[lld] r291459 - [ELF] Allow defined symbols to be assigned from linker script
Meador Inge via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 9 10:36:57 PST 2017
Author: meadori
Date: Mon Jan 9 12:36:57 2017
New Revision: 291459
URL: http://llvm.org/viewvc/llvm-project?rev=291459&view=rev
Log:
[ELF] Allow defined symbols to be assigned from linker script
This patch allows for linker scripts to assign a new value
to a symbol that is already defined (either in an object file
or the linker script itself).
Modified:
lld/trunk/ELF/LinkerScript.cpp
lld/trunk/test/ELF/linkerscript/symbol-assignexpr.s
lld/trunk/test/ELF/mips-gp-ext.s
Modified: lld/trunk/ELF/LinkerScript.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LinkerScript.cpp?rev=291459&r1=291458&r2=291459&view=diff
==============================================================================
--- lld/trunk/ELF/LinkerScript.cpp (original)
+++ lld/trunk/ELF/LinkerScript.cpp Mon Jan 9 12:36:57 2017
@@ -56,29 +56,30 @@ using namespace lld::elf;
LinkerScriptBase *elf::ScriptBase;
ScriptConfiguration *elf::ScriptConfig;
-template <class ELFT> static void addRegular(SymbolAssignment *Cmd) {
+template <class ELFT> static SymbolBody *addRegular(SymbolAssignment *Cmd) {
uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
- Symbol *Sym = Symtab<ELFT>::X->addRegular(Cmd->Name, Visibility, STT_NOTYPE,
- 0, 0, STB_GLOBAL, nullptr, nullptr);
- Cmd->Sym = Sym->body();
-
- // If we have no SECTIONS then we don't have '.' and don't call
- // assignAddresses(). We calculate symbol value immediately in this case.
- if (!ScriptConfig->HasSections)
- cast<DefinedRegular<ELFT>>(Cmd->Sym)->Value = Cmd->Expression(0);
+ Symbol *Sym = Symtab<ELFT>::X->addUndefined(
+ Cmd->Name, /*IsLocal=*/false, STB_GLOBAL, Visibility,
+ /*Type*/ 0,
+ /*CanOmitFromDynSym*/ false, /*File*/ nullptr);
+
+ replaceBody<DefinedRegular<ELFT>>(Sym, Cmd->Name, /*IsLocal=*/false,
+ Visibility, STT_NOTYPE, 0, 0, nullptr,
+ nullptr);
+ return Sym->body();
}
-template <class ELFT> static void addSynthetic(SymbolAssignment *Cmd) {
- // If we have SECTIONS block then output sections haven't been created yet.
+template <class ELFT> static SymbolBody *addSynthetic(SymbolAssignment *Cmd) {
+ uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
const OutputSectionBase *Sec =
ScriptConfig->HasSections ? nullptr : Cmd->Expression.Section();
- Symbol *Sym = Symtab<ELFT>::X->addSynthetic(
- Cmd->Name, Sec, 0, Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT);
- Cmd->Sym = Sym->body();
-
- // If we already know section then we can calculate symbol value immediately.
- if (Sec)
- cast<DefinedSynthetic>(Cmd->Sym)->Value = Cmd->Expression(0) - Sec->Addr;
+ Symbol *Sym = Symtab<ELFT>::X->addUndefined(
+ Cmd->Name, /*IsLocal=*/false, STB_GLOBAL, Visibility,
+ /*Type*/ 0,
+ /*CanOmitFromDynSym*/ false, /*File*/ nullptr);
+
+ replaceBody<DefinedSynthetic>(Sym, Cmd->Name, 0, Sec);
+ return Sym->body();
}
static bool isUnderSysroot(StringRef Path) {
@@ -90,21 +91,39 @@ static bool isUnderSysroot(StringRef Pat
return false;
}
-template <class ELFT> static void addSymbol(SymbolAssignment *Cmd) {
- if (Cmd->Expression.IsAbsolute())
- addRegular<ELFT>(Cmd);
- else
- addSynthetic<ELFT>(Cmd);
+template <class ELFT> static void assignSymbol(SymbolAssignment *Cmd) {
+ // If there are sections, then let the value be assigned later in
+ // `assignAddresses`.
+ if (ScriptConfig->HasSections)
+ return;
+
+ uint64_t Value = Cmd->Expression(0);
+ if (Cmd->Expression.IsAbsolute()) {
+ cast<DefinedRegular<ELFT>>(Cmd->Sym)->Value = Value;
+ } else {
+ const OutputSectionBase *Sec = Cmd->Expression.Section();
+ if (Sec)
+ cast<DefinedSynthetic>(Cmd->Sym)->Value = Value - Sec->Addr;
+ }
}
-// If a symbol was in PROVIDE(), we need to define it only when
-// it is an undefined symbol.
-template <class ELFT> static bool shouldDefine(SymbolAssignment *Cmd) {
+
+template <class ELFT> static void addSymbol(SymbolAssignment *Cmd) {
if (Cmd->Name == ".")
