Michael Kerrisk [Tue, 26 May 2020 10:10:55 +0000 (12:10 +0200)]
y0.3: srcfix: Note on "Range error: result underflow" and FE_UNDERFLOW
The fact that an FE_UNDERFLOW exception is not raised for
"Range error: result underflow" is intended behavior.
See https://www.sourceware.org/bugzilla/show_bug.cgi?id=6806.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
printf.3: Prevent signed integer overflow in example
The function make_message illustrates how to use vsnprintf to
determine the required amount of memory for a specific format and
its arguments.
If make_message is called with a format which will use exactly
INT_MAX characters (excluding '\0'), then the size++ calculation
will overflow the signed integer "size", which is an undefined
behaviour in C.
Since malloc and vsnprintf rightfully take a size_t argument, I
decided to use a size_t variable for size calculation. Therefore,
this patched code uses variables of the same data types as
expected by function arguments.
Proof of concept (tested on Linux/glibc amd64):
int main() { make_message("%647s%2147483000s", "", ""); }
If the code is compiled with address sanitizer (gcc
-fsanitize=address) you can see the following line, assuming that
a signed integer overflow simply leads to INT_MIN:
==3094==WARNING: AddressSanitizer failed to allocate 0xffffffff80000000 bytes
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk [Mon, 25 May 2020 13:15:14 +0000 (15:15 +0200)]
pow.3: Minor tweak to BUGS
Remove the text ("rare)" after a note from Vincent Lefèvre:
Subject: [Bug math/13932] dbl-64 pow unexpectedly slow for some inputs
Date: Sat, 23 May 2020 21:31:52 +0000
From: vincent-srcware at vinc17 dot net <sourceware-bugzilla@sourceware.org>
To: mtk.manpages@gmail.com
--- Comment #26 from Vincent Lefèvre <vincent-srcware at vinc17 dot net> ---
(In reply to Michael Kerrisk from comment #25)
> Fix documented for man-pages-5.07.
[...]
> -On 64-bits,
> +Before glibc 2.28,
> .\"
> .\" https://sourceware.org/bugzilla/show_bug.cgi?id=13932
> +on some architectures (e.g., x86-64)
> .BR pow ()
> may be more than 10,000 times slower for some (rare) inputs
> than for other nearby inputs.
[...]
The problematic values are uncommon, but not so rare, in the sense
that they are close to simple values, i.e. are likely to occur in
practice. An example given above: pow(0.999999999999999889, 1.5)
1 and 1.5 are very simple values, which are more likely to occur
in practice than some fixed random value. Then it suffices to have
a small rounding error on 1...
For instance, this is very different from hard-to-round cases of
exp, which are also very slow IMHO, but unless one writes a
specific program for them, no-one should notice the slowness
because such a case would typically occur only once among billions
(I don't remember the accuracy before the slowest path in this
library).
Reported-by: Vincent Lefèvre <vincent-srcware@vinc17.net> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk [Wed, 20 May 2020 12:45:23 +0000 (14:45 +0200)]
standards.7: Remove mention of bogus "POSIX" names
The terms POSIX.1-{2003,2004,2013,2016} were inventions of
my imagination, as confirmed by consulting Geoff Clare of
The Open Group. Remove these names.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Avoid implying that use of IFUNC is the only way to produce a
symbol with NULL value. Give more scenarios how a symbol may get
NULL value, but explain that in those scenarios dlsym() will fail
with Glibc's ld.so due to an implementation inconsistency.
Signed-off-by: Alexander Monakov <amonakov@ispras.ru> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Devin J. Pohly [Mon, 18 May 2020 20:58:28 +0000 (15:58 -0500)]
veth.4: Add a more direct example
iproute2 allows you to specify the netns for either side of a veth
interface at creation time. Add an example of this to veth(4) so
it doesn't sound like you have to move the interfaces in a
separate step.
Verified with commands:
# ip netns add alpha
# ip netns add bravo
# ip link add foo netns alpha type veth peer bar netns bravo
# ip -n alpha link show
# ip -n bravo link show
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Thomas Piekarski [Tue, 19 May 2020 15:34:33 +0000 (17:34 +0200)]
hier.7: Updating from FHS 2.3 to 3.0
Adding description of new directories (/run, /usr/libexec,
/usr/share/color,/usr/share/ppd, /var/lib/color), stating
/usr/X11R6 as removed and updating URL to and version of FHS.
See https://bugzilla.kernel.org/show_bug.cgi?id=206693
Reported-by: Gary Perkins <glperkins@lit.edu> Signed-off-by: Thomas Piekarski <t.piekarski@deloquencia.de> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk [Tue, 19 May 2020 19:41:08 +0000 (21:41 +0200)]
clone.2: Note a performance benefit of CLONE_INTO_CGROUP
As noted in email by Christian Brauner:
I forgot to mention that spawning directly into a target
cgroup is also more efficient than moving it after creation.
