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Fix kernel module symbol tables.
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The symbol addresses for kernel modules in the
simpleperf symbol tables are already relative to
the base address, unlike the addresses for the
main kernel image.
We were subtracting with overflow. This is now fixed.
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@mstange
mstange committed Apr 25, 2024
1 parent 0a35958 commit 31f9206
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Showing 3 changed files with 51 additions and 35 deletions.
4 changes: 2 additions & 2 deletions Cargo.lock
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2 changes: 1 addition & 1 deletion samply/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ fxprof-processed-profile = { version = "0.7", path = "../fxprof-processed-profil
# framehop = { path = "../../framehop" }
framehop = "0.11.1"
# linux-perf-data = { path = "../../linux-perf-data" }
linux-perf-data = "0.10.0"
linux-perf-data = "0.10.1"

tokio = { version = "1.37.0", features = ["rt", "rt-multi-thread", "macros"] }
tokio-util = "0.7.10"
Expand Down
80 changes: 48 additions & 32 deletions samply/src/linux_shared/converter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ use fxprof_processed_profile::{
SymbolTable, ThreadHandle,
};
use linux_perf_data::linux_perf_event_reader;
use linux_perf_data::simpleperf_dso_type::{DSO_KERNEL, DSO_KERNEL_MODULE};
use linux_perf_data::{
DsoInfo, DsoKey, Endianness, SimpleperfFileRecord, SimpleperfSymbol, SimpleperfTypeSpecificInfo,
};
Expand Down Expand Up @@ -75,7 +76,8 @@ where
kernel_symbols: Option<KernelSymbols>,
kernel_image_mapping: Option<KernelImageMapping>,
simpleperf_symbol_tables_user: HashMap<Vec<u8>, SymbolTableFromSimpleperf>,
simpleperf_symbol_tables_kernel: HashMap<Vec<u8>, Vec<SimpleperfSymbol>>,
simpleperf_symbol_tables_kernel_image: Option<Vec<SimpleperfSymbol>>,
simpleperf_symbol_tables_kernel_modules: HashMap<Vec<u8>, SymbolTableFromSimpleperf>,
pe_mappings: PeMappings,
jit_category_manager: JitCategoryManager,
cpus: Option<Cpus>,
Expand Down Expand Up @@ -127,17 +129,13 @@ where
};

let mut simpleperf_symbol_tables_user = HashMap::new();
let mut simpleperf_symbol_tables_kernel = HashMap::new();
let mut simpleperf_symbol_tables_kernel_image = None;
let mut simpleperf_symbol_tables_kernel_modules = HashMap::new();
if let Some(simpleperf_symbol_tables) = simpleperf_symbol_tables {
for f in simpleperf_symbol_tables {
let path = f.path.clone().into_bytes();
if f.path == "[kernel.kallsyms]"
|| matches!(
f.type_specific_msg,
Some(SimpleperfTypeSpecificInfo::KernelModule(_))
)
{
simpleperf_symbol_tables_kernel.insert(path, f.symbol);
if f.r#type == DSO_KERNEL {
simpleperf_symbol_tables_kernel_image = Some(f.symbol);
} else {
let file_offset_of_min_vaddr_in_elf_file = match f.type_specific_msg {
Some(SimpleperfTypeSpecificInfo::ElfFile(elf)) => {
Expand All @@ -160,7 +158,11 @@ where
min_vaddr: f.min_vaddr,
symbol_table: Arc::new(symbol_table),
};
simpleperf_symbol_tables_user.insert(path, symbol_table);
if f.r#type == DSO_KERNEL_MODULE {
simpleperf_symbol_tables_kernel_modules.insert(path, symbol_table);
} else {
simpleperf_symbol_tables_user.insert(path, symbol_table);
}
}
}
}
Expand Down Expand Up @@ -199,7 +201,8 @@ where
kernel_symbols,
kernel_image_mapping: None,
simpleperf_symbol_tables_user,
simpleperf_symbol_tables_kernel,
simpleperf_symbol_tables_kernel_image,
simpleperf_symbol_tables_kernel_modules,
pe_mappings: PeMappings::new(),
jit_category_manager: JitCategoryManager::new(),
fold_recursive_prefix: profile_creation_props.fold_recursive_prefix,
Expand Down Expand Up @@ -975,7 +978,6 @@ where
build_id: Option<&[u8]>,
path_slice: &[u8],
) {
let original_path = path_slice;
let path = std::str::from_utf8(path_slice).unwrap().to_string();
let build_id: Option<Vec<u8>> = match (build_id, self.kernel_symbols.as_ref()) {
(None, Some(kernel_symbols)) if kernel_symbols.base_avma == base_address => {
Expand All @@ -991,34 +993,46 @@ where
.map(|id| DebugId::from_identifier(id, self.endian == Endianness::LittleEndian));

