Mach-O support #2
Conversation
This greatly simplifies the code by avoiding duplications of the logic, and getting symbol/debugging information for a different architecture than the current one is not useful anyway.
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Thanks. Since this code is used in various projects I want to make sure that the licensing is OK. Have you signed the FSF copyright assignment or the Google CLA? |
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No but if you point me in the right direction I'd be happy to :) |
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The Google CLA is easier: go to https://cla.developers.google.com/about/google-individual . That is all I need. But if you want to do an FSF copyright assignment, fill out the below and e-mail to assign@gnu.org. Thanks. Please email the following information to assign@gnu.org. Please also CC the package maintainer(s). If you are uncomfortable We will send you the assignment form for your past and future changes. PLEASE USE YOUR FULL NAME AS THE SUBJECT LINE OF THE MESSAGE.* [What is the name of the program or package you're contributing to?] [Did you copy any files or text written by someone else in these changes? [Do you have an employer who might have a basis to claim to own [For the copyright registration, what country are you a citizen of?] [What year were you born?] [Please write your email address here.] [Please write your snail address here.] [Which files have you changed so far, and which new files have you written |
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I've signed the Google CLA. |
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Hello, I tried pulling this patch to play around with it. I was able to get it to build on my macbook (Sierra 10.12.3), but one of the tests doesn't seem to run correctly: Is this expected? The code itself looks OK, but I have little exposure to Mac development, so not sure how much I can contribute there. I was surprised to see byte-swapping, but I guess that makes sense given the fat binary approach. |
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That is because make builds btest without a corresponding dSYM (where the symbol/DWARF tables are actually stored). I'm not aware of any way to get autotools to do so. btest should work fine if you build it manually (with either clang or gcc) and then run dsymutil to generate the corresponding dSYM. The byte swapping is needed because of Mach-O's somewhat unusual endianness setup. It doesn't actually specify little or big endian directly (only by the byte ordering of the magic value), and the endianness isn't required to match that of the architecture. Interestingly enough, fat headers from gcc appear to be big endian even on x86, even though none of the contained architecture are big endian. |
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Thanks for the explanation. There is evidently a lot that I don't know about how thing work on the mac. I'll do some reading about dsymutil. |
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Does someone wait for something to change or be updated here ? 😄 |
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Sorry, I had no idea anybody was using this package seriously. I just threw it together for the convenience of a colleague. I'll try to take a look at this PR in the next day or two. |
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Hum Rust is using/will use some parts of this lib 😸 |
macho.c
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| /* macho.c -- Get debug data from an Mach-O file for backtraces. | ||
| Copyright (C) 2012-2016 Free Software Foundation, Inc. | ||
| Written by Ian Lance Taylor, Google. | ||
| Copyright (C) 2017 John Colanduoni. |
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I can't accept this change with an additional copyright statement like this. You can add your name, as in pecoff.c (and you don't need to put my name here), but I can only accept changes that are only copyright Free Software Foundation.
| #include <sys/types.h> | ||
| #include <sys/syslimits.h> | ||
| #include <string.h> | ||
| #include <mach-o/loader.h> |
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The ELF and PE/COFF support is careful to not rely on any system-specific header files, by defining all structs and constants themselves. Can we do that here?
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We can, but we're still reliant on mach-o/dyld.h for determining what images are loaded. AFIACT the only Mach-O loader other than Darwin's is Darling's one for Linux, which also includes these header files.
macho.c
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| #include "config.h" | ||
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| // We can't use autotools to detect the pointer width of our program because |
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Use the same long comment format used by other files here.
/* We can't use autotools...
foo bar
quux. */
macho.c
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| }; | ||
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| /* | ||
| * Mach-O symbols don't have a length. As a result we have to infer it |
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No leading '' on long comments in this project. Also start on the / line--see other files.
macho.c
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| macho_file_to_host_u16 (int file_bytes_swapped, uint16_t input) | ||
| { | ||
| if (file_bytes_swapped) | ||
| { |
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No need for braces for a single statement block.
macho.c
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| uintptr_t max_dwarf_offset = 0; | ||
| memset (dwarf_sections, 0, sizeof (dwarf_sections)); | ||
| offset = 0; | ||
| for (uint32_t i = 0; i < commands_view.commands_count; i++) |
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Don't define a variable in a for statement--this is old fashioned C code.
