BPF: Add more relocation kinds

Currently, BPF only contains three relocations: R_BPF_NONE for no relocation R_BPF_64_64 for LD_imm64 and normal 64-bit data relocation R_BPF_64_32 for call insn and normal 32-bit data relocation Also .BTF and .BTF.ext sections contain symbols in allocated program and data sections. These two sections reserved 32bit space to hold the offset relative to the symbol's section. When LLVM JIT is used, the LLVM ExecutionEngine RuntimeDyld may attempt to resolve relocations for .BTF and .BTF.ext, which we want to prevent. So we used R_BPF_NONE for such relocations. This all works fine until when we try to do linking of multiple objects. . R_BPF_64_64 handling of LD_imm64 vs. normal 64-bit data is different, so lld target->relocate() needs more context to do a correct job. . The same for R_BPF_64_32. More context is needed for lld target->relocate() to differentiate call insn vs. normal 32-bit data relocation. . Since relocations in .BTF and .BTF.ext are set to R_BPF_NONE, they will not be relocated properly when multiple .BTF/.BTF.ext sections are merged by lld. This patch intends to address this issue by adding additional relocation kinds: R_BPF_64_ABS64 for normal 64-bit data relocation R_BPF_64_ABS32 for normal 32-bit data relocation R_BPF_64_NODYLD32 for .BTF and .BTF.ext style relocations. The old R_BPF_64_{64,32} semantics: R_BPF_64_64 for LD_imm64 relocation R_BPF_64_32 for call insn relocation The existing R_BPF_64_64/R_BPF_64_32 mapping to numeric values is maintained. They are the most common use cases for bpf programs and we want to maintain backward compatibility as much as possible. ExecutionEngine RuntimeDyld BPF relocations are adjusted as well. R_BPF_64_{ABS64,ABS32} relocations will be resolved properly and other relocations will be ignored. Two tests are added for RuntimeDyld. Not handling R_BPF_64_NODYLD32 in RuntimeDyldELF.cpp will result in "Relocation type not implemented yet!" fatal error. FK_SecRel_4 usages in BPFAsmBackend.cpp and BPFELFObjectWriter.cpp are removed as they are not triggered in BPF backend. BPF backend used FK_SecRel_8 for LD_imm64 instruction operands. Differential Revision: https://reviews.llvm.org/D102712
llvm · May 25, 2021 · 6a2ea84 · 6a2ea84
1 parent 993f38d
commit 6a2ea84
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Showing 12 changed files with 215 additions and 19 deletions.
diff --git a/llvm/include/llvm/BinaryFormat/ELFRelocs/BPF.def b/llvm/include/llvm/BinaryFormat/ELFRelocs/BPF.def
@@ -5,4 +5,7 @@
 // No relocation
 ELF_RELOC(R_BPF_NONE,        0)
 ELF_RELOC(R_BPF_64_64,       1)
+ELF_RELOC(R_BPF_64_ABS64,    2)
+ELF_RELOC(R_BPF_64_ABS32,    3)
+ELF_RELOC(R_BPF_64_NODYLD32, 4)
 ELF_RELOC(R_BPF_64_32,      10)
diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
@@ -951,14 +951,17 @@ void RuntimeDyldELF::resolveBPFRelocation(const SectionEntry &Section,
     report_fatal_error("Relocation type not implemented yet!");
     break;
   case ELF::R_BPF_NONE:
+  case ELF::R_BPF_64_64:
+  case ELF::R_BPF_64_32:
+  case ELF::R_BPF_64_NODYLD32:
     break;
-  case ELF::R_BPF_64_64: {
+  case ELF::R_BPF_64_ABS64: {
     write(isBE, Section.getAddressWithOffset(Offset), Value + Addend);
     LLVM_DEBUG(dbgs() << "Writing " << format("%p", (Value + Addend)) << " at "
                       << format("%p\n", Section.getAddressWithOffset(Offset)));
     break;
   }
-  case ELF::R_BPF_64_32: {
+  case ELF::R_BPF_64_ABS32: {
     Value += Addend;
     assert(Value <= UINT32_MAX);
     write(isBE, Section.getAddressWithOffset(Offset), static_cast<uint32_t>(Value));

