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Don't create Python bytecode when building the kernel

PATCH Superseded Mauro Carvalho Chehab 4 participants 9 messages Apr 18, 2025 – Apr 19, 2025

Subsystems (5)
DRM drivers Documentation DRM misc Kbuild +1 more subsystems

v3 of 4 Superseded Latest is v4 →

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Mauro Carvalho Chehab

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#0 lore raw

v3 cover Don't create Python bytecode when building the kernel

As reported by Andy, the Kernel build system runs kernel-doc script for DRM, when W=1. Due to Python's normal behavior, its JIT compiler will create a bytecode and store it under scripts/lib/*/__pycache__. As one may be using O= and even having the sources on a read-only mount point, disable its creation during build time.

This is done by adding PYTHONDONTWRITEBYTECODE=1 on every place where the script is called within Kbuild and when called via another script.

This only solves half of the issue though, as one may be manually running the script by hand, without asking Python to not store any bytecode. This should be OK, but afterwards, git status will list the __pycache__ as not committed. To prevent that, add *.pyc to .gitignore.

This series contain 4 patches:

- patch 1 adjusts a variable that pass extra data to scripts/kerneldoc.py;
- patch 2moves scripts/kernel-doc location to the main makefile and exports it, as scripts/Makefile.build will need it;
- patch 3 disables __pycache__ generation and ensure that the entire Kbuild will use KERNELDOC var for the location of kernel-doc;
- patch 4 adds *.pyc at the list of object files to be ignored.

---

v3:
- move KERNELDOC to the main Makefile;
- get rid of the badly-named KERNELDOC_CONF var.

v2:
- added a .gitignore file;
- add PYTHONDONTWRITEBYTECODE=1 to the places where kernel-doc is called.

Mauro Carvalho Chehab (4):
docs: Makefile: get rid of KERNELDOC_CONF env variable
Makefile: move KERNELDOC macro to the main Makefile scripts/kernel-doc.py: don't create *.pyc files .gitignore: ignore Python compiled bytecode

 .gitignore                    | 1 +
 Documentation/Makefile        | 5 ++---
 Makefile                      | 5 +++++
 drivers/gpu/drm/Makefile      | 2 +-
 drivers/gpu/drm/i915/Makefile | 2 +-
 include/drm/Makefile          | 2 +-
 scripts/Makefile.build        | 2 +-
 scripts/find-unused-docs.sh   | 2 +-
 8 files changed, 13 insertions(+), 8 deletions(-)
Signature · 1 line
2.49.0
author
#1 lore raw

PATCH v3 1/4 docs: Makefile: get rid of KERNELDOC_CONF env variable

Despite its name, what's there is a set of Sphinx arguments that are passed to sphinx/kerneldoc.py:

- kerneldoc_srctree: location of the source tree;
- kerneldoc_bin: external script to excecute kernel-doc

Drop it, and just place the values at the already-existing ALLSPHINXOPTS variable.

Signed-off-by Mauro Carvalho Chehab <[email protected]>
---
 Documentation/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
Documentation/Makefile +2 -2
index c022b97c487e..a006c7681412 100644
@@ -61,8 +61,8 @@ endif #HAVE_LATEXMK
 PAPEROPT_a4     = -D latex_paper_size=a4
 PAPEROPT_letter = -D latex_paper_size=letter
 KERNELDOC       = $(srctree)/scripts/kernel-doc.py
-KERNELDOC_CONF  = -D kerneldoc_srctree=$(srctree) -D kerneldoc_bin=$(KERNELDOC)
-ALLSPHINXOPTS   =  $(KERNELDOC_CONF) $(PAPEROPT_$(PAPER)) $(SPHINXOPTS)
+ALLSPHINXOPTS   = -D kerneldoc_srctree=$(srctree) -D kerneldoc_bin=$(KERNELDOC)
+ALLSPHINXOPTS   += $(PAPEROPT_$(PAPER)) $(SPHINXOPTS)
 ifneq ($(wildcard $(srctree)/.config),)
 ifeq ($(CONFIG_RUST),y)
 	# Let Sphinx know we will include rustdoc
Signature · 1 line
2.49.0
author
#2 lore raw

PATCH v3 2/4 Makefile: move KERNELDOC macro to the main Makefile

In reply to Mauro Carvalho Chehab

As kernel-doc script is used not only on Documentation, but also on scripts and drivers/drm Makefiles, move it to the main makefile, as otherwise sub-makefiles may not have it.

