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[ELF] Move (copy relocation/canonical PLT) before error checking 

In processRelocAux(), we handle errors before copy relocation/canonical PLT.
This makes error checking a bit complex because we have to check for
conditions that will be allowed by copy relocation/canonical PLT.

Instead, move copy relocation/canonical PLT before error checking. This
simplifies the previous clumsy error checking code

`config->shared || (config->pie && expr == R_ABS && type != target->symbolicRel)`

to the simple `config->isPic`. Some diagnostics can be reported in
different ways. The code motion changes diagnostics for some contrived
test cases:

* copy-rel-pie-error.s -> copy-rel-pie2.s:
  It was rejected before but accepted now. ld.bfd also accepts the case.
* copy-errors.s: "cannot preempt symbol" changes to "symbol 'bar' has no type"
* got32{,x}-i386.s: the suggestion changes from "-fPIC or -Wl,-z,notext" to "-fPIE"
* x86-64-dyn-rel-error5.s: one diagnostic changes for -pie case

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D66007

llvm-svn: 369262
This commit is contained in:
Fangrui Song 2019-08-19 14:30:12 +00:00
parent 0776da5236
commit ac0e6c6502
7 changed files with 81 additions and 86 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

116
lld/ELF/Relocations.cpp
View File

@ -993,56 +993,29 @@ static void processRelocAux(InputSectionBase &sec, RelExpr expr, RelType type,
}
}
if (!canWrite && (config->isPic && !isRelExpr(expr))) {
error(
"can't create dynamic relocation " + toString(type) + " against " +
(sym.getName().empty() ? "local symbol" : "symbol: " + toString(sym)) +
" in readonly segment; recompile object files with -fPIC "
"or pass '-Wl,-z,notext' to allow text relocations in the output" +
getLocation(sec, sym, offset));
return;
}
// Copy relocations (for STT_OBJECT) and canonical PLT (for STT_FUNC) are only
// possible in an executable.
//
// Among R_ABS relocatoin types, symbolicRel has the same size as the word
// size. Others have fewer bits and may cause runtime overflow in -pie/-shared
// mode. Disallow them.
if (config->shared ||
(config->pie && expr == R_ABS && type != target->symbolicRel)) {
errorOrWarn(
"relocation " + toString(type) + " cannot be used against " +
(sym.getName().empty() ? "local symbol" : "symbol " + toString(sym)) +
"; recompile with -fPIC" + getLocation(sec, sym, offset));
return;
}
// If the symbol is undefined we already reported any relevant errors.
if (sym.isUndefined())
return;
if (!canDefineSymbolInExecutable(sym)) {
error("cannot preempt symbol: " + toString(sym) +
getLocation(sec, sym, offset));
return;
}
if (sym.isObject()) {
// Produce a copy relocation.
if (auto *ss = dyn_cast<SharedSymbol>(&sym)) {
if (!config->zCopyreloc)
error("unresolvable relocation " + toString(type) +
" against symbol '" + toString(*ss) +
"'; recompile with -fPIC or remove '-z nocopyreloc'" +
getLocation(sec, sym, offset));
addCopyRelSymbol<ELFT>(*ss);
// When producing an executable, we can perform copy relocations (for
// STT_OBJECT) and canonical PLT (for STT_FUNC).
if (!config->shared) {
if (!canDefineSymbolInExecutable(sym)) {
errorOrWarn("cannot preempt symbol: " + toString(sym) +
getLocation(sec, sym, offset));
return;
}
if (sym.isObject()) {
// Produce a copy relocation.
if (auto *ss = dyn_cast<SharedSymbol>(&sym)) {
if (!config->zCopyreloc)
error("unresolvable relocation " + toString(type) +
" against symbol '" + toString(*ss) +
"'; recompile with -fPIC or remove '-z nocopyreloc'" +
getLocation(sec, sym, offset));
addCopyRelSymbol<ELFT>(*ss);
}
sec.relocations.push_back({expr, type, offset, addend, &sym});
return;
}
sec.relocations.push_back({expr, type, offset, addend, &sym});
return;
}
if (sym.isFunc()) {
// This handles a non PIC program call to function in a shared library. In
// an ideal world, we could just report an error saying the relocation can
// overflow at runtime. In the real world with glibc, crt1.o has a
@ -1070,21 +1043,44 @@ static void processRelocAux(InputSectionBase &sec, RelExpr expr, RelType type,
// compiled without -fPIE/-fPIC and doesn't maintain ebx.
// * If a library definition gets preempted to the executable, it will have
// the wrong ebx value.
if (config->pie && config->emachine == EM_386)
errorOrWarn("symbol '" + toString(sym) +
"' cannot be preempted; recompile with -fPIE" +
getLocation(sec, sym, offset));
if (!sym.isInPlt())
addPltEntry<ELFT>(in.plt, in.gotPlt, in.relaPlt, target->pltRel, sym);
if (!sym.isDefined())
replaceWithDefined(
sym, in.plt,
target->pltHeaderSize + target->pltEntrySize * sym.pltIndex, 0);
sym.needsPltAddr = true;
sec.relocations.push_back({expr, type, offset, addend, &sym});
if (sym.isFunc()) {
if (config->pie && config->emachine == EM_386)
errorOrWarn("symbol '" + toString(sym) +
"' cannot be preempted; recompile with -fPIE" +
getLocation(sec, sym, offset));
if (!sym.isInPlt())
addPltEntry<ELFT>(in.plt, in.gotPlt, in.relaPlt, target->pltRel, sym);
if (!sym.isDefined())
replaceWithDefined(
sym, in.plt,
target->pltHeaderSize + target->pltEntrySize * sym.pltIndex, 0);
sym.needsPltAddr = true;
sec.relocations.push_back({expr, type, offset, addend, &sym});
return;
}
}
if (config->isPic) {
if (!canWrite && !isRelExpr(expr))
errorOrWarn(
"can't create dynamic relocation " + toString(type) + " against " +
(sym.getName().empty() ? "local symbol"
: "symbol: " + toString(sym)) +
" in readonly segment; recompile object files with -fPIC "
"or pass '-Wl,-z,notext' to allow text relocations in the output" +
getLocation(sec, sym, offset));
else
errorOrWarn(
"relocation " + toString(type) + " cannot be used against " +
(sym.getName().empty() ? "local symbol" : "symbol " + toString(sym)) +
"; recompile with -fPIC" + getLocation(sec, sym, offset));
return;
}
// If the symbol is undefined we already reported any relevant errors.
if (sym.isUndefined())
return;
errorOrWarn("symbol '" + toString(sym) + "' has no type" +
getLocation(sec, sym, offset));
}

