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mysterymathmysterymath
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Address review comments
- Add comments clarifying invariants and getEnclosinSymbol rationale - Remove extraneous "-" from ld.lld.1 - Replace "-NOT: >>>" with "-EMPTY:" - Use split-file to simplify paths
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4 files changed

+169
-155
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4 files changed

+169
-155
lines changed

‎lld/ELF/MarkLive.cpp

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Original file line numberDiff line numberDiff line change
@@ -87,7 +87,10 @@ template <class ELFT, bool TrackWhyLive> class MarkLive {
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// identifiers, so we just store a SmallVector instead of a multimap.
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DenseMap<StringRef, SmallVector<InputSectionBase *, 0>> cNamedSections;
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// The most proximate reason that something is live.
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// The most proximate reason that something is live. This forms a DAG between
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// LiveItems. Acyclicality is maintained by only admitting the first
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// discovered reason for each LiveItem; this captures the acyclic region of
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// the liveness graph around the GC roots.
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DenseMap<LiveItem, LiveReason> whyLive;
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};
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} // namespace
@@ -145,6 +148,10 @@ void MarkLive<ELFT, TrackWhyLive>::resolveReloc(InputSectionBase &sec,
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relSec->nextInSectionGroup))) {
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Symbol *canonicalSym = d;
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if (TrackWhyLive && d->isSection()) {
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// This is expensive, so ideally this would be deferred until it's known
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// whether this reference contributes to a printed whyLive chain, but
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// that determination cannot be made without knowing the enclosing
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// symbol.
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if (Symbol *s = relSec->getEnclosingSymbol(offset))
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canonicalSym = s;
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else

‎lld/docs/ld.lld.1

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Original file line numberDiff line numberDiff line change
@@ -755,7 +755,7 @@ Report unresolved symbols as warnings.
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Force load of all members in a static library.
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.It Fl -why-extract Ns = Ns Ar file
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Print to a file about why archive members are extracted.
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.It Fl --why-live Ns = Ns Ar glob
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.It Fl -why-live Ns = Ns Ar glob
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Report a chain of references preventing garbage collection for each symbol matching the glob.
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.It Fl -wrap Ns = Ns Ar symbol
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Redirect

‎lld/test/ELF/why-live.s

Lines changed: 0 additions & 153 deletions
This file was deleted.

