Previously, we make all PLT entries canonical if we are creating
a position dependent executable, because I was thinking that promoting
usual PLT entries to canonical ones is harmless; symbol equality still
holds.
However, it looks like Qt depends on the usual linker's behavior not
to make PLT canonical if not necessary. I believe they are maintaining
some hidden symbol as aliases for exported symbols and compare their
addresses at runtime.
Of course this doesn't work if your program is not compiled with -fPIC,
but qt5/QtCore/qglobal.h has a macro to abort compilation if PIC is
disabled. (They check for __PIC__ and __PIE__ macros.) So, all object
files are guaranteed to be compiled with -fPIC if they are using QT
functions, and they assume that the linker doesn't create a canonical
PLT for Qt functions.
This commit makes mold to create canonical PLTs only when needed.
That is, if an address of a function is directly taken (i.e. not via
GOT), then mold makes its PLT canonical.
Fixes https://github.com/rui314/mold/issues/352
glibc's -static-pie implementation expect that _GLOBAL_OFFSET_TABLE_
is at the beginning of .got.plt, as it uses the address of _DYNAMIC
which is stored at _GLOBAL_OFFSET_TABLE_[0].
In this patch, we always create .got.plt for x86-64 and i386.
With this change, you can now cross compile test cases and run
them on qemu-user. Here is an example to run our test suits in
an emulated ARM32 environment.
$ CC=arm-linux-gnueabihf-gcc \
CXX=arm-linux-gnueabihf-g++ \
GCC=arm-linux-gnueabihf-gcc \
GXX=arm-linux-gnueabihf-g++ \
OBJDUMP=arm-linux-gnueabihf-objdump \
MACHINE=arm \
QEMU='qemu-arm -L /usr/arm-linux-gnueabihf' \
make -j16 test
While running tests on UBSan instrumented mold binary 2 separated problems are reported:
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior elf/main.cc:592:15 in
elf/output-chunks.cc:1866:24: runtime error: member call on null pointer of type 'mold:🧝:VerdefSection<mold:🧝:X86_64> *'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior elf/output-chunks.cc:1866:24 in
elf/input-files.cc:1000:8: runtime error: load of value 190, which is not a valid value for type 'bool'
This change fixes both of them.
Signed-off-by: Dawid Jurczak <dawid_jurek@vp.pl>
