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Add support for Emscripten v4.0.12 to v6.0.11 #5610

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Merged
tgross35 merged 3 commits into from
Oct 16, 2026
+58 −14
Merged

Add support for Emscripten v4.0.12 to v6.0.11 #5610

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d1c69e6
test: fix ABI mismatch in cmsg_* test
madsmtm Oct 5, 2026
8122515
emscripten: update emsdk
madsmtm Oct 5, 2026
fd71da9
emscripten: fix ABI-breakages
madsmtm Oct 5, 2026
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35 changes: 30 additions & 5 deletions build.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,9 @@ enum Cfg {
LibcPauthtest,

EmscriptenOldStatAbi,
EmscriptenFsblkcntIs32bit,
EmscriptenSigsetLarge,
EmscriptenNfdsIsULong,

/// Should be enabled by users if esp-idf (>=6.0) is build with picolibc instead of newlib. Not
/// set by `libc` itself.
Expand Down Expand Up @@ -63,6 +66,9 @@ enum Cfg {
const ALLOWED_CFGS: &[Cfg] = &[
Cfg::LibcDenyWarnings,
Cfg::EmscriptenOldStatAbi,
Cfg::EmscriptenFsblkcntIs32bit,
Cfg::EmscriptenSigsetLarge,
Cfg::EmscriptenNfdsIsULong,
Cfg::EspidfPicolibc,
Cfg::EspidfTime32,
Cfg::Freebsd10,
Expand All @@ -88,6 +94,9 @@ impl fmt::Display for Cfg {
f.write_str(match self {
Cfg::LibcDenyWarnings => "libc_deny_warnings",
Cfg::EmscriptenOldStatAbi => "emscripten_old_stat_abi",
Cfg::EmscriptenFsblkcntIs32bit => "emscripten_fsblkcnt_is_32bit",
Cfg::EmscriptenSigsetLarge => "emscripten_sigset_large",
Cfg::EmscriptenNfdsIsULong => "emscripten_nfds_is_ulong",
Cfg::EspidfPicolibc => "espidf_picolibc",
Cfg::EspidfTime32 => "espidf_time32",
Cfg::Freebsd10 => "freebsd10",
Expand Down Expand Up @@ -214,10 +223,23 @@ fn main() {
}

if target_os == "emscripten" {
match emcc_version_code() {
Some(v) if (v < 30142) => cfgs.push(Cfg::EmscriptenOldStatAbi),
// Non-Emscripten or version >= 3.1.42.
_ => (),
if let Some(v) = emcc_version_code() {
// 3.1.42

@hoodmane hoodmane Oct 5, 2026 •
edited by rustbot
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Minimum supported version is 4.0.0 so let's drop this.

View changes since the review

@madsmtm madsmtm Oct 5, 2026

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But minimum supported version is only very recently v4.0.0, whereas libc can still be used with lower MSRV?

@hoodmane hoodmane Oct 5, 2026

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It's not much code to keep so if there's a reason then it's probably fine.

@tgross35 tgross35 Oct 10, 2026

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It's pretty small so we may as well keep it around for now. Could we document the versions we support at https://doc.rust-lang.org/beta/rustc/platform-support/wasm32-unknown-emscripten.html?

@madsmtm madsmtm Oct 10, 2026 •
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nightly: https://doc.rust-lang.org/nightly/rustc/platform-support/wasm32-unknown-emscripten.html#requirements ;)

@tgross35 tgross35 Oct 11, 2026

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Argh why do I always wind up on the beta version of those pages, thanks for the link

if v < 30142 {
cfgs.push(Cfg::EmscriptenOldStatAbi);
}
// 4.0.12
if v < 40012 {
cfgs.push(Cfg::EmscriptenFsblkcntIs32bit);
}
// 5.0.5
if v < 50005 {
cfgs.push(Cfg::EmscriptenSigsetLarge);
}
// 6.0.1
if v < 60001 {
cfgs.push(Cfg::EmscriptenNfdsIsULong);
}
}
}

Expand Down Expand Up @@ -452,7 +474,10 @@ fn validate_cfg(list: &[Cfg], target_env: &str, target_os: &str, target_ptr_widt
Cfg::EspidfPicolibc => (),
Cfg::EspidfTime32 => (),

Cfg::EmscriptenOldStatAbi => {
Cfg::EmscriptenOldStatAbi
| Cfg::EmscriptenFsblkcntIs32bit
| Cfg::EmscriptenSigsetLarge
| Cfg::EmscriptenNfdsIsULong => {
assert_eq!(
target_os, "emscripten",
"{cfg:?} set on non-freebsd platform"
Expand Down
2 changes: 1 addition & 1 deletion ci/emscripten.sh
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Expand Up @@ -4,7 +4,7 @@ set -eux

# Note: keep in sync with:
# https://github.com/rust-lang/rust/blob/master/src/doc/rustc/src/platform-support/wasm32-unknown-emscripten.md#requirements
emsdk_version=3.1.68
emsdk_version=6.0.11

@madsmtm madsmtm Oct 5, 2026 •
edited
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Ideally, we should test a range of emscripten versions, though I'm unsure how we'd go about doing that?