macho.c
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| goto end; | ||
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| // Get DWARF sections | ||
| struct found_dwarf_section dwarf_sections[DEBUG_MAX]; |
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Define variables at the start of a function or the start of a block.
macho.c
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| dwarf_sections[DEBUG_RANGES].file_size, | ||
| dwarf_sections[DEBUG_STR].data, | ||
| dwarf_sections[DEBUG_STR].file_size, | ||
| (__DARWIN_BYTE_ORDER == __DARWIN_BIG_ENDIAN) ^ |
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Expressions broken across a line are wrapped in parens, and the operator is at the start of the second line.
macho.c
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| if (directory_entry->d_type != DT_REG) | ||
| continue; | ||
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| strncpy(dwarf_filename, dwarf_image_dir_path, PATH_MAX); |
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Space before left parenthesis.
macho.c
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| strncat(dwarf_filename, "/", PATH_MAX); | ||
| strncat(dwarf_filename, directory_entry->d_name, PATH_MAX); | ||
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| int dwarf_matched; |
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Declarations at start of function.
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@JohnColanduoni Could you take a look at the requested changes (particularly copyright - I think the rest we might be able to fix) |
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@ianlancetaylor ping? |
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@JohnColanduoni @ianlancetaylor Any chance to give this another try? I switched to using the repo at https://github.com/rust-lang-nursery/libbacktrace for this but would prefer to eventually switch back to the upstream repo at some point in time. |
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@ianlancetaylor Any chance to get the Mach-O support upstream ? We are using libbacktrace on linux and mac right now and i also did some additional improvements for the Mach-O part and i would love to see this upstream, instead of living in the fork for rust. |
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From my perspective, I wrote a bunch of comments on the pull request and as far as I know they have not been addressed. |
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@JohnColanduoni What's your thinking about this, could we try it again and finally get the Mach-O support officially in ? |
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I just wrote my own version of Mach-O support and committed it. It doesn't fully pass the testsuite, as it is failing to understand some clang optimizations. lldb reports an "artificial" frame that libbacktrace is somehow failing to pick up. I wouldn't be surprised if there are other problems. Please report any bugs with precise reproduction instructions. Thanks. |
ghost
mentioned this pull request
This commit is a proof-of-concept for switching the standard library's backtrace symbolication mechanism on most platforms from libbacktrace to gimli. The standard library's support for `RUST_BACKTRACE=1` requires in-process parsing of object files and DWARF debug information to interpret it and print the filename/line number of stack frames as part of a backtrace. Historically this support in the standard library has come from a library called "libbacktrace". The libbacktrace library seems to have been extracted from gcc at some point and is written in C. We've had a lot of issues with libbacktrace over time, unfortunately, though. The library does not appear to be actively maintained since we've had patches sit for months-to-years without comments. We have discovered a good number of soundness issues with the library itself, both when parsing valid DWARF as well as invalid DWARF. This is enough of an issue that the libs team has previously decided that we cannot feed untrusted inputs to libbacktrace. This also doesn't take into account the portability of libbacktrace which has been difficult to manage and maintain over time. While possible there are lots of exceptions and it's the main C dependency of the standard library right now. For years it's been the desire to switch over to a Rust-based solution for symbolicating backtraces. It's been assumed that we'll be using the Gimli family of crates for this purpose, which are targeted at safely and efficiently parsing DWARF debug information. I've been working recently to shore up the Gimli support in the `backtrace` crate. As of a few weeks ago the `backtrace` crate, by default, uses Gimli when loaded from crates.io. This transition has gone well enough that I figured it was time to start talking seriously about this change to the standard library. This commit is a preview of what's probably the best way to integrate the `backtrace` crate into the standard library with the Gimli feature turned on. While today it's used as a crates.io dependency, this commit switches the `backtrace` crate to a submodule of this repository which will need to be updated manually. This is not done lightly, but is thought to be the best solution. The primary reason for this is that the `backtrace` crate needs to do some pretty nontrivial filesystem