Date: Sat, 7 Jan 2017 14:07:33 -0800 From: Mark Millard <markmi@dsl-only.net> To: Roman Divacky <rdivacky@vlakno.cz>, Ed Maste <emaste@freebsd.org> Cc: Justin Hibbits <chmeeedalf@gmail.com>, Nathan Whitehorn <nwhitehorn@freebsd.org>, FreeBSD Toolchain <freebsd-toolchain@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: clang 3.9.0 buildkernel on old powerpc64's vs. trying to build hwpmc_e500.o and the like. . . [Actually .__start code failure vs. working and R_PPC64_ADDR16_DS vs. R_PPC64_TOC16_DS] Message-ID: <2B5FDD60-4D8B-4803-B59C-3C569BA36E68@dsl-only.net> In-Reply-To: <20170107085126.GA82107@vlakno.cz> References: <D3DE2D12-9885-4154-B680-6DA5A8B62A56@dsl-only.net> <D9C54972-8D21-4D55-A707-4FFC2BDCD9FE@dsl-only.net> <20161207190057.GA58950@vlakno.cz> <E1376C20-C1BD-418D-81C6-CDDE479342CA@dsl-only.net> <CE88C1F4-B9BD-4D45-8DF0-F1079C3257A5@dsl-only.net> <20161208185541.GA33364@vlakno.cz> <E49F7EE4-7A62-4601-98DC-4C4791B7158D@dsl-only.net> <20161208221452.GA42380@vlakno.cz> <20161212210922.GA27403@vlakno.cz> <613BB28B-46F1-4959-B576-C8AD42A21200@dsl-only.net> <20170107085126.GA82107@vlakno.cz>
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On 2017-Jan-7, at 12:51 AM, Roman Divacky <rdivacky at vlakno.cz> wrote: > That's a great progress. Can you produce minimal self contained test = case that > exhibits this bug? And submit it to llvm bugzilla? >=20 > Also, clang3.9 defaults to using it's own internal asm, what happens = if you > add -no-integrated-as to CFLAGS and recompile the kernel? That should = remove > this llvm assembly problem. Does it boot? >=20 > Thanks Mark, really great progress. >=20 > Roman In attempting this I found how to control the behavior based on the assembler notation @toc being missing vs. being present. If llvm should change is strongly tied to llvm's criteria for gcc compatibility relative to filling-in/defaulting omitted @toc's in the assembler notation. FreeBSD has the option of always being explicit with @toc in order to avoid differences in handling of omitted notation. So I've no clue if FreebSD wants to claim that a llvm change is a requirement for using clang as the powerpc64 system compiler. [The issue of the distinction is submittable to llvm either way.] Details. . . For: .section ".toc","aw" tmpstk.L: .tc tmpstk[TC],tmpstk . . . /* Set up the stack pointer */ ld %r1,tmpstk.L(%r2) using devel/powerpc64-gcc gets: # /usr/local/bin/powerpc64-unknown-freebsd12.0-gcc \ = = = -c \ = = = = -x assembler-with-cpp \ = = = = -pipe \ = = = = locore64_simplified.S locore64_simplified.S: Assembler messages: locore64_simplified.S:80: Warning: assuming @toc on symbol and produces (with R_PPC64_TOC16_DS for .toc): # /usr/local/powerpc64-freebsd/bin/objdump -r locore64_simplified.o locore64_simplified.o: file format elf64-powerpc-freebsd RELOCATION RECORDS FOR [.text]: OFFSET TYPE VALUE=20 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000 0000000000000046 R_PPC64_TOC16_DS .toc RELOCATION RECORDS FOR [.toc]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 tmpstk RELOCATION RECORDS FOR [.opd]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 .__start 0000000000000008 R_PPC64_TOC *ABS* By contrast clang is silent (cross compiler used): # = /usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp/usr/bin/= cc \ = = -target = powerpc64-unknown-freebsd12.0 \ = = = = --sysroot=3D/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/= tmp \ = = = -B/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp/usr/bi= n \ = = -c \ = = = = -x assembler-with-cpp \ = = = = -pipe \ = = = = locore64_simplified.S and produces code with R_PPC64_ADDR16_DS for the .toc instead: # /usr/local/powerpc64-freebsd/bin/objdump -r locore64_simplified.o | = more = = =20 locore64_simplified.o: file format elf64-powerpc-freebsd RELOCATION RECORDS FOR [.text]: OFFSET TYPE VALUE=20 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000 0000000000000046 R_PPC64_ADDR16_DS .toc RELOCATION RECORDS FOR [.toc]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 tmpstk RELOCATION RECORDS FOR [.opd]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 .__start 0000000000000008 R_PPC64_TOC *ABS* But for: .section ".toc","aw" tmpstk.L: .tc tmpstk[TC],tmpstk . . . /* Set up the stack pointer */ ld %r1,tmpstk.L@toc(%r2) (note the @toc notation) both compilers agree and use R_PPC64_TOC16_DS for the .toc: # /usr/local/bin/powerpc64-unknown-freebsd12.0-gcc \ = = = -c \ = = = = -x assembler-with-cpp \ = = = = -pipe \ = = = = locore64_simplified.S # /usr/local/powerpc64-freebsd/bin/objdump -r locore64_simplified.o | = more = = =20 locore64_simplified.o: file format elf64-powerpc-freebsd RELOCATION RECORDS FOR [.text]: OFFSET TYPE VALUE=20 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000 0000000000000046 R_PPC64_TOC16_DS .toc RELOCATION RECORDS FOR [.toc]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 tmpstk RELOCATION RECORDS FOR [.opd]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 .__start 0000000000000008 R_PPC64_TOC *ABS* # = /usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp/usr/bin/= cc \ = = -target = powerpc64-unknown-freebsd12.0 \ = = = = --sysroot=3D/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/= tmp \ = = = -B/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp/usr/bi= n \ = = -c \ = = = = -x assembler-with-cpp \ = = = = -pipe \ = = = = locore64_simplified.S # /usr/local/powerpc64-freebsd/bin/objdump -r locore64_simplified.o | = more = = =20 locore64_simplified.o: file format elf64-powerpc-freebsd RELOCATION RECORDS FOR [.text]: OFFSET TYPE VALUE=20 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000 0000000000000046 R_PPC64_TOC16_DS .toc RELOCATION RECORDS FOR [.toc]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 tmpstk RELOCATION RECORDS FOR [.opd]: OFFSET TYPE VALUE=20 0000000000000000 R_PPC64_ADDR64 .__start 0000000000000008 R_PPC64_TOC *ABS* I omitted "-f -gdwarf-2" to simplify things but with such clang complains about: locore64_simplified.S:36:2: warning: DWARF2 only supports one section = per compilation unit .section ".toc","aw" ^ locore64_simplified.S:47:2: warning: DWARF2 only supports one section = per compilation unit .section ".opd","aw" ^ (buildkernel gets such messages.) I expect I can simplify the .S code more than I have so far but I figured I'd report the discovery of the choice FreeBSD needs to make for powerpc64 for if llvm changes are to be required vs. not. =3D=3D=3D Mark Millard markmi at dsl-only.net
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