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| H A D | arm.mk | 7f761274bdee764b074451ade98cbdd2dd3e225d Wed Feb 27 15:54:22 UTC 2019 Jerome Forissier <jerome.forissier@linaro.org> Compile user TAs with -fpic rather than -fpie
TA source files are compiled with the -fpie GCC flag in order to
generate a Position Independent Executable. This is not suitable to
produce a shared library as introduced by commit f8896d1301fc ("TA dev
kit: add support for creating shared libraries"). -fpic should be used
instead. Here is what the GCC man page has to say on these flags:
-fpic
Generate position-independent code (PIC) suitable for use in a
shared library [...]
-fpie
-fPIE
These options are similar to -fpic and -fPIC, but generated
position independent code can be only linked into executables.
So, it is quite clear that -fpie is wrong for a shared library. It is
not very clear however if -fpic can be used when generating code for an
executable. I think it can, and there is a bug report against the GCC
documentation that would confirm this [1]. Therefore we can simply use
-fpic in all cases. This is quite convenient because we currently make
no difference in the compile flags when we are building an executable,
a static library or a shared library.
The difference between -fpie and -fpic has to do with the kinds of
relocations that the compiler is allowed to emit. I stumbled upon this
issue when experimenting with shared libraries and the code proposed
by Jens to share read-only pages between TAs [2]. In my test case, a
shared library already loaded by one TA, is used by another TA. During
the load phase of the second TA, the TEE core crashed with a data-abort
(write permission fault) when trying to apply an R_ARM_REL32 relocation
to some literal pool data in the .text section of the library. The
whole .text being mapped read-only, there should be no relocation to do
here. And indeed the cause was the wrong flag (-fpie) used when
compiling the shared library.
Link: [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70419
Link: [2] https://github.com/OP-TEE/optee_os/pull/2801
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
CC: Jens Wiklander <jens.wiklander@linaro.org>
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (QEMU)
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (HiKey960 32 & 64-bit TA)
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Tested-by: Etienne Carriere <etienne.carriere@linaro.org> (stm32mp1 Armv7)
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