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linux: omit getauxval from binary if not needed #22276

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Merged
merged 1 commit into from Mar 26, 2025
Merged

linux: omit getauxval from binary if not needed #22276

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18 changes: 9 additions & 9 deletions lib/std/os/linux.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -475,22 +475,22 @@ pub const O = switch (native_arch) {
/// Set by startup code, used by `getauxval`.
pub var elf_aux_maybe: ?[*]std.elf.Auxv = null;

/// Whether an external or internal getauxval implementation is used.
const extern_getauxval = switch (builtin.zig_backend) {
// Calling extern functions is not yet supported with these backends
.stage2_aarch64, .stage2_arm, .stage2_riscv64, .stage2_sparc64 => false,
else => !builtin.link_libc,
};

comptime {
const root = @import("root");
// Export this only when building executable, otherwise it is overriding
// the libc implementation
if (extern_getauxval and (builtin.output_mode == .Exe or @hasDecl(root, "main"))) {
@export(&getauxvalImpl, .{ .name = "getauxval", .linkage = .weak });
}
}

pub const getauxval = if (extern_getauxval) struct {
comptime {
const root = @import("root");
// Export this only when building an executable, otherwise it is overriding
// the libc implementation
if (builtin.output_mode == .Exe or @hasDecl(root, "main")) {
@export(&getauxvalImpl, .{ .name = "getauxval", .linkage = .weak });
}
Comment on lines +488 to +492
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@alexrp alexrp Jan 26, 2025

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Just for my edification, what's the technical reason for needing this @export?

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@ghost ghost Jan 29, 2025 •
edited by ghost
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Honestly, I don't know. Maybe it can be removed in a different PR.
I'm not really easily able to learn much more about it right now because there hasn't been a new master build for download in over a week.

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@alexrp alexrp Mar 26, 2025 •
edited
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I went digging through the history. The reason is that we only want a single getauxval implementation to be used at runtime (only the one that has elf_aux_maybe set from the start code is actually functional), so we're using weak linkage to accomplish that.

This is mainly relevant when linking multiple Zig compilation units together.

}
extern fn getauxval(index: usize) usize;
}.getauxval else getauxvalImpl;

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