lld is being too smart for its own good, and places non-relocatable data
right after the program headers, which prevents the program headers from
growing. But elfhack wasn't checking for that, so happily placed the
non-relocatable data at its non-relocated location, overwriting the last
item of the program headers.
--HG--
extra : rebase_source : 6f26d475f0a19d88ddf21399dbce8ceac62b492d
Bug 1385783 changed things such that the two elfhack sections are not
adjacent anymore. They can even be in different segments in some cases,
but the undo code doesn't know how to actually handle that case.
So for now, allow non adjacent sections, but still verify that they are
in the same segment.
--HG--
extra : rebase_source : da95ef7df19eeea8dfd07b24f22e7bee18939b69
With all of our builds in Taskcluster now, we should never be uploading
symbols from build tasks. Unfortunately Windows builds were still doing so.
This patch removes MOZ_AUTOMATION_UPLOAD_SYMBOLS from all the in-tree
mozconfigs and a few other places so that it should always default off
(per moz-automation.mk). The rest of the uploadsymbols bits will be
removed once Thunderbird fixes their automation.
This patch was mostly autogenerated by running:
rg --files-with-matches UPLOAD_SYMBOLS browser/config/mozconfigs/ mobile/android/config/mozconfigs/ | xargs sed -ri '/.*UPLOAD_SYMBOLS.*/d'
sed -ri '/.*UPLOAD_SYMBOLS.*/d' build/unix/mozconfig.linux build/mozconfig.win-common build/macosx/local-mozconfig.common build/mozconfig.automation
Then mobile/android/config/mozconfigs/common and
taskcluster/scripts/builder/build-linux.sh were hand-edited.
MozReview-Commit-ID: Cy8kSEodSg4
--HG--
extra : rebase_source : 01caf1651b4eb428313e1f371aa585f8f34c4151
--enable-elf-hack is the default on all platforms where it's supported,
and is completely ignored on platforms where it's not supported.
While moving the flag to moz.configure, we're going to make it only
work on platforms where elfhack is supported, so we at least need to
remove it from mozconfigs for those platforms where it's not supported.
But generally speaking, we want less things in mozconfigs, so just
remove it from there, since it's the default anyways.
This is similar to what we had until bug 1278456 removed them when we dropped
support for older libstdc++, but for a different symbol.
--HG--
extra : rebase_source : 641fc6c86c8f47e3dbd752bc20056f61646541a7
That the wrapper implementation works has been verified by creating a
dummy program such as:
$ cat test.cc
#include <thread>
int main() {
std::thread([]() {
printf("foo\n");
}).join();
return 0;
}
And compiling it with and without the hack:
$ g++ -fno-rtti -o test test.cc -lpthread
$ objdump -TC test | grep UND.*GLIBCXX_3.4.22
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.22 std:🧵:_State::~_State()
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4.22 std:🧵:_M_start_thread(std::unique_ptr<std:🧵:_State, std::default_delete<std:🧵:_State> >, void (*)())
$ ./test
foo
$ g++ -fno-rtti -o test test.cc $objdir/build/unix/stdc++compat/stdc++compat.o -lpthread
$ objdump -TC test | grep UND.*GLIBCXX_3.4.22
$ ./test
foo
--HG--
extra : rebase_source : 53ca8e2d0424eaeb539d50510c441c8a3252c819
In bug 635961, elfhack was made to (ab)use the bss section as a
temporary space for a pointer. To find it, it scanned writable PT_LOAD
segments to find one that has a different file and memory size,
indicating the presence of .bss. This usually works fine, but when
the binary is linked with lld and relro is enabled, the end of the
file-backed part of the PT_LOAD segment containing the .bss section
ends up in the RELRO segment, making that location read-only and
subsequently making the elfhacked binary crash when it tries to restore
the .bss to a clean state, because it's not actually writing in the .bss
section: lld page aligns it after the RELRO segment.
So instead of scanning PT_LOAD segments, we scan for SHT_NOBITS
sections that are not SHF_TLS (i.e. not .tbss).
--HG--
extra : rebase_source : f18c43897fd0139aa8535f983e13eb785088cb18
In some cases, we can end up linking some things with
--static-libstdc++. The notable (only?) example of that is for the
clang-plugin, and that happens because it gets some of its flags from
llvm-config, which contains --static-libstdc++ because clang itself is
built that way.
When that happens, the combination of --static-libstdc++ and
stdc++compat breaks the build because they have conflicting symbols,
which is very much by design.
