Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
Masahiro Yamada
authored
scripts/pahole-flags.sh is executed so many times.
You can confirm it, as follows:
$ cat <<EOF >> scripts/pahole-flags.sh
> echo "scripts/pahole-flags.sh was executed" >&2
> EOF
$ make -s
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
[ lots of repeated lines... ]
This scripts is executed more than 20 times during the kernel build
because PAHOLE_FLAGS is a recursively expanded variable and exported
to sub-processes.
With GNU Make >= 4.4, it is executed more than 60 times because
exported variables are also passed to other $(shell ) invocations.
Without careful coding, it is known to cause an exponential fork
explosion. [1]
The use of $(shell ) in an exported recursive variable is likely wrong
because $(shell ) is always evaluated due to the 'export' keyword, and
the evaluation can occur multiple times by the nature of recursive
variables.
Convert the shell script to a Makefile, which is included only when
CONFIG_DEBUG_INFO_BTF=y.
[1]: https://savannah.gnu.org/bugs/index.php?64746
Signed-off-by: 
Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: 
Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: 
Nicolas Schier <n.schier@avm.de>
Tested-by: 
Miguel Ojeda <ojeda@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: 
Jiri Olsa <jolsa@kernel.org>
Reviewed-by: 
Martin Rodriguez Reboredo <yakoyoku@gmail.com>