Add stack read cache to better handle deep stacks during unwind#5
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GuillaumeLagrange merged 7 commits intoJun 11, 2026
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samply injects DYLD_INSERT_LIBRARIES + SAMPLY_BOOTSTRAP_SERVER_NAME into the whole descendant tree. Each descendant that loads samply-mac-preload runs a dyld initializer that sends its mach task-self port to samply so it can be profiled. For an Apple *platform binary* (CS_PLATFORM_BINARY) the task-self port is immovable. Transferring an immovable port to another process raises a fatal EXC_GUARD / GUARD_TYPE_MACH_PORT (ILLEGAL_MOVE) and the kernel SIGKILLs the process — inside the preload's mach_msg, before main(). This is not specific to dsymutil: the entire Xcode toolchain is affected (clang, ld, nm, strip, lipo, dsymutil, ... all confirmed killed by signal 9; clang++, swift(c), ar, ranlib, otool, dwarfdump, objdump, llvm-* share the same CS_PLATFORM_BINARY + non-restricted property). dsymutil was just the binary the original report hit (Go's linker invokes it). Any compile/link step run under `samply record` breaks as soon as a build tool invokes a toolchain binary by absolute path (the norm); going through the restricted /usr/bin shims hides it because they strip DYLD_*. Symptom: "running dsymutil failed: signal: killed". Confirmed via the crash report (EXC_GUARD "ILLEGAL_MOVE on mach port 515", port 515 == mach_task_self()) and by probing csops(2): the only distinguishing bit between a killed platform binary and a surviving locally-built binary is CS_PLATFORM_BINARY. Fix: in the preload, detect platform binaries via csops(getpid(), CS_OPS_STATUS) and skip the task handoff for them. samply cannot profile a platform binary through this mechanism anyway (its task port is protected), so nothing is lost; the process runs normally instead of being killed. Descendant profiling of all normal binaries is unchanged. Includes a regression test (samply/tests/dsymutil_sigkill.rs). Preload rebuilt for x86_64/arm64/arm64e. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Resolve SDKROOT via `xcrun --show-sdk-path` instead of a hardcoded Xcode.app path, and pin clang as the linker for the arm64e -Zbuild-std target so the build works outside the default toolchain.
Add a no-alloc stderr logger (heapless fixed buffer, no allocator in a preload) installed from the constructor only when SAMPLY_PRELOAD_DEBUG is set. Makes it possible to see whether the preload loaded and completed the samply handoff in a given process.
SIP strips DYLD_* when execing a protected system binary, killing the preload for that subtree. Publish the preload path under a second, non-DYLD-prefixed alias that survives stripping, so a downstream choke point (e.g. CodSpeed's node.sh shim) can restore DYLD_INSERT_LIBRARIES and re-arm the preload.
Interpose execve/posix_spawn{,p} to detect when a process is about to
exec a SIP-protected Apple system binary (directly or via a shebang
interpreter). macOS strips DYLD_* on that exec, so the preload — and
samply's visibility — silently dies for the whole subtree. We don't
modify the exec; we only print a warning naming the binary, emitted
as a ::warning:: annotation under GitHub Actions.
Rebuild the bundled preload dylibs with the new code.
not-matthias
approved these changes
Jun 11, 2026
…ange This is the strategy that HotSpot uses, and is mostly safe. If we need this, the call chain would have been truncated in the first place anyway.
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