[PATCH] objtool: fix build with future Make

[PATCH] objtool: fix build with future Make

[Rasmus Villemoes]

I tried building using a freshly built Make (4.2.1-69-g8a731d1), but the
objtool build broke with

orc_dump.c: In function ‘orc_dump’:
orc_dump.c:106:2: error: ‘elf_getshnum’ is deprecated [-Werror=deprecated-declarations]
  if (elf_getshdrnum(elf, &nr_sections)) {

Turns out that with that new Make, the backslash was not removed, so cpp
didn't see a #include directive, grep found nothing, and
-DLIBELF_USE_DEPRECATED was wrongly put in CFLAGS.

Now, that new Make behaviour is documented in their NEWS file:

  * WARNING: Backward-incompatibility!
    Number signs (#) appearing inside a macro reference or function invocation
    no longer introduce comments and should not be escaped with backslashes:
    thus a call such as:
      foo := $(shell echo '#')
    is legal.  Previously the number sign needed to be escaped, for example:
      foo := $(shell echo '\#')
    Now this latter will resolve to "\#".  If you want to write makefiles
    portable to both versions, assign the number sign to a variable:
      C := \#
      foo := $(shell echo '$C')
    This was claimed to be fixed in 3.81, but wasn't, for some reason.
    To detect this change search for 'nocomment' in the .FEATURES variable.

There are likely other places in the tree that will need fixing, so
cc-ing Kbuild, but with this at least a x86-64 defconfig builds.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 tools/objtool/Makefile         | 2 +-
 tools/scripts/Makefile.include | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index e6acc281dd37..8ae824dbfca3 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -35,7 +35,7 @@ CFLAGS   += -Wall -Werror $(WARNINGS) -fomit-frame-pointer -O2 -g $(INCLUDES)
 LDFLAGS  += -lelf $(LIBSUBCMD)
 
 # Allow old libelf to be used:
-elfshdr := $(shell echo '\#include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
+elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
 CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
 
 AWK = awk
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index dd614463d4d6..495066bafbe3 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -120,3 +120,5 @@ ifneq ($(silent),1)
 	QUIET_UNINST   = @printf '  UNINST   %s\n' $1;
   endif
 endif
+
+pound := \#
-- 
2.15.1

[PATCH 2/1] Kbuild: fix # escaping in .cmd files for future Make

[Rasmus Villemoes]

The latest official Make release is 4.2.1 from mid-2016, but the current
git release has this relevant note in the NEWS file:

  * WARNING: Backward-incompatibility!
    Number signs (#) appearing inside a macro reference or function invocation
    no longer introduce comments and should not be escaped with backslashes:
    thus a call such as:
      foo := $(shell echo '#')
    is legal.  Previously the number sign needed to be escaped, for example:
      foo := $(shell echo '\#')
    Now this latter will resolve to "\#".  If you want to write makefiles
    portable to both versions, assign the number sign to a variable:
      C := \#
      foo := $(shell echo '$C')
    This was claimed to be fixed in 3.81, but wasn't, for some reason.
    To detect this change search for 'nocomment' in the .FEATURES variable.

Prepare for whatever future Make release contains that change by fixing
up the .cmd file escaping - without this, make always thinks the command
string has changed and hence rebuilds everything.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
So the previous patch made everything build, but building again
revealed that this central place very much also needed fixing.

 scripts/Kbuild.include | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 065324a8046f..7a926e4688f4 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -10,6 +10,7 @@ space   := $(empty) $(empty)
 space_escape := _-_SPACE_-_
 right_paren := )
 left_paren := (
+pound := \#
 
 ###
 # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
@@ -328,7 +329,7 @@ endif
 # (needed for make)
 # Replace >'< with >'\''< to be able to enclose the whole string in '...'
 # (needed for the shell)
-make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))
+make-cmd = $(call escsq,$(subst $(pound),\\$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
 
 # Find any prerequisites that is newer than target or that does not exist.
 # PHONY targets skipped in both cases.
-- 
2.15.1

Re: [PATCH] objtool: fix build with future Make

[Randy Dunlap]

