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kconfig: unify cc-option and as-option

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cc-option and as-option are almost the same; both pass the flag to
$(CC). The main difference is the cc-option stops before the assemble
stage (-S option) whereas as-option stops after (-c option).

I chose -S because it is slightly faster, but $(cc-option,-gz=zlib)
returns a wrong result (https://lkml.org/lkml/2020/6/9/1529).
It has been fixed by commit 7b16994437 ("Makefile: Improve compressed
debug info support detection"), but the assembler should always be
invoked for more reliable compiler option tests.

However, you cannot simply replace -S with -c because the following
code in lib/Kconfig.debug would break:

    depends on $(cc-option,-gsplit-dwarf)

The combination of -c and -gsplit-dwarf does not accept /dev/null as
output.

  $ cat /dev/null | gcc -gsplit-dwarf -S -x c - -o /dev/null
  $ echo $?
  0

  $ cat /dev/null | gcc -gsplit-dwarf -c -x c - -o /dev/null
  objcopy: Warning: '/dev/null' is not an ordinary file
  $ echo $?
  1

  $ cat /dev/null | gcc -gsplit-dwarf -c -x c - -o tmp.o
  $ echo $?
  0

There is another flag that creates an separate file based on the
object file path:

  $ cat /dev/null | gcc -ftest-coverage -c -x c - -o /dev/null
  <stdin>:1: error: cannot open /dev/null.gcno

So, we cannot use /dev/null to sink the output.

Align the cc-option implementation with scripts/Kbuild.include.

With -c option used in cc-option, as-option is unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
This commit is contained in:
Masahiro Yamada 2020-06-14 23:43:41 +09:00
parent f2f02ebd8f
commit 4d0831e8a0
3 changed files with 2 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm64/Kconfig
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@ -1564,7 +1564,7 @@ config CC_HAS_SIGN_RETURN_ADDRESS
def_bool $(cc-option,-msign-return-address=all)
config AS_HAS_PAC
def_bool $(as-option,-Wa$(comma)-march=armv8.3-a)
def_bool $(cc-option,-Wa$(comma)-march=armv8.3-a)
config AS_HAS_CFI_NEGATE_RA_STATE
def_bool $(as-instr,.cfi_startproc\n.cfi_negate_ra_state\n.cfi_endproc\n)

1
lib/Kconfig.debug
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@ -229,7 +229,6 @@ config DEBUG_INFO_COMPRESSED
bool "Compressed debugging information"
depends on DEBUG_INFO
depends on $(cc-option,-gz=zlib)
depends on $(as-option,-gz=zlib)
depends on $(ld-option,--compress-debug-sections=zlib)
help
Compress the debug information using zlib. Requires GCC 5.0+ or Clang

8
scripts/Kconfig.include
View File

@ -25,18 +25,12 @@ failure = $(if-success,$(1),n,y)
# $(cc-option,<flag>)
# Return y if the compiler supports <flag>, n otherwise
cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -S -x c /dev/null -o /dev/null)
cc-option = $(success,mkdir .tmp_$$$$; trap "rm -rf .tmp_$$$$" EXIT; $(CC) -Werror $(CLANG_FLAGS) $(1) -c -x c /dev/null -o .tmp_$$$$/tmp.o)
# $(ld-option,<flag>)
# Return y if the linker supports <flag>, n otherwise
ld-option = $(success,$(LD) -v $(1))
# $(as-option,<flag>)
# /dev/zero is used as output instead of /dev/null as some assembler cribs when
# both input and output are same. Also both of them have same write behaviour so
# can be easily substituted.
as-option = $(success, $(CC) $(CLANG_FLAGS) $(1) -c -x assembler /dev/null -o /dev/zero)
# $(as-instr,<instr>)
# Return y if the assembler supports <instr>, n otherwise
as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler -o /dev/null -)