416707754f
As a side-effect of PR #101222, GlobalMerge started making transforms which are unsafe on Mach-O platforms. Two issues, in particular, are fixed here: 1. We must never merge symbols in the `__cfstring` section, as the linker assumes each object in this section is only ever referenced directly, and that it can split the section as it likes. Previously, we avoided this problem because CFString literals are identified by private-linkage symbols. This patch adds a list of section-names with special behavior, to avoid merging under Mach-O. 2. When GlobalMerge code was originally written, it had to be careful about emitting symbol aliases, due to issues with Mach-O's subsection splitting in the linker with `-dead_strip` enabled. The underlying cause of this problem was fixed in 2016, via creation of the `.alt_entry` assembler directive, which allows a symbol to not also imply the start of a new subsection. GlobalMerge's workaround for that issue was never removed. In the meantime, Apple's new ld-prime linker was written, and has a bug in `.alt_entry` handling. Therefore, even though the original issue was fixed, we must _continue_ to be careful not to emit any such symbol aliases. The existing workaround avoided it for InternalLinkage symbols, but after the above-mentioned PR, we also must avoid emitting aliases for PrivateLinkage symbols. I will file an Apple bug-report about this issue, so that it can be fixed in a future version of ld-prime. But, in the meantime, the workaround is sufficient for GlobalMerge, unless `-global-merge-on-externals` is enabled (which it is already not by default, on MachO platforms, due to the original issue). Fixes #104625
32 lines
1.6 KiB
LLVM
32 lines
1.6 KiB
LLVM
; RUN: opt -global-merge -global-merge-max-offset=100 -S -o - %s | FileCheck %s
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; RUN: opt -passes='global-merge<max-offset=100>' -S -o - %s | FileCheck %s
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;; Check that we do _not_ merge globals which are in certain special
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;; sections under Mach-O.
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target datalayout = "e-p:64:64"
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target triple = "x86_64-apple-macos11"
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; CHECK: @cfstring1 = private global i32 1, section "__DATA,__cfstring"
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@cfstring1 = private global i32 1, section "__DATA,__cfstring"
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; CHECK: @cfstring2 = private global i32 2, section "__DATA,__cfstring"
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@cfstring2 = private global i32 2, section "__DATA,__cfstring"
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; CHECK: @objcclassrefs1 = private global i32 3, section "__DATA,__objc_classrefs,regular,no_dead_strip"
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@objcclassrefs1 = private global i32 3, section "__DATA,__objc_classrefs,regular,no_dead_strip"
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; CHECK: @objcclassrefs2 = private global i32 4, section "__DATA,__objc_classrefs,regular,no_dead_strip"
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@objcclassrefs2 = private global i32 4, section "__DATA,__objc_classrefs,regular,no_dead_strip"
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; CHECK: @objcselrefs1 = private global i32 5, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip"
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@objcselrefs1 = private global i32 5, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip"
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; CHECK: @objcselrefs2 = private global i32 6, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip"
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@objcselrefs2 = private global i32 6, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip"
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define void @use() {
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load ptr, ptr @cfstring1
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load ptr, ptr @cfstring2
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load ptr, ptr @objcclassrefs1
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load ptr, ptr @objcclassrefs2
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load ptr, ptr @objcselrefs1
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load ptr, ptr @objcselrefs2
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ret void
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}
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