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symtab/elf: bound symbols by st_size to avoid misattributing stripped code #4

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Merged
def merged 2 commits into from
Aug 4, 2026
+43 −6
Merged

symtab/elf: bound symbols by st_size to avoid misattributing stripped code #4

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8b34a06
symtab/elf: bound symbols by st_size to avoid misattributing stripped…
gecube Jul 6, 2026
419b46a
symtab/elf: use end-of-symbol sentinels instead of a per-symbol Sizes…
def Aug 4, 2026
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17 changes: 14 additions & 3 deletions ebpf/symtab/elf/elf_sym.go
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,14 @@ func (f *InMemElfFile) getSymbols(typ elf.SectionType, opt *SymbolsOptions) ([]S
// if there is no such section in the File.
var ErrNoSymbols = errors.New("no symbol section")

func clampSymSize(size uint64) uint32 {
const maxU32 = uint64(^uint32(0))
if size > maxU32 {
return uint32(maxU32)
}
return uint32(size)
}

func (f *InMemElfFile) getSymbols64(typ elf.SectionType, opt *SymbolsOptions) ([]SymbolIndex, uint32, error) {
symtabSection := f.sectionByType(typ)
if symtabSection == nil {
Expand Down Expand Up @@ -88,7 +96,7 @@ func (f *InMemElfFile) getSymbols64(typ elf.SectionType, opt *SymbolsOptions) ([
//Other: rawSym[5],
//Shndx: f.ByteOrder.Uint16(rawSym[6:8]), // not used
Value: f.ByteOrder.Uint64(rawSym[8:16]),
//Size: f.ByteOrder.Uint64(rawSym[16:24]), // not used
Size: f.ByteOrder.Uint64(rawSym[16:24]),
}

if sym.Value != 0 && sym.Info&0xf == byte(elf.STT_FUNC) {
Expand All @@ -101,6 +109,7 @@ func (f *InMemElfFile) getSymbols64(typ elf.SectionType, opt *SymbolsOptions) ([
}
symbols[i].Value = pc
symbols[i].Name = NewName(sym.Name, linkIndex)
symbols[i].Size = clampSymSize(sym.Size)
i++
}
}
Expand Down Expand Up @@ -142,8 +151,8 @@ func (f *InMemElfFile) getSymbols32(typ elf.SectionType, opt *SymbolsOptions) ([
sym = elf.Sym32{
Name: f.ByteOrder.Uint32(rawSym[:4]),
Value: f.ByteOrder.Uint32(rawSym[4:8]),
//Size: f.ByteOrder.Uint32(rawSym[8:12]),
Info: rawSym[12],
Size: f.ByteOrder.Uint32(rawSym[8:12]),
Info: rawSym[12],
//Other: rawSym[13],
//Shndx: f.ByteOrder.Uint16(rawSym[14:16]),
}
Expand All @@ -156,7 +165,9 @@ func (f *InMemElfFile) getSymbols32(typ elf.SectionType, opt *SymbolsOptions) ([
if pc >= opt.FilterFrom && pc < opt.FilterTo {
continue
}
symbols[i].Value = pc
symbols[i].Name = NewName(sym.Name, linkIndex)
symbols[i].Size = sym.Size
i++
}
}
Expand Down
32 changes: 29 additions & 3 deletions ebpf/symtab/elf/symbol_table.go
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Original file line number Diff line number Diff line change
Expand Up @@ -25,8 +25,10 @@ type SymbolTableInterface interface {
}

type SymbolIndex struct {
Name Name
Value uint64
Name Name
// st_size, or 0 when unknown; build-time only (see addEndOfSymbolSentinels)
Size uint32
}

type SectionLinkIndex uint8
Expand All @@ -48,6 +50,26 @@ func (n *Name) LinkIndex() SectionLinkIndex {
return SectionLinkIndex(*n >> 31)
}

const sentinelNameIndex = 0x7fffffff

const minGapSentinel = 64

func addEndOfSymbolSentinels(all []SymbolIndex) []SymbolIndex {
out := make([]SymbolIndex, 0, len(all)+len(all)/64+1)
for i := range all {
out = append(out, all[i])
if all[i].Size == 0 {
continue
}
end := all[i].Value + uint64(all[i].Size)
if i+1 < len(all) && all[i+1].Value < end+minGapSentinel {
continue
}
out = append(out, SymbolIndex{Name: NewName(sentinelNameIndex, sectionTypeSym), Value: end})
}
return out
}

type FlatSymbolIndex struct {
Links []elf.SectionHeader
Names []Name
Expand Down Expand Up @@ -104,6 +126,9 @@ func (st *SymbolTable) Resolve(addr uint64) string {
if i == -1 {
return ""
}
if st.Index.Names[i].NameIndex() == sentinelNameIndex {
return ""
}
name, _ := st.symbolName(i)
return name
}
Expand Down Expand Up @@ -136,14 +161,15 @@ func (f *InMemElfFile) NewSymbolTable(opt *SymbolsOptions, symReader ElfSymbolRe
}
return all[i].Value < all[j].Value
})
all = addEndOfSymbolSentinels(all)

res := &SymbolTable{Index: FlatSymbolIndex{
Links: []elf.SectionHeader{
f.Sections[sectionSym], // should be at 0 - SectionTypeSym
f.Sections[sectionDynSym], // should be at 1 - SectionTypeDynSym
},
Names: make([]Name, total),
Values: gosym.NewPCIndex(total),
Names: make([]Name, len(all)),
Values: gosym.NewPCIndex(len(all)),
},
hasSection: map[elf.SectionType]bool{
elf.SHT_SYMTAB: len(sym) > 0,
Expand Down
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