diff --git a/llvm/lib/Target/BPF/MCTargetDesc/BPFAsmBackend.cpp b/llvm/lib/Target/BPF/MCTargetDesc/BPFAsmBackend.cpp
@@ -63,7 +63,7 @@ void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                                MutableArrayRef<char> Data, uint64_t Value,
                                bool IsResolved,
                                const MCSubtargetInfo *STI) const {
-  if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
+  if (Fixup.getKind() == FK_SecRel_8) {
     // The Value is 0 for global variables, and the in-section offset
     // for static variables. Write to the immediate field of the inst.
     assert(Value <= UINT32_MAX);

diff --git a/llvm/lib/Target/BPF/MCTargetDesc/BPFELFObjectWriter.cpp b/llvm/lib/Target/BPF/MCTargetDesc/BPFELFObjectWriter.cpp
@@ -43,12 +43,13 @@ unsigned BPFELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
   default:
     llvm_unreachable("invalid fixup kind!");
   case FK_SecRel_8:
+    // LD_imm64 instruction.
     return ELF::R_BPF_64_64;
   case FK_PCRel_4:
-  case FK_SecRel_4:
+    // CALL instruction.
     return ELF::R_BPF_64_32;
   case FK_Data_8:
-    return ELF::R_BPF_64_64;
+    return ELF::R_BPF_64_ABS64;
   case FK_Data_4:
     if (const MCSymbolRefExpr *A = Target.getSymA()) {
       const MCSymbol &Sym = A->getSymbol();
@@ -63,23 +64,22 @@ unsigned BPFELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
         if (Sym.isTemporary()) {
           // .BTF.ext generates FK_Data_4 relocations for
           // insn offset by creating temporary labels.
-          // The insn offset is within the code section and
-          // already been fulfilled by applyFixup(). No
-          // further relocation is needed.
           // The reloc symbol should be in text section.
+          // Use a different relocation to instruct ExecutionEngine
+          // RuntimeDyld not to do relocation for it, yet still to
+          // allow lld to do proper adjustment when merging sections.
           if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR))
-            return ELF::R_BPF_NONE;
+            return ELF::R_BPF_64_NODYLD32;
         } else {
           // .BTF generates FK_Data_4 relocations for variable
-          // offset in DataSec kind. Similar to the above .BTF.ext
-          // insn offset, no further relocation is needed.
+          // offset in DataSec kind.
           // The reloc symbol should be in data section.
           if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_WRITE))
-            return ELF::R_BPF_NONE;
+            return ELF::R_BPF_64_NODYLD32;
         }
       }
     }
-    return ELF::R_BPF_64_32;
+    return ELF::R_BPF_64_ABS32;
   }
 }
 