interactions to locate debug information. Working without `std::fs` is not an option, and while it might be possible to do some sort of trait-based solution when prototyped it was found to be too unergonomic. Using a submodule allows the `backtrace` crate to build as a submodule of the `std` crate itself, enabling it to use `std::fs` and such. Otherwise this adds new dependencies to the standard library. This step requires extra attention because this means that these crates are now going to be included with all Rust programs by default. It's important to note, however, that we're already shipping libbacktrace with all Rust programs by default and it has a bunch of C code implementing all of this internally anyway, so we're basically already switching already-shipping functionality to Rust from C. * `object` - this crate is used to parse object file headers and contents. Very low-level support is used from this crate and almost all of it is disabled. Largely we're just using struct definitions as well as convenience methods internally to read bytes and such. * `addr2line` - this is the main meat of the implementation for symbolication. This crate depends on `gimli` for DWARF parsing and then provides interfaces needed by the `backtrace` crate to turn an address into a filename / line number. This crate is actually pretty small (fits in a single file almost!) and mirrors most of what `dwarf.c` does for libbacktrace. * `miniz_oxide` - the libbacktrace crate transparently handles compressed debug information which is compressed with zlib. This crate is used to decompress compressed debug sections. * `gimli` - not actually used directly, but a dependency of `addr2line`. * `adler32`- not used directly either, but a dependency of `miniz_oxide`. The goal of this change is to improve the safety of backtrace symbolication in the standard library, especially in the face of possibly malformed DWARF debug information. Even to this day we're still seeing segfaults in libbacktrace which could possibly become security vulnerabilities. This change should almost entirely eliminate this possibility whilc also paving the way forward to adding more features like split debug information. Some references for those interested are: * Original addition of libbacktrace - rust-lang#12602 * OOM with libbacktrace - rust-lang#24231 * Backtrace failure due to use of uninitialized value - rust-lang#28447 * Possibility to feed untrusted data to libbacktrace - rust-lang#21889 * Soundness fix for libbacktrace - rust-lang#33729 * Crash in libbacktrace - rust-lang#39468 * Support for macOS, never merged - ianlancetaylor/libbacktrace#2 * Performance issues with libbacktrace - rust-lang#29293, rust-lang#37477 * Update procedure is quite complicated due to how many patches we need to carry - rust-lang#50955 * Libbacktrace doesn't work on MinGW with dynamic libs - rust-lang#71060 * Segfault in libbacktrace on macOS - rust-lang#71397 Switching to Rust will not make us immune to all of these issues. The crashes are expected to go away, but correctness and performance may still have bugs arise. The gimli and `backtrace` crates, however, are actively maintained unlike libbacktrace, so this should enable us to at least efficiently apply fixes as situations come up.
…Simulacrum std: Switch from libbacktrace to gimli This commit is a proof-of-concept for switching the standard library's backtrace symbolication mechanism on most platforms from libbacktrace to gimli. The standard library's support for `RUST_BACKTRACE=1` requires in-process parsing of object files and DWARF debug information to interpret it and print the filename/line number of stack frames as part of a backtrace. Historically this support in the standard library has come from a library called "libbacktrace". The libbacktrace library seems to have been extracted from gcc at some point and is written in C. We've had a lot of issues with libbacktrace over time, unfortunately, though. The library does not appear to be actively maintained since we've had patches sit for months-to-years without comments. We have discovered a good number of soundness issues with the library itself, both when parsing valid DWARF as well as invalid DWARF. This is enough of an issue that the libs team has previously decided that we cannot feed untrusted inputs to libbacktrace. This also doesn't take into account the portability of libbacktrace which has been difficult to manage and maintain over time. While possible there are lots of exceptions and it's the main C dependency of the standard library right now. For years it's been the desire to switch over to a Rust-based solution for symbolicating backtraces. It's been assumed that we'll be using the Gimli family of crates for this purpose, which are targeted at safely and efficiently parsing DWARF debug information. I've been working recently to shore up the Gimli support in the `backtrace` crate. As of a few weeks ago the `backtrace` crate, by default, uses Gimli when loaded from crates.io. This transition has gone well enough that I figured it was time to start talking seriously about this change to the standard library. This commit is a preview of what's probably the best way to integrate the `backtrace` crate into the standard library with the Gimli feature turned on. While today it's used as a crates.io dependency, this commit switches the `backtrace` crate to a