[PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[Masahiro Yamada]

When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
show awkward "mkdir -p ..." logs.

  $ make -j16
    [ snip ]
  mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
  mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids

Defining MAKEFLAGS=<value> on the command line wipes out command line
switches from the resultant MAKEFLAGS definition, even though the command
line switches are active. [1]

The first word of $(MAKEFLAGS) is a possibly empty group of characters
representing single-letter options that take no argument. However, this
breaks if MAKEFLAGS=<value> is given on the command line.

The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
line, which breaks the following code in tools/scripts/Makefile.include:

    short-opts := $(firstword -$(MAKEFLAGS))

If MAKEFLAGS really needs modification, it should be done through the
environment variable, as follows:

    MAKEFLAGS=<value> $(MAKE) ...

That said, I question whether modifying MAKEFLAGS is necessary here.
The only flag we might want to exclude is --no-print-directory, as the
tools build system changes the working directory. However, people might
find the "Entering/Leaving directory" logs annoying.

I simply removed the offending MAKEFLAGS=.

[1]: https://savannah.gnu.org/bugs/?62469

Fixes: a50e43332756 ("perf tools: Honor parallel jobs")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 Makefile | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index 89628e354ca7..52207bcb1a9d 100644
--- a/Makefile
+++ b/Makefile
@@ -1421,18 +1421,13 @@ ifneq ($(wildcard $(resolve_btfids_O)),)
 	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
 endif
 
-# Clear a bunch of variables before executing the submake
-ifeq ($(quiet),silent_)
-tools_silent=s
-endif
-
 tools/: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
+	$(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
 
 tools/%: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
+	$(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
 
 # ---------------------------------------------------------------------------
 # Kernel selftest
-- 
2.43.0

Re: [PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[Masahiro Yamada]

Frank and Matt,
Please ignore this.
This is intended for kbuild ML.



On Tue, Feb 11, 2025 at 9:29 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
> show awkward "mkdir -p ..." logs.
>
>   $ make -j16
>     [ snip ]
>   mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
>   mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids
>
> Defining MAKEFLAGS=<value> on the command line wipes out command line
> switches from the resultant MAKEFLAGS definition, even though the command
> line switches are active. [1]
>
> The first word of $(MAKEFLAGS) is a possibly empty group of characters
> representing single-letter options that take no argument. However, this
> breaks if MAKEFLAGS=<value> is given on the command line.
>
> The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
> line, which breaks the following code in tools/scripts/Makefile.include:
>
>     short-opts := $(firstword -$(MAKEFLAGS))
>
> If MAKEFLAGS really needs modification, it should be done through the
> environment variable, as follows:
>
>     MAKEFLAGS=<value> $(MAKE) ...
>
> That said, I question whether modifying MAKEFLAGS is necessary here.
> The only flag we might want to exclude is --no-print-directory, as the
> tools build system changes the working directory. However, people might
> find the "Entering/Leaving directory" logs annoying.
>
> I simply removed the offending MAKEFLAGS=.
>
> [1]: https://savannah.gnu.org/bugs/?62469
>
> Fixes: a50e43332756 ("perf tools: Honor parallel jobs")
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
>  Makefile | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 89628e354ca7..52207bcb1a9d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1421,18 +1421,13 @@ ifneq ($(wildcard $(resolve_btfids_O)),)
>         $(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
>  endif
>
> -# Clear a bunch of variables before executing the submake
> -ifeq ($(quiet),silent_)
> -tools_silent=s
> -endif
> -
>  tools/: FORCE
>         $(Q)mkdir -p $(objtree)/tools
> -       $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
> +       $(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
>
>  tools/%: FORCE
>         $(Q)mkdir -p $(objtree)/tools
> -       $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
> +       $(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
>
>  # ---------------------------------------------------------------------------
>  # Kernel selftest
> --
> 2.43.0
>


-- 
Best Regards
Masahiro Yamada

[PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[Masahiro Yamada]

When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
show awkward "mkdir -p ..." logs.

  $ make -j16
    [ snip ]
  mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
  mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids

Defining MAKEFLAGS=<value> on the command line wipes out command line
switches from the resultant MAKEFLAGS definition, even though the command
line switches are active. [1]

The first word of $(MAKEFLAGS) is a possibly empty group of characters
representing single-letter options that take no argument. However, this
breaks if MAKEFLAGS=<value> is given on the command line.

The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
line, which breaks the following code in tools/scripts/Makefile.include:

    short-opts := $(firstword -$(MAKEFLAGS))

If MAKEFLAGS really needs modification, it should be done through the
environment variable, as follows:

    MAKEFLAGS=<value> $(MAKE) ...

