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stack overflow handler specific openbsd change. #87528

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Oct 9, 2021
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stack overflow handler specific openbsd change. #87528

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17 changes: 9 additions & 8 deletions library/std/src/sys/unix/stack_overflow.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -143,14 +143,15 @@ mod imp {
}

unsafe fn get_stackp() -> *mut libc::c_void {
let stackp = mmap(
ptr::null_mut(),
SIGSTKSZ + page_size(),
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON,
-1,
0,
);
// OpenBSD requires this flag for stack mapping
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"this flag" is referring to MAP_STACK? If so the comment is on the wrong line.

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indeed :)

// otherwise the said mapping will fail as a no-op on most systems
// and has a different meaning on FreeBSD
#[cfg(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux",))]
let flags = MAP_PRIVATE | MAP_ANON | libc::MAP_STACK;
#[cfg(not(any(target_os = "openbsd", target_os = "netbsd", target_os = "linux",)))]
let flags = MAP_PRIVATE | MAP_ANON;
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Linux supports MAP_STACK too. It is a no-op on all architectures. FreeBSD supports it too. For example macOS doesn't support it though.

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yes but not necessary on these oses plus solaris/illumos does not have it and I believe haiku neither.

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yes but not necessary

Not currently necessary. A future architecture may need it. That is why it exists as no-op at all.

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ok can add for linux, netbsd but I m less sure about FreeBSD the flag is working but does not seem to work well with null start addresses, seems little usage difference.

let stackp =
mmap(ptr::null_mut(), SIGSTKSZ + page_size(), PROT_READ | PROT_WRITE, flags, -1, 0);
if stackp == MAP_FAILED {
panic!("failed to allocate an alternative stack: {}", io::Error::last_os_error());
}
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