On 03/25/2018 03:32 PM, Rasmus Villemoes wrote:
> I tried building using a freshly built Make (4.2.1-69-g8a731d1), but the
> objtool build broke with
> 
> orc_dump.c: In function ‘orc_dump’:
> orc_dump.c:106:2: error: ‘elf_getshnum’ is deprecated [-Werror=deprecated-declarations]
>   if (elf_getshdrnum(elf, &nr_sections)) {
> 
> Turns out that with that new Make, the backslash was not removed, so cpp
> didn't see a #include directive, grep found nothing, and
> -DLIBELF_USE_DEPRECATED was wrongly put in CFLAGS.
> 
> Now, that new Make behaviour is documented in their NEWS file:
> 
>   * WARNING: Backward-incompatibility!
>     Number signs (#) appearing inside a macro reference or function invocation
>     no longer introduce comments and should not be escaped with backslashes:
>     thus a call such as:
>       foo := $(shell echo '#')
>     is legal.  Previously the number sign needed to be escaped, for example:
>       foo := $(shell echo '\#')
>     Now this latter will resolve to "\#".  If you want to write makefiles
>     portable to both versions, assign the number sign to a variable:
>       C := \#
>       foo := $(shell echo '$C')
>     This was claimed to be fixed in 3.81, but wasn't, for some reason.
>     To detect this change search for 'nocomment' in the .FEATURES variable.
> 
> There are likely other places in the tree that will need fixing, so
> cc-ing Kbuild, but with this at least a x86-64 defconfig builds.

Hi,

For one of these patches, can we say:
Fixes https://bugzilla.kernel.org/show_bug.cgi?id=197847
?

Thanks.

> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
>  tools/objtool/Makefile         | 2 +-
>  tools/scripts/Makefile.include | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
> index e6acc281dd37..8ae824dbfca3 100644
> --- a/tools/objtool/Makefile
> +++ b/tools/objtool/Makefile
> @@ -35,7 +35,7 @@ CFLAGS   += -Wall -Werror $(WARNINGS) -fomit-frame-pointer -O2 -g $(INCLUDES)
>  LDFLAGS  += -lelf $(LIBSUBCMD)
>  
>  # Allow old libelf to be used:
> -elfshdr := $(shell echo '\#include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
> +elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
>  CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
>  
>  AWK = awk
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index dd614463d4d6..495066bafbe3 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -120,3 +120,5 @@ ifneq ($(silent),1)
>  	QUIET_UNINST   = @printf '  UNINST   %s\n' $1;
>    endif
>  endif
> +
> +pound := \#
> 


-- 
~Randy

Re: [PATCH 2/1] Kbuild: fix # escaping in .cmd files for future Make

[Masahiro Yamada]

2018-03-26 8:09 GMT+09:00 Rasmus Villemoes <linux@rasmusvillemoes.dk>:
> The latest official Make release is 4.2.1 from mid-2016, but the current
> git release has this relevant note in the NEWS file:
>
>   * WARNING: Backward-incompatibility!
>     Number signs (#) appearing inside a macro reference or function invocation
>     no longer introduce comments and should not be escaped with backslashes:
>     thus a call such as:
>       foo := $(shell echo '#')
>     is legal.  Previously the number sign needed to be escaped, for example:
>       foo := $(shell echo '\#')
>     Now this latter will resolve to "\#".  If you want to write makefiles
>     portable to both versions, assign the number sign to a variable:
>       C := \#
>       foo := $(shell echo '$C')
>     This was claimed to be fixed in 3.81, but wasn't, for some reason.
>     To detect this change search for 'nocomment' in the .FEATURES variable.
>
> Prepare for whatever future Make release contains that change by fixing
> up the .cmd file escaping - without this, make always thinks the command
> string has changed and hence rebuilds everything.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
> So the previous patch made everything build, but building again
> revealed that this central place very much also needed fixing.
>
>  scripts/Kbuild.include | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 065324a8046f..7a926e4688f4 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -10,6 +10,7 @@ space   := $(empty) $(empty)
>  space_escape := _-_SPACE_-_
>  right_paren := )
>  left_paren := (
> +pound := \#
>
>  ###
>  # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
> @@ -328,7 +329,7 @@ endif
>  # (needed for make)
>  # Replace >'< with >'\''< to be able to enclose the whole string in '...'
>  # (needed for the shell)
> -make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))
> +make-cmd = $(call escsq,$(subst $(pound),\\$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
>

Thanks for the patch, but this changes the behavior.
With '#' replaced with $(pound), '\\' does not escape anything,
so it is treated as '\\'.


