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Last updated：2026-10-12

Debugging Bazel Builds with LLDB

Today, while debugging, I found that files compiled by Bazel could no longer be debugged on my Mac — all I got was assembly.

* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100000fd0 hello_world`main
hello_world`main:
->  0x100000fd0 <+0>: pushq  %rbp
    0x100000fd1 <+1>: movq   %rsp, %rbp
    0x100000fd4 <+4>: subq   $0x60, %rsp
    0x100000fd8 <+8>: movl   $0x0, -0x4(%rbp)
(lldb) quit

How to solve it?

The default is standalone, and we need to disable it; here we use local, which means the output will be linked against its dependencies instead of using the default standalone strategy.

build --spawn_strategy=local

With this, the code becomes visible.

* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100000fdf hello_world`main at hello_world.cc:14:21
   11  
   12   int main() {
   13     // Create a thread pool
-> 14     auto threadPool = GetCpuThreadPool();
   15     if (!threadPool) {

Why This Happens

Why is that? Bazel's default standalone spawn strategy runs compile actions inside a sandbox; on macOS the sandbox implementation (sandbox-exec) skews debug info paths and dSYM generation, and the binary ends up with a broken symbol table — so LLDB can only show you assembly.

Switch to:

build --spawn_strategy=local

This means compile actions run directly on the local machine without entering the sandbox; symbol information is fully preserved, and breakpoints land on the correct source lines. I recommend writing it straight into the project's .bazelrc, once and for all:

build --spawn_strategy=local
build --compilation_mode=dbg   # 调试构建记得带 -c dbg

(1) when debugging, use bazel build -c dbg //... or bazel run -c dbg to make sure -O0 -g is on;

(2) on Linux the default sandbox generally does not affect debug symbols; this problem mainly shows up on macOS;

(3) if you still cannot see the source code, check the dSYM: dsymutil ./hello_world && lldb ./hello_world.

With that, Bazel + LLDB work happily together. If you have hit other pitfalls, feel free to add them in the comments~

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