diff --git a/llvm/test/CodeGen/BPF/reloc-2.ll b/llvm/test/CodeGen/BPF/reloc-2.ll
@@ -0,0 +1,60 @@
+; RUN: llc -march=bpfel -filetype=obj -o %t.el < %s
+; RUN: llvm-objdump -r %t.el | FileCheck --check-prefix=RELOC %s
+; RUN: llvm-objdump -d --no-show-raw-insn %t.el | FileCheck --check-prefix=DUMP %s
+; RUN: llc -march=bpfeb -filetype=obj -o %t.eb < %s
+; RUN: llvm-objdump -r %t.eb | FileCheck --check-prefix=RELOC %s
+; RUN: llvm-objdump -d --no-show-raw-insn %t.eb | FileCheck --check-prefix=DUMP %s
+
+; source code:
+;   static __attribute__((noinline)) __attribute__((section("sec1")))
+;   int add(int a, int b) {
+;     return a + b;
+;   }
+;   static __attribute__((noinline))
+;   int sub(int a, int b) {
+;     return a - b;
+;   }
+;   int test(int a, int b) {
+;     return add(a, b) + sub(a, b);
+;   }
+; compilation flag:
+;   clang -target bpf -O2 -emit-llvm -S test.c
+
+define dso_local i32 @test(i32 %a, i32 %b) local_unnamed_addr #0 {
+entry:
+  %call = tail call fastcc i32 @add(i32 %a, i32 %b)
+  %call1 = tail call fastcc i32 @sub(i32 %a, i32 %b)
+  %add = add nsw i32 %call1, %call
+  ret i32 %add
+}
+
+define internal fastcc i32 @add(i32 %a, i32 %b) unnamed_addr #1 section "sec1" {
+entry:
+  %add = add nsw i32 %b, %a
+  ret i32 %add
+}
+
+; Function Attrs: nofree noinline norecurse nosync nounwind readnone willreturn mustprogress
+define internal fastcc i32 @sub(i32 %a, i32 %b) unnamed_addr #1 {
+entry:
+  %sub = sub nsw i32 %a, %b
+  ret i32 %sub
+}
+
+; DUMP:       .text:
+; DUMP-EMPTY:
+; DUMP-NEXT:  <test>
+; DUMP-NEXT:  r[[#]] = r[[#]]
+; DUMP-NEXT:  r[[#]] = r[[#]]
+; DUMP-NEXT:  call -1
+
+; DUMP:       sec1:
+; DUMP-EMPTY:
+; DUMP-NEXT:  <add>
+
+; RELOC:      RELOCATION RECORDS FOR [.text]:
+; RELOC:      R_BPF_64_32            sec1
+; RELOC-NOT:  R_BPF_64_32
+
+attributes #0 = { nofree norecurse nosync nounwind readnone willreturn mustprogress "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+attributes #1 = { nofree noinline norecurse nosync nounwind readnone willreturn mustprogress "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
diff --git a/llvm/test/CodeGen/BPF/reloc-3.ll b/llvm/test/CodeGen/BPF/reloc-3.ll
@@ -0,0 +1,25 @@
+; RUN: llc -march=bpfel -filetype=obj -o %t.el < %s
+; RUN: llvm-readelf -r %t.el | FileCheck %s
+; RUN: llc -march=bpfeb -filetype=obj -o %t.eb < %s
+; RUN: llvm-readelf -r %t.eb | FileCheck %s
+
+; source code:
+;   int g() { return 0; }
+;   struct t { void *p; } gbl = { g };
+; compilation flag:
+;   clang -target bpf -O2 -emit-llvm -S test.c
+
+%struct.t = type { i8* }
+
+@gbl = dso_local local_unnamed_addr global %struct.t { i8* bitcast (i32 ()* @g to i8*) }, align 8
+
+; CHECK: '.rel.data'
+; CHECK: 0000000000000000  0000000200000002 R_BPF_64_ABS64         0000000000000000 g
+
+; Function Attrs: nofree norecurse nosync nounwind readnone willreturn mustprogress
+define dso_local i32 @g() #0 {
+entry:
+  ret i32 0
+}
+
+attributes #0 = { nofree norecurse nosync nounwind readnone willreturn mustprogress "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
diff --git a/llvm/test/CodeGen/BPF/reloc-btf-2.ll b/llvm/test/CodeGen/BPF/reloc-btf-2.ll
@@ -23,8 +23,8 @@ define dso_local i32 @test() local_unnamed_addr #0 !dbg !14 {
 
 ; CHECK-RELOC: file format elf64-bpf
 ; CHECK-RELOC: RELOCATION RECORDS FOR [.BTF]:
-; CHECK-RELOC: R_BPF_NONE .bss
-; CHECK-RELOC: R_BPF_NONE g
+; CHECK-RELOC: R_BPF_64_NODYLD32 .bss
+; CHECK-RELOC: R_BPF_64_NODYLD32 g
 ; CHECK-RELOC: RELOCATION RECORDS FOR [.BTF.ext]:
 
 attributes #0 = { norecurse nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "frame-pointer"="all" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }

diff --git a/llvm/test/CodeGen/BPF/reloc-btf.ll b/llvm/test/CodeGen/BPF/reloc-btf.ll
@@ -8,10 +8,10 @@ entry:
 
 ; CHECK-RELOC: file format elf64-bpf
 ; CHECK-RELOC: RELOCATION RECORDS FOR [.debug_info]:
-; CHECK-RELOC: R_BPF_64_32 .debug_abbrev
-; CHECK-RELOC: R_BPF_64_64 .text
+; CHECK-RELOC: R_BPF_64_ABS32 .debug_abbrev
+; CHECK-RELOC: R_BPF_64_ABS64 .text
 ; CHECK-RELOC: RELOCATION RECORDS FOR [.BTF.ext]:
-; CHECK-RELOC: R_BPF_NONE .text
+; CHECK-RELOC: R_BPF_64_NODYLD32 .text
 
 attributes #0 = { norecurse nounwind readnone "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "frame-pointer"="all" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
 

diff --git a/llvm/test/CodeGen/BPF/reloc.ll b/llvm/test/CodeGen/BPF/reloc.ll
@@ -34,7 +34,7 @@ define i32 @bpf_prog1(%struct.bpf_context* nocapture %ctx) #0 section "events/ne
 
 ; CHECK-RELOC: file format elf64-bpf
 ; CHECK-RELOC: RELOCATION RECORDS FOR [.eh_frame]:
-; CHECK-RELOC: R_BPF_64_64 events/net/netif_receive_skb
+; CHECK-RELOC: R_BPF_64_ABS64 events/net/netif_receive_skb
 }
 