7
lld/test/ELF/copy-errors.s
View File

@ -4,7 +4,7 @@
// RUN: ld.lld %t2.o -o %t2.so -shared
// RUN: not ld.lld %t.o %t2.so -o %t 2>&1 | FileCheck %s
// CHECK: cannot preempt symbol: bar
// CHECK: error: cannot preempt symbol: bar
// CHECK: >>> defined in {{.*}}.so
// CHECK: >>> referenced by {{.*}}.o:(.text+0x1)
@ -12,7 +12,10 @@
// CHECK-NEXT: >>> defined in {{.*}}.so
// CHECK-NEXT: >>> referenced by {{.*}}.o:(.text+0x6)
// RUN: not ld.lld --noinhibit-exec %t.o %t2.so -o %t 2>&1 | FileCheck %s --check-prefix=NOINHIBIT
// RUN: ld.lld --noinhibit-exec %t.o %t2.so -o %t 2>&1 | FileCheck %s --check-prefix=NOINHIBIT
// NOINHIBIT: warning: cannot preempt symbol: bar
// NOINHIBIT-NEXT: >>> defined in {{.*}}.so
// NOINHIBIT-NEXT: >>> referenced by {{.*}}.o:(.text+0x1)
// NOINHIBIT: warning: symbol 'zed' has no type
// NOINHIBIT-NEXT: >>> defined in {{.*}}.so
// NOINHIBIT-NEXT: >>> referenced by {{.*}}.o:(.text+0x6)

