[PATCH] kbuild: don't delete in-flight filechk temporaries in asm-headers

[Vlad Poenaru <vlad.wing@gmail.com>]

Commit 2d69b891e646 ("kbuild: Support generated asm-headers in
subdirectories") switched the stale-wrapper sweep in
scripts/Makefile.asm-headers from $(wildcard $(obj)/*.h) to a find(1)
invocation, so that generated headers in subdirectories are considered.

The two do not match the same set of files. Make's $(wildcard) uses glob
semantics, where a leading '.' has to be matched explicitly, whereas
find's -name uses fnmatch() without FNM_PERIOD, so '*.h' matches
dotfiles as well. filechk writes its output to $(dir $@).tmp_$(notdir $@)
before renaming it into place, so such a scratch file, if it happens to
exist in $(obj) when the sub-make is parsed, is now picked up in
old-headers. It appears in neither generic-y, generated-y nor syscall-y,
is therefore classified as unwanted, and cmd_remove deletes it.

On x86 this races with archprepare, which lists both asm-generic and
arch/x86/include/generated/asm/cpufeaturemasks.h as prerequisites. Under
-j they run concurrently against the same directory, and the build fails
intermittently:

  mv: cannot stat 'arch/x86/include/generated/asm/.tmp_cpufeaturemasks.h': No such file or directory
  make[1]: *** [arch/x86/Makefile:269: arch/x86/include/generated/asm/cpufeaturemasks.h] Error 1

The same commit also converted the generic wrapper rule to filechk, so
those wrappers now create .tmp_*.h in $(obj) too and can race among
themselves.

Restore the previous behaviour by excluding dotfiles from the sweep.
Subdirectories, which is what the find(1) conversion was for, keep being
descended into. While at it, quote the -name argument: it is currently
expanded by the shell against the build directory before find sees it.

Fixes: 2d69b891e646 ("kbuild: Support generated asm-headers in subdirectories")
Signed-off-by: Vlad Poenaru <vlad.wing@gmail.com>
---
#regzbot introduced: 2d69b891e646

 scripts/Makefile.asm-headers | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/Makefile.asm-headers b/scripts/Makefile.asm-headers
index b38931314ad7c..f1c3d287c14b0 100644
--- a/scripts/Makefile.asm-headers
+++ b/scripts/Makefile.asm-headers
@@ -48,7 +48,7 @@ syscall-y   := $(addprefix $(obj)/, $(syscall-y))
 generated-y := $(addprefix $(obj)/, $(generated-y))
 
 # Remove stale wrappers when the corresponding files are removed from generic-y
-old-headers := $(shell test -d $(obj) && find $(obj) -name *.h)
+old-headers := $(shell test -d $(obj) && find $(obj) -name '*.h' ! -name '.*')
 unwanted    := $(filter-out $(generic-y) $(generated-y) $(syscall-y),$(old-headers))
 
 filechk_wrap = echo "\#include <asm-generic/$*.h>"
-- 
2.53.0-Meta