forked from OSchip/llvm-project
lldb: Add support for R_386_32 relocations to ObjectFileELF
I encountered an issue where `p &variable` was finding an incorrect address for 32-bit PIC ELF files loaded into a running process. The problem was that the R_386_32 ELF relocations were not being applied to the DWARF section, so all variables in that file were reporting as being at the start of their respective section. There is an assert that catches this on debug builds, but silently ignores the issue on non-debug builds. In this changeset, I added handling for the R_386_32 relocation type to ObjectFileELF, and a supporting function to ELFRelocation to differentiate between DT_REL & DT_RELA in ObjectFileELF::ApplyRelocations(). Demonstration of issue: ``` [dmlary@host work]$ cat rel.c volatile char padding[32] = "make sure var isnt at .data+0"; volatile char var[] = "test"; [dmlary@host work]$ gcc -c rel.c -FPIC -fpic -g -m32 [dmlary@host work]$ lldb ./exec (lldb) target create "./exec" Current executable set to '/home/dmlary/src/work/exec' (i386). (lldb) process launch --stop-at-entry Process 21278 stopped * thread #1, name = 'exec', stop reason = signal SIGSTOP frame #0: 0xf7fdb150 ld-2.17.so`_start ld-2.17.so`_start: -> 0xf7fdb150 <+0>: movl %esp, %eax 0xf7fdb152 <+2>: calll 0xf7fdb990 ; _dl_start ld-2.17.so`_dl_start_user: 0xf7fdb157 <+0>: movl %eax, %edi 0xf7fdb159 <+2>: calll 0xf7fdb140 Process 21278 launched: '/home/dmlary/src/work/exec' (i386) (lldb) image add ./rel.o (lldb) image load --file rel.o .text 0x40000000 .data 0x50000000 section '.text' loaded at 0x40000000 section '.data' loaded at 0x50000000 (lldb) image dump symtab rel.o Symtab, file = rel.o, num_symbols = 13: Debug symbol |Synthetic symbol ||Externally Visible ||| Index UserID DSX Type File Address/Value Load Address Size Flags Name ------- ------ --- --------------- ------------------ ------------------ ------------------ ---------- ---------------------------------- [ 0] 1 SourceFile 0x0000000000000000 0x0000000000000000 0x00000004 rel.c [ 1] 2 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 2] 3 Invalid 0x0000000000000000 0x50000000 0x0000000000000020 0x00000003 [ 3] 4 Invalid 0x0000000000000025 0x0000000000000000 0x00000003 [ 4] 5 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 5] 6 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 6] 7 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 7] 8 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 8] 9 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 9] 10 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 10] 11 Invalid 0x0000000000000000 0x0000000000000020 0x00000003 [ 11] 12 X Data 0x0000000000000000 0x50000000 0x0000000000000020 0x00000011 padding [ 12] 13 X Data 0x0000000000000020 0x50000020 0x0000000000000005 0x00000011 var (lldb) p &var (volatile char (*)[5]) $1 = 0x50000000 ``` Reviewed By: labath Differential Revision: https://reviews.llvm.org/D132954
This commit is contained in:
David M. Lary
Pavel Labath
parent
d3649c2be4
commit
f4fc405631
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@ -121,6 +121,8 @@ public:
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static unsigned RelocAddend64(const ELFRelocation &rel);
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bool IsRela() { return (reloc.is<ELFRela *>()); }
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private:
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typedef llvm::PointerUnion<ELFRel *, ELFRela *> RelocUnion;
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@ -2597,25 +2599,46 @@ unsigned ObjectFileELF::ApplyRelocations(
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}
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for (unsigned i = 0; i < num_relocations; ++i) {
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if (!rel.Parse(rel_data, &offset))
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if (!rel.Parse(rel_data, &offset)) {
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GetModule()->ReportError(".rel%s[%d] failed to parse relocation",
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rel_section->GetName().AsCString(), i);
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break;
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}
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Symbol *symbol = nullptr;
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if (hdr->Is32Bit()) {
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switch (reloc_type(rel)) {
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case R_386_32:
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symbol = symtab->FindSymbolByID(reloc_symbol(rel));
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if (symbol) {
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addr_t f_offset =
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rel_section->GetFileOffset() + ELFRelocation::RelocOffset32(rel);
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DataBufferSP &data_buffer_sp = debug_data.GetSharedDataBuffer();
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// ObjectFileELF creates a WritableDataBuffer in CreateInstance.
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WritableDataBuffer *data_buffer =
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llvm::cast<WritableDataBuffer>(data_buffer_sp.get());
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uint32_t *dst = reinterpret_cast<uint32_t *>(
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data_buffer->GetBytes() + f_offset);
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addr_t value = symbol->GetAddressRef().GetFileAddress();
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if (rel.IsRela()) {
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value += ELFRelocation::RelocAddend32(rel);
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} else {
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value += *dst;
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}
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*dst = value;
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} else {
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GetModule()->ReportError(".rel%s[%u] unknown symbol id: %d",
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rel_section->GetName().AsCString(), i,
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reloc_symbol(rel));
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}
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break;
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case R_386_PC32:
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default:
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// FIXME: This asserts with this input:
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//
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// foo.cpp
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// int main(int argc, char **argv) { return 0; }
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//
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// clang++.exe --target=i686-unknown-linux-gnu -g -c foo.cpp -o foo.o
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//
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// and running this on the foo.o module.
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assert(false && "unexpected relocation type");
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GetModule()->ReportError("unsupported 32-bit relocation:"
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" .rel%s[%u], type %u",
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rel_section->GetName().AsCString(), i,
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reloc_type(rel));
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}
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} else {
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switch (reloc_type(rel)) {
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@ -0,0 +1,57 @@
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# RUN: yaml2obj %s -o %t
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# RUN: lldb-test object-file --contents %t | FileCheck %s
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#
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# CHECK-LABEL: Name: .debug_info
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# CHECK: Data: (
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# CHECK-NEXT: 0000: 22222222
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#
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# CHECK-LABEL: Name: .debug_lines
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# CHECK: Data: (
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# CHECK-NEXT: 0000: 33333333
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--- !ELF
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FileHeader:
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Class: ELFCLASS32
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Data: ELFDATA2LSB
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Type: ET_REL
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Machine: EM_386
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Sections:
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- Name: .data
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Type: SHT_PROGBITS
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Flags: [ SHF_WRITE, SHF_ALLOC ]
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AddressAlign: 0x20
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- Name: .debug_info
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Type: SHT_PROGBITS
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AddressAlign: 0x1
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Content: 11111111
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- Name: .debug_lines
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Type: SHT_PROGBITS
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AddressAlign: 0x1
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Content: 99999999
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- Name: .rel.debug_info
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Type: SHT_REL
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Flags: [ SHF_INFO_LINK ]
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Link: .symtab
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AddressAlign: 0x0
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Info: .debug_info
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Relocations:
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- Offset: 0x0
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Symbol: var
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Type: R_386_32
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- Name: .rela.debug_lines
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Type: SHT_RELA
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Link: .symtab
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AddressAlign: 0x4
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Info: .debug_lines
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Relocations:
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- Offset: 0x0
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Addend: 0x22222222
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Symbol: var
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Type: R_386_32
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Symbols:
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- Name: var
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Type: STT_OBJECT
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Section: .data
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Binding: STB_GLOBAL
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Value: 0x11111111
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Size: 0x5
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...
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