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makemake.sh: honour CFLAGS from the environment - #356
Exporting CFLAGS before running makemake.sh silently does nothing: the generated Makefile assigns CFLAGS = ... with =, and a Makefile assignment overrides the environment. The only way to build with different flags has been to edit the script, which is what the five sanitizer jobs in ci.yml do with sed -i 's/^CFLAGS = .*/.../' makemake.sh.
This makes makemake.sh honour CFLAGS:
If CFLAGS is set, it replaces the default optimization, debug, warning and LTO flags (-Wall -Wextra -g -O3, -flto=auto/-flto, -fdiagnostics-color). That matches the usual convention, e.g. autoconf, and it is what the sanitizer jobs need: they want -Og and no LTO, not the defaults with more flags added.
-std=gnu99 is always kept, since the code needs it.
The SIMD build-mode flags (-DUSE_AVX2 -mavx2, -DUSE_AVX512 ..., -march=native and so on) are added separately, as before, so CFLAGS='-g -Og' bash makemake.sh avx2 is still an AVX2 build.
When it uses them, the script prints Using CFLAGS from the environment instead of the default flags: .... Some environments export CFLAGS globally (a cross-compilation SDK, a distribution's packaging setup), and until now those flags were ignored, so this makes the change visible instead of silent.
CPPFLAGS and LDFLAGS are unchanged: the Makefile already appends to them with +=.
In ci.yml, the five sanitizer jobs now put their flags in CFLAGS (via $GITHUB_ENV) instead of editing makemake.sh. The k1om job sources the Xeon Phi SDK's environment script, which exports its own CFLAGS; it had a commented-out # unset CFLAGS CPPFLAGS, and now runs unset CFLAGS, so that it keeps building with the defaults it uses today.
The README's build section has a short paragraph on it.
#56 also makes the Makefile's CFLAGS overridable, as part of a much broader rework of the script for parallel LTO. This is only the CFLAGS part, kept small so it can land separately. If #56 lands later, the two will need reconciling there.
Tested
ShellCheck with the CI's options: clean.
No CFLAGS set: makemake.sh mfac avx2 generates a Makefile byte-identical to the one main generates.
CFLAGS='-Wall -Wextra -g -Og -fsanitize=address,undefined': the generated Makefile is byte-identical to the one produced by main plus the old sed line from the ASan job (CFLAGS = -std=gnu99 -Wall -Wextra -g -Og -fsanitize=address,undefined). The binary is ASan-instrumented, and Mfactor -m 521 -bmax 20 runs clean under it.
Custom CFLAGS can now be used when building, replacing default compiler flags while retaining -std=gnu99 and SIMD build-mode flags. Without custom flags, default compiler settings remain, with checks for supported optimization options.
CPPFLAGS and LDFLAGS are added to the default flags rather than replacing them.
Documentation
Build instructions explain how to provide custom compiler flags and clarify how CPPFLAGS and LDFLAGS are applied.
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This change was previously made in #67, but later reverted in #251/#103, as BSD Make sets a default CFLAGS value.
I agree that this change would be an improvements, but I am unsure how we could implement it without breaking the script in environments that set a default CFLAGS value.
Thanks, I've taken the suggestion: an empty CFLAGS now gets the default flags too, rather than building with -std=gnu99 alone.
On BSD make: I think this version avoids what went wrong with #67. #67 relied on CFLAGS ?= in the generated Makefile to defer to the environment, so FreeBSD make's built-in default (CFLAGS ?= -O2 -pipe in sys.mk) got there first and the computed flags were dropped. This PR leaves the Makefile's hard CFLAGS = in place, and instead makemake.sh itself reads CFLAGS from the shell environment before writing it. make's built-in defaults live inside make and never reach the shell environment, so they can't affect it.
This PR's CI run bears that out: all six FreeBSD cells (10 through 15) built and passed, and none printed the Using CFLAGS from the environment notice, so they all used the default flags. The four red cells in that run are the known failures on main, fixed by #312, #332 and #355.
The case it does change is a shell that genuinely exports CFLAGS, which some packaging setups do. Those flags are now used where before they were silently ignored, and the script says so when it happens.
The generated Makefile assigns CFLAGS with "=", which overrides the
environment, so exporting CFLAGS before running makemake.sh silently
did nothing. Builds that need different flags - the sanitizer CI jobs -
have had to sed the "CFLAGS =" line of makemake.sh itself instead.
If CFLAGS is set, use it in place of the default optimization, debug,
warning and LTO flags. -std=gnu99 is always kept, since the code needs
it, and the SIMD-mode flags are added separately, as before. The script
says when it does this, because some environments export CFLAGS globally
and those flags used to be ignored. CPPFLAGS and LDFLAGS were already
appended to with "+=" and are unchanged.
In ci.yml, the five sanitizer jobs now set CFLAGS instead of editing
makemake.sh; the generated Makefile is byte-identical to what the sed
produced. The k1om job sources an SDK environment that exports its own
CFLAGS, so it now unsets CFLAGS to keep building with the defaults.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Review suggestion: test for a non-empty CFLAGS rather than a set one, so
'CFLAGS=' falls back to the default flags instead of building with
-std=gnu99 alone.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Walkthrough
The build script now uses nonempty environment CFLAGS and keeps its default flags when CFLAGS is empty. The README documents custom flags. CI sanitizer jobs export flags through GITHUB_ENV.
