cmd/link: place Darwin bind entries on the __DATA_CONST segment

[qmuntal]

#38830 moved the .rodata, .typelink, .itablink, and .gopclntab sections to the __DATA_CONST segment. Looks like the .got section can also go into that new segment. It is currently passed in the __DATA segment.

You can verify that the macOS clang linker already does what I'm suggesting here by following these steps:

1. Build a hello world binary with go build -ldflags=linkmode=external -o ext
2. Get the bind table by running objdump --macho --bind ./ext

The result is something like this:

Bind table:
segment  section            address     type       addend dylib            symbol
__DATA_CONST __got              0x100088000 bind ptr        0 libSystem        ___error
__DATA_CONST __got              0x100088008 bind ptr        0 libSystem        ___stderrp
...

While the same binary built with the Go internal linker has the following bind table:

Bind table:
segment  section            address    type       addend dylib            symbol
__DATA   __nl_symbol_ptr    0x1000EC2B0 pointer         0 libSystem        ___error
__DATA   __nl_symbol_ptr    0x1000EC2B8 pointer         0 libSystem        ___stderrp
...

Also note that clang names the.got section as __got on ARM, while we use __nl_symbol_ptr uncoditionally. Don't know if this makes any real difference, but clang made that change consciously in this commit: https://cgit.geodns-americas.gentoo.org/fork/llvm-project.git/commit/?h=release/3.8.x&id=e8d9df4ea52a5652a13f080614507d70e9f9ad79.

Go version:

go version go1.23.3 darwin/arm64

Clang version:

Apple clang version 16.0.0 (clang-1600.0.26.4)

@golang/compiler @golang/darwin

[gabyhelp]

Related Issues

• cmd/link: use __DATA_CONST on darwin? #38830 (closed)

Related Code Changes

• cmd/link: put read-only data in __DATA_CONST segment
• cmd/link/internal/ld, cmd/go: -buildmode=c-shared support for darwin/amd64
• cmd/link: always use symbol-targeted relocations on Mach-O
• liblink, cmd/ld, cmd/5l: darwin/arm support

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[gopherbot]

Change https://go.dev/cl/644055 mentions this issue: cmd/link: put .got section in __DATA_CONST segment