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author | Fangrui Song <maskray@google.com> | 2018-12-20 22:46:01 +0000 |
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committer | Fangrui Song <maskray@google.com> | 2018-12-20 22:46:01 +0000 |
commit | a88ca95c45bb380d58af2a893cf93d87d9cfdceb (patch) | |
tree | a875dab27d126c215960ceda7fc2b2c50dae8881 /lld | |
parent | 962b7200f38a6697699a6aedeb958e7f10b69028 (diff) |
[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
Diffstat (limited to 'lld')
-rw-r--r-- | lld/ELF/MarkLive.cpp | 8 | ||||
-rw-r--r-- | lld/ELF/SymbolTable.cpp | 3 | ||||
-rw-r--r-- | lld/test/ELF/as-needed-in-regular.s | 24 | ||||
-rw-r--r-- | lld/test/ELF/as-needed-not-in-regular.s | 26 |
4 files changed, 57 insertions, 4 deletions
diff --git a/lld/ELF/MarkLive.cpp b/lld/ELF/MarkLive.cpp index 7264e1ca7c4..817a0c8b65f 100644 --- a/lld/ELF/MarkLive.cpp +++ b/lld/ELF/MarkLive.cpp @@ -267,10 +267,16 @@ template <class ELFT> static void doGcSections() { // input sections. This function make some or all of them on // so that they are emitted to the output file. template <class ELFT> void elf::markLive() { - // If -gc-sections is missing, no sections are removed. if (!Config->GcSections) { + // If -gc-sections is missing, no sections are removed. for (InputSectionBase *Sec : InputSections) Sec->Live = true; + + // If a DSO defines a symbol referenced in a regular object, it is needed. + for (Symbol *Sym : Symtab->getSymbols()) + if (auto *S = dyn_cast<SharedSymbol>(Sym)) + if (S->IsUsedInRegularObj && !S->isWeak()) + S->getFile<ELFT>().IsNeeded = true; return; } diff --git a/lld/ELF/SymbolTable.cpp b/lld/ELF/SymbolTable.cpp index 8f320a5778b..5545617487e 100644 --- a/lld/ELF/SymbolTable.cpp +++ b/lld/ELF/SymbolTable.cpp @@ -503,14 +503,11 @@ void SymbolTable::addShared(StringRef Name, SharedFile<ELFT> &File, if ((S->isUndefined() || S->isLazy()) && S->Visibility == STV_DEFAULT) { uint8_t Binding = S->Binding; - bool WasUndefined = S->isUndefined(); replaceSymbol<SharedSymbol>(S, File, Name, Sym.getBinding(), Sym.st_other, Sym.getType(), Sym.st_value, Sym.st_size, Alignment, VerdefIndex); S->Binding = Binding; - if (!S->isWeak() && !Config->GcSections && WasUndefined) - File.IsNeeded = true; } } diff --git a/lld/test/ELF/as-needed-in-regular.s b/lld/test/ELF/as-needed-in-regular.s new file mode 100644 index 00000000000..2ba646f8530 --- /dev/null +++ b/lld/test/ELF/as-needed-in-regular.s @@ -0,0 +1,24 @@ +# REQUIRES: x86 + +# RUN: echo '.globl a; .type a, @function; .type a, @function; a: ret' | \ +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %ta.o +# RUN: ld.lld %ta.o --shared --soname=a.so -o %ta.so + +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o +# RUN: ld.lld %t.o --as-needed %ta.so -o %t +# RUN: llvm-readelf -d %t | FileCheck %s +# RUN: ld.lld %t.o --as-needed %ta.so --gc-sections -o %t +# RUN: llvm-readelf -d %t | FileCheck %s + +# The order of %ta.so and %t.o does not matter. + +# RUN: ld.lld --as-needed %ta.so %t.o -o %t +# RUN: llvm-readelf -d %t | FileCheck %s +# RUN: ld.lld --as-needed %ta.so %t.o --gc-sections -o %t +# RUN: llvm-readelf -d %t | FileCheck %s + +# CHECK: a.so + +.global _start +_start: + jmp a@PLT diff --git a/lld/test/ELF/as-needed-not-in-regular.s b/lld/test/ELF/as-needed-not-in-regular.s new file mode 100644 index 00000000000..a78f7742d57 --- /dev/null +++ b/lld/test/ELF/as-needed-not-in-regular.s @@ -0,0 +1,26 @@ +# REQUIRES: x86 + +# RUN: echo '.globl a1, a2; .type a1, @function; .type a2, @function; a1: a2: ret' | \ +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %ta.o +# RUN: ld.lld %ta.o --shared --soname=a.so -o %ta.so + +# RUN: echo '.globl b; .type b, @function; b: jmp a1@PLT' | \ +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux - -o %tb.o +# RUN: ld.lld %tb.o %ta.so --shared --soname=b.so -o %tb.so + +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o +# RUN: ld.lld %t.o %tb.so --as-needed %ta.so -o %t +# RUN: llvm-readelf -d %t | FileCheck %s + +# RUN: ld.lld %t.o %tb.so --as-needed %ta.so --gc-sections -o %t +# RUN: llvm-readelf -d %t | FileCheck %s + +# The symbol a1 (defined in a.so) is not referenced by a regular object, +# the reference to a2 is weak, don't add a DT_NEEDED entry for a.so. +# CHECK-NOT: a.so + +.global _start +.weak a2 +_start: + jmp b@PLT + jmp a2 |