Long link times with --incompatible_sandbox_hermetic_tmp

[robinlinden]

When using Bazel 7, --incompatible_sandbox_hermetic_tmp is flipped, leading to incredibly long link times.

I ran into this when bumping one of my projects to Bazel 7 where it caused the aarch64 cross-compilation job that normally takes 10-15 minutes to hit the 30-minute limit I've got set for it.

This can short-term be worked around with --noincompatible_sandbox_hermetic_tmp, but it feels like something that needs to be looked into somewhere.

robin@x:~/code/hastur$ bazel clean
INFO: Starting clean (this may take a while). Consider using --async if the clean takes more than several minutes.

robin@x:~/code/hastur$ time bazel test --config=linux-aarch64-musl util/unicode_test
INFO: Analyzed target //util:unicode_test (48 packages loaded, 5896 targets configured).
INFO: From Linking util/unicode_test:
In file included from external/zig_sdk/lib/libc/musl/crt/rcrt1.c:3:
external/zig_sdk/lib/libc/musl/crt/../ldso/dlstart.c:146:20: warning: a function declaration without a prototype is deprecated in all versions of C and is treated as a zero-parameter prototype in C2x, conflicting with a subsequent definition [-Wdeprecated-non-prototype]
        GETFUNCSYM(&dls2, __dls2, base+dyn[DT_PLTGOT]);
                          ^
external/zig_sdk/lib/libc/musl/crt/rcrt1.c:11:13: note: conflicting prototype is here
hidden void __dls2(unsigned char *base, size_t *sp)
            ^
1 warning generated.
INFO: Found 1 test target...
Target //util:unicode_test up-to-date:
  bazel-bin/util/unicode_test
INFO: Elapsed time: 25.911s, Critical Path: 25.37s
INFO: 10 processes: 3 internal, 7 linux-sandbox.
INFO: Build completed successfully, 10 total actions

Executed 1 out of 1 test: 1 test passes.

real    0m25.921s
user    0m0.018s
sys     0m0.000s

robin@x:~/code/hastur$ bazel clean
INFO: Starting clean (this may take a while). Consider using --async if the clean takes more than several minutes.

robin@x:~/code/hastur$ time bazel test --config=linux-aarch64-musl --noincompatible_sandbox_hermetic_tmp util/unicode_test
INFO: Analyzed target //util:unicode_test (48 packages loaded, 5896 targets configured).
INFO: Found 1 test target...
Target //util:unicode_test up-to-date:
  bazel-bin/util/unicode_test
INFO: Elapsed time: 2.562s, Critical Path: 2.04s
INFO: 10 processes: 3 internal, 7 linux-sandbox.
INFO: Build completed successfully, 10 total actions

Executed 1 out of 1 test: 1 test passes.

real    0m2.571s
user    0m0.010s
sys     0m0.000s

[motiejus]

Thanks! Covered in #135, please review that and see if it works for you.

We recommend --sandbox_add_mount_pair=/tmp or, if you can, --sandbox_add_mount_pair=/tmp/zig-cache instead of incompatible_sandbox_hermetic_tmp.

[robinlinden]

Thanks for the quick response! --sandbox_add_mount_pair=/tmp seems to work fine and give me the normal speedier link times, so will switch to that. :)