The following keeps the current behavior:

make-cmd = $(call escsq,$(subst $(pound),\$(pound),$(subst
$$,$$$$,$(cmd_$(1)))))



But, I think the following is an even better fix:

make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst
$$,$$$$,$(cmd_$(1)))))



The following 4 test cases produce the same foo.txt,
but insane .cmd file is produced for some case.
Adjusting the number of back-slashes is not a perfect solution.

Replacing # with $(pound) works for all the cases.


[test code 1]
extra-y := foo.txt

quiet_cmd_foo = DEFINE   $@
      cmd_foo = echo '\#define FOO' >$@

$(obj)/foo.txt: FORCE
        $(call if_changed,foo)


[test code 2]
extra-y := foo.txt

quiet_cmd_foo = DEFINE   $@
      cmd_foo = echo \\\#define FOO >$@

$(obj)/foo.txt: FORCE
        $(call if_changed,foo)


[test code3]
extra-y := foo.txt

quiet_cmd_foo = DEFINE   $@
      cmd_foo = echo '$(pound)define FOO' >$@

$(obj)/foo.txt: FORCE
        $(call if_changed,foo)



[test code4]
extra-y := foo.txt

quiet_cmd_foo = DEFINE   $@
      cmd_foo = echo \$(pound)define FOO >$@

$(obj)/foo.txt: FORCE
        $(call if_changed,foo)





           | current | \$(pound) | \\$(pound) | $$(pound)
----------------------------------------------------------
test code1 |    OK   |    OK     |     NG     |   OK
test code2 |    NG   |    NG     |     OK     |   OK
test code3 |    OK   |    OK     |     NG     |   OK
test code4 |    NG   |    NG     |     OK     |   OK




-- 
Best Regards
Masahiro Yamada

Re: [PATCH] objtool: fix build with future Make

[Masahiro Yamada]

2018-03-26 7:32 GMT+09:00 Rasmus Villemoes <linux@rasmusvillemoes.dk>:
> I tried building using a freshly built Make (4.2.1-69-g8a731d1), but the
> objtool build broke with
>
> orc_dump.c: In function ‘orc_dump’:
> orc_dump.c:106:2: error: ‘elf_getshnum’ is deprecated [-Werror=deprecated-declarations]
>   if (elf_getshdrnum(elf, &nr_sections)) {
>
> Turns out that with that new Make, the backslash was not removed, so cpp
> didn't see a #include directive, grep found nothing, and
> -DLIBELF_USE_DEPRECATED was wrongly put in CFLAGS.
>
> Now, that new Make behaviour is documented in their NEWS file:
>
>   * WARNING: Backward-incompatibility!
>     Number signs (#) appearing inside a macro reference or function invocation
>     no longer introduce comments and should not be escaped with backslashes:
>     thus a call such as:
>       foo := $(shell echo '#')
>     is legal.  Previously the number sign needed to be escaped, for example:
>       foo := $(shell echo '\#')
>     Now this latter will resolve to "\#".  If you want to write makefiles
>     portable to both versions, assign the number sign to a variable:
>       C := \#
>       foo := $(shell echo '$C')
>     This was claimed to be fixed in 3.81, but wasn't, for some reason.
>     To detect this change search for 'nocomment' in the .FEATURES variable.
>
> There are likely other places in the tree that will need fixing, so
> cc-ing Kbuild, but with this at least a x86-64 defconfig builds.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---

Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>




-- 
Best Regards
Masahiro Yamada

Re: [PATCH 2/1] Kbuild: fix # escaping in .cmd files for future Make

[Rasmus Villemoes]

