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Missing rust-gdb pretty printer for cdylib shared objects #96365

Open cjermain opened 2 years ago

cjermain commented 2 years ago

Problem

Debugging in rust-gdb with a shared object library does not activate pretty-printers supplied by rustup.

Running cargo build with crate-type of bin or lib results in a .debug_gdb_scripts section on the target or library, allowing rust-gdb to auto-load the Python pretty printers dynamically during debugging. The pretty printers are great! https://github.com/rust-lang/rust/blob/91a0600a5c22b9d159e3c57526af83e71d1120f8/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs#L39-L40

However, for crate-type of cdylib, the .debug_gdb_scripts section is not written. This results in a lack of pretty printing in rust-gdb, and makes it more challenging to use rust-gdb to best effect. I'm seeing this when working with Python bindings of Rust code with pyo3. Is there a reason cdylib did not receive this pretty-printer support?

Workaround

I've confirmed that manually adding the .debug_gdb_scripts section to a .so library generated with crate-type=cdylib activates the pretty printers. I did noticed some Python exceptions in the pretty printers, but have not investigated further.

$ objcopy --add-section .debug_gdb_scripts=<(echo -ne "\x01gdb_load_rust_pretty_printers.py\0") ./libmytest_lib.so
$ objdump -sj .debug_gdb_scripts libmytest_lib.so

libmytest_lib.so:     file format elf64-x86-64

Contents of section .debug_gdb_scripts:
 0000 01676462 5f6c6f61 645f7275 73745f70  .gdb_load_rust_p
 0010 72657474 795f7072 696e7465 72732e70  retty_printers.p
 0020 7900                                 y.

Version information

rustc 1.60.0 (7737e0b5c 2022-04-04) cargo 1.60.0 (d1fd9fe 2022-03-01)

cjermain commented 2 years ago

@tromey, I noticed you have experience in this area. Any thoughts on this, or who might be the right person?

Enselic commented 1 year ago

It seems to be the linker arg --gc-sections ("garbage collect sections") that removes the .debug_gdb_scripts section for cdylib. But for some reason the same arg does not remove the section for bins.

Do check this, first create these two files:

// lib.rs
pub extern "C" fn yep() -> bool {
    true
}

// main.rs
#![feature(start)]
#[start]
fn start(_: isize, _: *const *const u8) -> isize {
    return 0;
}

Then build a bin and a cdylib in a way that prints the linker args and saves the intermediate files so that the linker can be re-invoked. I am using nightly-2023-02-19.

$ rustc +nightly \
    -C save-temps \
    -C debuginfo=2 \
    -C codegen-units=1 \
    --print link-args \
    --out-dir /tmp/bin-out \
    --crate-type bin \
    main.rs
LC_ALL="C" PATH="/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/martin/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/wsl/lib:/mnt/c/Windows/system32:/mnt/c/Windows:/mnt/c/Windows/System32/Wbem:/mnt/c/Windows/System32/WindowsPowerShell/v1.0/:/mnt/c/Windows/System32/OpenSSH/:/mnt/c/Program Files/Git/cmd:/mnt/c/Program Files/Docker/Docker/resources/bin:/mnt/c/Users/ensel/.cargo/bin:/mnt/c/Users/ensel/AppData/Local/Microsoft/WindowsApps:/mnt/c/Users/ensel/AppData/Local/Programs/Microsoft VS Code/bin" VSLANG="1033" "cc" "-m64" "/tmp/rustcVhABaM/symbols.o" "/tmp/bin-out/main.main.bb53c12c-cgu.0.rcgu.o" "/tmp/bin-out/main.149e45n1nrd5pscg.rcgu.o" "-Wl,--as-needed" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-67e0fe4bfa018a5e.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-6e25273444177929.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-05da49d3cca73bff.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-616c9bd2710f0982.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-d9df84ec1a8a7a8f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-0242ef3eea1e9db2.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-127f477a16f3f8f8.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-eb235cc34134320b.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-c5f20f2274212453.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-4483c8bc4648568f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-94da6a76998341a3.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-22a9646e8f27a6e4.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-eb91273024ac0258.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-323da837c64ef472.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-6d46d38f739892fe.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-8212dcd77adfe144.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-522518611024dce5.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-05898138a596088a.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-b78d27aa9e5e005b.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/tmp/bin-out/main" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro,-znow" "-nodefaultlibs"

