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]
Mark Millard
markmi at dsl-only.net
Sat Jan 7 23:13:09 UTC 2017
[I've supplied a list of places that adding @toc notation should
make clang 3.9.1 targeting powerpc64 do the right thing for
this issue.]
On 2017-Jan-7, at 2:07 PM, Mark Millard <markmi at dsl-only.net> wrote:
> 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?
>>
>> 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?
>>
>> Thanks Mark, really great progress.
>>
>> 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
> 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000
> 0000000000000046 R_PPC64_TOC16_DS .toc
>
>
> RELOCATION RECORDS FOR [.toc]:
> OFFSET TYPE VALUE
> 0000000000000000 R_PPC64_ADDR64 tmpstk
>
>
> RELOCATION RECORDS FOR [.opd]:
> OFFSET TYPE VALUE
> 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=/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp \ -B/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp/usr/bin \
> -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
> locore64_simplified.o: file format elf64-powerpc-freebsd
>
> RELOCATION RECORDS FOR [.text]:
> OFFSET TYPE VALUE
> 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000
> 0000000000000046 R_PPC64_ADDR16_DS .toc
>
>
> RELOCATION RECORDS FOR [.toc]:
> OFFSET TYPE VALUE
> 0000000000000000 R_PPC64_ADDR64 tmpstk
>
>
> RELOCATION RECORDS FOR [.opd]:
> OFFSET TYPE VALUE
> 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 at 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
> locore64_simplified.o: file format elf64-powerpc-freebsd
>
> RELOCATION RECORDS FOR [.text]:
> OFFSET TYPE VALUE
> 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000
> 0000000000000046 R_PPC64_TOC16_DS .toc
>
>
> RELOCATION RECORDS FOR [.toc]:
> OFFSET TYPE VALUE
> 0000000000000000 R_PPC64_ADDR64 tmpstk
>
>
> RELOCATION RECORDS FOR [.opd]:
> OFFSET TYPE VALUE
> 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=/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp \ -B/usr/obj/powerpc64vtsc_clang_kernel/powerpc.powerpc64/usr/src/tmp/usr/bin \
> -c \ -x assembler-with-cpp \ -pipe \ locore64_simplified.S
>
> # /usr/local/powerpc64-freebsd/bin/objdump -r locore64_simplified.o | more
> locore64_simplified.o: file format elf64-powerpc-freebsd
>
> RELOCATION RECORDS FOR [.text]:
> OFFSET TYPE VALUE
> 0000000000000028 R_PPC64_REL64 __tocbase+0x0000000000008000
> 0000000000000046 R_PPC64_TOC16_DS .toc
>
>
> RELOCATION RECORDS FOR [.toc]:
> OFFSET TYPE VALUE
> 0000000000000000 R_PPC64_ADDR64 tmpstk
>
>
> RELOCATION RECORDS FOR [.opd]:
> OFFSET TYPE VALUE
> 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.
The following should be a list of the places that adding @toc usage
would fix some things for using clang 3.9.1 to target powerpc64:
# grep "@toc[^b]" /root/sys_typescripts/typescript_make_powerpc64vtsc_nodebug_incl_clang_xtoolchain_kernel-amd64-host-2017-01-03:23:48:41 | more
/usr/src/sys/powerpc/aim/locore64.S:102: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/aim/trap_subr64.S:320: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/aim/trap_subr64.S:797: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/ofw/ofwcall64.S:104: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/ofw/ofwcall64.S:108: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/ofw/ofwcall64.S:116: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/ofw/ofwcall64.S:226: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/ofw/ofwcall64.S:228: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/ofw/ofwcall64.S:235: Warning: assuming @toc on symbol
/usr/src/sys/powerpc/powerpc/swtch64.S:153: Warning: assuming @toc on symbol
devel/powerpc64-gcc and devel/powerpc64-binutils together happens to report
on missing @toc 's.
But, of course, if some sections of code are conditionally compiled and
excluded above they would not be listed.
===
Mark Millard
markmi at dsl-only.net
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