On 2018-03-26 13:48, Masahiro Yamada wrote:
> 2018-03-26 8:09 GMT+09:00 Rasmus Villemoes <linux@rasmusvillemoes.dk>:
>> The latest official Make release is 4.2.1 from mid-2016, but the current
>> git release has this relevant note in the NEWS file:
>>
>>   * WARNING: Backward-incompatibility!
>>     Number signs (#) appearing inside a macro reference or function invocation
>>     no longer introduce comments and should not be escaped with backslashes:
>>     thus a call such as:
>>       foo := $(shell echo '#')
>>     is legal.  Previously the number sign needed to be escaped, for example:
>>       foo := $(shell echo '\#')
>>     Now this latter will resolve to "\#".  If you want to write makefiles
>>     portable to both versions, assign the number sign to a variable:
>>       C := \#
>>       foo := $(shell echo '$C')
>>     This was claimed to be fixed in 3.81, but wasn't, for some reason.
>>     To detect this change search for 'nocomment' in the .FEATURES variable.
>>
>> Prepare for whatever future Make release contains that change by fixing
>> up the .cmd file escaping - without this, make always thinks the command
>> string has changed and hence rebuilds everything.
>>
>> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
>> ---
>> So the previous patch made everything build, but building again
>> revealed that this central place very much also needed fixing.
>>
>>  scripts/Kbuild.include | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
>> index 065324a8046f..7a926e4688f4 100644
>> --- a/scripts/Kbuild.include
>> +++ b/scripts/Kbuild.include
>> @@ -10,6 +10,7 @@ space   := $(empty) $(empty)
>>  space_escape := _-_SPACE_-_
>>  right_paren := )
>>  left_paren := (
>> +pound := \#
>>
>>  ###
>>  # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
>> @@ -328,7 +329,7 @@ endif
>>  # (needed for make)
>>  # Replace >'< with >'\''< to be able to enclose the whole string in '...'
>>  # (needed for the shell)
>> -make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))
>> +make-cmd = $(call escsq,$(subst $(pound),\\$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
>>
> 
> Thanks for the patch, but this changes the behavior.
> With '#' replaced with $(pound), '\\' does not escape anything,
> so it is treated as '\\'.
> 
> 
> The following keeps the current behavior:
> 
> make-cmd = $(call escsq,$(subst $(pound),\$(pound),$(subst
> $$,$$$$,$(cmd_$(1)))))
> 
> 
> 
> But, I think the following is an even better fix:
> 
> make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst
> $$,$$$$,$(cmd_$(1)))))

Makefile quoting has never been my strong suit. I actually thought I
tested my change by looking at some .o.cmd files containing \# before
and after, but I was fooled by tools/ containing and using their own
copy of make-cmd - so tools/build/Build.include will also need fixing.

Yes, writing $(pound) to the .cmd file seems like the safest choice. Do
you want me to respin or can/will you do the patch(es) yourself?

Rasmus

Re: [PATCH 2/1] Kbuild: fix # escaping in .cmd files for future Make

[Masahiro Yamada]