- return false;
- if (!Cmd->Provide)
- return true;
+ return;
+
+ // If a symbol was in PROVIDE(), we need to define it only when
+ // it is a referenced undefined symbol.
SymbolBody *B = Symtab<ELFT>::X->find(Cmd->Name);
- return B && B->isUndefined();
+ if (Cmd->Provide && (!B || B->isDefined()))
+ return;
+
+ // Otherwise, create a new symbol if one does not exist or an
+ // undefined one does exist.
+ if (Cmd->Expression.IsAbsolute())
+ Cmd->Sym = addRegular<ELFT>(Cmd);
+ else
+ Cmd->Sym = addSynthetic<ELFT>(Cmd);
+ assignSymbol<ELFT>(Cmd);
}
bool SymbolAssignment::classof(const BaseCommand *C) {
@@ -283,8 +302,7 @@ void LinkerScript<ELFT>::processCommands
// Handle symbol assignments outside of any output section.
if (auto *Cmd = dyn_cast<SymbolAssignment>(Base1.get())) {
- if (shouldDefine<ELFT>(Cmd))
- addSymbol<ELFT>(Cmd);
+ addSymbol<ELFT>(Cmd);
continue;
}
@@ -326,8 +344,7 @@ void LinkerScript<ELFT>::processCommands
// ".foo : { ...; bar = .; }". Handle them.
for (const std::unique_ptr<BaseCommand> &Base : Cmd->Commands)
if (auto *OutCmd = dyn_cast<SymbolAssignment>(Base.get()))
- if (shouldDefine<ELFT>(OutCmd))
- addSymbol<ELFT>(OutCmd);
+ addSymbol<ELFT>(OutCmd);
// Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
// is given, input sections are aligned to that value, whether the
Modified: lld/trunk/test/ELF/linkerscript/symbol-assignexpr.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/symbol-assignexpr.s?rev=291459&r1=291458&r2=291459&view=diff
==============================================================================
--- lld/trunk/test/ELF/linkerscript/symbol-assignexpr.s (original)
+++ lld/trunk/test/ELF/linkerscript/symbol-assignexpr.s Mon Jan 9 12:36:57 2017
@@ -13,14 +13,20 @@
# RUN: symbol9 = - 4; \
# RUN: symbol10 = 0xfedcba9876543210; \
# RUN: symbol11 = ((0x28000 + 0x1fff) & ~(0x1000 + -1)); \
+# RUN: symbol12 = 0x1234; \
+# RUN: symbol12 += 1; \
+# RUN: bar = 0x5678; \
+# RUN: baz = 0x9abc; \
# RUN: }" > %t.script
# RUN: ld.lld -o %t1 --script %t.script %t
# RUN: llvm-objdump -t %t1 | FileCheck %s
# CHECK: SYMBOL TABLE:
# CHECK-NEXT: 0000000000000000 *UND* 00000000
-# CHECK-NEXT: .text 00000000 _start
-# CHECK-NEXT: .text 00000000 foo
+# CHECK-NEXT: 0000000000000000 .text 00000000 _start
+# CHECK-NEXT: 0000000000005678 *ABS* 00000000 bar
+# CHECK-NEXT: 0000000000009abc *ABS* 00000000 baz
+# CHECK-NEXT: 0000000000000001 .text 00000000 foo
# CHECK-NEXT: 0000000000001000 *ABS* 00000000 symbol
# CHECK-NEXT: 0000000000002234 *ABS* 00000000 symbol2
# CHECK-NEXT: 0000000000002234 *ABS* 00000000 symbol3
@@ -32,6 +38,7 @@
# CHECK-NEXT: fffffffffffffffc *ABS* 00000000 symbol9
# CHECK-NEXT: fedcba9876543210 *ABS* 00000000 symbol10
# CHECK-NEXT: 0000000000029000 *ABS* 00000000 symbol11
+# CHECK-NEXT: 0000000000001235 *ABS* 00000000 symbol12
# RUN: echo "SECTIONS { \
# RUN: symbol2 = symbol; \
@@ -46,3 +53,9 @@ _start:
.global foo
foo:
+ nop
+
+.global bar
+bar = 0x1234
+
+.comm baz,8,8
Modified: lld/trunk/test/ELF/mips-gp-ext.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/mips-gp-ext.s?rev=291459&r1=291458&r2=291459&view=diff
==============================================================================
--- lld/trunk/test/ELF/mips-gp-ext.s (original)
+++ lld/trunk/test/ELF/mips-gp-ext.s Mon Jan 9 12:36:57 2017
@@ -1,8 +1,10 @@
# Check that the linker use a value of _gp symbol defined
# in a linker script to calculate GOT relocations.
-# FIXME: This test is xfailed because it depends on D27276 patch
-# that enables absolute symbols redefinition by a linker's script.
+# FIXME: This test is xfailed because there is currently a bug
+# that causes symbols defined by linker scripts to be put in the
+# wrong sections. In particular, `_gp = . + 0x100` ends up in
+# `.text` when it should be in `*ABS*`.
# XFAIL: *
# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s -o %t.o
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