That said, I question whether modifying MAKEFLAGS is necessary here.
The only flag we might want to exclude is --no-print-directory, as the
tools build system changes the working directory. However, people might
find the "Entering/Leaving directory" logs annoying.

I simply removed the offending MAKEFLAGS=.

[1]: https://savannah.gnu.org/bugs/?62469

Fixes: a50e43332756 ("perf tools: Honor parallel jobs")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 Makefile | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index 89628e354ca7..52207bcb1a9d 100644
--- a/Makefile
+++ b/Makefile
@@ -1421,18 +1421,13 @@ ifneq ($(wildcard $(resolve_btfids_O)),)
 	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
 endif
 
-# Clear a bunch of variables before executing the submake
-ifeq ($(quiet),silent_)
-tools_silent=s
-endif
-
 tools/: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
+	$(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
 
 tools/%: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
+	$(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
 
 # ---------------------------------------------------------------------------
 # Kernel selftest
-- 
2.43.0

Re: [PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[Daniel Xu]

Hi Masahiro,

Thanks for looking into this! Much better than my attempt :P

On Tue, Feb 11, 2025 at 09:29:06AM +0900, Masahiro Yamada wrote:
> When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
> show awkward "mkdir -p ..." logs.
> 
>   $ make -j16
>     [ snip ]
>   mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
>   mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids
> 
> Defining MAKEFLAGS=<value> on the command line wipes out command line
> switches from the resultant MAKEFLAGS definition, even though the command
> line switches are active. [1]
> 
> The first word of $(MAKEFLAGS) is a possibly empty group of characters
> representing single-letter options that take no argument. However, this
> breaks if MAKEFLAGS=<value> is given on the command line.
> 
> The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
> line, which breaks the following code in tools/scripts/Makefile.include:
> 
>     short-opts := $(firstword -$(MAKEFLAGS))
> 
> If MAKEFLAGS really needs modification, it should be done through the
> environment variable, as follows:
> 
>     MAKEFLAGS=<value> $(MAKE) ...
> 
> That said, I question whether modifying MAKEFLAGS is necessary here.
> The only flag we might want to exclude is --no-print-directory, as the
> tools build system changes the working directory. However, people might
> find the "Entering/Leaving directory" logs annoying.
> 
> I simply removed the offending MAKEFLAGS=.
> 
> [1]: https://savannah.gnu.org/bugs/?62469
> 
> Fixes: a50e43332756 ("perf tools: Honor parallel jobs")
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Tested-by: Daniel Xu <dxu@dxuuu.xyz>

Re: [PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[Doug Anderson]

Hi,

On Mon, Feb 10, 2025 at 4:30 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
> show awkward "mkdir -p ..." logs.
>
>   $ make -j16
>     [ snip ]
>   mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
>   mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids
>
> Defining MAKEFLAGS=<value> on the command line wipes out command line
> switches from the resultant MAKEFLAGS definition, even though the command
> line switches are active. [1]
>
> The first word of $(MAKEFLAGS) is a possibly empty group of characters
> representing single-letter options that take no argument. However, this
> breaks if MAKEFLAGS=<value> is given on the command line.
>
> The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
> line, which breaks the following code in tools/scripts/Makefile.include:
>
>     short-opts := $(firstword -$(MAKEFLAGS))
>
> If MAKEFLAGS really needs modification, it should be done through the
> environment variable, as follows:
>
>     MAKEFLAGS=<value> $(MAKE) ...
>
> That said, I question whether modifying MAKEFLAGS is necessary here.
> The only flag we might want to exclude is --no-print-directory, as the
> tools build system changes the working directory. However, people might
> find the "Entering/Leaving directory" logs annoying.
>
> I simply removed the offending MAKEFLAGS=.
>
> [1]: https://savannah.gnu.org/bugs/?62469
>
> Fixes: a50e43332756 ("perf tools: Honor parallel jobs")
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
>  Makefile | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)

I happened to sync up to mainline today and noticed that my build was
broken. I bisected it to this change and reverting this change fixes
my build on mainline.

In my case I'm building in a ChromeOS environment and using clang as
my compiler. I'm also cross-compiling an arm64 kernel on x86 host.
...but the pure mainline kernel should work there. Presumably the
environment is a bit different compared to the typical one, though?