18
lld/test/ELF/copy-rel-pie-error.s
View File

@ -1,18 +0,0 @@
// REQUIRES: x86
// RUN: llvm-mc %s -o %t.o -filetype=obj -triple=x86_64-pc-linux
// RUN: llvm-mc %p/Inputs/copy-rel-pie.s -o %t2.o -filetype=obj -triple=x86_64-pc-linux
// RUN: ld.lld %t2.o -o %t2.so -shared
// RUN: not ld.lld %t.o %t2.so -o /dev/null -pie 2>&1 | FileCheck %s
// CHECK: can't create dynamic relocation R_X86_64_64 against symbol: bar in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
// CHECK: >>> defined in {{.*}}.so
// CHECK: >>> referenced by {{.*}}.o:(.text+0x0)
// CHECK: can't create dynamic relocation R_X86_64_64 against symbol: foo in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
// CHECK: >>> defined in {{.*}}.so
// CHECK: >>> referenced by {{.*}}.o:(.text+0x8)
.global _start
_start:
.quad bar
.quad foo

13
lld/test/ELF/copy-rel-pie2.s Normal file
View File

@ -0,0 +1,13 @@
// REQUIRES: x86
// RUN: llvm-mc %s -o %t.o -filetype=obj -triple=x86_64-pc-linux
// RUN: llvm-mc %p/Inputs/copy-rel-pie.s -o %t2.o -filetype=obj -triple=x86_64-pc-linux
// RUN: ld.lld %t2.o -o %t2.so -shared
// RUN: ld.lld %t.o %t2.so -o %t -pie
// RUN: llvm-readobj -r %t | FileCheck %s
// CHECK: R_X86_64_COPY
// CHECK: R_X86_64_JUMP_SLOT
.rodata
.quad bar
.quad foo

2
lld/test/ELF/got32-i386.s
View File

@ -20,4 +20,4 @@ _start:
# CHECK: .got 00000004 0000000000402000
# RUN: not ld.lld %t.o -o %t -pie 2>&1 | FileCheck %s --check-prefix=ERR
# ERR: error: can't create dynamic relocation R_386_GOT32 against symbol: foo in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
# ERR: error: symbol 'foo' cannot be preempted; recompile with -fPIE

3
lld/test/ELF/got32x-i386.s
View File

@ -43,5 +43,4 @@
# RUN: not ld.lld %S/Inputs/i386-got32x-baseless.elf -o %t1 -pie 2>&1 | \
# RUN: FileCheck %s --check-prefix=ERR
# ERR: error: can't create dynamic relocation R_386_GOT32X against symbol: foo in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
# ERR: error: can't create dynamic relocation R_386_GOT32X against symbol: foo in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
# ERR-COUNT-2: error: symbol 'foo' cannot be preempted; recompile with -fPIE

8
lld/test/ELF/x86-64-dyn-rel-error5.s
View File

@ -1,7 +1,7 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
# RUN: not ld.lld -pie %t.o -o /dev/null 2>&1 | FileCheck %s
# RUN: not ld.lld -shared %t.o -o /dev/null 2>&1 | FileCheck %s
# RUN: not ld.lld -pie %t.o -o /dev/null 2>&1 | FileCheck --check-prefixes=CHECK,PIE %s
# RUN: not ld.lld -shared %t.o -o /dev/null 2>&1 | FileCheck --check-prefixes=CHECK,SHARED %s
## Check we don't create dynamic relocations in a writable section,
## if the number of bits is smaller than the wordsize.
@ -16,7 +16,9 @@ hidden:
# CHECK-NEXT: >>> referenced by {{.*}}.o:(.data+0x0)
# CHECK: error: relocation R_X86_64_16 cannot be used against local symbol; recompile with -fPIC
# CHECK: error: relocation R_X86_64_32 cannot be used against local symbol; recompile with -fPIC
# CHECK: error: relocation R_X86_64_32 cannot be used against symbol hidden; recompile with -fPIC
# PIE: error: cannot preempt symbol: hidden
# SHARED: error: relocation R_X86_64_32 cannot be used against symbol hidden; recompile with -fPIC
.data
.byte local # R_X86_64_8