ccc: doesn't pass -Wp,-MD, to clang

[edwintorok]

Bugzilla Link	3602
Resolution	FIXED
Resolved on	Mar 31, 2009 15:56
Version	unspecified
OS	Linux
Depends On	llvm/llvm-bugzilla-archive#3603

Extended Description

I tried to build the linux kernel with clang, it gets this far:

ccc -Wp,-MD,kernel/.bounds.s.d -nostdinc -isystem include -Iinclude -I/home/edwin/builds/linux-2.6/arch/x86/include -include include/linux/autoconf.h -D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -O2 -m64 -march=core2 -mno-red-zone -mcmodel=kernel -funit-at-a-time -maccumulate-outgoing-args -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -Iarch/x86/include/asm/mach-default -Wframe-larger-than=2048 -fno-stack-protector -fno-omit-frame-pointer -fno-optimize-sibling-calls -Wdeclaration-after-statement -Wno-pointer-sign -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(bounds)" -D"KBUILD_MODNAME=KBUILD_STR(bounds)" -fverbose-asm -S -o kernel/bounds.s kernel/bounds.c

ccc: include: linker input file unused when -S is present
fixdep: kernel/.bounds.s.d: No such file or directory
make[1]: *** [kernel/bounds.s] Error 2

[llvmbot]

This is a pain. Using -Wp, to pass this option down is pretty gross.

The annoying thing here is that we want the flexibility to translate gcc options to clang options. Properly supporting this requires reparsing the -Wp, arguments so that we can translate them to clang. This is pretty gross.

We could just forward the -Wp, options as a temporary solution and hope that clang eats them, but this still will not work in this case because the command line is passing the cc1-level option "-MD " whereas clang currently recognizes -MD as the gcc option (which does not take an argument).

So gross.

[llvmbot]

If the makefile is patched to use the more proper "-MD -MF kernel/.bounds.s.d", how far does the compilation get?

[llvmbot]

git-diff changes to Linux kernel Makefiles

[llvmbot]

output of amended Linux kernel make system using ccc and clang

[llvmbot]

I've looked at all the places that the "-Wp,-MD,$(depfile)" is used in the Makefile (in linux-2.6/Makefile, linux-2.6/scripts/Makefile.host and linux-2.6/scripts/Makefile.lib -- note that I don't work with UserMode Linux or PPC so haven't changed those targets[1]) and swapped them to see how far the "-MD -MF $(depfile)" version gets.

[I had issue with the reference to "autoconf.h", but reading around the subject tells me it's nonexistent in the 2.6.29 kernel I'm using.]

Attached is git-diff patchfile to swap the Makefiles around. I can't promise it's the right collection of changes. Also, for the curious, is how far CCC got on with the rest of the build: something like 136 diagnostics,

[llvmbot]

It just looks like the kernel isn't getting the appropriate configuration defines (probably something to do with autconf.h). Does the same file actually build (with the same command) with gcc?

[llvmbot]

Duh. Skipping out 'include/linx/autoconf.h' was causing that problem.

Now that I've hardcoded the path in (for now), the "make -V 1 kernel/bounds.s" reports 'make[1]: `kernel/bounds.s' is up to date."

At present trying a Linux kernel build on my system chokes here (full details in attachment):

CC arch/x86/kernel/process_64.o
Unsupported asm: input constraint with a matching output constraint of incompatible type!
make[1]: *** [arch/x86/kernel/process_64.o] Error 1
make: *** [arch/x86/kernel] Error 2

[llvmbot]

output of amended make using ccc -- dies at first asm stage.

[edwintorok]

Duh. Skipping out 'include/linx/autoconf.h' was causing that problem.

Now that I've hardcoded the path in (for now), the "make -V 1 kernel/bounds.s"
reports 'make[1]: `kernel/bounds.s' is up to date."

At present trying a Linux kernel build on my system chokes here (full details
in attachment):

CC arch/x86/kernel/process_64.o
Unsupported asm: input constraint with a matching output constraint of
incompatible type!
make[1]: *** [arch/x86/kernel/process_64.o] Error 1
make: *** [arch/x86/kernel] Error 2

That is a problem with llvm-gcc as well, you can use my patches for example:
http://patchwork.kernel.org/patch/3882/

[llvmbot]

I implemented -Wp, and -Xpreprocessor here:
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20090330/014832.html

That won't fix the filed test case because clang-cc expects to see a different set of options for dependency files. Using -Wp, to pass gcc options to the underlying preprocessor is broken; the build system should use -MD and -MF.

Separate bugs should be filed for the other issues mentioned, I am closing this.

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#3603