There are two ways out of this:
- avoiding either -static-libstdc++ or stdc++compat
- work around the symbol conflicts
The former is not totally reliable ; we'd have to accurately determine
if we're in a potentially conflicting case, and remove one of the two in
that case, and while we can do that for the cases we explicitly know
about, that's not future-proof, and might fail just as much in the
future.
So we go with the latter. The way we do this is by defining all the
std++compat symbols weak, such that at link time, they're overridden by
any symbol with the same name. When building with -static-libstdc++,
libstdc++.a provides those symbols so the linker eliminates the weak
ones. When not building with -static-libstdc++, the linker keeps the
symbols from stdc++compat. That last assertion is validated by the
long-standing CHECK_STDCXX test that we run when linking shared
libraries and programs.
That still leaves the symbols weak in the final shared
libraries/programs, which is a change from the current setup, but
shouldn't cause problems because when using versions of libstdc++.so
that do provide those symbols, it's fine to use the libstdc++.so version
anyways.
It becomes a library of some sort, so that multiple scripts can benefit
from it to build different versions of GCC.
The GPG key associated with GCC is also refreshed from keys.gnupg.net,
adding a new subkey, used to sign newer versions of GCC (and
postprocessed with pgpstrip to make it smaller).
The lld linker creates separate segments for purely executable sections
(such as .text) and sections preceding those (such as .rel.dyn). Neither
gold nor bfd ld do that, and just put all those sections in the same
executable segment.
Since elfhack is putting its executable code between the two relocation
sections, it ends up in a non-executable segment, leading to a crash
when it's time to run that code.
We thus insert the elfhack code before the first executable section
instead of between the two relocation sections (which is where the
elfhack data lies, and stays).
--HG--
extra : rebase_source : ab18eb9ac518d69a8639ad0e785741395b662112
Since bug 635961, building with relro makes elfhack try to use the bss
data for a temporary function pointer. If there is not enough space for
a pointer in the bss, elfhack will complain it couldn't find the bss.
In normal circumstances, this is most likely fine. Libraries with a bss
so small that it can't fit a pointer are already too small to be
elfhacked anyways. In Firefox, the two libraries with the smallest bss
have enough space for two pointers, and aren't elfhacked (libmozgtk.so
and libplds4.so).
However, the testcase that is used during the build to validate that
elfhack works doesn't have a large enough bss on x86-64, making elfhack
bail out, and the build fail as a consequence.
This, in turn, is due to the only non-thread-local zeroed data being an
int, which is not enough to fit a pointer on x86-64. We thus make it a
size_t.
--HG--
extra : rebase_source : bca2ddbf9d4a5e8786881fc524d642c38d610227
The PT_PHDR segment is optional, but the Android toolchain decides to
create one in some cases, and places it first. When that happens, the
work around for bug 1233963 fails, because the fake phdr section has not
been adjusted yet (it only happens when we see a PT_LOAD).
So we adjust the fake phdr section when we see a PT_PHDR segment (and
avoid re-updating it when we see a subsequent PT_LOAD).
--HG--
extra : rebase_source : 2190ec2f20ba9d144b8828874f9f8d70dd5ad2f6
Somehow, with the Android toolchain, we end up with
non-empty-but-really-empty DT_INIT_ARRAYs.
In practical terms, they are arrays with no relocations, and content
that is meaningless:
$ objdump -s -j .init_array libnss3.so
libnss3.so: file format elf32-little
Contents of section .init_array:
1086e0 00000000 ....
$ readelf -r libnss3.so | grep 1086e0
$ objdump -s -j .init_array libplugin-container-pie.so
libplugin-container-pie.so: file format elf32-little
Contents of section .init_array:
4479c ffffffff 00000000 ffffffff 00000000 ................
$ readelf -r libplugin-container-pie.so | grep 4479c
Because so far, elfhack expected meaningful DT_INIT_ARRAYs, it bailed out
early in that case.
--HG--
extra : rebase_source : 217aacb42fdfabb466ed1f8149dfaeb4a595eda8
When the clang plugin is used, building something during export needs to
happen after the plugin is built. But there is no dependency ensuring
this happens.
OTOH, these sources in elfhack/inject don't need to be built that early,
so we'll just leave to the build system to build it at a proper time.
--HG--
extra : rebase_source : a6bef8ec6eece3a1b0e45f84c907c2fbc0800863
Mike Hommey
Tom Prince
Dorel Luca
Ted Mielczarek
Chris Manchester
Nathan Froyd
Tom Ritter
Robert-André Mauchin
Sebastian Hengst
Eugen Sawin
Wes Kocher
Sylvestre Ledru
Cameron McCormack
rforbes
Steve Fink
Lee Salzman
Ting-Yu Chou