$ rustc +nightly \
    -C save-temps \
    -C debuginfo=2 \
    -C codegen-units=1 \
    --print link-args \
    --out-dir /tmp/lib-out \
    --crate-type cdylib \
    lib.rs
LC_ALL="C" PATH="/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/martin/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/wsl/lib:/mnt/c/Windows/system32:/mnt/c/Windows:/mnt/c/Windows/System32/Wbem:/mnt/c/Windows/System32/WindowsPowerShell/v1.0/:/mnt/c/Windows/System32/OpenSSH/:/mnt/c/Program Files/Git/cmd:/mnt/c/Program Files/Docker/Docker/resources/bin:/mnt/c/Users/ensel/.cargo/bin:/mnt/c/Users/ensel/AppData/Local/Microsoft/WindowsApps:/mnt/c/Users/ensel/AppData/Local/Programs/Microsoft VS Code/bin" VSLANG="1033" "cc" "-Wl,--version-script=/tmp/rustc0bhGIi/list" "-m64" "/tmp/rustc0bhGIi/symbols.o" "/tmp/lib-out/lib.lib.447e930b-cgu.0.rcgu.o" "/tmp/lib-out/lib.23es8ilvqvufl30n.rcgu.o" "-Wl,--as-needed" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-67e0fe4bfa018a5e.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-6e25273444177929.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-05da49d3cca73bff.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-616c9bd2710f0982.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-d9df84ec1a8a7a8f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-0242ef3eea1e9db2.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-127f477a16f3f8f8.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-eb235cc34134320b.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-c5f20f2274212453.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-4483c8bc4648568f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-94da6a76998341a3.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-22a9646e8f27a6e4.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-eb91273024ac0258.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-323da837c64ef472.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-6d46d38f739892fe.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-8212dcd77adfe144.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-522518611024dce5.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-05898138a596088a.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-b78d27aa9e5e005b.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/tmp/lib-out/liblib.so" "-Wl,--gc-sections" "-shared" "-Wl,-zrelro,-znow" "-nodefaultlibs"

We can see that the bin contains the section but the cdylib does not:

$ readelf -x .debug_gdb_scripts /tmp/bin-out/main /tmp/lib-out/liblib.so

File: /tmp/bin-out/main

Hex dump of section '.debug_gdb_scripts':
  0x00002000 01676462 5f6c6f61 645f7275 73745f70 .gdb_load_rust_p
  0x00002010 72657474 795f7072 696e7465 72732e70 retty_printers.p
  0x00002020 7900                                y.

File: /tmp/lib-out/liblib.so
readelf: Warning: Section '.debug_gdb_scripts' was not dumped because it does not exist

However, if we remove the "-Wl,--gc-sections" from both of the commands above and re-run them, both the bin and the cdylib does contain the section:

