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bpf: do not invoke lld when linking eBPF relocatables

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Due to a deficiency in LLD, we need to special-case BPF to a simple
file copy when generating relocatables. Normally, we would expect
`lld -r` to work. However, because LLD wants to resolve BPF relocations
which it shouldn't, it fails before even generating the relocatable.

Co-authored-by: Matthew Knight <mattnite@protonmail.com>
This commit is contained in:
Jakub Konka 2021-11-26 10:46:40 +01:00
parent a96b6ad83f
commit d6f43a1eac
3 changed files with 16 additions and 4 deletions
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11
lib/std/target.zig
View File

@ -895,6 +895,13 @@ pub const Target = struct {
};
}
pub fn isBpf(arch: Arch) bool {
return switch (arch) {
.bpfel, .bpfeb => true,
else => false,
};
}
pub fn parseCpuModel(arch: Arch, cpu_name: []const u8) !*const Cpu.Model {
for (arch.allCpuModels()) |cpu| {
if (mem.eql(u8, cpu_name, cpu.name)) {
@ -1421,6 +1428,10 @@ pub const Target = struct {
return self.os.tag.isBSD();
}
pub fn isBpfFreestanding(self: Target) bool {
return self.cpu.arch.isBpf() and self.os.tag == .freestanding;
}
pub fn isGnuLibC_os_tag_abi(os_tag: Os.Tag, abi: Abi) bool {
return os_tag == .linux and abi.isGnu();
}

3
src/link.zig
View File

@ -532,9 +532,6 @@ pub const File = struct {
return;
}
if (base.options.output_mode == .Obj)
return;
const use_lld = build_options.have_llvm and base.options.use_lld;
if (use_lld and base.options.output_mode == .Lib and base.options.link_mode == .Static) {
return base.linkAsArchive(comp);

6
src/link/Elf.zig
View File

@ -1381,7 +1381,11 @@ fn linkWithLLD(self: *Elf, comp: *Compilation) !void {
}
const full_out_path = try directory.join(arena, &[_][]const u8{self.base.options.emit.?.sub_path});
if (self.base.options.output_mode == .Obj and self.base.options.lto) {
// Due to a deficiency in LLD, we need to special-case BPF to a simple file copy when generating
// relocatables. Normally, we would expect `lld -r` to work. However, because LLD wants to resolve
// BPF relocations which it shouldn't, it fails before even generating the relocatable.
if (self.base.options.output_mode == .Obj and (self.base.options.lto or target.isBpfFreestanding())) {
// In this case we must do a simple file copy
// here. TODO: think carefully about how we can avoid this redundant operation when doing
// build-obj. See also the corresponding TODO in linkAsArchive.