WDYT @tgross35?

@tgross35 tgross35 Oct 10, 2026

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It wouldn't hurt but I also wouldn't prioritize it, hopefully any ABI breaks continue to be small.


git clone https://github.com/emscripten-core/emsdk.git /emsdk-portable
cd /emsdk-portable
Expand Down
10 changes: 5 additions & 5 deletions libc-test/tests/cmsg.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,17 +9,17 @@ mod t {
use libc::{
self,
c_uchar,
c_uint,
c_void,
cmsghdr,
msghdr,
size_t,
};

extern "C" {
pub fn cmsg_firsthdr(msgh: *const msghdr) -> *mut cmsghdr;
pub fn cmsg_nxthdr(mhdr: *const msghdr, cmsg: *const cmsghdr) -> *mut cmsghdr;
pub fn cmsg_space(length: c_uint) -> usize;
pub fn cmsg_len(length: c_uint) -> usize;
pub fn cmsg_space(length: size_t) -> size_t;
pub fn cmsg_len(length: size_t) -> size_t;
pub fn cmsg_data(cmsg: *const cmsghdr) -> *mut c_uchar;
}

Expand Down Expand Up @@ -51,7 +51,7 @@ mod t {
fn test_cmsg_len() {
for l in 0..128 {
unsafe {
assert_eq!(libc::CMSG_LEN(l) as usize, cmsg_len(l));
assert_eq!(libc::CMSG_LEN(l) as usize, cmsg_len(l as usize));
}
}
}
Expand Down Expand Up @@ -118,7 +118,7 @@ mod t {
fn test_cmsg_space() {
unsafe {
for l in 0..128 {
assert_eq!(libc::CMSG_SPACE(l) as usize, cmsg_space(l));
assert_eq!(libc::CMSG_SPACE(l) as usize, cmsg_space(l as usize));
}
}
}
Expand Down
25 changes: 22 additions & 3 deletions src/unix/linux_like/emscripten/mod.rs
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Expand Up @@ -9,6 +9,11 @@ pub type shmatt_t = c_ulong;
pub type mqd_t = c_int;
pub type msgqnum_t = c_ulong;
pub type msglen_t = c_ulong;
// nfds_t is 32-bit on wasm64 since 6.0.1:
// https://github.com/emscripten-core/emscripten/pull/27115
#[cfg(not(emscripten_nfds_is_ulong))]
pub type nfds_t = c_uint;
#[cfg(emscripten_nfds_is_ulong)]
pub type nfds_t = c_ulong;
pub type nl_item = c_int;
pub type idtype_t = c_uint;
Expand All @@ -23,8 +28,17 @@ pub type off_t = i64;
pub type blkcnt_t = i32;

pub type blksize_t = c_long;
pub type fsblkcnt_t = u32;
pub type fsfilcnt_t = u32;
cfg_if! {
// `fsblkcnt_t` and `fsfilcnt_t` are 64-bit since v4.0.12, see:
// https://github.com/emscripten-core/emscripten/pull/24769
if #[cfg(not(emscripten_fsblkcnt_is_32bit))] {
pub type fsblkcnt_t = u64;
pub type fsfilcnt_t = u64;
} else {
pub type fsblkcnt_t = u32;
pub type fsfilcnt_t = u32;
}
}
pub type rlim_t = u64;
pub type nlink_t = u32;

Expand Down Expand Up @@ -212,7 +226,12 @@ s! {
}

pub struct sigset_t {
__val: [c_ulong; 32],
// sigset_t is smaller since Emscripten v5.0.5:
// https://github.com/emscripten-core/emscripten/pull/26574
#[cfg(not(emscripten_sigset_large))]
__val: [c_ulong; 2],
#[cfg(emscripten_sigset_large)]
__val: [c_ulong; 128 / size_of::<c_long>()],
}

pub struct msghdr {
Expand Down