$ LC_ALL="C" PATH="/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/martin/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/wsl/lib:/mnt/c/Windows/system32:/mnt/c/Windows:/mnt/c/Windows/System32/Wbem:/mnt/c/Windows/System32/WindowsPowerShell/v1.0/:/mnt/c/Windows/System32/OpenSSH/:/mnt/c/Program Files/Git/cmd:/mnt/c/Program Files/Docker/Docker/resources/bin:/mnt/c/Users/ensel/.cargo/bin:/mnt/c/Users/ensel/AppData/Local/Microsoft/WindowsApps:/mnt/c/Users/ensel/AppData/Local/Programs/Microsoft VS Code/bin" VSLANG="1033" "cc" "-m64" "/tmp/rustcVhABaM/symbols.o" "/tmp/bin-out/main.main.bb53c12c-cgu.0.rcgu.o" "/tmp/bin-out/main.149e45n1nrd5pscg.rcgu.o" "-Wl,--as-needed" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-67e0fe4bfa018a5e.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-6e25273444177929.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-05da49d3cca73bff.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-616c9bd2710f0982.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-d9df84ec1a8a7a8f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-0242ef3eea1e9db2.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-127f477a16f3f8f8.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-eb235cc34134320b.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-c5f20f2274212453.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-4483c8bc4648568f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-94da6a76998341a3.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-22a9646e8f27a6e4.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-eb91273024ac0258.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-323da837c64ef472.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-6d46d38f739892fe.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-8212dcd77adfe144.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-522518611024dce5.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-05898138a596088a.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-b78d27aa9e5e005b.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/tmp/bin-out/main" "-pie" "-Wl,-zrelro,-znow" "-nodefaultlibs"
$ LC_ALL="C" PATH="/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/martin/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/wsl/lib:/mnt/c/Windows/system32:/mnt/c/Windows:/mnt/c/Windows/System32/Wbem:/mnt/c/Windows/System32/WindowsPowerShell/v1.0/:/mnt/c/Windows/System32/OpenSSH/:/mnt/c/Program Files/Git/cmd:/mnt/c/Program Files/Docker/Docker/resources/bin:/mnt/c/Users/ensel/.cargo/bin:/mnt/c/Users/ensel/AppData/Local/Microsoft/WindowsApps:/mnt/c/Users/ensel/AppData/Local/Programs/Microsoft VS Code/bin" VSLANG="1033" "cc" "-Wl,--version-script=/tmp/rustc0bhGIi/list" "-m64" "/tmp/rustc0bhGIi/symbols.o" "/tmp/lib-out/lib.lib.447e930b-cgu.0.rcgu.o" "/tmp/lib-out/lib.23es8ilvqvufl30n.rcgu.o" "-Wl,--as-needed" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-67e0fe4bfa018a5e.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-6e25273444177929.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-05da49d3cca73bff.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-616c9bd2710f0982.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-d9df84ec1a8a7a8f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-0242ef3eea1e9db2.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-127f477a16f3f8f8.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-eb235cc34134320b.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-c5f20f2274212453.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-4483c8bc4648568f.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-94da6a76998341a3.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-22a9646e8f27a6e4.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-eb91273024ac0258.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-323da837c64ef472.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-6d46d38f739892fe.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-8212dcd77adfe144.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-522518611024dce5.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-05898138a596088a.rlib" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-b78d27aa9e5e005b.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/tmp/lib-out/liblib.so" "-shared" "-Wl,-zrelro,-znow" "-nodefaultlibs"
$ readelf -x .debug_gdb_scripts /tmp/bin-out/main /tmp/lib-out/liblib.so

File: /tmp/bin-out/main

Hex dump of section '.debug_gdb_scripts':
  0x000f9e80 01676462 5f6c6f61 645f7275 73745f70 .gdb_load_rust_p
  0x000f9e90 72657474 795f7072 696e7465 72732e70 retty_printers.p
  0x000f9ea0 7900                                y.

File: /tmp/lib-out/liblib.so

Hex dump of section '.debug_gdb_scripts':
  0x000f9e70 01676462 5f6c6f61 645f7275 73745f70 .gdb_load_rust_p
  0x000f9e80 72657474 795f7072 696e7465 72732e70 retty_printers.p
  0x000f9e90 7900                                y.

In other words, the object files emitted by rustc contains .debug_gdb_scripts both in the bin and cdylib case, but it gets lost in the linking phase for cdylib, but not for bin.

Workaround

As a workaround it seems to work to pass -C link-args=-Wl,--no-gc-sections to rustc:

$ cargo rustc --lib
   Compiling issue-96365-repro v0.1.0 (/home/martin/src/issue-96365-repro)
    Finished dev [unoptimized + debuginfo] target(s) in 0.13s
$ readelf -x .debug_gdb_scripts ./target/debug/libissue_96365_repro.so
readelf: Warning: Section '.debug_gdb_scripts' was not dumped because it does not exist
$ cargo rustc --lib -- -C link-args=-Wl,--no-gc-sections
   Compiling issue-96365-repro v0.1.0 (/home/martin/src/issue-96365-repro)
    Finished dev [unoptimized + debuginfo] target(s) in 0.14s
$ readelf -x .debug_gdb_scripts ./target/debug/libissue_96365_repro.so

Hex dump of section '.debug_gdb_scripts':
  0x000f2d68 01676462 5f6c6f61 645f7275 73745f70 .gdb_load_rust_p
  0x000f2d78 72657474 795f7072 696e7465 72732e70 retty_printers.p
  0x000f2d88 7900                                y.

but be aware of unintended consequences, especially for release builds.

bjorn3 commented 1 year ago

Adding .debug_gdb_scripts to exported_symbols with used: true when needs_gdb_debug_scripts_section() is true may be enough to fix this.