Remove a longstanding mystery in the text of the page, by
explaining a case where the value returned for a symbol may be
NULL. (However, there are presumably other cases, since the text
in the dlsym(3) manual page pre-dates the invention of IFUNCs.)
See also
https://stackoverflow.com/questions/13941944/why-can-the-value-of-the-symbol-returned-by-dlsym-be-null
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Quoting Branden:
*roff escape sequences may sometimes look like C escapes, but that
is misleading. *roff is in part a macro language and that means
recursive expansion to arbitrary depths.
You can get away with "\\" in a context where no macro expansion
is taking place, but try to spell a literal backslash this way in
the argument to a macro and you will likely be unhappy with
results.
Try viewing the attached file with "man -l".
"\e" is the preferred and portable way to get a portable "escape
literal" going back to CSTR #54, the original Bell Labs troff
paper.
groff(7) discusses the issue:
\\ reduces to a single backslash; useful to delay its
interpretation as escape character in copy mode. For a
printable backslash, use \e, or even better \[rs], to be
independent from the current escape character.
As of groff 1.22.4, groff_man(7) does as well:
\e Widely used in man pages to represent a backslash output
glyph. It works reliably as long as the .ec request is
not used, which should never happen in man pages, and it
is slightly more portable than the more exact ‘\(rs’
(“reverse solidus”) escape sequence.
People not concerned with portability to extremely old troffs should
probably just use \(rs (or \[rs]), as it means "the backslash
glyph", not "the glyph corresponding to whatever the current escape
character is".
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Quoting Branden:
*roff systems will interpret the period in the unpatched
page as sentence-ending punctuation and put inter-sentence
spacing after it. (This might not be visible on
nroff/terminal devices, but it is more likely to be on
typesetter/PostScript/PDF output).
groff_man(7) in groff 1.22.4 attempts to throw man page
writers a bone here:
\& Zero‐width space. Append to an input line to prevent
an end‐of‐ sentence punctuation sequence from being
recognized as such, or insert at the beginning of an
input line to prevent a dot or apostrophe from being
interpreted as the beginning of a roff request.
Reported-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Reported-by: G. Branden Robinson <g.branden.robinson@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Use a single-font-style macro (".B", ".I") for a single argument.
Remove unneeded quotation marks (").
The output from "nroff" and "groff" is unchanged, except for the change
1) '-1' to '\-1' in the file "timegm.3"
2) to separate ',' from a word in the file "uselocale.3".
Signed-off-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Historically, at least FIFOs and pipes yielded the error EINVAL.
Reported-by: Jakub Wilk <jwilk@jwilk.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
According to the latest glibc, the bsd_signal() function is just
declared when POSIX.1-2008 (or newer) instead of POSIX.1-2001 is
not set since glibc v2.26.
Please see the following code from signal/signal.h:
-----------------------------------------------------------------
/* The X/Open definition of `signal' conflicts with the BSD version.
So they defined another function `bsd_signal'. */
extern __sighandler_t bsd_signal (int __sig, __sighandler_t __handler)
__THROW;
-----------------------------------------------------------------
Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The notes in pthread_rwlockattr_setkind_np.3 imply there is a bug
in glibc's implementation of PTHREAD_RWLOCK_PREFER_WRITER_NP (a
non-portable constant anyway), but this is not true. The
implementation of PTHREAD_RWLOCK_PREFER_WRITER_NP is made almost
impossible by the POSIX standard requirement that reader locks be
allowed to be recursive, and that requirement makes writer
preference deadlock without an impossibly complex requirement that
we track all reader locks. Therefore the only sensible solution
was to add PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP and
disallow recursive reader locks if you want writer preference.
This patch removes the bug description and documents the current
state and recommendations for glibc. I have also updated bug 7057
with this information, answering Steven Munroe's almost 10 year
old question :-) I hope Steven is enjoying his much earned
retirement.
Should we move the glibc discussion to some footnote? Some libc
may be able to implement the requirement to avoid deadlocks in the
future, but I doubt it (fundamental CS stuff).
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The strfry(3) function does not use rand(). The original version
from 1995 did, but it was changed to use a different PRNG in glibc
commit 4770745624b7f7f25623f1f10d46a4c4d6aec25c, 1996-12-04.
This C program demonstrates the behavior. By not calling srand(),
it gets the same values for successive calls to rand(), but
strfry() returns a different value each time the program is run.
If strfry() called srand(), it would alter the sequence of numbers
return by rand().
int main(void) {
printf("%d\n", rand());
char alphabet[] = "abcdefghijklmnopqrstuvwxyz";
puts(strfry(alphabet));
printf("%d\n", rand());
}
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This doesn't actually matter on any C library I know of --- they
all just do a NULL check and forward to fclose(3). (The actual
mistake I saw was someone not realizing that they had to call
*anything*.)
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Since adding checking to Android's bionic for file descriptor
double-closes, we've found that the most common cause of these
bugs is incorrect use of fileno(3). There appears to be a common
misconception that it transfers ownership of the file descriptor
to the caller.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Ian Turner: The exact return calls are at the discretion of the
underlying VFS, but I'm pretty sure that EINTR is a possibility.
Or, if it's not, then the flock() manpage should be amended
accordingly, since the two share the same underlying
implementation.
mtk: lockf(3) is implemented on top of fcntl() locking, so
EINTR is of course a possibility.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Add text to CONFORMING TO explaining that the "_np"
suffix is because these functions are non-portable.
Signed-off-by: Jakub Wilk <jwilk@jwilk.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Perhaps some people might misunderstand memory allocated by
alloca() to be like other memory allocated on the stack: that when
the allocation (or the pointer to the allocation) goes out of
scope, the memory is freed. Add some text to prevent that
misunderstanding.
Reported-by: Robin Kuzmin <kuzmin.robin@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
There is not an acceptable reason to use these functions ever in
new code. For example, just observe the implementation of the
KDF:
/*
* Turn password into DES key
*/
void
passwd2des_internal (char *pw, char *key)
{
int i;
memset (key, 0, 8);
for (i = 0; *pw && i < 8; ++i)
key[i] ^= *pw++ << 1;
des_setparity (key);
}
This kind of nonsense isn't okay in the year 2017. Therefore, we
enlighten our poor users.
[Note from mtk: I think Jason knows that of which he talks.]
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
There's a detailed explanation in glob(7), so reuse the same text
glob(3) uses to redirect the reader, rather than inlining a short
explanation.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The double negative is a little confusing, but required. But try
to make the semantics a little clearer in the wording (which is
now closer to the wording in the C standard).
Reported-by: Eric Benton <erbenton@comcast.net>
Reported-by: G. Branden Robinson <g.branden.robinson@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk