Hi Ethan,
On 29/10/2019 21:02, Ethan Sommer wrote:
> removes the bc build dependency introduced when timeconst.pl was
> replaced by timeconst.bc:
> commit 70730bca1331 ("kernel: Replace timeconst.pl with a bc script")
>
> the reason for this change is that this is the only use of bc in the
> actual compilation of the kernel, so by replacing it with a shell script
> compiling the kernel no longer depends on bc.
>
> Signed-off-by: Ethan Sommer <e5ten.arch@xxxxxxxxx>
> ---
> Documentation/process/changes.rst | 6 --
> Kbuild | 4 +-
> kernel/time/timeconst.bc | 117 ------------------------------
> kernel/time/timeconst.sh | 111 ++++++++++++++++++++++++++++
Running shellcheck on kernel/time/timeconst.sh produces the following
warnings:
shellcheck kernel/time/timeconst.sh
In kernel/time/timeconst.sh line 11:
local i=1 j=0
^-- SC2039: In POSIX sh, 'local' is undefined.
In kernel/time/timeconst.sh line 20:
local i="$1" j="$2" k
^-- SC2039: In POSIX sh, 'local' is undefined.
In kernel/time/timeconst.sh line 34:
local i
^-- SC2039: In POSIX sh, 'local' is undefined.
In kernel/time/timeconst.sh line 44:
local i=0 j
^-- SC2039: In POSIX sh, 'local' is undefined.
Will this cause an issue for people running posix shells?
Which shells have you tested your script on ?
Furthermore, I fear this conversion may not be suitable at present, as
it produces potentially different results for CONFIG_HZ < 100
(There may be more diffs, but I haven't yet compared a larger search space)
using a quick script I put together to compare the output of
timeconst.sh and timeconst.bc for a given CONFIG_HZ:
https://gist.github.com/kbingham/76e8718df7b7dc97361405cc1801a160
$ for i in `seq 0 300`; do ./check-timeconst.sh $i; done
produces a diff on almost every value 2 - 243
http://paste.ubuntu.com/p/wNggrfFZXB/
Or rather 137 faults to be exact:
for i in `seq 0 250`; \
do ./check-timeconst.sh $i; \
done | grep -- "--- BC" | wc -l
I think that might be considered a blocker to this implementation, or
those values and the impact should certainly be investigated thoroughly.
I haven't looked into detail into the change of any of those values, so
I can not ascertain which one is more correct (though I suspect it's
likely to be bc that will have the 'more correct' value)
I would fear doing this in shell just isn't going to maintain the
correct precision, which is likely a strong reason why bc was selected
in the first place.
If you can find the issue that causes this diff in your shell
processing, and clarify or fix it - then it might be possible to gain
some backing to the implementation, but even then it might become a
shell specific precision issue ...
--
Regards
Kieran
> 4 files changed, 113 insertions(+), 125 deletions(-)
> delete mode 100644 kernel/time/timeconst.bc
> create mode 100644 kernel/time/timeconst.sh
>
> diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
> index 2284f2221f02..3ae168387109 100644
> --- a/Documentation/process/changes.rst
> +++ b/Documentation/process/changes.rst
> @@ -105,12 +105,6 @@ Perl
> You will need perl 5 and the following modules: ``Getopt::Long``,
> ``Getopt::Std``, ``File::Basename``, and ``File::Find`` to build the kernel.
>
> -BC
> ---
> -
> -You will need bc to build kernels 3.10 and higher
> -
> -
> OpenSSL
> -------
>
> diff --git a/Kbuild b/Kbuild
> index 3109ac786e76..7eba24cbdb78 100644
> --- a/Kbuild
> +++ b/Kbuild
> @@ -18,9 +18,9 @@ $(bounds-file): kernel/bounds.s FORCE
>
> timeconst-file := include/generated/timeconst.h
>
> -filechk_gentimeconst = echo $(CONFIG_HZ) | bc -q $<
> +filechk_gentimeconst = $(CONFIG_SHELL) $< $(CONFIG_HZ)
>
> -$(timeconst-file): kernel/time/timeconst.bc FORCE
> +$(timeconst-file): kernel/time/timeconst.sh FORCE
> $(call filechk,gentimeconst)
>
> #####
> diff --git a/kernel/time/timeconst.bc b/kernel/time/timeconst.bc
> deleted file mode 100644
> index 7ed0e0fb5831..000000000000
> --- a/kernel/time/timeconst.bc
> +++ /dev/null
> @@ -1,117 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0 */
> -
> -scale=0
