ee5d1a0449
MC currently produces monolithic .gcc_except_table section. GCC can split up .gcc_except_table: * if comdat: `.section .gcc_except_table._Z6comdatv,"aG",@progbits,_Z6comdatv,comdat` * otherwise, if -ffunction-sections: `.section .gcc_except_table._Z3fooi,"a",@progbits` This ensures that (a) non-prevailing copies are discarded and (b) .gcc_except_table associated to discarded text sections can be discarded by a .gcc_except_table-aware linker (GNU ld, but not gold or LLD) This patches matches the GCC behavior. If -fno-unique-section-names is specified, we don't append the suffix. If -ffunction-sections is additionally specified, use `.section ...,unique`. Note, if clang driver communicates that the linker is LLD and we know it is new (11.0.0 or later) we can use SHF_LINK_ORDER to avoid string table costs, at least in the -fno-unique-section-names case. We cannot use it on GNU ld because as of binutils 2.35 it does not support mixed SHF_LINK_ORDER & non-SHF_LINK_ORDER components in an output section https://sourceware.org/bugzilla/show_bug.cgi?id=26256 For RISC-V -mrelax, this patch additionally fixes an assembler-linker interaction problem: because a section is shrinkable, the length of a call-site code range is not a constant. Relocations referencing the associated text section (STT_SECTION) are needed. However, a STB_LOCAL relocation referencing a discarded section group member from outside the group is disallowed by the ELF specification (PR46675): ``` // a.cc inline int comdat() { try { throw 1; } catch (int) { return 1; } return 0; } int main() { return comdat(); } // b.cc inline int comdat() { try { throw 1; } catch (int) { return 1; } return 0; } int foo() { return comdat(); } clang++ -target riscv64-linux -c a.cc b.cc -fPIC -mno-relax ld.lld -shared a.o b.o => ld.lld: error: relocation refers to a symbol in a discarded section: ``` -fbasic-block-sections= is similar to RISC-V -mrelax: there are outstanding relocations. Reviewed By: jrtc27, rahmanl Differential Revision: https://reviews.llvm.org/D83655
59 lines
2.6 KiB
LLVM
59 lines
2.6 KiB
LLVM
; RUN: llc < %s -mtriple=x86_64 | FileCheck %s --check-prefixes=CHECK,NORMAL
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; RUN: llc < %s -mtriple=x86_64 -unique-section-names=false | FileCheck %s --check-prefixes=CHECK,NOUNIQUE
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; RUN: llc < %s -mtriple=x86_64 -function-sections | FileCheck %s --check-prefixes=CHECK,SEP
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; RUN: llc < %s -mtriple=x86_64 -function-sections -unique-section-names=false | FileCheck %s --check-prefixes=CHECK,SEP_NOUNIQUE
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;; Don't use `,unique` if GNU as<2.35.
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; RUN: llc < %s -mtriple=x86_64 -function-sections -unique-section-names=false -no-integrated-as | FileCheck %s --check-prefixes=CHECK,SEP_NOUNIQUE_GAS
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@_ZTIi = external constant i8*
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;; If the function is in a comdat group, the generated .gcc_except_table should
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;; be placed in the same group, so that .gcc_except_table can be discarded if
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;; the comdat is not prevailing. If -funique-section-names, append the function name.
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$group = comdat any
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define i32 @group() uwtable comdat personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
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; CHECK-LABEL: group:
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; CHECK: .cfi_endproc
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; NORMAL-NEXT: .section .gcc_except_table.group,"aG",@progbits,group,comdat{{$}}
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; NOUNIQUE-NEXT: .section .gcc_except_table,"aG",@progbits,group,comdat{{$}}
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; SEP-NEXT: .section .gcc_except_table.group,"aG",@progbits,group,comdat{{$}}
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; SEP_NOUNIQUE-NEXT: .section .gcc_except_table,"aG",@progbits,group,comdat,unique,2
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; SEP_NOUNIQUE_GAS-NEXT: .section .gcc_except_table,"aG",@progbits,group,comdat{{$}}
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entry:
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invoke void @ext() to label %try.cont unwind label %lpad
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lpad:
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%0 = landingpad { i8*, i32 } catch i8* bitcast (i8** @_ZTIi to i8*)
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br label %eh.resume
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try.cont:
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ret i32 0
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eh.resume:
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resume { i8*, i32 } %0
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}
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;; If the function is not in a comdat group, but function sections is enabled,
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;; use a separate section by either using a unique ID (integrated assembler) or
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;; a suffix (GNU as<2.35).
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define i32 @foo() uwtable personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
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; CHECK-LABEL: foo:
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; CHECK: .cfi_endproc
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; NORMAL-NEXT: .section .gcc_except_table,"a",@progbits{{$}}
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; NOUNIQUE-NEXT: .section .gcc_except_table,"a",@progbits{{$}}
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; SEP-NEXT: .section .gcc_except_table.foo,"a",@progbits{{$}}
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; SEP_NOUNIQUE-NEXT: .section .gcc_except_table,"a",@progbits,unique,4
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; SEP_NOUNIQUE_GAS-NEXT: .section .gcc_except_table,"a",@progbits{{$}}
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entry:
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invoke void @ext() to label %try.cont unwind label %lpad
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lpad:
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%0 = landingpad { i8*, i32 } catch i8* bitcast (i8** @_ZTIi to i8*)
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br label %eh.resume
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try.cont:
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ret i32 0
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eh.resume:
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resume { i8*, i32 } %0
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}
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declare void @ext()
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declare i32 @__gxx_personality_v0(...)
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