[ELF][PowerPC] Support R_PPC_COPY and R_PPC64_COPY

[merge_guards_bot]

Unit tests: pass. 62087 tests passed, 0 failed and 784 were skipped.

clang-tidy: pass.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[jhenderson]

lld/test/ELF/ppc64-reloc-copy.s

1 ↗

(On Diff #239785)

Does it make sense to fold this and the other test together? They're practically identical...

llvm/include/llvm/BinaryFormat/ELFRelocs/PowerPC64.def

30

I think you need an undef here, right?

[MaskRay]

Address review comments

[Bdragon28]

For anyone who is curious about this, copy relocations are especially needed on powerpc32, where they are used to implement global data (such as sharing a pointer between a .so and the main program) in situations where the main program's copy lives in .bss.

Given that FreeBSD libc's API uses this extensively for things such as providing stderr in stdio, this fix is critical on ppc32, as the lack of it prevents anything more complex than /bin/echo from running without crashing due to dereferencing a null pointer.

I am currently running though a powerpc32 buildworld and testing on a G4 so I can see just how much closer that gets us to switching FreeBSD powerpc32 to lld.

On PPC64, the need for copy relocations is much reduced, as generally things go through the TOC in the first place (when using PIC), so it is sufficient to generate an R_PPC64_ADDR64 relocation against the TOC entry, instead of a copy relocation against an offset into .bss.

[merge_guards_bot]

Unit tests: fail. 62137 tests passed, 5 failed and 811 were skipped.

failed: libc++.std/language_support/cmp/cmp_partialord/partialord.pass.cpp
failed: libc++.std/language_support/cmp/cmp_strongeq/cmp.strongeq.pass.cpp
failed: libc++.std/language_support/cmp/cmp_strongord/strongord.pass.cpp
failed: libc++.std/language_support/cmp/cmp_weakeq/cmp.weakeq.pass.cpp
failed: libc++.std/language_support/cmp/cmp_weakord/weakord.pass.cpp

clang-tidy: pass.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[grimar]

Aside from a minor nit I have no more comments, looks fine to me.

lld/test/ELF/ppc-reloc-copy.s

10

It was a bit strange to see t1 again.
I'd suggest to rename t1.o, t1.so, t.o and t to something else.
Perhaps use ppc/ppc64 suffixes somewhere?

[MaskRay]

%t1 -> %t1.32 / %t1.64

[MaskRay]

lld/test/ELF/ppc64-reloc-copy.s

1 ↗

(On Diff #239785)

Agree.

Placed in ppc-reloc-copy.s

[merge_guards_bot]

Unit tests: fail. 62153 tests passed, 5 failed and 811 were skipped.

failed: libc++.std/language_support/cmp/cmp_partialord/partialord.pass.cpp
failed: libc++.std/language_support/cmp/cmp_strongeq/cmp.strongeq.pass.cpp
failed: libc++.std/language_support/cmp/cmp_strongord/strongord.pass.cpp
failed: libc++.std/language_support/cmp/cmp_weakeq/cmp.weakeq.pass.cpp
failed: libc++.std/language_support/cmp/cmp_weakord/weakord.pass.cpp

clang-tidy: fail. clang-tidy found 0 errors and 1 warnings. 0 of them are added as review comments below (why?).

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[jhenderson]

LGTM, but as I'm a bit rusty on some parts of LLD, and know very little about PPC, I can't be particularly confident about the LLD-aspects of this change, so it's probably worth somebody else confirming.

[grimar]

LGTM. I know nothing about PPC. From LLD code POV this looks fine.

[sfertile]

LGTM.

[Bdragon28]

While I ran into further problems on ppc32, I think it's just because there are further problems on ppc32 (unrelated to this one). At the very least this gets FreeBSD ppc32/lld10 as far as the rescue shell, which is great progress!

[MaskRay]

Thanks to everyone for review!