 ; Function Attrs: nounwind

diff --git a/llvm/test/ExecutionEngine/RuntimeDyld/BPF/abs64-relocation.s b/llvm/test/ExecutionEngine/RuntimeDyld/BPF/abs64-relocation.s
@@ -0,0 +1,26 @@
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: llvm-mc -triple=bpfel -filetype=obj -o %t/test_reloc_abs64.o %s
+# RUN: llvm-rtdyld -triple=bpfel -verify -check=%s %t/test_reloc_abs64.o
+
+# test R_BPF_64_ABS64 which should have relocation resolved properly.
+
+	.text
+	.file	"t1.c"
+	.globl	g                               # -- Begin function g
+	.p2align	3
+	.type	g,@function
+g:                                      # @g
+	r0 = 0
+	exit
+.Lfunc_end0:
+	.size	g, .Lfunc_end0-g
+                                        # -- End function
+	.type	gbl,@object                     # @gbl
+	.data
+	.globl	gbl
+	.p2align	3
+gbl:
+	.quad	g
+	.size	gbl, 8
+
+# rtdyld-check: *{8}gbl = section_addr(test_reloc_abs64.o, .text)
diff --git a/llvm/test/ExecutionEngine/RuntimeDyld/BPF/lit.local.cfg b/llvm/test/ExecutionEngine/RuntimeDyld/BPF/lit.local.cfg
@@ -0,0 +1,2 @@
+if not 'BPF' in config.root.targets:
+    config.unsupported = True
diff --git a/llvm/test/ExecutionEngine/RuntimeDyld/BPF/nodyld32-64-relocations.s b/llvm/test/ExecutionEngine/RuntimeDyld/BPF/nodyld32-64-relocations.s
@@ -0,0 +1,77 @@
+# RUN: llvm-mc -triple=bpfel -filetype=obj -o %t %s
+# RUN: llvm-rtdyld -triple=bpfel -verify -check=%s %t
+
+# test R_BPF_64_64 and R_BPF_64_NODYLD32 relocations, both should be ignored.
+
+	.globl	_main
+	.p2align	3
+	.type	_main,@function
+_main:                                  # @_main
+	r1 = a ll
+
+# rtdyld-check: decode_operand(_main, 1)[31:0] = 0x0
+
+	r0 = *(u32 *)(r1 + 0)
+	exit
+.Lfunc_end0:
+	.size	_main, .Lfunc_end0-_main
+                                        # -- End function
+
+	.type	a,@object                       # @a
+	.section	.bss,"aw",@nobits
+	.globl	a
+	.p2align	2
+a:
+	.long	0                               # 0x0
+	.size	a, 4
+
+# rtdyld-check: *{4}a = 0
+
+	.section	.BTF,"",@progbits
+	.short	60319                           # 0xeb9f
+	.byte	1
+	.byte	0
+	.long	24
+	.long	0
+	.long	80
+	.long	80
+	.long	87
+	.long	0                               # BTF_KIND_FUNC_PROTO(id = 1)
+	.long	218103808                       # 0xd000000
+	.long	2
+	.long	1                               # BTF_KIND_INT(id = 2)
+	.long	16777216                        # 0x1000000
+	.long	4
+	.long	16777248                        # 0x1000020
+	.long	5                               # BTF_KIND_FUNC(id = 3)
+	.long	201326593                       # 0xc000001
+	.long	1
+	.long	80                              # BTF_KIND_VAR(id = 4)
+	.long	234881024                       # 0xe000000
+	.long	2
+	.long	1
+	.long	82                              # BTF_KIND_DATASEC(id = 5)
+	.long	251658241                       # 0xf000001
+	.long	0
+	.long	4
+btf_a:
+	.long	a
+
+# rtdyld-check: *{4}btf_a = 0
+
+	.long	4
+	.byte	0                               # string offset=0
+	.ascii	"int"                           # string offset=1
+	.byte	0
+	.ascii	"_main"                         # string offset=5
+	.byte	0
+	.ascii	".text"                         # string offset=11
+	.byte	0
+	.ascii	"/home/yhs/work/tests/llvm/rtdyld/t.c" # string offset=17
+	.byte	0
+	.ascii	"int _main() { return a; }"     # string offset=54
+	.byte	0
+	.byte	97                              # string offset=80
+	.byte	0
+	.ascii	".bss"                          # string offset=82
+	.byte	0