Re: [Xen-devel] [XEN PATCH for-4.13] xen: Fix race to build arch/x86/efi/relocs-dummy.o

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Fri, Nov 15, 2019 at 11:06:27AM +0100, Jan Beulich wrote:
> On 14.11.2019 19:05, Anthony PERARD wrote:
> > With $(TARGET).efi depending on efi/relocs-dummy.o, arch/x86/Makefile
> > will attempt to build that object. This result in the dependency file
> > been generated with relocs-dummy.o depending on efi/relocs-dummy.o.
> 
> I cannot confirm this, what I see is
> 
> efi/relocs-dummy.o: efi/relocs-dummy.S \
>  ...


I've written the commit message base on few evidences, but I don't know
if the race comes from trying to build $(TARGET).efi. Here is what I
have:

# Building Xen with make -j8 after git clean
make[3]: *** No rule to make target 'efi/relocs-dummy.S', needed by 
'relocs-dummy.o'.
$ head -1 arch/x86/efi/.relocs-dummy.o.d
relocs-dummy.o: efi/relocs-dummy.S \

arch/x86/.relocs-dummy.o.d doesn't exist.

looking back at the make output, relocs-dummy was built with:
gcc -D__ASSEMBLY__ -m64 -DBUILD_ID -fno-strict-aliasing -Wall 
-Wstrict-prototypes -Wdeclaration-after-statement -Wno-unused-but-set-variable 
-Wno-unused-local-typedefs -O1 -fno-omit-frame-pointer -nostdinc -fno-builtin 
-fno-common -Werror -Wredundant-decls -Wno-pointer-arith -Wvla -pipe -D__XEN__ 
-include /local/home/sheep/work/xen/xen/include/xen/config.h 
'-D__OBJECT_FILE__="efi/relocs-dummy.o"' -Wa,--strip-local-absolute -g -MMD -MF 
efi/.relocs-dummy.o.d -DXEN_BUILD_EFI -I/local/home/sheep/work/xen/xen/include 
-I/local/home/sheep/work/xen/xen/include/asm-x86/mach-generic 
-I/local/home/sheep/work/xen/xen/include/asm-x86/mach-default 
-DXEN_IMG_OFFSET=0x200000 '-D__OBJECT_LABEL__=arch$x86$efi$relocs_dummy.o' 
-msoft-float -fno-stack-protector -fno-exceptions -Wnested-externs 
-DHAVE_AS_VMX -DHAVE_AS_SSE4_2 -DHAVE_AS_EPT -DHAVE_AS_RDRAND 
-DHAVE_AS_FSGSBASE -DHAVE_AS_XSAVEOPT -DHAVE_AS_RDSEED -DHAVE_AS_CLWB 
-U__OBJECT_LABEL__ -DHAVE_AS_QUOTED_SYM 
'-D__OBJECT_LABEL__=arch/x86/efi/relocs-dummy.o' -DHAVE_AS_INVPCID 
-DHAVE_AS_NEGATIVE_TRUE -DHAVE_AS_NOPS_DIRECTIVE -mno-red-zone -fpic 
-fno-asynchronous-unwind-tables -mno-sse -mskip-rax-setup 
-DGCC_HAS_VISIBILITY_ATTRIBUTE -mindirect-branch=thunk-extern 
-mindirect-branch-register -DCONFIG_INDIRECT_THUNK -fno-jump-tables 
-mpreferred-stack-boundary=3 -Wa,-I/local/home/sheep/work/xen/xen/include 
-DBUILD_ID_EFI -c efi/relocs-dummy.S -o efi/relocs-dummy.o

$ gcc --version
gcc (GCC) 9.2.0

I'm guessing that gcc behave differently between both our system?
On mine, `man gcc` seems to imply there's nothing wrong on my system.
If we want gcc to produce "efi/reloc-dummy.o: .." on my system, I think
we would need to add the -MT or -MQ option to the cflags.

Cheers,

-- 
Anthony PERARD

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