How far back should older glibc support go?

[rootbeer]

Zig Version

0.12.0-dev.1333+8b1073341

Steps to Reproduce and Observed Behavior

Zig can compile against many specific glibc versions successfully:

$ zig build-exe hello.zig -lc -target x86-linux-gnu.2.33
$ zig build-exe hello.zig -lc -target aarch64-linux-gnu.2.33
$ zig build-exe hello.zig -lc -target x86-linux-gnu.2.17
$ zig build-exe hello.zig -lc -target aarch64-linux-gnu.2.17

However, if the glibc version gets too old, errors crop up. E.g., on x86 (and x86_64) glibc versions before v2.16 fail due to the getauxval symbol used by start.zig:

$ zig build-exe hello.zig -lc -target x86-linux-gnu.2.15
error: ld.lld: undefined symbol: getauxval
    note: referenced by start.zig:476 (/home/pat/projects/ziglang/zig/lib/std/start.zig:476)
    note:               hello.o:(main)
    note: referenced by start.zig:477 (/home/pat/projects/ziglang/zig/lib/std/start.zig:477)
    note:               hello.o:(main)

On aarch64, there are a ton of errors at v2.16 and earlier (these look extra suspicious, like the glibc runtime libraries are being mis-built?):

$ zig build-exe hello.zig -lc -target aarch64-linux-gnu.2.16
error: ld.lld: undefined symbol: __libc_start_main
    note: referenced by start-2.33.S:92 (/home/pat/projects/ziglang/zig/lib/libc/glibc/sysdeps/aarch64/start-2.33.S:92)
    note:               /home/pat/.cache/zig/o/3fec5149eac3449eef162626281b911d/Scrt1.o:(.text+0x30)
error: ld.lld: undefined symbol: abort
    note: referenced by start-2.33.S:95 (/home/pat/projects/ziglang/zig/lib/libc/glibc/sysdeps/aarch64/start-2.33.S:95)
    note:               /home/pat/.cache/zig/o/3fec5149eac3449eef162626281b911d/Scrt1.o:(.text+0x34)
    note: referenced by os.zig:608 (/home/pat/projects/ziglang/zig/lib/std/os.zig:608)
    note:               hello.o:(os.abort)
error: ld.lld: undefined symbol: __fxstat64
    note: referenced by fstat64-2.32.c:51 (/home/pat/projects/ziglang/zig/lib/libc/glibc/io/fstat64-2.32.c:51)
    note:               /home/pat/.cache/zig/o/79fd86fc882e9274904ca70a9f85d0f1/fstat64-2.32.o:(fstat64) in archive /home/pat/.cache/zig/o/be11b83084d20d5d4a81b606d601713a/libc_nonshared.a
error: ld.lld: undefined symbol: __stack_chk_guard
...
(lots more missing symbols)

Zig claims support going back to 2.0.0!

$  zig4 targets | jq -c '.glibc'
["2.0.0","2.1.0","2.1.1","2.1.2","2.1.3","2.2.0","2.2.1","2.2.2","2.2.3","2.2.4","2.2.5","2.2.6","2.3.0","2.3.2","2.3.3","2.3.4","2.4.0","2.5.0","2.6.0","2.7.0","2.8.0","2.9.0","2.10.0","2.11.0","2.12.0","2.13.0","2.14.0","2.15.0","2.16.0","2.17.0","2.18.0","2.19.0","2.20.0","2.21.0","2.22.0","2.23.0","2.24.0","2.25.0","2.26.0","2.27.0","2.28.0","2.29.0","2.30.0","2.31.0","2.32.0","2.33.0","2.34.0","2.35.0","2.36.0","2.37.0","2.38.0"]

For context, GNU glibc v2.17 is from 2012, and 2.0.0 is from the previous millennium (see https://sourceware.org/glibc/wiki/Glibc%20Timeline).

Should these older versions work? Or is cutting things off at 2.17 (or maybe 2.20 from 2014?) a reasonable "fix"?

Expected Behavior

hello.zig compiles against all the supported glibc versions on all the supported architectures.

[andrewrk]

Certainly not older than 2.17. Let's hard cap it there.

[mikdusan]

also old version capping varies by architecture:

• aarch64 was added in glibc 2.17
• powerpc64le was added in glibc 2.19
• riscv was added in glibc 2.27

[rootbeer]

I'll add patches for these bounds checks to my fix-libc PR. I can do the Zig-wide v2.17+ check, but am not sure where I might put per-architecture checks. Are there other similar checks I can look for?