From 1d5e3cd80b66a3abd274107e75854476c603617d Mon Sep 17 00:00:00 2001 From: Josh Stone Date: Wed, 5 Jul 2017 12:03:17 -0700 Subject: [PATCH] Skip the main thread's manual stack guard on Linux Linux doesn't allocate the whole stack right away, and the kernel has its own stack-guard mechanism to fault when growing too close to an existing mapping. If we map our own guard, then the kernel starts enforcing a rather large gap above that, rendering much of the possible stack space useless. Instead, we'll just note where we expect rlimit to start faulting, so our handler can report "stack overflow", and trust that the kernel's own stack guard will work. Fixes #43052. --- src/libstd/sys/unix/thread.rs | 44 ++++++++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 15 deletions(-) diff --git a/src/libstd/sys/unix/thread.rs b/src/libstd/sys/unix/thread.rs index 1642baa34d63..15747746611c 100644 --- a/src/libstd/sys/unix/thread.rs +++ b/src/libstd/sys/unix/thread.rs @@ -264,23 +264,37 @@ pub mod guard { as *mut libc::c_void; } - // Rellocate the last page of the stack. - // This ensures SIGBUS will be raised on - // stack overflow. - let result = mmap(stackaddr, psize, PROT_NONE, - MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0); - - if result != stackaddr || result == MAP_FAILED { - panic!("failed to allocate a guard page"); - } - - let offset = if cfg!(any(target_os = "linux", target_os = "freebsd")) { - 2 + if cfg!(target_os = "linux") { + // Linux doesn't allocate the whole stack right away, and + // the kernel has its own stack-guard mechanism to fault + // when growing too close to an existing mapping. If we map + // our own guard, then the kernel starts enforcing a rather + // large gap above that, rendering much of the possible + // stack space useless. See #43052. + // + // Instead, we'll just note where we expect rlimit to start + // faulting, so our handler can report "stack overflow", and + // trust that the kernel's own stack guard will work. + Some(stackaddr as usize) } else { - 1 - }; + // Reallocate the last page of the stack. + // This ensures SIGBUS will be raised on + // stack overflow. + let result = mmap(stackaddr, psize, PROT_NONE, + MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0); + + if result != stackaddr || result == MAP_FAILED { + panic!("failed to allocate a guard page"); + } - Some(stackaddr as usize + offset * psize) + let offset = if cfg!(target_os = "freebsd") { + 2 + } else { + 1 + }; + + Some(stackaddr as usize + offset * psize) + } } #[cfg(target_os = "solaris")] -- 2.13.3