The error comes up when doing a clean build and the first error messages are:

In file included from libbpf.c:36:
.../tools/include/uapi/linux/bpf_perf_event.h:14:21: error: field has
incomplete type
      'bpf_user_pt_regs_t' (aka 'struct user_pt_regs')
   14 |         bpf_user_pt_regs_t regs;
      |                            ^
.../tools/include/../../arch/arm64/include/uapi/asm/bpf_perf_event.h:7:16:
note: forward
      declaration of 'struct user_pt_regs'
    7 | typedef struct user_pt_regs bpf_user_pt_regs_t;
      |                ^

btf_dump.c:1860:10: error: cast to smaller integer type 'uintptr_t'
(aka 'unsigned int') from 'const void *'
      [-Werror,-Wvoid-pointer-to-int-cast]
 1860 |         return ((uintptr_t)data) % alignment == 0;
      |                 ^~~~~~~~~~~~~~~
btf_dump.c:2045:4: error: format specifies type 'ssize_t' (aka 'long')
but the argument has type 'ssize_t' (aka 'int')
      [-Werror,-Wformat]
 2044 |                 pr_warn("unexpected elem size %zd for array
type [%u]\n",
      |                                               ~~~
      |                                               %d
 2045 |                         (ssize_t)elem_size, id);
      |                         ^~~~~~~~~~~~~~~~~~
./libbpf_internal.h:171:52: note: expanded from macro 'pr_warn'
  171 | #define pr_warn(fmt, ...)       __pr(LIBBPF_WARN, fmt, ##__VA_ARGS__)
      |                                                   ~~~    ^~~~~~~~~~~


I don't have time to dig right now, but I figured I'd at least post in
case the problem is obvious to someone else.


-Doug

Re: [PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[Masahiro Yamada]

On Wed, Mar 19, 2025 at 1:41 AM Doug Anderson <dianders@chromium.org> wrote:
>
> Hi,
>
> On Mon, Feb 10, 2025 at 4:30 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
> > show awkward "mkdir -p ..." logs.
> >
> >   $ make -j16
> >     [ snip ]
> >   mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
> >   mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids
> >
> > Defining MAKEFLAGS=<value> on the command line wipes out command line
> > switches from the resultant MAKEFLAGS definition, even though the command
> > line switches are active. [1]
> >
> > The first word of $(MAKEFLAGS) is a possibly empty group of characters
> > representing single-letter options that take no argument. However, this
> > breaks if MAKEFLAGS=<value> is given on the command line.
> >
> > The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
> > line, which breaks the following code in tools/scripts/Makefile.include:
> >
> >     short-opts := $(firstword -$(MAKEFLAGS))
> >
> > If MAKEFLAGS really needs modification, it should be done through the
> > environment variable, as follows:
> >
> >     MAKEFLAGS=<value> $(MAKE) ...
> >
> > That said, I question whether modifying MAKEFLAGS is necessary here.
> > The only flag we might want to exclude is --no-print-directory, as the
> > tools build system changes the working directory. However, people might
> > find the "Entering/Leaving directory" logs annoying.
> >
> > I simply removed the offending MAKEFLAGS=.
> >
> > [1]: https://savannah.gnu.org/bugs/?62469
> >
> > Fixes: a50e43332756 ("perf tools: Honor parallel jobs")
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > ---
> >
> >  Makefile | 9 ++-------
> >  1 file changed, 2 insertions(+), 7 deletions(-)
>
> I happened to sync up to mainline today and noticed that my build was
> broken. I bisected it to this change and reverting this change fixes
> my build on mainline.
>
> In my case I'm building in a ChromeOS environment and using clang as
> my compiler. I'm also cross-compiling an arm64 kernel on x86 host.
> ...but the pure mainline kernel should work there. Presumably the
> environment is a bit different compared to the typical one, though?
>
> The error comes up when doing a clean build and the first error messages are:
>
> In file included from libbpf.c:36:
> .../tools/include/uapi/linux/bpf_perf_event.h:14:21: error: field has
> incomplete type
>       'bpf_user_pt_regs_t' (aka 'struct user_pt_regs')
>    14 |         bpf_user_pt_regs_t regs;
>       |                            ^
> .../tools/include/../../arch/arm64/include/uapi/asm/bpf_perf_event.h:7:16:
> note: forward
>       declaration of 'struct user_pt_regs'
>     7 | typedef struct user_pt_regs bpf_user_pt_regs_t;
>       |                ^
>
> btf_dump.c:1860:10: error: cast to smaller integer type 'uintptr_t'
> (aka 'unsigned int') from 'const void *'
>       [-Werror,-Wvoid-pointer-to-int-cast]
>  1860 |         return ((uintptr_t)data) % alignment == 0;
>       |                 ^~~~~~~~~~~~~~~
> btf_dump.c:2045:4: error: format specifies type 'ssize_t' (aka 'long')
> but the argument has type 'ssize_t' (aka 'int')
>       [-Werror,-Wformat]
>  2044 |                 pr_warn("unexpected elem size %zd for array
> type [%u]\n",
>       |                                               ~~~
>       |                                               %d
>  2045 |                         (ssize_t)elem_size, id);
>       |                         ^~~~~~~~~~~~~~~~~~
> ./libbpf_internal.h:171:52: note: expanded from macro 'pr_warn'
>   171 | #define pr_warn(fmt, ...)       __pr(LIBBPF_WARN, fmt, ##__VA_ARGS__)
>       |                                                   ~~~    ^~~~~~~~~~~
>
>
> I don't have time to dig right now, but I figured I'd at least post in
> case the problem is obvious to someone else.