> -
> -define gcd(a,b) {
> - auto t;
> - while (b) {
> - t = b;
> - b = a % b;
> - a = t;
> - }
> - return a;
> -}
> -
> -/* Division by reciprocal multiplication. */
> -define fmul(b,n,d) {
> - return (2^b*n+d-1)/d;
> -}
> -
> -/* Adjustment factor when a ceiling value is used. Use as:
> - (imul * n) + (fmulxx * n + fadjxx) >> xx) */
> -define fadj(b,n,d) {
> - auto v;
> - d = d/gcd(n,d);
> - v = 2^b*(d-1)/d;
> - return v;
> -}
> -
> -/* Compute the appropriate mul/adj values as well as a shift count,
> - which brings the mul value into the range 2^b-1 <= x < 2^b. Such
> - a shift value will be correct in the signed integer range and off
> - by at most one in the upper half of the unsigned range. */
> -define fmuls(b,n,d) {
> - auto s, m;
> - for (s = 0; 1; s++) {
> - m = fmul(s,n,d);
> - if (m >= 2^(b-1))
> - return s;
> - }
> - return 0;
> -}
> -
> -define timeconst(hz) {
> - print "/* Automatically generated by kernel/time/timeconst.bc */\n"
> - print "/* Time conversion constants for HZ == ", hz, " */\n"
> - print "\n"
> -
> - print "#ifndef KERNEL_TIMECONST_H\n"
> - print "#define KERNEL_TIMECONST_H\n\n"
> -
> - print "#include <linux/param.h>\n"
> - print "#include <linux/types.h>\n\n"
> -
> - print "#if HZ != ", hz, "\n"
> - print "#error \qinclude/generated/timeconst.h has the wrong HZ value!\q\n"
> - print "#endif\n\n"
> -
> - if (hz < 2) {
> - print "#error Totally bogus HZ value!\n"
> - } else {
> - s=fmuls(32,1000,hz)
> - obase=16
> - print "#define HZ_TO_MSEC_MUL32\tU64_C(0x", fmul(s,1000,hz), ")\n"
> - print "#define HZ_TO_MSEC_ADJ32\tU64_C(0x", fadj(s,1000,hz), ")\n"
> - obase=10
> - print "#define HZ_TO_MSEC_SHR32\t", s, "\n"
> -
> - s=fmuls(32,hz,1000)
> - obase=16
> - print "#define MSEC_TO_HZ_MUL32\tU64_C(0x", fmul(s,hz,1000), ")\n"
> - print "#define MSEC_TO_HZ_ADJ32\tU64_C(0x", fadj(s,hz,1000), ")\n"
> - obase=10
> - print "#define MSEC_TO_HZ_SHR32\t", s, "\n"
> -
> - obase=10
> - cd=gcd(hz,1000)
> - print "#define HZ_TO_MSEC_NUM\t\t", 1000/cd, "\n"
> - print "#define HZ_TO_MSEC_DEN\t\t", hz/cd, "\n"
> - print "#define MSEC_TO_HZ_NUM\t\t", hz/cd, "\n"
> - print "#define MSEC_TO_HZ_DEN\t\t", 1000/cd, "\n"
> - print "\n"
> -
> - s=fmuls(32,1000000,hz)
> - obase=16
> - print "#define HZ_TO_USEC_MUL32\tU64_C(0x", fmul(s,1000000,hz), ")\n"
> - print "#define HZ_TO_USEC_ADJ32\tU64_C(0x", fadj(s,1000000,hz), ")\n"
> - obase=10
> - print "#define HZ_TO_USEC_SHR32\t", s, "\n"
> -
> - s=fmuls(32,hz,1000000)
> - obase=16
> - print "#define USEC_TO_HZ_MUL32\tU64_C(0x", fmul(s,hz,1000000), ")\n"
> - print "#define USEC_TO_HZ_ADJ32\tU64_C(0x", fadj(s,hz,1000000), ")\n"
> - obase=10
> - print "#define USEC_TO_HZ_SHR32\t", s, "\n"
> -
> - obase=10
> - cd=gcd(hz,1000000)
> - print "#define HZ_TO_USEC_NUM\t\t", 1000000/cd, "\n"
> - print "#define HZ_TO_USEC_DEN\t\t", hz/cd, "\n"
> - print "#define USEC_TO_HZ_NUM\t\t", hz/cd, "\n"
> - print "#define USEC_TO_HZ_DEN\t\t", 1000000/cd, "\n"
> -
> - cd=gcd(hz,1000000000)
> - print "#define HZ_TO_NSEC_NUM\t\t", 1000000000/cd, "\n"
> - print "#define HZ_TO_NSEC_DEN\t\t", hz/cd, "\n"
> - print "#define NSEC_TO_HZ_NUM\t\t", hz/cd, "\n"
> - print "#define NSEC_TO_HZ_DEN\t\t", 1000000000/cd, "\n"
> - print "\n"
> -
> - print "#endif /* KERNEL_TIMECONST_H */\n"
> - }
> - halt
> -}
> -
> -hz = read();
> -timeconst(hz)
> diff --git a/kernel/time/timeconst.sh b/kernel/time/timeconst.sh
> new file mode 100644
> index 000000000000..d1aa25f46be8
> --- /dev/null
> +++ b/kernel/time/timeconst.sh
> @@ -0,0 +1,111 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +
> +if [ -z "$1" ]; then
> + printf '%s <HZ>\n' "$0" >&2
> + exit 1
> +fi
> +
> +# 2 to the power of n
> +pot() {
> + local i=1 j=0
> + while [ "$((j += 1))" -le "$1" ]; do
> + : "$((i *= 2))"
> + done
> + printf '%u' "${i}"
> +}
> +
> +# Greatest common denominator
> +gcd() {
> + local i="$1" j="$2" k
> + while [ "${j}" -ne 0 ]; do
> + k="${j}" j="$((i % j))" i="${k}"
> + done
> + printf '%u' "${i}"
> +}
> +
> +# Division by reciprocal multiplication.
