e018cbf720
There are two motivations. `-fno-pic -fstack-protector -mstack-protector-guard=global` created `__stack_chk_guard` is referenced directly on all ELF OSes except FreeBSD. This patch allows referencing the symbol indirectly with -fno-direct-access-external-data. Some Linux kernel folks want `-fno-pic -fstack-protector -mstack-protector-guard-reg=gs -mstack-protector-guard-symbol=__stack_chk_guard` created `__stack_chk_guard` to be referenced directly, avoiding R_X86_64_REX_GOTPCRELX (even if the relocation may be optimized out by the linker). https://github.com/llvm/llvm-project/issues/60116 Why they need this isn't so clear to me. --- Add module flag "direct-access-external-data" and set the dso_local property of the stack protector symbol. The module flag can benefit other LLVMCodeGen synthesized symbols that are not represented in LLVM IR. Nowadays, with `-fno-pic` being uncommon, ideally we should set "direct-access-external-data" when it is true. However, doing so would require ~90 clang/test tests to be updated, which are too much. As a compromise, we set "direct-access-external-data" only when it's different from the implied default value. Reviewed By: nickdesaulniers Differential Revision: https://reviews.llvm.org/D150841
25 lines
833 B
LLVM
25 lines
833 B
LLVM
define i32 @fn(i8* %str) #0 {
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entry:
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%str.addr = alloca i8*, align 4
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%buffer = alloca [65536 x i8], align 1
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store i8* %str, i8** %str.addr, align 4
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%arraydecay = getelementptr inbounds [65536 x i8], [65536 x i8]* %buffer, i32 0, i32 0
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%0 = load i8*, i8** %str.addr, align 4
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%call = call i8* @strcpy(i8* %arraydecay, i8* %0)
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%arraydecay1 = getelementptr inbounds [65536 x i8], [65536 x i8]* %buffer, i32 0, i32 0
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%call2 = call i32 @puts(i8* %arraydecay1)
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%arrayidx = getelementptr inbounds [65536 x i8], [65536 x i8]* %buffer, i32 0, i32 65535
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%1 = load i8, i8* %arrayidx, align 1
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%conv = zext i8 %1 to i32
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ret i32 %conv
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}
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declare i8* @strcpy(i8*, i8*)
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declare i32 @puts(i8*)
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attributes #0 = { noinline nounwind optnone ssp }
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!llvm.module.flags = !{!0}
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!0 = !{i32 7, !"direct-access-external-data", i32 1}
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