I do not understand how to reproduce this.

Your build machine is Chrome OS, or other distributions?
Did you build the upstream kernel or downstream one?
What is the build command?  Just "make" ?









-- 
Best Regards
Masahiro Yamada

Re: [PATCH] tools: fix annoying "mkdir -p ..." logs when building tools in parallel

[Doug Anderson]

Hi,

On Sat, Mar 22, 2025 at 7:50 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Wed, Mar 19, 2025 at 1:41 AM Doug Anderson <dianders@chromium.org> wrote:
> >
> > Hi,
> >
> > On Mon, Feb 10, 2025 at 4:30 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > When CONFIG_OBJTOOL=y or CONFIG_DEBUG_INFO_BTF=y, parallel builds
> > > show awkward "mkdir -p ..." logs.
> > >
> > >   $ make -j16
> > >     [ snip ]
> > >   mkdir -p /home/masahiro/ref/linux/tools/objtool && make O=/home/masahiro/ref/linux subdir=tools/objtool --no-print-directory -C objtool
> > >   mkdir -p /home/masahiro/ref/linux/tools/bpf/resolve_btfids && make O=/home/masahiro/ref/linux subdir=tools/bpf/resolve_btfids --no-print-directory -C bpf/resolve_btfids
> > >
> > > Defining MAKEFLAGS=<value> on the command line wipes out command line
> > > switches from the resultant MAKEFLAGS definition, even though the command
> > > line switches are active. [1]
> > >
> > > The first word of $(MAKEFLAGS) is a possibly empty group of characters
> > > representing single-letter options that take no argument. However, this
> > > breaks if MAKEFLAGS=<value> is given on the command line.
> > >
> > > The tools/ and tools/% targets set MAKEFLAGS=<value> on the command
> > > line, which breaks the following code in tools/scripts/Makefile.include:
> > >
> > >     short-opts := $(firstword -$(MAKEFLAGS))
> > >
> > > If MAKEFLAGS really needs modification, it should be done through the
> > > environment variable, as follows:
> > >
> > >     MAKEFLAGS=<value> $(MAKE) ...
> > >
> > > That said, I question whether modifying MAKEFLAGS is necessary here.
> > > The only flag we might want to exclude is --no-print-directory, as the
> > > tools build system changes the working directory. However, people might
> > > find the "Entering/Leaving directory" logs annoying.
> > >
> > > I simply removed the offending MAKEFLAGS=.
> > >
> > > [1]: https://savannah.gnu.org/bugs/?62469
> > >
> > > Fixes: a50e43332756 ("perf tools: Honor parallel jobs")
> > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > > ---
> > >
> > >  Makefile | 9 ++-------
> > >  1 file changed, 2 insertions(+), 7 deletions(-)
> >
> > I happened to sync up to mainline today and noticed that my build was
> > broken. I bisected it to this change and reverting this change fixes
> > my build on mainline.
> >
> > In my case I'm building in a ChromeOS environment and using clang as
> > my compiler. I'm also cross-compiling an arm64 kernel on x86 host.
> > ...but the pure mainline kernel should work there. Presumably the
> > environment is a bit different compared to the typical one, though?
> >
> > The error comes up when doing a clean build and the first error messages are:
> >
> > In file included from libbpf.c:36:
> > .../tools/include/uapi/linux/bpf_perf_event.h:14:21: error: field has
> > incomplete type
> >       'bpf_user_pt_regs_t' (aka 'struct user_pt_regs')
> >    14 |         bpf_user_pt_regs_t regs;
> >       |                            ^
> > .../tools/include/../../arch/arm64/include/uapi/asm/bpf_perf_event.h:7:16:
> > note: forward
> >       declaration of 'struct user_pt_regs'
> >     7 | typedef struct user_pt_regs bpf_user_pt_regs_t;
> >       |                ^
> >
> > btf_dump.c:1860:10: error: cast to smaller integer type 'uintptr_t'
> > (aka 'unsigned int') from 'const void *'
> >       [-Werror,-Wvoid-pointer-to-int-cast]
> >  1860 |         return ((uintptr_t)data) % alignment == 0;
> >       |                 ^~~~~~~~~~~~~~~
> > btf_dump.c:2045:4: error: format specifies type 'ssize_t' (aka 'long')
> > but the argument has type 'ssize_t' (aka 'int')
> >       [-Werror,-Wformat]
> >  2044 |                 pr_warn("unexpected elem size %zd for array
> > type [%u]\n",
> >       |                                               ~~~
> >       |                                               %d
> >  2045 |                         (ssize_t)elem_size, id);
> >       |                         ^~~~~~~~~~~~~~~~~~
> > ./libbpf_internal.h:171:52: note: expanded from macro 'pr_warn'
> >   171 | #define pr_warn(fmt, ...)       __pr(LIBBPF_WARN, fmt, ##__VA_ARGS__)
> >       |                                                   ~~~    ^~~~~~~~~~~
> >
> >
> > I don't have time to dig right now, but I figured I'd at least post in
> > case the problem is obvious to someone else.
>
> I do not understand how to reproduce this.
>
> Your build machine is Chrome OS, or other distributions?
> Did you build the upstream kernel or downstream one?
> What is the build command?  Just "make" ?

