[wan9chi]

Motivation

execl, execlp and execle pass their arguments as a variadic list, so the interposer has to build an argv array before it can handle the exec. It used a 32-slot stack array, fell back to libc malloc for longer lists, and failed with E2BIG past a hardcoded 4096 arguments. That split is where #865's out-of-bounds write lived, and the malloc fallback isn't async-signal-safe: exec may run in the child of fork(), where malloc's lock may be held by a thread that no longer exists.

Change

• A small collect_argv pushes arg and the variadic arguments, up to and including the NULL, into an allocator_api2::vec::Vec in the call's pooled_bump(), and leaves the VaList where execle reads envp.
• Each of the three interposers creates one bump and passes it to both collect_argv and handle_exec, as execveat already does.
• with_argv.rs is removed along with the stack/heap split and the 4096-argument limit; the real execve reports E2BIG instead.

The rest of the exec path still allocates through libc malloc (RawExec::to_exec/from_exec, fexecve); the PR stacked on this one removes that.

🤖 Generated with Claude Code

[github-actions]

fspy benchmark

linux

dynamic/launch             change  +0.57%  [ -3.04% ..  +4.58%]  overhead   +52.55%
dynamic/access             change  +0.04%  [ -3.25% ..  +4.12%]  overhead   +21.84%
dynamic/access-relative    change  +1.81%  [ -1.14% ..  +5.61%]  overhead   +73.48%
dynamic/access-contended   change  -1.89%  [-10.18% ..  +2.56%]  overhead   +23.00%
static/launch              change  +0.32%  [ -3.28% ..  +3.71%]  overhead  +186.67%
static/access              change  +0.07%  [ -2.04% ..  +2.06%]  overhead +1366.06%
static/access-relative     change  -0.07%  [ -1.15% ..  +1.01%]  overhead +1863.99%
static/access-contended    change  +0.52%  [ -0.78% ..  +0.94%]  overhead +1942.85%

macos

dynamic/launch             change  -0.13%  [ -4.87% ..  +5.02%]  overhead  +232.68%
dynamic/access             change  +0.34%  [-10.28% .. +26.92%]  overhead    +2.94%
dynamic/access-relative    change  +0.28%  [ -8.55% .. +25.35%]  overhead  +246.84%
dynamic/access-contended   change  +2.01%  [ -9.98% .. +698.93%]  overhead    -2.08%

windows

dynamic/launch             change  -0.15%  [ -1.50% ..  +1.74%]  overhead   +25.75%
dynamic/access             change  -0.19%  [ -0.75% ..  +0.77%]  overhead    +0.99%
dynamic/access-relative    change  +0.18%  [ -1.08% ..  +1.09%]  overhead    +1.28%
dynamic/access-contended   change  +0.00%  [ -1.05% ..  +0.90%]  overhead    +1.26%