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fix(android/aarch64): use libc::ucontext_t from Android NDK #5189

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fix(android/aarch64): use libc::ucontext_t from Android NDK #5189

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2 changes: 1 addition & 1 deletion src/unix/linux_like/android/b32/arm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ s! {

pub struct __c_anonymous_uc_sigmask_with_padding {
pub uc_sigmask: crate::sigset_t,
/* Android has a wrong (smaller) sigset_t on x86. */
/* Android has a wrong (smaller) sigset_t on ARM. */
__padding_rt_sigset: Padding<u32>,
}

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26 changes: 25 additions & 1 deletion src/unix/linux_like/android/b64/aarch64/mod.rs
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Expand Up @@ -63,7 +63,10 @@ s! {
pub uc_flags: c_ulong,
pub uc_link: *mut ucontext_t,
pub uc_stack: crate::stack_t,
pub uc_sigmask: crate::sigset_t,
pub uc_sigmask__c_anonymous_union: __c_anonymous_uc_sigmask,
/* The kernel adds extra padding after uc_sigmask to match
* glibc sigset_t on ARM64. */
__padding: Padding<[c_char; 128 - size_of::<crate::sigset_t>()]>,

@teor2345 teor2345 Jun 25, 2026 •
edited by rustbot
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Why is this subtracting sigset_t (32 bit?), but the comment refers to ARM64?

This calculation seems weird for either 32-bit or 64-bit, and might need further comments:

  • the union is the size of sigset64_t (assuming it's bigger) but we subtract sigset_t (the 32-bit size) from the padding

View changes since the review

@StackOverflowExcept1on StackOverflowExcept1on Jun 25, 2026

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https://android.googlesource.com/platform/bionic/+/refs/tags/ndk-r29/libc/include/sys/ucontext.h#102
image

pub uc_mcontext: mcontext_t,
}

Expand All @@ -85,12 +88,33 @@ s! {
}

s_no_extra_traits! {
pub union __c_anonymous_uc_sigmask {
uc_sigmask: crate::sigset_t,
uc_sigmask64: crate::sigset64_t,
}

#[repr(align(16))]
pub struct max_align_t {
priv_: [f32; 8],
}
}

cfg_if! {
if #[cfg(feature = "extra_traits")] {
impl PartialEq for __c_anonymous_uc_sigmask {
fn eq(&self, other: &__c_anonymous_uc_sigmask) -> bool {
unsafe { self.uc_sigmask == other.uc_sigmask }

@teor2345 teor2345 Jun 25, 2026

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Is this sound and correct if the 64-bit sigmask was initialised in the union?

  • if the 64-bit sigmask is larger and has no padding, then the equality check misses some bytes
  • if the 32-bit sigmask is larger (unlikely), then we're comparing uninitialised bytes
  • if there's padding, then does it need to be ignored?

}
}
impl Eq for __c_anonymous_uc_sigmask {}
impl hash::Hash for __c_anonymous_uc_sigmask {
fn hash<H: hash::Hasher>(&self, state: &mut H) {
unsafe { self.uc_sigmask.hash(state) }

@teor2345 teor2345 Jun 25, 2026

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Same here, not sure we can do this with unions, without some guarantee they are the same size.

@StackOverflowExcept1on StackOverflowExcept1on Jun 25, 2026 •
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This code was simply borrowed from the ARM module:

libc/src/unix/linux_like/android/b32/arm.rs

Lines 59 to 73 in a8e2958

cfg_if! {
if #[cfg(feature = "extra_traits")] {
impl PartialEq for __c_anonymous_uc_sigmask {
fn eq(&self, other: &__c_anonymous_uc_sigmask) -> bool {
unsafe { self.uc_sigmask == other.uc_sigmask }
}
}
impl Eq for __c_anonymous_uc_sigmask {}
impl hash::Hash for __c_anonymous_uc_sigmask {
fn hash<H: hash::Hasher>(&self, state: &mut H) {
unsafe { self.uc_sigmask.hash(state) }
}
}
}
}

@StackOverflowExcept1on StackOverflowExcept1on Jun 25, 2026

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x86_64 has same layout:

libc/src/unix/linux_like/android/b64/x86_64/mod.rs

Lines 170 to 184 in a8e2958

cfg_if! {
if #[cfg(feature = "extra_traits")] {
impl PartialEq for __c_anonymous_uc_sigmask {
fn eq(&self, other: &__c_anonymous_uc_sigmask) -> bool {
unsafe { self.uc_sigmask == other.uc_sigmask }
}
}
impl Eq for __c_anonymous_uc_sigmask {}
impl hash::Hash for __c_anonymous_uc_sigmask {
fn hash<H: hash::Hasher>(&self, state: &mut H) {
unsafe { self.uc_sigmask.hash(state) }
}
}
}
}

}
}
}
}

pub const O_DIRECT: c_int = 0x10000;
pub const O_DIRECTORY: c_int = 0x4000;
pub const O_NOFOLLOW: c_int = 0x8000;
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