Changes: Build flags
Layer / File(s)
Summary
CFLAGS selection and documentation makemake.sh, README.md
makemake.sh uses nonempty environment CFLAGS with -std=gnu99. When CFLAGS is empty, it uses default flags and probes for color-diagnostics and LTO support. The README describes custom CFLAGS, SIMD flags, and how CPPFLAGS and LDFLAGS augment defaults.
CI flag setup .github/workflows/ci.yml
Linux, macOS, and Windows sanitizer jobs export flags through GITHUB_ENV. The K1OM setup unsets CFLAGS.
primesearch/Mlucas#316: PR #316 adds a probed compiler flag in makemake.sh; this change alters how environment CFLAGS replaces generated compiler flags.
primesearch/Mlucas#367: PR #367 changes the Windows ASan job to build native SIMD modes, which use the flag-handling behavior changed here.
Suggested labels:enhancement, github_actions, bug
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @makemake.sh:
- Around line 603-604: Update the CFLAGS handling that populates C_ARGS so
newline-separated flags are preserved: replace newlines with spaces before
storing the flags, ensuring every flag is included in the generated Makefile.
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read -a stops at the first newline, so CFLAGS=$'-Og\n-fsanitize=address' put only -Og in the
Makefile while the message reported the whole value. Turn newlines into spaces before splitting.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @makemake.sh:
- Around line 602-604: Update the old-GCC warning-flag probe in makemake.sh to
run only when CFLAGS is empty, so custom CFLAGS do not cause
-Wno-maybe-uninitialized to be appended; preserve the existing probe behavior
when default flags are used.
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A non-empty CFLAGS in the environment replaces the default warning flags,
but the GCC < 5 probe still appended -Wno-maybe-uninitialized after the
user's flags, so it changed the generated Makefile and overrode a
-Wmaybe-uninitialized the user had asked for. Skip the probe when CFLAGS
is set, like the other defaults.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Add -Werror=strict-aliasing -Wstrict-aliasing=2 to the CPPFLAGS of the gcc cells of the Linux, Linux-32-bit and Linux-Singlethread jobs, which makemake.sh appends to its compile command since primesearch#356. Those jobs already build every translation unit in every SIMD mode and Mfactor word size, on x86-64, 32-bit x86, Arm and 32-bit Arm, so no new job is needed.
The level has to be 2: -Wall's level 3 reports none of the violations this tree has had. The order matters, as -Werror=strict-aliasing after -Wstrict-aliasing=2 resets the level to 3 (checked with gcc 13.3 and 16.2), and -Werror=strict-aliasing=2 leaves the warning a warning.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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Exporting
CFLAGSbefore runningmakemake.shsilently does nothing: the generated Makefile assignsCFLAGS = ...with=, and a Makefile assignment overrides the environment. The only way to build with different flags has been to edit the script, which is what the five sanitizer jobs inci.ymldo withsed -i 's/^CFLAGS = .*/.../' makemake.sh.This makes
makemake.shhonourCFLAGS:CFLAGSis set, it replaces the default optimization, debug, warning and LTO flags (-Wall -Wextra -g -O3,-flto=auto/-flto,-fdiagnostics-color). That matches the usual convention, e.g. autoconf, and it is what the sanitizer jobs need: they want-Ogand no LTO, not the defaults with more flags added.-std=gnu99is always kept, since the code needs it.-DUSE_AVX2 -mavx2,-DUSE_AVX512 ...,-march=nativeand so on) are added separately, as before, soCFLAGS='-g -Og' bash makemake.sh avx2is still an AVX2 build.Using CFLAGS from the environment instead of the default flags: .... Some environments exportCFLAGSglobally (a cross-compilation SDK, a distribution's packaging setup), and until now those flags were ignored, so this makes the change visible instead of silent.CPPFLAGSandLDFLAGSare unchanged: the Makefile already appends to them with+=.In
ci.yml, the five sanitizer jobs now put their flags inCFLAGS(via$GITHUB_ENV) instead of editingmakemake.sh. The k1om job sources the Xeon Phi SDK's environment script, which exports its ownCFLAGS; it had a commented-out# unset CFLAGS CPPFLAGS, and now runsunset CFLAGS, so that it keeps building with the defaults it uses today.The README's build section has a short paragraph on it.
#56 also makes the Makefile's
CFLAGSoverridable, as part of a much broader rework of the script for parallel LTO. This is only theCFLAGSpart, kept small so it can land separately. If #56 lands later, the two will need reconciling there.Tested
CFLAGSset:makemake.sh mfac avx2generates a Makefile byte-identical to the onemaingenerates.CFLAGS='-Wall -Wextra -g -Og -fsanitize=address,undefined': the generated Makefile is byte-identical to the one produced bymainplus the oldsedline from the ASan job (CFLAGS = -std=gnu99 -Wall -Wextra -g -Og -fsanitize=address,undefined). The binary is ASan-instrumented, andMfactor -m 521 -bmax 20runs clean under it.🤖 Generated with Claude Code
Summary by CodeRabbit
CFLAGScan now be used when building, replacing default compiler flags while retaining-std=gnu99and SIMD build-mode flags. Without custom flags, default compiler settings remain, with checks for supported optimization options.CPPFLAGSandLDFLAGSare added to the default flags rather than replacing them.CPPFLAGSandLDFLAGSare applied.