The specific reason is mentioned in the commit message
[ef2c41cf38a], the write lock of the semaphore need not be
taken in contrast to when it is moved afterwards. That
implementation details is not that interesting but it might
be interesting to know that it provides performance benefits
in general.
Reported-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Kir Kolyshkin [Sat, 16 May 2020 23:34:25 +0000 (16:34 -0700)]
Various pages: Add missing commas in SEE ALSO part II
This is a sequel to commit baf17bc4f2a3f3b02d, addressing the
issues with missing commas in the middle of SEE ALSO lists that
emerged since.
The awk script from the original commit was not working and had to
be slightly modified (s/["]SEE ALSO["]/"?SEE ALSO/), otherwise it
works like a charm. Here's the fixed script and its output just
before this commit:
for f in man*/*; do
awk '
/^.SH "?SEE ALSO/ {
sa=1; print "== " FILENAME " =="; print; next
}
/^\.(PP|SH)/ {
sa=0; no=0; next
}
/^\.BR/ {
if (sa==1) {
print;
if (no == 1)
print "Missing comma in " FILENAME " +" FNR-1; no=0
}
}
/^\.BR .*)$/ {
if (sa==1)
no=1;
next
}
/\.\\"/ {next}
/.*/ {
if (sa==1) {
print; next
}
}
' $f; done | grep Missing
Missing comma in man1/memusage.1 +272
Missing comma in man2/adjtimex.2 +597
Missing comma in man2/adjtimex.2 +598
Missing comma in man2/mkdir.2 +252
Missing comma in man2/sigaction.2 +1045
Missing comma in man2/sigaction.2 +1047
Missing comma in man3/mbsnrtowcs.3 +198
Missing comma in man3/ntp_gettime.3 +142
Missing comma in man3/strcmp.3 +219
Missing comma in man3/strtol.3 +302
Missing comma in man3/wcstombs.3 +120
Missing comma in man7/user_namespaces.7 +1378
Missing comma in man7/xattr.7 +198
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Dave Martin [Tue, 12 May 2020 16:36:57 +0000 (17:36 +0100)]
prctl.2: Clarify the unsupported hardware case of EINVAL
prctls that are architecture-specific won't work on other
architectures, and arch-specific prctls that manipulate optional
hardware features likewise won't work if that hardware feature is
not present.
The established pattern seems to be to treat such prctls as if they
are unimplemented, when attempted on the wrong hardware.
Cover these cases with some generic weasel words in the closet
existing EINVAL clause.
Signed-off-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Dave Martin [Tue, 12 May 2020 16:36:52 +0000 (17:36 +0100)]
prctl.2: Document removal of Intel MPX prctls
The Intel MPX API was removed from Linux 5.4. See Linux
commit f240652b6032 ("x86/mpx: Remove MPX APIs")
Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Signed-off-by: Dave Martin <Dave.Martin@arm.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Dave Martin [Tue, 12 May 2020 16:36:50 +0000 (17:36 +0100)]
prctl.2: Sort prctls into alphabetical order
The prctl list has historically been sorted by prctl name (ignoring
any SET_ or GET_ prefix) to make individual prctls easier to find.
Some noise seems to have crept in since.
Sort the list back into order. Similarly, reorder the list of
prctls specified to return non-zero values on success.
Content movement only. No semantic change.
Signed-off-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Dave Martin [Tue, 12 May 2020 16:36:49 +0000 (17:36 +0100)]
prctl.2: srcfix: add comments for navigation
The prctl.2 source is unnecessarily hard to navigate, not least
because prctl option flags are traditionally named PR_* and so look
just like prctl names.
For each actual prctl, add a comment of the form
.\" prctl PR_FOO
to make it move obvious where each top-level prctl starts.
Of course, we could add some clever macros, but let's not confuse
dumb parsers.
Signed-off-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Dave Martin [Tue, 12 May 2020 16:36:47 +0000 (17:36 +0100)]
prctl.2: Add health warning
In reality, almost every prctl interferes with assumptions that the
compiler and C library / runtime rely on. prctl() can therefore
make userspace explode in a variety ways that are likely to be hard
to debug.
This is not obvious to the uninitiated, so add a warning.
Signed-off-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Dave Martin [Tue, 12 May 2020 16:36:48 +0000 (17:36 +0100)]
prctl.2: Fix mis-description of thread ID values in procfs
Under PR_SET_NAME, the [tid] value seen in procfs as
/proc/self/task/[tid] is mistakenly described as the name of the
thread, whereas really the name is on /proc/self/task/[tid]/comm.
Fix it.
Signed-off-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
projects / thirdparty / man-pages.git / log
