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kbuild: avoid split lines in .mod files 

"xargs echo" is not a safe way to remove line breaks because the input
may exceed the command line limit and xargs may break it up into
multiple invocations of echo. This should never happen because
scripts/gen_autoksyms.sh expects all undefined symbols are placed in
the second line of .mod files.

One possible way is to replace "xargs echo" with
"sed ':x;N;$!bx;s/\n/ /g'" or something, but I rewrote the code by
using awk because it is more readable.

This issue was reported by Sami Tolvanen; in his Clang LTO patch set,
$(multi-used-m) is no longer an ELF object, but a thin archive that
contains LLVM bitcode files. llvm-nm prints out symbols for each
archive member separately, which results a lot of dupications, in some
places, beyond the system-defined limit.

This problem must be fixed irrespective of LTO, and we must ensure
zero possibility of having this issue.

Link: https://lkml.org/lkml/2020/12/1/1658
Reported-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
This commit is contained in:
Masahiro Yamada 2020-12-04 02:55:51 +09:00
parent d5750cd3c5
commit 7d32358be8
1 changed files with 4 additions and 8 deletions
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12
scripts/Makefile.build
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@ -252,6 +252,9 @@ objtool_dep = $(objtool_obj) \
ifdef CONFIG_TRIM_UNUSED_KSYMS
cmd_gen_ksymdeps = \
$(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
# List module undefined symbols
undefined_syms = $(NM) $< | $(AWK) '$$1 == "U" { printf("%s%s", x++ ? " " : "", $$2) }';
endif
define rule_cc_o_c
@ -271,13 +274,6 @@ define rule_as_o_S
$(call cmd,modversions_S)
endef
# List module undefined symbols (or empty line if not enabled)
ifdef CONFIG_TRIM_UNUSED_KSYMS
cmd_undef_syms = $(NM) $< | sed -n 's/^ *U //p' | xargs echo
else
cmd_undef_syms = echo
endif
# Built-in and composite module parts
$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
$(call if_changed_rule,cc_o_c)
@ -285,7 +281,7 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
cmd_mod = { \
echo $(if $($*-objs)$($*-y)$($*-m), $(addprefix $(obj)/, $($*-objs) $($*-y) $($*-m)), $(@:.mod=.o)); \
$(cmd_undef_syms); \
$(undefined_syms) echo; \
} > $@
$(obj)/%.mod: $(obj)/%.o FORCE