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Unexec removal: Documentation adjustments

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* doc/lispref/internals.texi (Building Emacs):
* doc/lispref/os.texi (Command-Line Arguments): Remove documentation for
'unexec'-specific code and arguments.
* etc/PROBLEMS: Remove unexec-specific problems.
This commit is contained in:
Pip Cet 2024-08-21 08:45:13 +00:00 • committed by Stefan Kangas
parent 9a0728af9d
commit 0e37b11e65
3 changed files with 4 additions and 122 deletions
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28
doc/lispref/internals.texi
View file

@ -76,23 +76,6 @@ Like @samp{pdump}, but used while @dfn{bootstrapping} Emacs, when no
previous Emacs binary and no @file{*.elc} byte-compiled Lisp files are
available. The produced dump file is usually named
@file{bootstrap-emacs.pdmp} in this case.
@item dump
@cindex unexec
This method causes @command{temacs} to dump out an executable program,
called @file{emacs}, which has all the standard Lisp files already
preloaded into it. (The @samp{-batch} argument prevents
@command{temacs} from trying to initialize any of its data on the
terminal, so that the tables of terminal information are empty in the
dumped Emacs.) This method is also known as @dfn{unexec}, because it
produces a program file from a running process, and thus is in some
sense the opposite of executing a program to start a process.
Although this method was the way that Emacs traditionally saved its
state, it is now deprecated.
@item bootstrap
Like @samp{dump}, but used when bootstrapping Emacs with the
@code{unexec} method.
@end table
@cindex preloaded Lisp files
@ -227,17 +210,6 @@ that problem, you can put functions on the
Emacs.
@end defun
@defun dump-emacs to-file from-file
@cindex unexec
This function dumps the current state of Emacs into an executable file
@var{to-file}, using the @code{unexec} method. It takes symbols from
@var{from-file} (this is normally the executable file @file{temacs}).
This function cannot be used in an Emacs that was already dumped.
This function is deprecated, and by default Emacs is built without
@code{unexec} support so this function is not available.
@end defun
@defun pdumper-stats
If the current Emacs session restored its state from a dump
file, this function returns information about the dump file and the

8
doc/lispref/os.texi
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@ -590,10 +590,10 @@ displays the startup messages.
The value of this variable is @code{t} once the command line has been
processed.
If you redump Emacs by calling @code{dump-emacs} (@pxref{Building
Emacs}), you may wish to set this variable to @code{nil} first in
order to cause the new dumped Emacs to process its new command-line
arguments.
If you redump Emacs by calling @code{dump-emacs-portable}
(@pxref{Building Emacs}), you may wish to set this variable to
@code{nil} first in order to cause the new dumped Emacs to process its
new command-line arguments.
@end defvar
@defvar command-switch-alist

90
etc/PROBLEMS
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@ -2936,20 +2936,6 @@ This was observed for Emacs 28.1 on Solaris 10 32-bit sparc, with
Oracle Developer Studio 12.6 (Sun C 5.15). The failure was intermittent,
and running GNU Make a second time would typically finish the build.
*** On Solaris 10, Emacs crashes during the build process.
(This applies only with './configure --with-unexec=yes', which is rare.)
This was reported for Emacs 25.2 on i386-pc-solaris2.10 with Sun
Studio 12 (Sun C 5.9) and with Oracle Developer Studio 12.6 (Sun C
5.15), and intermittently for sparc-sun-solaris2.10 with Oracle
Developer Studio 12.5 (Sun C 5.14). Disabling compiler optimization
seems to fix the bug, as does upgrading the Solaris 10 operating
system to Update 11. The cause of the bug is unknown: it may be that
Emacs's archaic memory-allocation scheme is not compatible with
slightly-older versions of Solaris and/or Oracle Studio, or it may be
something else. Since the cause is not known, possibly the bug is
still present in newer versions of Emacs, Oracle Studio, and/or
Solaris. See Bug#26638.
*** On Solaris, C-x doesn't get through to Emacs when you use the console.
This is a Solaris feature (at least on Intel x86 cpus). Type C-r
@ -4085,71 +4071,6 @@ minimum supported Windows version is 8.1, and the computer hardware
(CPU, memory, disk) should also match the minimum Windows 8.1
requirements.
*** Segfault during 'make'
If Emacs segfaults when 'make' executes one of these commands:
LC_ALL=C ./temacs -batch -l loadup bootstrap
LC_ALL=C ./temacs -batch -l loadup dump
the problem may be due to inadequate workarounds for address space
layout randomization (ASLR), an operating system feature that
randomizes the virtual address space of a process. ASLR is commonly
enabled in Linux and NetBSD kernels, and is intended to deter exploits
of pointer-related bugs in applications. If ASLR is enabled, the
command:
cat /proc/sys/kernel/randomize_va_space # GNU/Linux
sysctl security.pax.aslr.global # NetBSD
outputs a nonzero value.
These segfaults should not occur on most modern systems, because the
Emacs build procedure uses the command 'setfattr' or 'paxctl' to mark
the Emacs executable as requiring non-randomized address space, and
Emacs uses the 'personality' system call to disable address space
randomization when dumping. However, older kernels may not support
'setfattr', 'paxctl', or 'personality', and newer Linux kernels have a
secure computing mode (seccomp) that can be configured to disable the
'personality' call.
It may be possible to work around the 'personality' problem in a newer
Linux kernel by configuring seccomp to allow the 'personality' call.
For example, if you are building Emacs under Docker, you can run the
Docker container with a security profile that allows 'personality' by
using Docker's --security-opt option with an appropriate profile; see
<https://docs.docker.com/engine/security/seccomp/>.
To work around the ASLR problem in either an older or a newer kernel,
you can temporarily disable the feature while building Emacs. On
GNU/Linux you can do so using the following command (as root).
echo 0 > /proc/sys/kernel/randomize_va_space
You can re-enable the feature when you are done, by echoing the
original value back to the file. NetBSD uses a different command,
e.g., 'sysctl -w security.pax.aslr.global=0'.
Alternatively, you can try using the 'setarch' command when building
temacs like this, where -R disables address space randomization:
setarch $(uname -m) -R make
ASLR is not the only problem that can break Emacs dumping. Another
issue is that in Red Hat Linux kernels, Exec-shield is enabled by
default, and this creates a different memory layout. Emacs should
handle this at build time, but if this fails the following
instructions may be useful. Exec-shield is enabled on your system if
cat /proc/sys/kernel/exec-shield
prints a nonzero value. You can temporarily disable it as follows:
echo 0 > /proc/sys/kernel/exec-shield
As with randomize_va_space, you can re-enable Exec-shield when you are
done, by echoing the original value back to the file.
*** openSUSE 10.3: Segfault in bcopy during dumping.
This is due to a bug in the bcopy implementation in openSUSE 10.3.
@ -4297,17 +4218,6 @@ should do.
pen@lysator.liu.se says (Feb 1998) that the Compose key does work
if you link with the MIT X11 libraries instead of the Solaris X11 libraries.
** OpenBSD
*** OpenBSD 4.0 macppc: Segfault during dumping.
The build aborts with signal 11 when the command './temacs --batch
--load loadup bootstrap' tries to load files.el. A workaround seems
to be to reduce the level of compiler optimization used during the
build (from -O2 to -O1). It is possible this is an OpenBSD
GCC problem specific to the macppc architecture, possibly only
occurring with older versions of GCC (e.g. 3.3.5).
** AIX
*** AIX 4.3.x or 4.4: Compiling fails.