Signed-off-by Mauro Carvalho Chehab <[email protected]>
---
 Documentation/Makefile | 1 -
 Makefile               | 5 +++++
 2 files changed, 5 insertions(+), 1 deletion(-)
Documentation/Makefile +0 -1
index a006c7681412..8c1f6a3dfc44 100644
@@ -60,7 +60,6 @@ endif #HAVE_LATEXMK
 # Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
 PAPEROPT_letter = -D latex_paper_size=letter
-KERNELDOC       = $(srctree)/scripts/kernel-doc.py
 ALLSPHINXOPTS   = -D kerneldoc_srctree=$(srctree) -D kerneldoc_bin=$(KERNELDOC)
 ALLSPHINXOPTS   += $(PAPEROPT_$(PAPER)) $(SPHINXOPTS)
 ifneq ($(wildcard $(srctree)/.config),)
Makefile +5 -0
index 38689a0c3605..2a05988740a9 100644
@@ -458,6 +458,11 @@ endif
 HOSTRUSTC = rustc
 HOSTPKG_CONFIG	= pkg-config
 
+# the KERNELDOC macro needs to be exported, as scripts/Makefile.build
+# has a logic to call it
+KERNELDOC       = $(srctree)/scripts/kernel-doc.py
+export KERNELDOC
+
 KBUILD_USERHOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
 			 -O2 -fomit-frame-pointer -std=gnu11
 KBUILD_USERCFLAGS  := $(KBUILD_USERHOSTCFLAGS) $(USERCFLAGS)
Signature · 1 line
2.49.0
author
#3 lore raw

PATCH v3 3/4 scripts/kernel-doc.py: don't create *.pyc files

In reply to Mauro Carvalho Chehab

As reported by Andy, kernel-doc.py is creating a __pycache__ directory at build time.

Disable creation of __pycache__ for the libraries used by kernel-doc.py, when excecuted via the build system or via scripts/find-unused-docs.sh.

Reported-by Andy Shevchenko <[email protected]>
Closes https://lore.kernel.org/linux-doc/[email protected]/ open here
Signed-off-by Mauro Carvalho Chehab <[email protected]>
---
 drivers/gpu/drm/Makefile      | 2 +-
 drivers/gpu/drm/i915/Makefile | 2 +-
 include/drm/Makefile          | 2 +-
 scripts/Makefile.build        | 2 +-
 scripts/find-unused-docs.sh   | 2 +-
 5 files changed, 5 insertions(+), 5 deletions(-)
drivers/gpu/drm/Makefile +1 -1
index ed54a546bbe2..d21d0cd2c752 100644
@@ -236,7 +236,7 @@ always-$(CONFIG_DRM_HEADER_TEST) += \
 quiet_cmd_hdrtest = HDRTEST $(patsubst %.hdrtest,%.h,$@)
       cmd_hdrtest = \
 		$(CC) $(c_flags) -fsyntax-only -x c /dev/null -include $< -include $<; \
-		$(srctree)/scripts/kernel-doc -none $(if $(CONFIG_WERROR)$(CONFIG_DRM_WERROR),-Werror) $<; \
+		 PYTHONDONTWRITEBYTECODE=1 $(KERNELDOC) -none $(if $(CONFIG_WERROR)$(CONFIG_DRM_WERROR),-Werror) $<; \
 		touch $@
 
 $(obj)/%.hdrtest: $(src)/%.h FORCE
drivers/gpu/drm/i915/Makefile +1 -1
index ed05b131ed3a..ab6b89a163e7 100644
@@ -408,7 +408,7 @@ obj-$(CONFIG_DRM_I915_GVT_KVMGT) += kvmgt.o
 #
 # Enable locally for CONFIG_DRM_I915_WERROR=y. See also scripts/Makefile.build
 ifdef CONFIG_DRM_I915_WERROR
-    cmd_checkdoc = $(srctree)/scripts/kernel-doc -none -Werror $<
+    cmd_checkdoc = PYTHONDONTWRITEBYTECODE=1 $(KERNELDOC) -none -Werror $<
 endif
 
 # header test
include/drm/Makefile +1 -1
index a7bd15d2803e..1df6962556ef 100644
@@ -11,7 +11,7 @@ always-$(CONFIG_DRM_HEADER_TEST) += \
 quiet_cmd_hdrtest = HDRTEST $(patsubst %.hdrtest,%.h,$@)
       cmd_hdrtest = \
 		$(CC) $(c_flags) -fsyntax-only -x c /dev/null -include $< -include $<; \
-		$(srctree)/scripts/kernel-doc -none $(if $(CONFIG_WERROR)$(CONFIG_DRM_WERROR),-Werror) $<; \
+		PYTHONDONTWRITEBYTECODE=1 $(KERNELDOC) -none $(if $(CONFIG_WERROR)$(CONFIG_DRM_WERROR),-Werror) $<; \
 		touch $@
 
