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Skip label symbols when inferring symbol sizes

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COFF objects in particular don't contain the size of
symbols. We infer the size of these symbols by
extending them to the next symbol. If a tool emits
symbols for branch targets, this causes the inferred
size to be too small.

This checks if a symbol starts with a certain prefix
(right now, just .L or LAB_), and skips over it
during symbol size inference.

Resolves #174
This commit is contained in:
Luke Street 2025-05-13 22:36:02 -06:00
parent e865f3d598
commit 8e8ab6bef8
6 changed files with 204 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
objdiff-core/src/arch/arm.rs
View File

@ -225,7 +225,7 @@ impl Arch for ArchArm {
let mut address = start_addr;
while address < end_addr {
while let Some(next) = next_mapping.take_if(|x| address >= x.address) {
while let Some(next) = next_mapping.filter(|x| address >= x.address) {
// Change mapping
mode = next.mapping;
next_mapping = mappings_iter.next();

2
objdiff-core/src/obj/mod.rs
View File

@ -118,7 +118,7 @@ impl Section {
Err(i) => self
.relocations
.get(i)
.take_if(|r| r.address < ins_ref.address + ins_ref.size as u64),
.filter(|r| r.address < ins_ref.address + ins_ref.size as u64),
}
.and_then(|relocation| {
let symbol = obj.symbols.get(relocation.target_symbol)?;

34
objdiff-core/src/obj/read.rs
View File

@ -121,6 +121,15 @@ fn map_symbols(
Ok((symbols, symbol_indices))
}
/// When inferring a symbol's size, we ignore symbols that start with specific prefixes. They are
/// usually emitted as branch targets and do not represent the start of a function or object.
fn is_local_label(symbol: &Symbol) -> bool {
const LABEL_PREFIXES: &[&str] = &[".L", "LAB_"];
symbol.size == 0
&& symbol.flags.contains(SymbolFlag::Local)
&& LABEL_PREFIXES.iter().any(|p| symbol.name.starts_with(p))
}
fn infer_symbol_sizes(symbols: &mut [Symbol], sections: &[Section]) {
// Create a sorted list of symbol indices by section
let mut symbols_with_section = Vec::<usize>::with_capacity(symbols.len());
@ -167,10 +176,7 @@ fn infer_symbol_sizes(symbols: &mut [Symbol], sections: &[Section]) {
if last_end.0 == section_idx && last_end.1 > symbol.address {
continue;
}
let next_symbol = match symbol.kind {
// For function/object symbols, find the next function/object symbol (in other words:
// skip over labels)
SymbolKind::Function | SymbolKind::Object => loop {
let next_symbol = loop {
if iter_idx >= symbols_with_section.len() {
break None;
}
@ -178,16 +184,20 @@ fn infer_symbol_sizes(symbols: &mut [Symbol], sections: &[Section]) {
if next_symbol.section != Some(section_idx) {
break None;
}
if let SymbolKind::Function | SymbolKind::Object = next_symbol.kind {
if match symbol.kind {
SymbolKind::Function | SymbolKind::Object => {
// For function/object symbols, find the next function/object
matches!(next_symbol.kind, SymbolKind::Function | SymbolKind::Object)
}
SymbolKind::Unknown | SymbolKind::Section => {
// For labels (or anything else), stop at any symbol
true
}
} && !is_local_label(next_symbol)
{
break Some(next_symbol);
}
iter_idx += 1;
},
// For labels (or anything else), simply use the next symbol's address
SymbolKind::Unknown | SymbolKind::Section => symbols_with_section
.get(iter_idx)
.map(|&i| &symbols[i])
.take_if(|s| s.section == Some(section_idx)),
};
let next_address = next_symbol.map(|s| s.address).unwrap_or_else(|| {
let section = &sections[section_idx];
@ -341,7 +351,7 @@ fn map_section_relocations(
let idx = if let Some(section_symbol) = obj_file
.symbol_by_index(idx)
.ok()
.take_if(|s| s.kind() == object::SymbolKind::Section)
.filter(|s| s.kind() == object::SymbolKind::Section)
{
let section_index =
section_symbol.section_index().context("Section symbol without section")?;

9
objdiff-core/tests/arch_x86.rs
View File

@ -68,3 +68,12 @@ fn read_x86_jumptable() {
let output = common::display_diff(&obj, &diff, symbol_idx, &diff_config);
insta::assert_snapshot!(output);
}
// Inferred size of functions should ignore symbols with specific prefixes
#[test]
#[cfg(feature = "x86")]
fn read_x86_local_labels() {
let diff_config = diff::DiffObjConfig::default();
let obj = obj::read::parse(include_object!("data/x86/local_labels.obj"), &diff_config).unwrap();
insta::assert_debug_snapshot!(obj);
}

BIN
objdiff-core/tests/data/x86/local_labels.obj Normal file
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Binary file not shown.

163
objdiff-core/tests/snapshots/arch_x86__read_x86_local_labels.snap Normal file
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@ -0,0 +1,163 @@
---
source: objdiff-core/tests/arch_x86.rs
expression: obj
---
Object {
arch: ArchX86 {
arch: X86,
endianness: Little,
},
endianness: Little,
symbols: [
Symbol {
name: "42b830_convertToUppercaseShiftJIS.obj",
demangled_name: None,
address: 0,
size: 0,
kind: Unknown,
section: None,
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "[.text]",
demangled_name: None,
address: 0,
size: 0,
kind: Section,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "LAB_0042b850",
demangled_name: None,
address: 32,
size: 0,
kind: Object,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "LAB_0042b883",
demangled_name: None,
address: 83,
size: 0,
kind: Object,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "LAB_0042b87c",
demangled_name: None,
address: 76,
size: 0,
kind: Object,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "LAB_0042b884",
demangled_name: None,
address: 84,
size: 0,
kind: Object,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "LAB_0042b889",
demangled_name: None,
address: 89,
size: 0,
kind: Object,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "LAB_0042b845",
demangled_name: None,
address: 21,
size: 0,
kind: Object,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "LAB_0042b869",
demangled_name: None,
address: 57,
size: 0,
kind: Object,
section: Some(
0,
),
flags: FlagSet(Local),
align: None,
virtual_address: None,
},
Symbol {
name: "ConvertToUppercaseShiftJIS",
demangled_name: None,
address: 0,
size: 92,
kind: Function,
section: Some(
0,
),
flags: FlagSet(Global | SizeInferred),
align: None,
virtual_address: None,
},
],
sections: [
Section {
id: ".text-0",
name: ".text",
address: 0,
size: 92,
kind: Code,
data: SectionData(
92,
),
flags: FlagSet(),
align: Some(
16,
),
relocations: [],
line_info: {},
virtual_address: None,
},
],
split_meta: None,
path: None,
timestamp: None,
}