[wan9chi]

Motivation

An exec of an empty path fails with ENOENT before the kernel looks anything up. Under fspy:

Entry point, path ""	Untraced	Traced, before
execve, execv, execl, execle, posix_spawn	ENOENT	the program aborts: shebang parsing reports "" as read, and making it absolute fails (Failed to get cwd)
execvp, execlp, execvpe, posix_spawnp	ENOENT	ENOENT (the PATH search already rejects "")
execveat(dirfd, "", …) without AT_EMPTY_PATH (Linux)	ENOENT	resolves "" against dirfd and tries to run what it refers to: EISDIR for AT_FDCWD, with the directory reported as read

Change

• Exec::resolve fails an empty program with ENOENT before anything else, as execve and libc's PATH search do, so nothing is read or reported.
• The execveat interposer forwards an empty path without AT_EMPTY_PATH to the real call. With AT_EMPTY_PATH it still resolves dirfd as before.
• crates/fspy/tests/exec_empty_path.rs makes every call untraced in the test process, then traced, and asserts the results are equal and that the working directory isn't reported. On musl, seccomp tracking still reports the directory an empty path is relative to, so that check is skipped there; the errno comparison still runs.

🤖 Generated with Claude Code

[github-actions]

fspy benchmark

linux

dynamic/launch             change  +0.28%  [ -6.44% ..  +6.61%]  overhead   +60.37%
dynamic/access             change  -0.40%  [ -5.58% ..  +4.26%]  overhead   +19.62%
dynamic/access-relative    change  -2.53%  [-14.33% ..  +3.02%]  overhead   +62.29%
dynamic/access-contended   change  -2.35%  [-11.98% ..  +6.72%]  overhead    +5.92%
static/launch              change  +1.08%  [ -5.55% ..  +7.03%]  overhead  +195.82%
static/access              change  +1.35%  [ -5.71% .. +25.89%]  overhead +1104.25%
static/access-relative     change  +0.87%  [ -3.24% .. +17.71%]  overhead +1680.90%
static/access-contended    change  -0.19%  [ -8.37% .. +13.95%]  overhead +1081.84%

macos

dynamic/launch             change  -0.03%  [ -3.93% ..  +4.77%]  overhead  +227.65%
dynamic/access             change  -0.34%  [-50.34% ..  +6.55%]  overhead    +0.40%
dynamic/access-relative    change  +0.91%  [ -3.66% ..  +3.50%]  overhead  +263.17%
dynamic/access-contended   change  +2.78%  [ -8.00% .. +38.37%]  overhead    +2.77%

windows

dynamic/launch             change  +0.15%  [ -1.43% ..  +1.89%]  overhead   +25.16%
dynamic/access             change  +0.00%  [ -0.38% ..  +0.56%]  overhead    +0.95%
dynamic/access-relative    change  +0.19%  [ -0.37% ..  +0.56%]  overhead    +1.12%
dynamic/access-contended   change  +0.13%  [ -0.36% ..  +0.54%]  overhead    +1.46%