diff mbox series

[1/5] try generic compiler name "cc" before falling back to "gcc".

Message ID 63c2936e-6bc7-67e3-eaf3-0123333381f8@landley.net
State New
Headers
Series Patches used to build mkroot. |

Commit Message

Rob Landley Feb. 21, 2023, 8:55 p.m. UTC 
  Distros like debian install the generic "cc" name for both gcc and clang,
and the plumbing already does CC_VERSION_TEXT to include Makefile.clang.

Previously: https://lkml.iu.edu/hypermail/linux/kernel/2202.0/01505.html
Signed-off-by: Rob Landley <rob@landley.net>
---
 Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Masahiro Yamada Feb. 23, 2023, 5:31 a.m. UTC | #1 
On Wed, Feb 22, 2023 at 5:41 AM Rob Landley <rob@landley.net> wrote:
>
> Distros like debian install the generic "cc" name for both gcc and clang,
> and the plumbing already does CC_VERSION_TEXT to include Makefile.clang.
>
> Previously: https://lkml.iu.edu/hypermail/linux/kernel/2202.0/01505.html
> Signed-off-by: Rob Landley <rob@landley.net>
> ---
>  Makefile | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 3f6628780eb2..0ac57ae3b45f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -456,7 +456,7 @@ endif
>  HOSTCC = $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
>  HOSTCXX        = $(LLVM_PREFIX)clang++$(LLVM_SUFFIX)
>  else
> -HOSTCC = gcc
> +HOSTCC := $(shell cc --version >/dev/null 2>&1 && echo cc || echo gcc)



'cc' only makes sense for the host compiler,
which is configured by 'update-alternative'.

I tried it before, but LLVM folks preferred
using $(LLVM) to choose clang/gcc.






>  HOSTCXX        = g++
>  endif
>  HOSTRUSTC = rustc
> @@ -503,7 +503,8 @@ OBJDUMP             = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
>  READELF                = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
>  STRIP          = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
>  else
> -CC             = $(CROSS_COMPILE)gcc
> +CC             := $(CROSS_COMPILE)$(shell $(CROSS_COMPILE)cc --version \
> +                       >/dev/null 2>&1 && echo cc || echo gcc)

This hunk sets up GCC/binutils.
So, cc does not make sense.  NACK.






>  LD             = $(CROSS_COMPILE)ld
>  AR             = $(CROSS_COMPILE)ar
>  NM             = $(CROSS_COMPILE)nm
Rob Landley Feb. 23, 2023, 1:50 p.m. UTC | #2 
On 2/22/23 23:31, Masahiro Yamada wrote:
> On Wed, Feb 22, 2023 at 5:41 AM Rob Landley <rob@landley.net> wrote:
>>
>> Distros like debian install the generic "cc" name for both gcc and clang,
>> and the plumbing already does CC_VERSION_TEXT to include Makefile.clang.
>>
>> Previously: https://lkml.iu.edu/hypermail/linux/kernel/2202.0/01505.html
>> Signed-off-by: Rob Landley <rob@landley.net>
>> ---
>>  Makefile | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/Makefile b/Makefile
>> index 3f6628780eb2..0ac57ae3b45f 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -456,7 +456,7 @@ endif
>>  HOSTCC = $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
>>  HOSTCXX        = $(LLVM_PREFIX)clang++$(LLVM_SUFFIX)
>>  else
>> -HOSTCC = gcc
>> +HOSTCC := $(shell cc --version >/dev/null 2>&1 && echo cc || echo gcc)
> 
> 'cc' only makes sense for the host compiler,

It was the generic posix name for "C compiler" until posix decided to put an
expiration date in the command name, which seems as widely honored as the
tar->pax switch or the removal of cpio.

The name "gcc" was like "gmake" and "gawk". (On macos homebrew there's "gsed".)

> which is configured by 'update-alternative'.

Hexagon only has llvm support, not gcc, so I had to add an llvm cross compiler
to my cross compiler set, prefixed hexagon-unknown-linux-musl-*, but the linux
kernel wants to call it as hexagon-unknown-linux-musl-gcc.

The kernel builds find with a "gcc" symlink to clang, but there _is_ a generic
name, which is widely installed.

> I tried it before, but LLVM folks preferred
> using $(LLVM) to choose clang/gcc.

So if we want generic behavior without having to specify, we should create a
"gcc" symlink to clang?

>>  HOSTCXX        = g++
>>  endif
>>  HOSTRUSTC = rustc
>> @@ -503,7 +503,8 @@ OBJDUMP             = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
>>  READELF                = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
>>  STRIP          = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
>>  else
>> -CC             = $(CROSS_COMPILE)gcc
>> +CC             := $(CROSS_COMPILE)$(shell $(CROSS_COMPILE)cc --version \
>> +                       >/dev/null 2>&1 && echo cc || echo gcc)
> 
> This hunk sets up GCC/binutils.

This is the codepath that's taken when you don't explicitly specify "LLVM=1".
The test there is falling back to (appropriately prefixed) gcc when it can't
find a working (appropriately prefixed) cc.