2018-04-06 6:43 GMT+09:00 Rasmus Villemoes <linux@rasmusvillemoes.dk>:
> On 2018-03-26 13:48, Masahiro Yamada wrote:
>> 2018-03-26 8:09 GMT+09:00 Rasmus Villemoes <linux@rasmusvillemoes.dk>:
>>> The latest official Make release is 4.2.1 from mid-2016, but the current
>>> git release has this relevant note in the NEWS file:
>>>
>>>   * WARNING: Backward-incompatibility!
>>>     Number signs (#) appearing inside a macro reference or function invocation
>>>     no longer introduce comments and should not be escaped with backslashes:
>>>     thus a call such as:
>>>       foo := $(shell echo '#')
>>>     is legal.  Previously the number sign needed to be escaped, for example:
>>>       foo := $(shell echo '\#')
>>>     Now this latter will resolve to "\#".  If you want to write makefiles
>>>     portable to both versions, assign the number sign to a variable:
>>>       C := \#
>>>       foo := $(shell echo '$C')
>>>     This was claimed to be fixed in 3.81, but wasn't, for some reason.
>>>     To detect this change search for 'nocomment' in the .FEATURES variable.
>>>
>>> Prepare for whatever future Make release contains that change by fixing
>>> up the .cmd file escaping - without this, make always thinks the command
>>> string has changed and hence rebuilds everything.
>>>
>>> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
>>> ---
>>> So the previous patch made everything build, but building again
>>> revealed that this central place very much also needed fixing.
>>>
>>>  scripts/Kbuild.include | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
>>> index 065324a8046f..7a926e4688f4 100644
>>> --- a/scripts/Kbuild.include
>>> +++ b/scripts/Kbuild.include
>>> @@ -10,6 +10,7 @@ space   := $(empty) $(empty)
>>>  space_escape := _-_SPACE_-_
>>>  right_paren := )
>>>  left_paren := (
>>> +pound := \#
>>>
>>>  ###
>>>  # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
>>> @@ -328,7 +329,7 @@ endif
>>>  # (needed for make)
>>>  # Replace >'< with >'\''< to be able to enclose the whole string in '...'
>>>  # (needed for the shell)
>>> -make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))
>>> +make-cmd = $(call escsq,$(subst $(pound),\\$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
>>>
>>
>> Thanks for the patch, but this changes the behavior.
>> With '#' replaced with $(pound), '\\' does not escape anything,
>> so it is treated as '\\'.
>>
>>
>> The following keeps the current behavior:
>>
>> make-cmd = $(call escsq,$(subst $(pound),\$(pound),$(subst
>> $$,$$$$,$(cmd_$(1)))))
>>
>>
>>
>> But, I think the following is an even better fix:
>>
>> make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst
>> $$,$$$$,$(cmd_$(1)))))
>
> Makefile quoting has never been my strong suit. I actually thought I
> tested my change by looking at some .o.cmd files containing \# before
> and after, but I was fooled by tools/ containing and using their own
> copy of make-cmd - so tools/build/Build.include will also need fixing.
>
> Yes, writing $(pound) to the .cmd file seems like the safest choice. Do
> you want me to respin or can/will you do the patch(es) yourself?
>

Can you send v2 please?

I will pick it up shortly.



-- 
Best Regards
Masahiro Yamada

[PATCH v2] Kbuild: fix # escaping in .cmd files for future Make

[Rasmus Villemoes]

I tried building using a freshly built Make (4.2.1-69-g8a731d1), but
already the objtool build broke with

orc_dump.c: In function ‘orc_dump’:
orc_dump.c:106:2: error: ‘elf_getshnum’ is deprecated [-Werror=deprecated-declarations]
  if (elf_getshdrnum(elf, &nr_sections)) {

Turns out that with that new Make, the backslash was not removed, so cpp
didn't see a #include directive, grep found nothing, and
-DLIBELF_USE_DEPRECATED was wrongly put in CFLAGS.

Now, that new Make behaviour is documented in their NEWS file:

  * WARNING: Backward-incompatibility!
    Number signs (#) appearing inside a macro reference or function invocation
    no longer introduce comments and should not be escaped with backslashes:
    thus a call such as:
      foo := $(shell echo '#')
    is legal.  Previously the number sign needed to be escaped, for example:
      foo := $(shell echo '\#')
    Now this latter will resolve to "\#".  If you want to write makefiles
    portable to both versions, assign the number sign to a variable:
      C := \#
      foo := $(shell echo '$C')
    This was claimed to be fixed in 3.81, but wasn't, for some reason.
    To detect this change search for 'nocomment' in the .FEATURES variable.

This also fixes up the two make-cmd instances to replace # with $(pound)
rather than with \#. There might very well be other places that need
similar fixup in preparation for whatever future Make release contains
the above change, but at least this builds an x86_64 defconfig with the
new make.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=197847
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
v2:

- squash the original objtool-only patch with the patch fixing up
  make-cmd, to avoid repeating the reference to the Make NEWS.

- use $(pound) in .cmd files to avoid backslash-counting issues (Masahiro).