submodule of this repository which will need to be updated manually. This is not done lightly, but is thought to be the best solution. The primary reason for this is that the `backtrace` crate needs to do some pretty nontrivial filesystem interactions to locate debug information. Working without `std::fs` is not an option, and while it might be possible to do some sort of trait-based solution when prototyped it was found to be too unergonomic. Using a submodule allows the `backtrace` crate to build as a submodule of the `std` crate itself, enabling it to use `std::fs` and such. Otherwise this adds new dependencies to the standard library. This step requires extra attention because this means that these crates are now going to be included with all Rust programs by default. It's important to note, however, that we're already shipping libbacktrace with all Rust programs by default and it has a bunch of C code implementing all of this internally anyway, so we're basically already switching already-shipping functionality to Rust from C. * `object` - this crate is used to parse object file headers and contents. Very low-level support is used from this crate and almost all of it is disabled. Largely we're just using struct definitions as well as convenience methods internally to read bytes and such. * `addr2line` - this is the main meat of the implementation for symbolication. This crate depends on `gimli` for DWARF parsing and then provides interfaces needed by the `backtrace` crate to turn an address into a filename / line number. This crate is actually pretty small (fits in a single file almost!) and mirrors most of what `dwarf.c` does for libbacktrace. * `miniz_oxide` - the libbacktrace crate transparently handles compressed debug information which is compressed with zlib. This crate is used to decompress compressed debug sections. * `gimli` - not actually used directly, but a dependency of `addr2line`. * `adler32`- not used directly either, but a dependency of `miniz_oxide`. The goal of this change is to improve the safety of backtrace symbolication in the standard library, especially in the face of possibly malformed DWARF debug information. Even to this day we're still seeing segfaults in libbacktrace which could possibly become security vulnerabilities. This change should almost entirely eliminate this possibility whilc also paving the way forward to adding more features like split debug information. Some references for those interested are: * Original addition of libbacktrace - rust-lang#12602 * OOM with libbacktrace - rust-lang#24231 * Backtrace failure due to use of uninitialized value - rust-lang#28447 * Possibility to feed untrusted data to libbacktrace - rust-lang#21889 * Soundness fix for libbacktrace - rust-lang#33729 * Crash in libbacktrace - rust-lang#39468 * Support for macOS, never merged - ianlancetaylor/libbacktrace#2 * Performance issues with libbacktrace - rust-lang#29293, rust-lang#37477 * Update procedure is quite complicated due to how many patches we need to carry - rust-lang#50955 * Libbacktrace doesn't work on MinGW with dynamic libs - rust-lang#71060 * Segfault in libbacktrace on macOS - rust-lang#71397 Switching to Rust will not make us immune to all of these issues. The crashes are expected to go away, but correctness and performance may still have bugs arise. The gimli and `backtrace` crates, however, are actively maintained unlike libbacktrace, so this should enable us to at least efficiently apply fixes as situations come up. --- I want to note that my purpose for creating a PR here is to start a conversation about this. I think that all the various pieces are in place that this is compelling enough that I think this transition should be talked about seriously. There are a number of items which still need to be addressed before actually merging this PR, however: * [ ] `gimli` needs to be published to crates.io * [ ] `addr2line` needs a publish * [ ] `miniz_oxide` needs a publish * [ ] Tests probably shouldn't recommend the `gimli` crate's traits for implementing * [ ] The `backtrace` crate's branch changes need to be merged to the master branch (rust-lang/backtrace-rs#349) * [ ] The support for `libbacktrace` on some platforms needs to be audited to see if we should support more strategies in the gimli implementation - rust-lang/backtrace-rs#325, rust-lang/backtrace-rs#326, rust-lang/backtrace-rs#350, rust-lang/backtrace-rs#351 Most of the merging/publishing I'm not actively pushing on right now. It's a bit wonky for crates to support libstd so I'm holding off on pulling the trigger everywhere until there's a bit more discussion about how to go through with this. Namely rust-lang/backtrace-rs#349 I'm going to hold off merging until we decide to go through with the submodule strategy. In any case this is a pretty major change, so I suspect that the compiler team is likely going to be interested in this. I don't mean to force changes by dumping a bunch of code by any means. Integration of external crates into the standard library is so difficult I wanted to have a proof-of-concept to review while talking about whether to do this at all (hence the PR), but I'm more than happy to follow any processes needed to merge this. I must admit though that I'm not entirely sure myself at this time what the process would be to decide to merge this, so I'm hoping others can help me figure that out!
