llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-libunwind Author: Raúl Marín (Algunenano) <details> <summary>Changes</summary> With `_LIBUNWIND_REMEMBER_STACK_ALLOC` (the default on Linux, Apple, Android, MinGW and bare metal), `DW_CFA_remember_state` allocates a `PrologInfoStackEntry` with `alloca` and `DW_CFA_restore_state` cannot free it. So interpreting an FDE takes stack proportional to the total number of remember/restore pairs before the target PC, rather than to their nesting depth. Compilers emit a pair around each epilogue in the middle of a function, and each entry holds a whole `PrologInfo`: about 570 bytes on x86-64 and about 1.6 KB on AArch64. We hit this in ClickHouse on AArch64. Its query profiler samples threads with a signal handler that captures a stack trace with libunwind, on whatever stack the thread is running. ClickHouse establishes connections to remote servers in Boost fibers, whose stacks are 320 KiB. Unwinding through a function with 191 remember/restore pairs, a single `parseFDEInstructions` call used about 300 KB and ran the fiber's stack into its guard page. This patch keeps the entries popped by `DW_CFA_restore_state` on a free list and reuses them for the next `DW_CFA_remember_state`, so the stack used is bounded by the nesting depth. With the heap allocator, the destructor frees both lists. Testing: the new `libunwind/test/remember_state_stack.pass.cpp` unwinds through a frame with 5000 pairs after lowering the soft `RLIMIT_STACK` to 256 KiB. On x86-64 Linux it crashes with `SIGSEGV` without the change and passes with it. `check-unwind` (shared and static configs) and `check-cxxabi` pass. This PR was prepared with the help of Claude Code; I reviewed the change and the test. --- Full diff: https://github.com/llvm/llvm-project/pull/226964.diff 2 Files Affected: - (modified) libunwind/src/DwarfParser.hpp (+24-10) - (added) libunwind/test/remember_state_stack.pass.cpp (+52) ``````````diff The server is unavailable at this time. Please wait a few minutes before you try again. `````````` </details> https://github.com/llvm/llvm-project/pull/226964 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
