feat(guest): replace musl with picolibc by andreiltd · Pull Request #831 · hyperlight-dev/hyperlight

andreiltd · 2025-08-28T11:48:24Z

No description provided.

jprendes

I love this PR!

jprendes · 2025-08-28T13:04:24Z

src/hyperlight_guest_bin/src/host_bridge.rs

+    )
+    .unwrap_or_default();
+
+    let n = bytes.len();


Do we want to assert n <= count?
A wrongly implemented HostRead could cause a buffer overflow

jprendes · 2025-08-28T13:06:08Z

src/hyperlight_guest_bin/src/host_bridge.rs

+    }
+
+    let slice = unsafe { core::slice::from_raw_parts(buf as *const u8, count) };
+    let s = core::str::from_utf8(slice).unwrap_or("<invalid utf8>");


question: what do you think of using String::from_utf8_lossy instead? we are doing s.to_string() anyway.

Sure! As long as from_utf8_lossy doesn't allocate if string is valid utf-8 which I believe is the case?

It returns a Cow, so, that's correct, but you will need to allocate a string to send it to the host function anyway... so... ¯\_(ツ)_/¯

jprendes · 2025-08-28T13:13:47Z

src/hyperlight_guest_bin/Cargo.toml

 [features]
-default = ["libc", "printf"]
-libc = [] # compile musl libc
-printf = [ "libc" ] # compile printf


opinion: I would just put everything under the same libc feature

Sure, I guess any code from libc if not referenced will be DCE anyway 🤷

jprendes · 2025-08-28T14:02:51Z

src/hyperlight_guest_bin/src/host_bridge.rs

+pub extern "C" fn write(fd: c_int, buf: *const c_void, count: usize) -> isize {
+    // Only stdout (fd=1) and stderr (fd=2)
+    if fd != 1 && fd != 2 {
+        return count as isize;


question: shuoldn't this return -1, or some other indication of error? and set errno?

Right, I think that in order to support this properly we would need to generate the bindings to libc headers and use that to reference errno, EBADF etc. But then, it might be better to just have picolibc-sys crate. Anyway I agree we should report an error here somehow.

jprendes · 2025-08-28T14:05:04Z

src/hyperlight_guest_bin/src/host_bridge.rs

+pub extern "C" fn read(fd: c_int, buf: *mut c_void, count: usize) -> isize {
+    // Only stdin (fd=0) and only if HostRead is defined
+    if fd != 0 || !CAPS.host_read() {
+        return 0;


question: should the case of fd != 0 return -1 and set errno instead?

jsturtevant · 2025-08-28T21:07:02Z

will help with #282

src/hyperlight_host/tests/sandbox_host_tests.rs

raftario · 2025-12-11T17:37:01Z

Is this still on the table ?

jsturtevant · 2025-12-11T20:50:19Z

Yes but need approval on licensing before being able to move forward: cncf/foundation#1117

jprendes · 2026-02-25T10:35:50Z

src/hyperlight_guest_bin/.cargo/config.toml

@@ -1,2 +1,3 @@
 [build]
 target = "x86_64-unknown-none"
+rustflags = ["-Zdirect-access-external-data"]


Where does this come from?

IIRC rustc generated unsupported reallocations without this flag

This is a nightly flag, right?
Also, this will not apply to comsumers of hyperlight-guest-bin, right?

I think it's worth to recheck and try to remove it.

Everything seems to work without the flag, I remove it for now 🤷‍♂️

Signed-off-by: Tomasz Andrzejak <andreiltd@gmail.com>

andreiltd requested review from danbugs, dblnz, devigned, jprendes, ludfjig, marosset, simongdavies and syntactically as code owners August 28, 2025 11:48

andreiltd marked this pull request as draft August 28, 2025 11:48

andreiltd force-pushed the libc-takeover branch from 617d834 to 3f8ffcf Compare August 28, 2025 12:01

andreiltd added the kind/enhancement For PRs adding features, improving functionality, docs, tests, etc. label Aug 28, 2025

andreiltd force-pushed the libc-takeover branch 6 times, most recently from eaf1d54 to b18a374 Compare August 28, 2025 13:44

jprendes reviewed Aug 28, 2025

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jsturtevant mentioned this pull request Aug 28, 2025

[License Exception Request] [Hyperlight] [Older BSD like licenses] cncf/foundation#1117

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12 tasks

andreiltd force-pushed the libc-takeover branch 5 times, most recently from 499c59d to 2ae0a3a Compare August 29, 2025 18:42

jprendes reviewed Sep 4, 2025

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src/hyperlight_host/tests/sandbox_host_tests.rs Outdated Show resolved Hide resolved

andreiltd force-pushed the libc-takeover branch from 2ae0a3a to d3826af Compare September 4, 2025 11:29

andreiltd mentioned this pull request Sep 5, 2025

Use mimalloc as a guest allocator #867

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andreiltd force-pushed the libc-takeover branch from d2043ac to 2bd1ff4 Compare September 9, 2025 09:31

andreiltd force-pushed the libc-takeover branch 5 times, most recently from 9f5c6c1 to a59c7ce Compare September 9, 2025 12:19

andreiltd force-pushed the libc-takeover branch 2 times, most recently from 65634a7 to 980cb20 Compare February 25, 2026 10:31

jprendes reviewed Feb 25, 2026

View reviewed changes

andreiltd force-pushed the libc-takeover branch 2 times, most recently from c24ce45 to d9fb9e5 Compare February 25, 2026 11:33

feat(guest): replace musl with picolibc

16db912

Signed-off-by: Tomasz Andrzejak <andreiltd@gmail.com>

andreiltd force-pushed the libc-takeover branch 2 times, most recently from e4caabe to 7b99307 Compare February 25, 2026 17:59

bump picolibc to 1.8.11

fb1549f

Signed-off-by: Tomasz Andrzejak <andreiltd@gmail.com>

andreiltd force-pushed the libc-takeover branch from 7b99307 to fb1549f Compare February 25, 2026 18:12

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jsturtevant commented Aug 28, 2025

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raftario commented Dec 11, 2025

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