musl toolchain

This project prepares a libc musl toolchain from scratch, for use with Elide and general Native Image projects which target linux-amd64. Prepackaged are the following libraries, all built from sources, with consistent CFLAGS and compat with musl:

• mimalloc, which is built with stage1 musl gcc, then injected at stage2
• musl, built with latest patches and then injected with mimalloc
• zlib, cloudflare's optimized fork
• zstd, compression algo from meta
• openssl, with optimizations turned on
• sqlite, latest version, properly built for musl, optimizations on
• capnp (cap'n'proto), latest version, built against musl
• llvm, matching our rustc version, built against musl

Architectures

This toolchain is built for x86-64 and aarch64 targets, with the following march/mtune settings:

Architecture	Target	Tune	Notes
amd64 / x86-64	x86-64-v4	znver4	Targets AMD Zen 4+
arm64 / aarch64	armv8.2-a+crypto+crc	generic	Targets Ampere Altra+

Caution

This is an intentionally over-modern architecture matrix, for now.

Toolchain

The following versions are pinned/established by this toolchain:

Software	Version	Notes
GCC	15.2.0	Upgraded in line with Ubuntu build machines (25.10)
Binutils	2.44	GCC dependencies
GMP	6.3.0	GCC dependencies
MPC	1.3.1	GCC dependencies
MPFR	4.2.2	GCC dependencies
ISL	0.27	GCC dependencies
Linux	6.15.7	Kernel headers only
Clang/LLVM	21.1.2	Matches pinned rustc toolchain version
Musl Libc	1.2.5+p3	Latest + two upstream patches + Elide's singular patch
Mimalloc	3.1.5
OpenSSL	3.6.0
Zlib	[email protected]	Cloudflare's accelerated fork of zlib
Zstd	1.5.7
SQLite	3.51.0
Cap'n'Proto	master (v1)	"v1 with bugfixes" (v2 is unsupported in Java)

Usage

1. Build.

./build.sh
# ...
-----------------------------------------------
Musl Sysroot (1.2.5-patched.2):
  Location: /.../musl/1.2.5
  Compiler: /.../musl/1.2.5/bin/musl-gcc
  Arch:     x86-64-v4
  Tune:     znver3

Compiler flags:
  CFLAGS:   -I/.../musl/1.2.5/include
  LDFLAGS:  -L/.../musl/1.2.5/lib -static
  CC:       /.../musl/1.2.5/bin/musl-gcc
  CFLAGS:   -march=x86-64-v4 -mtune=znver3 -O2 -ffat-lto-objects -fstack-protector-strong -Wl,-z,relro,-z,now -Wa,--noexecstack -D_FORTIFY_SOURCE=2 -I/.../musl/1.2.5/include -I/usr/include/x86_64-linux-musl -flto=auto -fPIE -fPIC
  LDFLAGS:  -ffat-lto-objects -L/.../musl/1.2.5/lib -flto=auto -static -Wl,-z,relro,-z,now,-z,noexecstack

Components:
  mimalloc:   3.1.5
  libc:       /.../musl/1.2.5/lib/libc.a: current ar archive
  zlib:       ([email protected]) /.../musl/1.2.5/lib/libz.a: current ar archive
  openssl:    3.6.0 /.../musl/1.2.5/lib64/libssl.a: current ar archive
  sqlite:     3.51.0 /.../musl/1.2.5/lib/libsqlite3.a: current ar archive

Features:
  Secure:         OFF
  Guarded:        OFF
  CFI:            no
  Mimalloc:       yes
  Musl+Mimalloc:  yes
-----------------------------------------------

2. In another native build: Set variables and run.

export CC=$PWD/latest/x86_64-linux-musl-gcc
// ... or ...
./configure --prefix=$PWD/latest

3. ????

4. PROFIT!

> env MIMALLOC_SHOW_STATS=1 ./.dev/artifacts/native/elide/elide --version

2.0.0-alpha.1
heap stats:     peak       total     current       block      total#
  reserved:     1.0 GiB     1.0 GiB     1.0 GiB
 committed:     2.5 MiB     2.6 MiB     2.3 MiB
     reset:     0
    purged:   257.0 KiB
   touched:     0           0           0                                ok
     pages:     4           4           0                                ok
-abandoned:     0           0           0                                ok
 -reclaima:     0
 -reclaimf:     0
-reabandon:     0
    -waits:     0
 -extended:     0
   -retire:     0
    arenas:     1
 -rollback:     0
     mmaps:     3
   commits:     4
    resets:     0
    purges:     1
   guarded:     0
   threads:     0           0           0                                ok
  searches:     0.0 avg
numa nodes:     1
   elapsed:     0.000 s
   process: user: 0.000 s, system: 0.000 s, faults: 0, rss: 6.0 MiB, commit: 2.5 Mi

Modifications / Settings

The prepared sysroot includes all libraries, built statically, with the bootstrapped compiler. Modifications to Musl and libraries are listed below:

• Musl Libc
  • Patches (1, 2) applied according to upstream advice
  • Patch (3) applied to swap memallocng for mimalloc, default to -O2
  • Musl is built with -O3 for subsystems internal,malloc,string
• Musl Cross-Make
  • Added GCC 15.2.0
• Mimalloc
  • Built in secure mode by default
  • Built with bootstrapped musl compiler, then used for stage2 build
• Zlib
  • Uses Cloudflare's accelerated fork of zlib
• OpenSSL
  • Builds with curve optimizations enabled, TLSv1.3 support

CFLAGS underwent a round of hardening and optimization. Barring build conflicts, the following settings are applied to all compiled code:

-O2
-flto=auto
-ffat-lto-objects
-fno-plt
-fstack-protector-strong
-fomit-frame-pointer
-Wl,-z,relro,-z,now -Wa,--noexecstack

# on amd64
-march=x86-64-v4
-mtune=znver3

# on arm64
-march=armv8.4-a+crypto+sve
-mtune=neoverse-v1