[ELF] Move IsNeeded logic from SymbolTable::addShared to MarkLive, and check IsUsedInRegularObj
Summary:
In glibc, libc.so is a linker script with an as-needed dependency on ld-linux-x86-64.so.2
GROUP ( /lib/x86_64-linux-gnu/libc.so.6 /usr/lib/x86_64-linux-gnu/libc_nonshared.a AS_NEEDED ( /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 ) )
ld-linux-x86-64.so.2 (as-needed) defines some symbols which resolve undefined references in libc.so.6, it will therefore be added as a DT_NEEDED entry, which isn't necessary.
The test case as-needed-not-in-regular.s emulates the libc.so scenario, where ld.bfd and gold don't add DT_NEEDED for a.so
The relevant code in gold/resolve.cc:
// If we have a non-WEAK reference from a regular object to a
// dynamic object, mark the dynamic object as needed.
if (to->is_from_dynobj() && to->in_reg() && !to->is_undef_binding_weak())
to->object()->set_is_needed();
in_reg() appears to do something similar to IsUsedInRegularObj.
This patch makes lld do the similar thing, but moves the check from
addShared to a later stage MarkLive where all symbols are scanned.
Reviewers: ruiu, pcc, espindola
Reviewed By: ruiu
Subscribers: emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D55902
llvm-svn: 349849
2018-12-21 06:46:01 +08:00
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# REQUIRES: x86
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# RUN: echo '.globl a1, a2; .type a1, @function; .type a2, @function; a1: a2: ret' | \
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# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %ta.o
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# RUN: ld.lld %ta.o --shared --soname=a.so -o %ta.so
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# RUN: echo '.globl b; .type b, @function; b: jmp a1@PLT' | \
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# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %tb.o
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# RUN: ld.lld %tb.o %ta.so --shared --soname=b.so -o %tb.so
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# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
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# RUN: ld.lld %t.o %tb.so --as-needed %ta.so -o %t
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# RUN: llvm-readelf -d %t | FileCheck %s
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# RUN: ld.lld %t.o %tb.so --as-needed %ta.so --gc-sections -o %t
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# RUN: llvm-readelf -d %t | FileCheck %s
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# The symbol a1 (defined in a.so) is not referenced by a regular object,
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# the reference to a2 is weak, don't add a DT_NEEDED entry for a.so.
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# CHECK-NOT: a.so
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2018-12-28 06:24:45 +08:00
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# RUN: ld.lld %t.o %tb.so --as-needed %ta.so --no-as-needed %ta.so -o %t
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# RUN: llvm-readelf -d %t | FileCheck %s -check-prefix=NEEDED
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# a.so is needed because one of its occurrences is needed.
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# NEEDED: a.so
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[ELF] Move IsNeeded logic from SymbolTable::addShared to MarkLive, and check IsUsedInRegularObj
Summary:
In glibc, libc.so is a linker script with an as-needed dependency on ld-linux-x86-64.so.2
GROUP ( /lib/x86_64-linux-gnu/libc.so.6 /usr/lib/x86_64-linux-gnu/libc_nonshared.a AS_NEEDED ( /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 ) )
ld-linux-x86-64.so.2 (as-needed) defines some symbols which resolve undefined references in libc.so.6, it will therefore be added as a DT_NEEDED entry, which isn't necessary.
The test case as-needed-not-in-regular.s emulates the libc.so scenario, where ld.bfd and gold don't add DT_NEEDED for a.so
The relevant code in gold/resolve.cc:
// If we have a non-WEAK reference from a regular object to a
// dynamic object, mark the dynamic object as needed.
if (to->is_from_dynobj() && to->in_reg() && !to->is_undef_binding_weak())
to->object()->set_is_needed();
in_reg() appears to do something similar to IsUsedInRegularObj.
This patch makes lld do the similar thing, but moves the check from
addShared to a later stage MarkLive where all symbols are scanned.
Reviewers: ruiu, pcc, espindola
Reviewed By: ruiu
Subscribers: emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D55902
llvm-svn: 349849
2018-12-21 06:46:01 +08:00
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.global _start
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.weak a2
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_start:
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jmp b@PLT
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jmp a2
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