‎lld/test/ELF/why-live.test

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@@ -0,0 +1,160 @@
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# REQUIRES: x86
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# RUN: rm -rf %t && split-file %s %t && cd %t
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# RUN: llvm-mc -n -filetype=obj -triple=x86_64 -o shared.o shared.s
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# RUN: ld.lld -shared shared.o -o a.so
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# RUN: llvm-mc -n -filetype=obj -triple=x86_64 -o a.o a.s
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#--- shared.s
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.globl test_shared
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.section .test_shared,"ax",@progbits
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test_shared:
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jmp test_shared
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#--- a.s
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## Simple live section
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.globl _start
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.section ._start,"ax",@progbits
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_start:
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jmp test_simple
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.quad .Lanonymous
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.quad .Lanonymous_within_symbol
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jmp test_shared
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.quad test_local
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.size _start, .-_start
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.globl test_simple
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.section .test_simple,"ax",@progbits
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test_simple:
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jmp test_simple
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jmp test_from_unsized
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_simple | FileCheck %s --check-prefix=SIMPLE
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# SIMPLE: live symbol: a.o:(test_simple)
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# SIMPLE-NEXT: >>> referenced by: a.o:(_start) (entry point)
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# SIMPLE-EMPTY:
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## Live only by being a member of .test_simple
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.globl test_incidental
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test_incidental:
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jmp test_incidental
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_incidental | FileCheck %s --check-prefix=INCIDENTAL
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# INCIDENTAL: live symbol: a.o:(test_incidental)
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# INCIDENTAL-NEXT: >>> in live section: a.o:(.test_simple)
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# INCIDENTAL-NEXT: >>> contained live symbol: a.o:(test_simple)
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# INCIDENTAL-NEXT: >>> referenced by: a.o:(_start) (entry point)
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# INCIDENTAL-EMPTY:
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## Reached from a reference in section .test_simple directly, since test_simple is an unsized symbol.
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.globl test_from_unsized
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.section .test_from_unsized,"ax",@progbits
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test_from_unsized:
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jmp test_from_unsized
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_from_unsized | FileCheck %s --check-prefix=FROM-UNSIZED
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# FROM-UNSIZED: live symbol: a.o:(test_from_unsized)
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# FROM-UNSIZED-NEXT: >>> referenced by: a.o:(.test_simple)
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# FROM-UNSIZED-NEXT: >>> contained live symbol: a.o:(test_simple)
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# FROM-UNSIZED-NEXT: >>> referenced by: a.o:(_start) (entry point)
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# FROM-UNSIZED-EMPTY:
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## Symbols in dead sections are dead and not reported.
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.globl test_dead
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.section .test_dead,"ax",@progbits
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test_dead:
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jmp test_dead
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_dead | count 0
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## Undefined symbols are considered live, since they are not in dead sections.
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_undef -u test_undef | FileCheck %s --check-prefix=UNDEFINED
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# UNDEFINED: live symbol: <internal>:(test_undef) (no section)
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# UNDEFINED-EMPTY:
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## Defined symbols without input section parents are live.
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.globl test_absolute
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test_absolute = 1234
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_absolute | FileCheck %s --check-prefix=ABSOLUTE
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# ABSOLUTE: live symbol: a.o:(test_absolute) (no section)
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# ABSOLUTE-EMPTY:
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## Retained sections are intrinsically live, and they make contained symbols live.
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.globl test_retained
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.section .test_retained,"axR",@progbits
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test_retained:
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jmp test_retained
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_retained | FileCheck %s --check-prefix=RETAINED
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# RETAINED: live symbol: a.o:(test_retained)
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# RETAINED-NEXT: >>> in live section: a.o:(.test_retained) (retained)
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# RETAINED-EMPTY:
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## Relocs that reference offsets from sections (e.g., from anonymous symbols) are considered to point to the section if no enclosing symbol exists.
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.globl test_section_offset
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.section .test_section_offset,"ax",@progbits
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test_section_offset:
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jmp test_section_offset
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.Lanonymous:
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jmp test_section_offset
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_section_offset | FileCheck %s --check-prefix=SECTION-OFFSET
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# SECTION-OFFSET: live symbol: a.o:(test_section_offset)
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# SECTION-OFFSET-NEXT: >>> in live section: a.o:(.test_section_offset)
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# SECTION-OFFSET-NEXT: >>> referenced by: a.o:(_start) (entry point)
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# SECTION-OFFSET-EMPTY:
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## Relocs that reference offsets from sections (e.g., from anonymous symbols) are considered to point to the enclosing symbol if one exists.
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.globl test_section_offset_within_symbol
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.section .test_section_offset_within_symbol,"ax",@progbits
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test_section_offset_within_symbol:
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jmp test_section_offset_within_symbol
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.Lanonymous_within_symbol:
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jmp test_section_offset_within_symbol
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.size test_section_offset_within_symbol, .-test_section_offset_within_symbol
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_section_offset_within_symbol | FileCheck %s --check-prefix=SECTION-OFFSET-WITHIN-SYMBOL
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# SECTION-OFFSET-WITHIN-SYMBOL: live symbol: a.o:(test_section_offset_within_symbol)
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# SECTION-OFFSET-WITHIN-SYMBOL-NEXT: >>> referenced by: a.o:(_start) (entry point)
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# SECTION-OFFSET-WITHIN-SYMBOL-EMPTY:
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## Local symbols can be queried just like global symbols.
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.section .test_local,"ax",@progbits
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test_local:
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jmp test_local
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.size test_local, .-test_local
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_local | FileCheck %s --check-prefix=LOCAL
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# LOCAL: live symbol: a.o:(test_local)
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# LOCAL-NEXT: >>> referenced by: a.o:(_start) (entry point)
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# LOCAL-EMPTY:
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## Shared symbols
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_shared | FileCheck %s --check-prefix=SHARED
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# SHARED: live symbol: a.so:(test_shared)
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# SHARED-NEXT: >>> referenced by: a.o:(_start) (entry point)
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# SHARED-EMPTY:
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## Globs match multiple cases. Multiple --why-live flags union.
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_s* | FileCheck %s --check-prefix=MULTIPLE
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# RUN: ld.lld a.o a.so --gc-sections --why-live=test_simple --why-live=test_shared | FileCheck %s --check-prefix=MULTIPLE
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# MULTIPLE-DAG: live symbol: a.o:(test_simple)
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# MULTIPLE-DAG: live symbol: a.so:(test_shared)

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