ddbug - Display debugging information

ddbug is a utility that can extract useful information from DWARF/PDB debugging data. Its goal is to use the debugging information to provide insights into the code generation. This can be used to guide improvements to the code. Examples of questions it hopes to answer (but not all are implemented yet):

• What is the memory layout of a struct?
• Which small functions aren't inlined?
• Which large functions are inlined many times?
• Which functions have bounds checks after optimization, or more generally, which functions can panic?
• What difference does a source code change make to code generation?
• What difference does a compiler version change make to code generation?

This is alpha software. It is likely to contain many bugs and incomplete features. Neverthless, it is in a state where it can still provide some use. Bug reports and feature requests are welcome.

Supports:

• ELF files with DWARF
• Mach-O files with DWARF
• Windows PDB files (mimimal support so far)

Installing

After installing Rust, run:

cargo install ddbug

Running

Find the file containing the debugging information, then run:

ddbug path-to-file

See ddbug --help for details on options to control which information is displayed.

Usually you will want to run ddbug on binaries that have been optimized, but which still contain debugging information. For rust, you can build your code using:

RUSTFLAGS=-g cargo build --release

Diff mode

When given the --diff option and two paths to files, ddbug will display the differences between the two binaries. There are some command line options to specify which differences are considered significant.

Example output

struct and union

struct core::fmt::Formatter
        size: 96
        members:
                0[16]   width: union core::option::Option<usize>
                16[16]  precision: union core::option::Option<usize>
                32[16]  buf: struct core::fmt::&mut Write
                48[16]  curarg: struct core::slice::Iter<core::fmt::ArgumentV1>
                64[16]  args: struct &[core::fmt::ArgumentV1]
                80[4]   flags: u32
                84[4]   fill: char
                88[1]   align: enum core::fmt::rt::v1::Alignment
                89[7]   <padding>

enum

Note that this is a C style enumeration. Rust enumerations are encoded in the debugging information as both a union and an enum.

enum core::result::Result
        size: 1
        enumerators:
                Ok(0)
                Err(1)

function

fn ddbug::main
        linkage name: _ZN5ddbug4mainE
        address: 0x601f0-0x629d9
        size: 10218
        inlined subroutines:
                [30]    log::__static_max_level
                [59]    log::max_log_level
        calls:
                0x40eee0 env_logger::init
                0x48870 core::result::Result<(), log::SetLoggerError>::ok<(),log::SetLoggerError>

fn log::__static_max_level
        linkage name: _ZN3log18__static_max_levelE
        inline: yes
        return type:
                [8]     enum log::LogLevelFilter

License

This software is licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

This software links with a number of libraries, which have their own licenses. In particular, it links with the panopticon library, which is licensed under GPL Version 3.