> So, cc does not make sense.  NACK.

Do you explicitly specify the "gold" linker vs the previous gnu one vs
lld.llvm.org on the kernel build command line?

Rob
Masahiro Yamada Feb. 24, 2023, 12:27 a.m. UTC | #3 
On Thu, Feb 23, 2023 at 10:36 PM Rob Landley <rob@landley.net> wrote:
>
> On 2/22/23 23:31, Masahiro Yamada wrote:
> > On Wed, Feb 22, 2023 at 5:41 AM Rob Landley <rob@landley.net> wrote:
> >>
> >> Distros like debian install the generic "cc" name for both gcc and clang,
> >> and the plumbing already does CC_VERSION_TEXT to include Makefile.clang.
> >>
> >> Previously: https://lkml.iu.edu/hypermail/linux/kernel/2202.0/01505.html
> >> Signed-off-by: Rob Landley <rob@landley.net>
> >> ---
> >>  Makefile | 5 +++--
> >>  1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/Makefile b/Makefile
> >> index 3f6628780eb2..0ac57ae3b45f 100644
> >> --- a/Makefile
> >> +++ b/Makefile
> >> @@ -456,7 +456,7 @@ endif
> >>  HOSTCC = $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
> >>  HOSTCXX        = $(LLVM_PREFIX)clang++$(LLVM_SUFFIX)
> >>  else
> >> -HOSTCC = gcc
> >> +HOSTCC := $(shell cc --version >/dev/null 2>&1 && echo cc || echo gcc)
> >
> > 'cc' only makes sense for the host compiler,
>
> It was the generic posix name for "C compiler" until posix decided to put an
> expiration date in the command name, which seems as widely honored as the
> tar->pax switch or the removal of cpio.
>
> The name "gcc" was like "gmake" and "gawk". (On macos homebrew there's "gsed".)
>
> > which is configured by 'update-alternative'.
>
> Hexagon only has llvm support, not gcc, so I had to add an llvm cross compiler
> to my cross compiler set, prefixed hexagon-unknown-linux-musl-*, but the linux
> kernel wants to call it as hexagon-unknown-linux-musl-gcc.
>
> The kernel builds find with a "gcc" symlink to clang, but there _is_ a generic
> name, which is widely installed.



In the discussion in the past [1], we decided to
go with LLVM=1 switch rather than 'cc'.
We do not need both.

[1]: https://lkml.org/lkml/2020/3/28/494








>
> > I tried it before, but LLVM folks preferred
> > using $(LLVM) to choose clang/gcc.
>
> So if we want generic behavior without having to specify, we should create a
> "gcc" symlink to clang?


If you mean "without LLVM=1 or HOSTCC=clang specified",
I think the answer is yes.






>
> >>  HOSTCXX        = g++
> >>  endif
> >>  HOSTRUSTC = rustc
> >> @@ -503,7 +503,8 @@ OBJDUMP             = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
> >>  READELF                = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
> >>  STRIP          = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
> >>  else
> >> -CC             = $(CROSS_COMPILE)gcc
> >> +CC             := $(CROSS_COMPILE)$(shell $(CROSS_COMPILE)cc --version \
> >> +                       >/dev/null 2>&1 && echo cc || echo gcc)
> >
> > This hunk sets up GCC/binutils.
>
> This is the codepath that's taken when you don't explicitly specify "LLVM=1".
> The test there is falling back to (appropriately prefixed) gcc when it can't
> find a working (appropriately prefixed) cc.


Unless LLVM=1 is specified, the toolchain defaults to GCC/binutils,
there is no need for such additional complexity.




>
> > So, cc does not make sense.  NACK.
>
> Do you explicitly specify the "gold" linker vs the previous gnu one vs
> lld.llvm.org on the kernel build command line?


gold is unsupported.
See 75959d44f9dc8e44410667009724e4e238515502


Yes, to override only LD, LD=ld.lld should be given in the command line.





>
> Rob
diff mbox series

Patch

diff --git a/Makefile b/Makefile
index 3f6628780eb2..0ac57ae3b45f 100644
--- a/Makefile
+++ b/Makefile
@@ -456,7 +456,7 @@  endif
 HOSTCC	= $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
 HOSTCXX	= $(LLVM_PREFIX)clang++$(LLVM_SUFFIX)
 else
-HOSTCC	= gcc
+HOSTCC	:= $(shell cc --version >/dev/null 2>&1 && echo cc || echo gcc)
 HOSTCXX	= g++
 endif
 HOSTRUSTC = rustc
@@ -503,7 +503,8 @@  OBJDUMP		= $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
 READELF		= $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
 STRIP		= $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
 else
-CC		= $(CROSS_COMPILE)gcc
+CC		:= $(CROSS_COMPILE)$(shell $(CROSS_COMPILE)cc --version \
+			>/dev/null 2>&1 && echo cc || echo gcc)
 LD		= $(CROSS_COMPILE)ld
 AR		= $(CROSS_COMPILE)ar
 NM		= $(CROSS_COMPILE)nm