This commit is a proof-of-concept for switching the standard library's backtrace symbolication mechanism on most platforms from libbacktrace to gimli. The standard library's support for `RUST_BACKTRACE=1` requires in-process parsing of object files and DWARF debug information to interpret it and print the filename/line number of stack frames as part of a backtrace. Historically this support in the standard library has come from a library called "libbacktrace". The libbacktrace library seems to have been extracted from gcc at some point and is written in C. We've had a lot of issues with libbacktrace over time, unfortunately, though. The library does not appear to be actively maintained since we've had patches sit for months-to-years without comments. We have discovered a good number of soundness issues with the library itself, both when parsing valid DWARF as well as invalid DWARF. This is enough of an issue that the libs team has previously decided that we cannot feed untrusted inputs to libbacktrace. This also doesn't take into account the portability of libbacktrace which has been difficult to manage and maintain over time. While possible there are lots of exceptions and it's the main C dependency of the standard library right now. For years it's been the desire to switch over to a Rust-based solution for symbolicating backtraces. It's been assumed that we'll be using the Gimli family of crates for this purpose, which are targeted at safely and efficiently parsing DWARF debug information. I've been working recently to shore up the Gimli support in the `backtrace` crate. As of a few weeks ago the `backtrace` crate, by default, uses Gimli when loaded from crates.io. This transition has gone well enough that I figured it was time to start talking seriously about this change to the standard library. This commit is a preview of what's probably the best way to integrate the `backtrace` crate into the standard library with the Gimli feature turned on. While today it's used as a crates.io dependency, this commit switches the `backtrace` crate to a submodule of this repository which will need to be updated manually. This is not done lightly, but is thought to be the best solution. The primary reason for this is that the `backtrace` crate needs to do some pretty nontrivial filesystem interactions to locate debug information. Working without `std::fs` is not an option, and while it might be possible to do some sort of trait-based solution when prototyped it was found to be too unergonomic. Using a submodule allows the `backtrace` crate to build as a submodule of the `std` crate itself, enabling it to use `std::fs` and such. Otherwise this adds new dependencies to the standard library. This step requires extra attention because this means that these crates are now going to be included with all Rust programs by default. It's important to note, however, that we're already shipping libbacktrace with all Rust programs by default and it has a bunch of C code implementing all of this internally anyway, so we're basically already switching already-shipping functionality to Rust from C. * `object` - this crate is used to parse object file headers and contents. Very low-level support is used from this crate and almost all of it is disabled. Largely we're just using struct definitions as well as convenience methods internally to read bytes and such. * `addr2line` - this is the main meat of the implementation for symbolication. This crate depends on `gimli` for DWARF parsing and then provides interfaces needed by the `backtrace` crate to turn an address into a filename / line number. This crate is actually pretty small (fits in a single file almost!) and mirrors most of what `dwarf.c` does for libbacktrace. * `miniz_oxide` - the libbacktrace crate transparently handles compressed debug information which is compressed with zlib. This crate is used to decompress compressed debug sections. * `gimli` - not actually used directly, but a dependency of `addr2line`. * `adler32`- not used directly either, but a dependency of `miniz_oxide`. The goal of this change is to improve the safety of backtrace symbolication in the standard library, especially in the face of possibly malformed DWARF debug information. Even to this day we're still seeing segfaults in libbacktrace which could possibly become security vulnerabilities. This change should almost entirely eliminate this possibility whilc also paving the way forward to adding more features like split debug information. Some references for those interested are: * Original addition of libbacktrace - rust-lang#12602 * OOM with libbacktrace - rust-lang#24231 * Backtrace failure due to use of uninitialized value - rust-lang#28447 * Possibility to feed untrusted data to libbacktrace - rust-lang#21889 * Soundness fix for libbacktrace - rust-lang#33729 * Crash in libbacktrace - rust-lang#39468 * Support for macOS, never merged - ianlancetaylor/libbacktrace#2 * Performance issues with libbacktrace - rust-lang#29293, rust-lang#37477 * Update procedure is quite complicated due to how many patches we need to carry - rust-lang#50955 * Libbacktrace doesn't work on MinGW with dynamic libs - rust-lang#71060 * Segfault in libbacktrace on macOS - rust-lang#71397 Switching to Rust will not make us immune to all of these issues. The crashes are expected to go away, but correctness and performance may still have bugs arise. The gimli and `backtrace` crates, however, are actively maintained unlike libbacktrace, so this should enable us to at least efficiently apply fixes as situations come up.
Adds support for loading DWARF and symbol table data from Mach-O images, allowing libbacktrace to be used on Darwin systems (macOS, iOS, etc.).