maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[lld][ELF]Add option to make .dynamic read only 

The .dynamic section of an ELF almost doesn't need to be written to with
the exception of the DT_DEBUG entry. For several reasons having a read
only .dynamic section would be useful. This change adds the -z keyword
"rodynamic" which forces .dynamic to be read-only. In this case DT_DEBUG
will not be emited.

Patch by Jake Ehrlich

Differential Revision: https://reviews.llvm.org/D33251

llvm-svn: 304024
This commit is contained in:
Petr Hosek 2017-05-26 19:12:38 +00:00
parent 9bce1ad232
commit ffa786f465
5 changed files with 53 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
lld/ELF/Config.h
View File

@ -145,6 +145,7 @@ struct Configuration {
bool ZNow;
bool ZOrigin;
bool ZRelro;
bool ZRodynamic;
bool ZText;
bool ExitEarly;
bool ZWxneeded;

1
lld/ELF/Driver.cpp
View File

@ -692,6 +692,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
Config->ZNow = hasZOption(Args, "now");
Config->ZOrigin = hasZOption(Args, "origin");
Config->ZRelro = !hasZOption(Args, "norelro");
Config->ZRodynamic = hasZOption(Args, "rodynamic");
Config->ZStackSize = getZOptionValue(Args, "stack-size", 0);
Config->ZText = !hasZOption(Args, "notext");
Config->ZWxneeded = hasZOption(Args, "wxneeded");

15
lld/ELF/SyntheticSections.cpp
View File

@ -1005,10 +1005,11 @@ DynamicSection<ELFT>::DynamicSection()
".dynamic") {
this->Entsize = ELFT::Is64Bits ? 16 : 8;
// .dynamic section is not writable on MIPS.
// .dynamic section is not writable on MIPS and on Fuchsia OS
// which passes -z rodynamic.
// See "Special Section" in Chapter 4 in the following document:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (Config->EMachine == EM_MIPS)
if (Config->EMachine == EM_MIPS || Config->ZRodynamic)
this->Flags = SHF_ALLOC;
addEntries();
@ -1053,7 +1054,15 @@ template <class ELFT> void DynamicSection<ELFT>::addEntries() {
if (DtFlags1)
add({DT_FLAGS_1, DtFlags1});
if (!Config->Shared && !Config->Relocatable)
// DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We
// need it for each process, so we don't write it for DSOs. The loader writes
// the pointer into this entry.
//
// DT_DEBUG is the only .dynamic entry that needs to be written to. Some
// systems (currently only Fuchsia OS) provide other means to give the
// debugger this information. Such systems may choose make .dynamic read-only.
// If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
if (!Config->Shared && !Config->Relocatable && !Config->ZRodynamic)
add({DT_DEBUG, (uint64_t)0});
}

4
lld/test/ELF/Inputs/rodynamic.s Normal file
View File

@ -0,0 +1,4 @@
.global foo
.type foo, @function
foo:
ret

35
lld/test/ELF/rodynamic.s Normal file
View File

@ -0,0 +1,35 @@
# RUN: llvm-mc %s -o %t.o -filetype=obj -triple=x86_64-pc-linux
# RUN: llvm-mc %p/Inputs/rodynamic.s -o %t.so.o -filetype=obj -triple=x86_64-pc-linux
# RUN: ld.lld -shared %t.so.o -o %t.so
# RUN: ld.lld %t.o %t.so -o %t.exe
# RUN: llvm-readobj -dynamic-table %t.exe | FileCheck -check-prefix=DEFDEBUG %s
# RUN: llvm-readobj -sections %t.exe | FileCheck -check-prefix=DEFSEC %s
# RUN: ld.lld -shared -z rodynamic %t.so.o -o %t.so
# RUN: ld.lld -z rodynamic %t.o %t.so -o %t.exe
# RUN: llvm-readobj -dynamic-table %t.exe | FileCheck -check-prefix=RODEBUG %s
# RUN: llvm-readobj -sections %t.exe | FileCheck -check-prefix=ROSEC %s
.globl _start
_start:
call foo
# DEFDEBUG: DEBUG
# DEFSEC: Section {
# DEFSEC: Name: .dynamic
# DEFSEC-NEXT: Type: SHT_DYNAMIC
# DEFSEC-NEXT: Flags [
# DEFSEC-NEXT: SHF_ALLOC
# DEFSEC-NEXT: SHF_WRITE
# DEFSEC-NEXT: ]
# RODEBUG-NOT: DEBUG
# ROSEC: Section {
# ROSEC: Name: .dynamic
# ROSEC-NEXT: Type: SHT_DYNAMIC
# ROSEC-NEXT: Flags [
# ROSEC-NEXT: SHF_ALLOC
# ROSEC-NEXT: ]