Unfortunately, it's not a simple set of steps to reproduce and would
take a lot of time / disk space. :( Essentially, the steps are:

1. Setup a ChromeOS development environment. This is a pretty massive
thing. You'd have to follow the Developer Guide [1].

2. Enter the "chroot" in the development environment and build for a
board like "trogdor". This is an arm64 Chromebook.

3. The "trogdor" board normally builds a v6.6-based kernel, so it
looks for the kernel sources in `src/third_party/kernel/v6.6`. ...but
you can go into that folder and simply checkout a pure upstream kernel
as talked about in [2].

3. Inside the ChromeOS "chroot", you can do `cros-workon-trogdor start
chromeos-kernel-6_6` and `emerge-trogdor chromeos-kernel-6_6`. Since
you've checked out the upstream kernel to the v6.6 directory this
won't actually be building 6.6 but will be building the upstream
kernel.

...and that's where I see the error, which is "fixed" by reverting this patch.

FWIW: the actual build instructions for building the kernel are mostly
in cros-kernel.eclass [3].


Given how time consuming that would be to reproduce, I'm not sure it's
worth your time. Let me do some simple debugging... So I added these
extra printouts:

 tools/: FORCE
+       echo DOUGa new: "$(MAKEFLAGS)"
+       echo DOUGa old: "$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))"

 tools/%: FORCE
+       echo DOUGb new "$(MAKEFLAGS)"
+       echo DOUBb old: "$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))"

...and when I build, I see:

DOUGb new krR -j128 --jobserver-auth=3,4 --no-print-directory --
CLANG_CROSS_FLAGS=--target=aarch64-cros-linux-gnu
HOSTLD=x86_64-pc-linux-gnu-ld.lld
HOSTPKG_CONFIG=x86_64-pc-linux-gnu-pkg-config
HOSTCXX=x86_64-pc-linux-gnu-clang++ HOSTCC=x86_64-pc-linux-gnu-clang
CXX=aarch64-cros-linux-gnu-clang++\
CC_COMPAT=armv7a-cros-linux-gnueabihf-clang
CC=aarch64-cros-linux-gnu-clang\  AR=llvm-ar NM=llvm-nm
STRIP=llvm-strip REAL_STRIP=llvm-strip OBJCOPY=llvm-objcopy
LD_COMPAT=ld.lld LD=ld.lld
O=/build/trogdor/var/cache/portage/sys-kernel/chromeos-kernel-6_6 V=0

DOUBb old:  --jobserver-auth=3,4

...so pretty different! :-) I guess it used to be filtering out all
the cross-compiler info and now it isn't?


[1] https://www.chromium.org/chromium-os/developer-library/guides/development/developer-guide/
[2] https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/HEAD/eclass/cros-kernel/README.md
[3] https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/HEAD/eclass/cros-kernel.eclass