let debug_path = match self.linux_version.as_deref() {
Some(linux_version) if path.starts_with("[kernel.kallsyms]") => {
Some(linux_version) if dso_key == DsoKey::Kernel => {
// Take a guess at the vmlinux debug file path.
format!("/usr/lib/debug/boot/vmlinux-{linux_version}")
}
_ => path.clone(),
};
let symbol_table = if let Some(symbols) =
self.simpleperf_symbol_tables_kernel.remove(original_path)
{
let symbols: Vec<_> = symbols
.into_iter()
.map(|s| fxprof_processed_profile::Symbol {
address: (s.vaddr - base_address) as u32,
size: Some(s.len),
name: s.name,
})
.collect();
Some(Arc::new(SymbolTable::new(symbols)))
} else {
match (&dso_key, &build_id, self.kernel_symbols.as_ref()) {
(DsoKey::Kernel, Some(build_id), Some(kernel_symbols))

let symbol_table = if dso_key == DsoKey::Kernel {
match (&build_id, self.kernel_symbols.as_ref()) {
(Some(build_id), Some(kernel_symbols))
if build_id == &kernel_symbols.build_id && kernel_symbols.base_avma != 0 =>
{
// Run `echo '0' | sudo tee /proc/sys/kernel/kptr_restrict` to get here without root.
Some(kernel_symbols.symbol_table.clone())
}
_ => None,
_ => {
if let Some(symbols) = self.simpleperf_symbol_tables_kernel_image.take() {
let symbols: Vec<_> = symbols
.into_iter()
.filter_map(|s| {
let address = s.vaddr.checked_sub(base_address)?;
let address = u32::try_from(address).ok()?;
let sym = fxprof_processed_profile::Symbol {
address,
size: Some(s.len),
name: s.name,
};
Some(sym)
})
.collect();
Some(Arc::new(SymbolTable::new(symbols)))
} else {
None
}
}
}
} else {
self.simpleperf_symbol_tables_kernel_modules
.get(path_slice)
.map(|s| s.symbol_table.clone())
};

let lib_handle = self.profile.add_lib(LibraryInfo {
Expand All @@ -1036,7 +1050,7 @@ where
self.profile
.add_kernel_lib_mapping(lib_handle, base_address, end_address, 0);

if path_slice == b"[kernel.kallsyms]" {
if dso_key == DsoKey::Kernel {
// Store information about this mapping so that we can later adjust the mapping,
// if we find that other kernel modules overlap with it.
self.kernel_image_mapping = Some(KernelImageMapping {
Expand Down Expand Up @@ -1139,14 +1153,16 @@ where
let relative_address_at_start = if let Some(file_offset_of_min_vaddr) =
&symbol_table.file_offset_of_min_vaddr_in_elf_file
{
let min_vaddr = symbol_table.min_vaddr;
// Example:
// - start_avma: 0x721e13c000
// - mapping_start_file_offset: 0x4535000
// - file_offset_of_min_vaddr: 0x45357e0
// - min_vaddr: 0x45367e0,
// println!("file_offset_of_min_vaddr={file_offset_of_min_vaddr:x}, mapping_start_file_offset={mapping_start_file_offset:x}, min_vaddr={min_vaddr:x}, path={path}");
let min_vaddr_offset_from_mapping_start =
file_offset_of_min_vaddr - mapping_start_file_offset;
let vaddr_at_start = symbol_table.min_vaddr - min_vaddr_offset_from_mapping_start;
file_offset_of_min_vaddr.wrapping_sub(mapping_start_file_offset);
let vaddr_at_start = min_vaddr.wrapping_sub(min_vaddr_offset_from_mapping_start);

// Assume vaddr = SVMA == relative address
vaddr_at_start as u32
Expand Down

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