix=/home/blc/.local --enable-checking=structs
--with-file-notification=yes --with-x-toolkit=lucid --with-x'
Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
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Important settings:
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value of $XMODIFIERS: @im=ibus
locale-coding-system: utf-8-unix
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--- Begin Message ---
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Subject: |
Re: bug#57211: 29.0.50; generate-new-buffer-name sprintf format overflow warning |
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Date: |
Sun, 14 Aug 2022 13:54:08 -0700 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 |
On 8/14/22 09:50, Basil L. Contovounesios wrote:
Can the upper bound 9 ever be achieved? If so, how? If not, is this a
GCC bug? Either way, is there a way to pacify the warning?
It can't be achieved, and it's arguably a GCC bug. I installed the
attached to pacify GCC.
int i = r % 1000000;
can the result of % ever exceed INT_MAX?
No.
On 8/14/22 11:59, Matt Armstrong wrote:
Gcc doesn't know that get_random() returns only non-negative numbers,
and the eassume() call doesn't seem to be enough to convince gcc this
fact, or gcc does not infer i is also non-negative.
It's worse than that. Even if you add 'eassume (0 <= i && i < 1000000);"
GCC still doesn't assume that the sprintf is in range.
Personally, I'd change this code to use a buffer
INT_BUFSIZE_BOUND(int) + sizeof "-"
The problem with overallocating buffers is not the memory loss (it's
trivial, as you say), it's that later readers like me will wonder why
the buffer is being overallocated, which is maintenance overhead.
I installed the attached to pacify GCC while also attempting to not
entirely mystify later readers.
0001-Work-around-Bug-57211.patch
Description: Text Data
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