 $(obj)/%.hdrtest: $(src)/%.h FORCE
scripts/Makefile.build +1 -1
index 13dcd86e74ca..884dc86ce04e 100644
@@ -83,7 +83,7 @@ else ifeq ($(KBUILD_CHECKSRC),2)
 endif
 
 ifneq ($(KBUILD_EXTRA_WARN),)
-  cmd_checkdoc = $(srctree)/scripts/kernel-doc -none $(KDOCFLAGS) \
+  cmd_checkdoc = PYTHONDONTWRITEBYTECODE=1 $(KERNELDOC) -none $(KDOCFLAGS) \
         $(if $(findstring 2, $(KBUILD_EXTRA_WARN)), -Wall) \
         $<
 endif
scripts/find-unused-docs.sh +1 -1
index ee6a50e33aba..d6d397fbf917 100755
@@ -54,7 +54,7 @@ for file in `find $1 -name '*.c'`; do
 	if [[ ${FILES_INCLUDED[$file]+_} ]]; then
 	continue;
 	fi
-	str=$(scripts/kernel-doc -export "$file" 2>/dev/null)
+	str=$(PYTHONDONTWRITEBYTECODE=1 scripts/kernel-doc -export "$file" 2>/dev/null)
 	if [[ -n "$str" ]]; then
 	echo "$file"
 	fi
Signature · 1 line
2.49.0
author
#4 lore raw

PATCH v3 4/4 .gitignore: ignore Python compiled bytecode

In reply to Mauro Carvalho Chehab

While the building system doesn't create any Python JIT bytecode, if one manually runs kernel-doc.py or get_abi.py, Python will, by default, create a bytecode and store it under scripts/lib/*.

This is normal, and not controlled by the Kernel itself. So, add *.pyc as an extension to be ignored.

Signed-off-by Mauro Carvalho Chehab <[email protected]>
---
 .gitignore | 1 +
 1 file changed, 1 insertion(+)
.gitignore +1 -0
index f2f63e47fb88..2e01bc0b2d2a 100644
@@ -39,6 +39,7 @@
 *.mod.c
 *.o
 *.o.*
+*.pyc
 *.patch
 *.rmeta
 *.rpm
Signature · 1 line
2.49.0
#5 lore raw

Re: [PATCH v3 4/4] .gitignore: ignore Python compiled bytecode

Quoted 3 lines · Mauro Carvalho Chehab

+*.pyc
*.patch

I think the list is intended to be sorted.

Should *.pyo be added as well?

Thanks!

Cheers,
Miguel

#6 lore raw

Re: [PATCH v3 4/4] .gitignore: ignore Python compiled bytecode

Quoted 2 lines · Miguel Ojeda

Should *.pyo be added as well?

I think this one is a no, given even oldoldstable Debian ships new enough Python.

Cheers,
Miguel

#7 lore raw

Re: [PATCH v3 4/4] .gitignore: ignore Python compiled bytecode

In reply to Miguel Ojeda
Quoted 7 lines · Miguel Ojeda
Quoted 3 lines · Mauro Carvalho Chehab

+*.pyc
*.patch

I think the list is intended to be sorted.

+1, I told already twice, I dunno if my messages were seen.

Signature · 2 lines
With Best Regards,
Andy Shevchenko
Tested-by on the v3 series
#8 lore raw
In reply to Mauro Carvalho Chehab
Quoted 14 lines · Mauro Carvalho Chehab

As reported by Andy, the Kernel build system runs kernel-doc script for DRM, when W=1. Due to Python's normal behavior, its JIT compiler will create a bytecode and store it under scripts/lib/*/__pycache__. As one may be using O= and even having the sources on a read-only mount point, disable its creation during build time.

This is done by adding PYTHONDONTWRITEBYTECODE=1 on every place where the script is called within Kbuild and when called via another script.

This only solves half of the issue though, as one may be manually running the script by hand, without asking Python to not store any bytecode. This should be OK, but afterwards, git status will list the __pycache__ as not committed. To prevent that, add *.pyc to .gitignore.

Quoted 8 lines

This series contain 4 patches:

- patch 1 adjusts a variable that pass extra data to scripts/kerneldoc.py;
- patch 2moves scripts/kernel-doc location to the main makefile and exports it, as scripts/Makefile.build will need it;
- patch 3 disables __pycache__ generation and ensure that the entire Kbuild will use KERNELDOC var for the location of kernel-doc;
- patch 4 adds *.pyc at the list of object files to be ignored.

This one works for me, thanks!

Tested-by Andy Shevchenko <[email protected]>
Signature · 2 lines
With Best Regards,
Andy Shevchenko