Cherry picked the commit to release/10.x as f1dab29908d25a4044abff6ffc120c48b20f034d

lld/ELF/Arch/PPC.cpp

void writePPC32GlinkSection(uint8_t *buf, size_t numEntries) {
   }
 
   // Pad with nop. They should not be executed.
   for (; buf < end; buf += 4)
     write32(buf, 0x60000000);
 }
 
 PPC::PPC() {
+  copyRel = R_PPC_COPY;
   gotRel = R_PPC_GLOB_DAT;
   noneRel = R_PPC_NONE;
   pltRel = R_PPC_JMP_SLOT;
   relativeRel = R_PPC_RELATIVE;
   iRelativeRel = R_PPC_IRELATIVE;
   symbolicRel = R_PPC_ADDR32;
   gotBaseSymInGotPlt = false;
   gotHeaderEntriesNum = 3;

lld/ELF/Arch/PPC64.cpp

static void writeFromHalf16(uint8_t *loc, uint32_t insn) {
   write32(config->isLE ? loc : loc - 2, insn);
 }
 
 static uint32_t readFromHalf16(const uint8_t *loc) {
   return read32(config->isLE ? loc : loc - 2);
 }
 
 PPC64::PPC64() {
+  copyRel = R_PPC64_COPY;
   gotRel = R_PPC64_GLOB_DAT;
   noneRel = R_PPC64_NONE;
   pltRel = R_PPC64_JMP_SLOT;
   relativeRel = R_PPC64_RELATIVE;
   iRelativeRel = R_PPC64_IRELATIVE;
   symbolicRel = R_PPC64_ADDR64;
   pltHeaderSize = 60;
   pltEntrySize = 4;

lld/test/ELF/ppc-reloc-copy.s

+# REQUIRES: ppc
+# RUN: llvm-mc -filetype=obj -triple=powerpc %p/Inputs/relocation-copy.s -o %t1.32.o
+# RUN: ld.lld -shared %t1.32.o -soname=so -o %t1.32.so
+# RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.32.o
+# RUN: ld.lld %t.32.o %t1.32.so -o %t.32
+# RUN: llvm-readobj -r %t.32 | FileCheck --check-prefix=REL32 %s
+# RUN: llvm-nm -S %t.32 | FileCheck --check-prefix=NM32 %s
+
+# RUN: llvm-mc -filetype=obj -triple=powerpc64 %p/Inputs/relocation-copy.s -o %t1.64.o
+# RUN: ld.lld -shared %t1.64.o -soname=so -o %t1.64.so
+# RUN: llvm-mc -filetype=obj -triple=powerpc64 %s -o %t.64.o
+# RUN: ld.lld %t.64.o %t1.64.so -o %t.64
+# RUN: llvm-readobj -r %t.64 | FileCheck --check-prefix=REL64 %s
+# RUN: llvm-nm -S %t.64 | FileCheck --check-prefix=NM64 %s
+
+# REL32:      .rela.dyn {
+# REL32-NEXT:   0x10030210 R_PPC_COPY x 0x0
+# REL32-NEXT: }
+
+# NM32: 10030210 00000004 B x
+
+# REL64:      .rela.dyn {
+# REL64-NEXT:   0x10030350 R_PPC64_COPY x 0x0
+# REL64-NEXT: }
+
+# NM64: 0000000010030350 0000000000000004 B x
+
+lis 3, x@ha
+lwz 3, x@l(3)

llvm/include/llvm/BinaryFormat/ELFRelocs/PowerPC64.def

 #undef R_PPC64_REL24
 #undef R_PPC64_REL14
 #undef R_PPC64_REL14_BRTAKEN
 #undef R_PPC64_REL14_BRNTAKEN
 #undef R_PPC64_GOT16
 #undef R_PPC64_GOT16_LO
 #undef R_PPC64_GOT16_HI
 #undef R_PPC64_GOT16_HA
+#undef R_PPC64_COPY
 #undef R_PPC64_GLOB_DAT
 #undef R_PPC64_JMP_SLOT
 #undef R_PPC64_RELATIVE
 #undef R_PPC64_REL32
 #undef R_PPC64_ADDR64
 #undef R_PPC64_ADDR16_HIGHER
 #undef R_PPC64_ADDR16_HIGHERA
 #undef R_PPC64_ADDR16_HIGHEST
 #undef R_PPC64_ADDR16_HIGHESTA