- add bugzilla link (Randy).

 scripts/Kbuild.include         | 5 +++--
 tools/build/Build.include      | 5 +++--
 tools/objtool/Makefile         | 2 +-
 tools/scripts/Makefile.include | 2 ++
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index cce31ee876b6..50cee534fd64 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -10,6 +10,7 @@ space   := $(empty) $(empty)
 space_escape := _-_SPACE_-_
 right_paren := )
 left_paren := (
+pound := \#
 
 ###
 # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
@@ -322,11 +323,11 @@ endif
 
 # Replace >$< with >$$< to preserve $ when reloading the .cmd file
 # (needed for make)
-# Replace >#< with >\#< to avoid starting a comment in the .cmd file
+# Replace >#< with >$(pound)< to avoid starting a comment in the .cmd file
 # (needed for make)
 # Replace >'< with >'\''< to be able to enclose the whole string in '...'
 # (needed for the shell)
-make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))
+make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
 
 # Find any prerequisites that is newer than target or that does not exist.
 # PHONY targets skipped in both cases.
diff --git a/tools/build/Build.include b/tools/build/Build.include
index 418871d02ebf..a4bbb984941d 100644
--- a/tools/build/Build.include
+++ b/tools/build/Build.include
@@ -12,6 +12,7 @@
 # Convenient variables
 comma   := ,
 squote  := '
+pound   := \#
 
 ###
 # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
@@ -43,11 +44,11 @@ echo-cmd = $(if $($(quiet)cmd_$(1)),\
 ###
 # Replace >$< with >$$< to preserve $ when reloading the .cmd file
 # (needed for make)
-# Replace >#< with >\#< to avoid starting a comment in the .cmd file
+# Replace >#< with >$(pound)< to avoid starting a comment in the .cmd file
 # (needed for make)
 # Replace >'< with >'\''< to be able to enclose the whole string in '...'
 # (needed for the shell)
-make-cmd = $(call escsq,$(subst \#,\\\#,$(subst $$,$$$$,$(cmd_$(1)))))
+make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
 
 ###
 # Find any prerequisites that is newer than target or that does not exist.
diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index e6acc281dd37..8ae824dbfca3 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -35,7 +35,7 @@ CFLAGS   += -Wall -Werror $(WARNINGS) -fomit-frame-pointer -O2 -g $(INCLUDES)
 LDFLAGS  += -lelf $(LIBSUBCMD)
 
 # Allow old libelf to be used:
-elfshdr := $(shell echo '\#include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
+elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
 CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
 
 AWK = awk
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index dd614463d4d6..495066bafbe3 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -120,3 +120,5 @@ ifneq ($(silent),1)
 	QUIET_UNINST   = @printf '  UNINST   %s\n' $1;
   endif
 endif
+
+pound := \#
-- 
2.15.1

Re: [PATCH v2] Kbuild: fix # escaping in .cmd files for future Make

[Masahiro Yamada]

2018-04-09 6:35 GMT+09:00 Rasmus Villemoes <linux@rasmusvillemoes.dk>:
> I tried building using a freshly built Make (4.2.1-69-g8a731d1), but
> already the objtool build broke with
>
> orc_dump.c: In function ‘orc_dump’:
> orc_dump.c:106:2: error: ‘elf_getshnum’ is deprecated [-Werror=deprecated-declarations]
>   if (elf_getshdrnum(elf, &nr_sections)) {
>
> Turns out that with that new Make, the backslash was not removed, so cpp
> didn't see a #include directive, grep found nothing, and
> -DLIBELF_USE_DEPRECATED was wrongly put in CFLAGS.
>
> Now, that new Make behaviour is documented in their NEWS file:
>
>   * WARNING: Backward-incompatibility!
>     Number signs (#) appearing inside a macro reference or function invocation
>     no longer introduce comments and should not be escaped with backslashes:
>     thus a call such as:
>       foo := $(shell echo '#')
>     is legal.  Previously the number sign needed to be escaped, for example:
>       foo := $(shell echo '\#')
>     Now this latter will resolve to "\#".  If you want to write makefiles
>     portable to both versions, assign the number sign to a variable:
>       C := \#
>       foo := $(shell echo '$C')
>     This was claimed to be fixed in 3.81, but wasn't, for some reason.
>     To detect this change search for 'nocomment' in the .FEATURES variable.
>
> This also fixes up the two make-cmd instances to replace # with $(pound)
> rather than with \#. There might very well be other places that need
> similar fixup in preparation for whatever future Make release contains
> the above change, but at least this builds an x86_64 defconfig with the
> new make.
>
> Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=197847
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---

Applied to linux-kbuild.  Thanks!


-- 
Best Regards
Masahiro Yamada