> +fmul() {
> + printf '%u' "$((($(pot "$1") * $2 + $3 - 1) / $3))"
> +}
> +
> +# Adjustment factor when a ceiling value is used.
> +fadj() {
> + local i
> + i="$(gcd "$2" "$3")"
> + printf '%u' "$(($(pot "$1") * ($3 / i - 1) / ($3 / i)))"
> +}
> +
> +# Compute the appropriate mul/adj values as well as a shift count,
> +# which brings the mul value into the range 2^b-1 <= x < 2^b. Such
> +# a shift value will be correct in the signed integer range and off
> +# by at most one in the upper half of the unsigned range.
> +fmuls() {
> + local i=0 j
> + while true; do
> + j="$(fmul "${i}" "$2" "$3")"
> + if [ "${j}" -ge "$(pot "$(($1 - 1))")" ]; then
> + printf '%u' "${i}"
> + return
> + fi
> + : "$((i += 1))"
> + done
> +}
> +
> +printf '/* Automatically generated by kernel/time/timeconst.sh */\n'
> +printf '/* Time conversion constants for HZ == %u */\n\n' "$1"
> +
> +printf '#ifndef KERNEL_TIMECONST_H\n'
> +printf '#define KERNEL_TIMECONST_H\n\n'
> +
> +printf '#include <linux/param.h>\n'
> +printf '#include <linux/types.h>\n\n'
> +
> +printf '#if HZ != %u\n' "$1"
> +printf '#error "include/generated/timeconst.h has the wrong HZ value!"\n'
> +printf '#endif\n\n'
> +
> +if [ "$1" -lt 2 ]; then
> + printf '#error Totally bogus HZ value!\n'
> + exit 1
> +fi
> +
> +s="$(fmuls 32 1000 "$1")"
> +printf '#define HZ_TO_MSEC_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}" 1000 "$1")"
> +printf '#define HZ_TO_MSEC_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}" 1000 "$1")"
> +printf '#define HZ_TO_MSEC_SHR32\t%u\n' "${s}"
> +
> +s="$(fmuls 32 "$1" 1000)"
> +printf '#define MSEC_TO_HZ_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}" "$1" 1000)"
> +printf '#define MSEC_TO_HZ_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}" "$1" 1000)"
> +printf '#define MSEC_TO_HZ_SHR32\t%u\n' "${s}"
> +
> +cd="$(gcd "$1" 1000)"
> +printf '#define HZ_TO_MSEC_NUM\t\t%u\n' "$((1000 / cd))"
> +printf '#define HZ_TO_MSEC_DEN\t\t%u\n' "$(($1 / cd))"
> +printf '#define MSEC_TO_HZ_NUM\t\t%u\n' "$(($1 / cd))"
> +printf '#define MSEC_TO_HZ_DEN\t\t%u\n\n' "$((1000 / cd))"
> +
> +s="$(fmuls 32 1000000 "$1")"
> +printf '#define HZ_TO_USEC_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}" 1000000 "$1")"
> +printf '#define HZ_TO_USEC_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}" 1000000 "$1")"
> +printf '#define HZ_TO_USEC_SHR32\t%u\n' "${s}"
> +
> +s="$(fmuls 32 "$1" 1000000)"
> +printf '#define USEC_TO_HZ_MUL32\tU64_C(0x%X)\n' "$(fmul "${s}" "$1" 1000000)"
> +printf '#define USEC_TO_HZ_ADJ32\tU64_C(0x%X)\n' "$(fadj "${s}" "$1" 1000000)"
> +printf '#define USEC_TO_HZ_SHR32\t%u\n' "${s}"
> +
> +cd="$(gcd "$1" 1000000)"
> +printf '#define HZ_TO_USEC_NUM\t\t%u\n' "$((1000000 / cd))"
> +printf '#define HZ_TO_USEC_DEN\t\t%u\n' "$(($1 / cd))"
> +printf '#define USEC_TO_HZ_NUM\t\t%u\n' "$(($1 / cd))"
> +printf '#define USEC_TO_HZ_DEN\t\t%u\n' "$((1000000 / cd))"
> +
> +cd="$(gcd "$1" 1000000000)"
> +printf '#define HZ_TO_NSEC_NUM\t\t%u\n' "$((1000000000 / cd))"
> +printf '#define HZ_TO_NSEC_DEN\t\t%u\n' "$(($1 / cd))"
> +printf '#define NSEC_TO_HZ_NUM\t\t%u\n' "$(($1 / cd))"
> +printf '#define NSEC_TO_HZ_DEN\t\t%u\n' "$((1000000000 / cd))"
> +
> +printf '\n#endif /* KERNEL_TIMECONST_H */\n'
>
--
Regards
--
Kieran