 ELF_RELOC(R_PPC64_REL24,                10)
 ELF_RELOC(R_PPC64_REL14,                11)
 ELF_RELOC(R_PPC64_REL14_BRTAKEN,        12)
 ELF_RELOC(R_PPC64_REL14_BRNTAKEN,       13)
 ELF_RELOC(R_PPC64_GOT16,                14)
 ELF_RELOC(R_PPC64_GOT16_LO,             15)
 ELF_RELOC(R_PPC64_GOT16_HI,             16)
 ELF_RELOC(R_PPC64_GOT16_HA,             17)
+ELF_RELOC(R_PPC64_COPY,                 19)
 ELF_RELOC(R_PPC64_GLOB_DAT,             20)
 ELF_RELOC(R_PPC64_JMP_SLOT,             21)
 ELF_RELOC(R_PPC64_RELATIVE,             22)
 ELF_RELOC(R_PPC64_REL32,                26)
 ELF_RELOC(R_PPC64_ADDR64,               38)
 ELF_RELOC(R_PPC64_ADDR16_HIGHER,        39)
 ELF_RELOC(R_PPC64_ADDR16_HIGHERA,       40)
 ELF_RELOC(R_PPC64_ADDR16_HIGHEST,       41)

llvm/test/tools/llvm-readobj/ELF/reloc-types-elf-ppc64.test

 # CHECK: Type: R_PPC64_REL24 (10)
 # CHECK: Type: R_PPC64_REL14 (11)
 # CHECK: Type: R_PPC64_REL14_BRTAKEN (12)
 # CHECK: Type: R_PPC64_REL14_BRNTAKEN (13)
 # CHECK: Type: R_PPC64_GOT16 (14)
 # CHECK: Type: R_PPC64_GOT16_LO (15)
 # CHECK: Type: R_PPC64_GOT16_HI (16)
 # CHECK: Type: R_PPC64_GOT16_HA (17)
+# CHECK: Type: R_PPC64_COPY (19)
 # CHECK: Type: R_PPC64_GLOB_DAT (20)
 # CHECK: Type: R_PPC64_JMP_SLOT (21)
 # CHECK: Type: R_PPC64_RELATIVE (22)
 # CHECK: Type: R_PPC64_REL32 (26)
 # CHECK: Type: R_PPC64_ADDR64 (38)
 # CHECK: Type: R_PPC64_ADDR16_HIGHER (39)
 # CHECK: Type: R_PPC64_ADDR16_HIGHERA (40)
 # CHECK: Type: R_PPC64_ADDR16_HIGHEST (41)
Relocations:
         Type:   R_PPC64_GOT16
       - Offset: 0x0000000000000000
         Type:   R_PPC64_GOT16_LO
       - Offset: 0x0000000000000000
         Type:   R_PPC64_GOT16_HI
       - Offset: 0x0000000000000000
         Type:   R_PPC64_GOT16_HA
       - Offset: 0x0000000000000000
+        Type:   R_PPC64_COPY
+      - Offset: 0x0000000000000000
         Type:   R_PPC64_GLOB_DAT
       - Offset: 0x0000000000000000
         Type:   R_PPC64_JMP_SLOT
       - Offset: 0x0000000000000000
         Type:   R_PPC64_RELATIVE
       - Offset: 0x0000000000000000
         Type:   R_PPC64_REL32
       - Offset: 0x0000000000000000