RFE: Support "-Wp,-MD" option (req. for Linux kernel build)

[llvmbot]

Bugzilla Link	4062
Resolution	FIXED
Resolved on	Jun 14, 2010 16:37
Version	unspecified
OS	Linux
Blocks	llvm/llvm-bugzilla-archive#4068 llvm/llvm-bugzilla-archive#5511
Reporter	LLVM Bugzilla Contributor
CC	@efriedma-quic

Extended Description

The Linux kernel uses "-Wp,-MD..." for dependencies. Example command line, when attempting to use clang to build kernel:

clang -Wp,-MD,kernel/.bounds.s.d -nostdinc -isystem include -Iinclude -I/spare/repo/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 -Wframe-larger-than=2048 -fno-stack-protector -fno-omit-frame-pointer -fno-optimize-sibling-calls -pg -Wdeclaration-after-statement -Wno-pointer-sign -fwrapv -fno-dwarf2-cfi-asm -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
clang: warning: the clang compiler does not yet support '-pg'
clang: warning: argument unused during compilation: '-march=core2'
clang: warning: argument unused during compilation: '-mcmodel=kernel'
clang: warning: argument unused during compilation: '-funit-at-a-time'
clang: warning: argument unused during compilation: '-maccumulate-outgoing-args'
clang: warning: argument unused during compilation: '-fno-asynchronous-unwind-tables'
clang: warning: argument unused during compilation: '-fno-omit-frame-pointer'
clang: warning: argument unused during compilation: '-fno-optimize-sibling-calls'
clang: warning: argument unused during compilation: '-fwrapv'
clang: warning: argument unused during compilation: '-fno-dwarf2-cfi-asm'
clang-cc: Unknown command line argument '-MD'. Try: '/usr/local/bin/../libexec/clang-cc --help'
make[1]: *** [kernel/bounds.s] Error 1
make: *** [prepare0] Error 2

[llvmbot]

Using -Wp is a hack for doing this. Is there any reason the kernel can't use -MD directly?

I don't want the driver to need to get in the business of ripping apart the -Wp, argument and reinterpreting it, unless there is a very compelling reason.

[efriedma-quic]

I don't want the driver to need to get in the business of ripping apart the
-Wp, argument and reinterpreting it, unless there is a very compelling reason.

If the driver doesn't process it, what will? Eventually, we're going to eliminate clang-cc, no?

[llvmbot]

That is an excellent point Eli. At that point we will need to reparse Wp anyway, so I guess we might as well go ahead and do it.

[efriedma-quic]

The build system for elinks (a text-mode web-browser) also uses this option.

[llvmbot]

Likewise do btrfs-progs, syslinux and certainly others.

[llvmbot]

The build system for Firefox also depends on this option.

[llvmbot]

Fixed here:
http://llvm.org/viewvc/llvm-project?view=rev&revision=105966

Note that this fix is exactly for the case of -Wp,-MD,FOO. I can generalize it, but am only going to do so on an as needed basis.

[edwintorok]

mentioned in issue llvm/llvm-bugzilla-archive#4068

[efriedma-quic]

mentioned in issue llvm/llvm-bugzilla-archive#5511