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Support dynamically-linked FreeBSD libc when cross-compiling #23835

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@alexrp alexrp commented May 8, 2025

libc update instructions: https://github.com/ziglang/zig/wiki/Updating-libc#freebsd

ABI tooling: https://github.com/ziglang/libc-abi-tools/tree/main/freebsd

Caveats:

  • This only works for 14+ (we still target 13 by default).
    • The startup ABI between crt1 and libc changed significantly in 14. I don't see much value in making it work for 13 since 15 will be released later this year.
  • We only track major releases in the abilists file, not minor/patch.
  • As with glibc and musl, we only ship the latest system and libc headers (14.2.0 specifically).
  • We don't support _init/_fini because it's 2025 and people should be using .init_array/.fini_array.
  • I removed some silly GCJ support code from crt1.

Contributes to #2876.

My next priority will be dynamically-linked libc for NetBSD (#2877), after which I'll look at static linking for both.

@alexrp alexrp requested review from andrewrk and mikdusan May 8, 2025 19:48
@alexrp alexrp force-pushed the freebsd-libc branch 4 times, most recently from dac1fca to 40dfc11 Compare May 8, 2025 21:33
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andrewrk commented May 8, 2025

What is the delta installation size (both compressed and on disk)?

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alexrp commented May 8, 2025

Uncompressed lib/libc is going from 104M to 118M, and xz -9-compressed tarball of lib/libc is going from 9.7M to 12M. Not sure about the full release tarball; don't have free CPU cores to build that right now. 😰

Speaking of size savings: #21258

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andrewrk commented May 8, 2025

hmmmm, +13% / +24% is pretty bad for only gaining 1 new target. 14 megabytes of headers seems excessive. The files added look reasonable though.

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alexrp commented May 9, 2025 •
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I think it looks worse than it actually is because we tend to take for granted the Linux situation of kernel and libc headers being separate. Some perspective:

  • lib/libc/freebsd lib/libc/include/*freebsd*: 13M
  • lib/libc/glibc lib/libc/include/*glibc* lib/libc/include/*gnu* lib/libc/include/*linux*: 16M
  • lib/libc/musl lib/libc/include/*musl* lib/libc/include/*linux*: 16M
  • lib/libc/mingw lib/libc/include/*windows*: 75M
  • lib/libc/darwin lib/libc/include/*macos*: 6.8M (though it's known that we're missing quite a few macOS headers)

In that light, I don't think it looks that bad actually.

That said, there's definitely room to prune FreeBSD headers; some are really kernel-only, and there are probably still some that aren't strictly related to the kernel or libc. But pruning these is going to be a very manual and tedious process.

only gaining 1 new target

Also, just to be clear, this is adding all FreeBSD 14 targets:

  • aarch64-freebsd-none
  • arm-freebsd-eabihf
  • powerpc-freebsd-eabihf
  • powerpc64-freebsd-none
  • powerpc64le-freebsd-none
  • riscv64-freebsd-none
  • x86-freebsd-none
  • x86_64-freebsd-none

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alexrp commented May 9, 2025 •
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zig-bootstrap works:

❯ file out/zig-x86_64-freebsd.14.0-none-baseline/zig
out/zig-x86_64-freebsd.14.0-none-baseline/zig: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /libexec/ld-elf.so.1, FreeBSD-style, stripped

@mikdusan also verified that the resulting binary actually runs on FreeBSD 14.

This should be ready for review.

@alexrp alexrp mentioned this pull request May 9, 2025
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@alexrp alexrp force-pushed the freebsd-libc branch 3 times, most recently from 6edf506 to 12465d3 Compare May 9, 2025 12:07
alexrp added 14 commits May 10, 2025 12:19
@alexrp
test: Remove some nonsensical FreeBSD targets from llvm_targets.
ba9f257
@alexrp
std.Target: Fix requiresLibC() for FreeBSD.
4604217
@alexrp
std.Target: Add isFreeBSDLibC() function.
309ff9c
@alexrp
compiler: Move vendored library support to libs subdirectory.
610d3cf
@alexrp
libcxxabi: Pass -fPIC via module options instead of CFLAGS.
162b11b
@alexrp
process_headers: Add FreeBSD libc support.
df719f2
@alexrp
libc: Add FreeBSD system and libc headers from 14.2.0.
6e64bc8 
osreldate.h and sys/param.h were manually adjusted to not __FreeBSD_version
since it will be defined by the compiler.
@alexrp
std.zig.LibCDirs: Add FreeBSD libc support.
01390cc
@alexrp
libc: Add FreeBSD libc startup code from 14.2.0.
a36dcef 
* NT_FREEBSD_ABI_TAG was manually adjusted from using a hardcoded value to using
  __FreeBSD_version which will be defined by the compiler.
* GCJ stuff was removed.
* HAVE_CTORS definitions were removed.
@alexrp
update_freebsd_libc: Add tool for updating FreeBSD libc startup code.
68cd004
@alexrp
libc: Add FreeBSD libc abilists file.
be566a4 
Currently covers version 1.7 (FreeBSD 14.0.0).
@alexrp
compiler: Define __FreeBSD_version when targeting FreeBSD libc.
9e23e1d
@alexrp
std.zig.target: Add FreeBSD libc support.
eeaa1b1
@alexrp
std.Target: Factor arch/ABI into FreeBSD minimum OS version selection.
0e3609b 
Based on data in std.zig.target.
alexrp added 2 commits May 10, 2025 20:58
@alexrp
compiler: Support building FreeBSD crt1.o/Scrt1.o and stub shared lib…
d3a6236 
…raries.

Only works for FreeBSD 14+. Note that we still default to targeting FreeBSD 13.

Contributes to ziglang#2876.
@alexrp
Compilation: Don't pass -mabi to Clang on powerpc64(le)-freebsd.
2116f2e 
The driver doesn't support it, and FreeBSD 13+ on PPC64 uses ELFv2 anyway.
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In that light, I don't think it looks that bad actually.

I agree, thanks for sharing this additional insight!

andrewrk
andrewrk approved these changes May 10, 2025
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Looks great!

alexrp added 4 commits May 11, 2025 11:15
@alexrp
Compilation.Config: Default to dynamic linking with FreeBSD libc.
e8992af
@alexrp
test: Add {powerpc64,riscv32}-netbsd-none to llvm_targets.
6282129
@alexrp
freebsd: Create strong references to __progname and environ in stub l…
4c2f1e0 
…ibc.so.

These symbols are defined in the statically-linked startup code. The real
libc.so.7 contains strong references to them, so they need to be put into the
dynamic symbol table.
@alexrp
compiler: Link libc by default when targeting FreeBSD.
f3e851d 
We don't yet have a direct syscall layer in std.os.freebsd.
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@andrewrk andrewrk andrewrk approved these changes

@mikdusan mikdusan Awaiting requested review from mikdusan

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