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[RFC] Symbol versioning in libutee.so, the easy part #5833

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[RFC] Symbol versioning in libutee.so, the easy part #5833

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Commits on Feb 20, 2023

  1. build: mk/lib.mk: use full path to shared library in flags variable 

    To add link flags for a shared library, a makefile variable is used
that is called lib-ldflags$(libuuid). That's incorrect because the
UUID is not enough to uniquely identify a shared library in the build.
For example when both 32-bit and 64-bit user space is generated there
are two versions of the shared library with the same UUID. It is not
a problem at the moment because lib-ldflags$(libuuid) is used only
for one target: ta_arm64, but fix this anyways so that the variable
may be used for more complex cases.

Signed-off-by: Jerome Forissier <jerome.forissier@lnaro.org>
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  2. lib: link shared user space libraries with version script if it exists 

    If a user-space library such as lib/libutee is compiled as a shared
library (CFG_ULIBS_SHARED=y) and a file called lib/libutee/libutee.ver
exists, then use this file as a version script for the linker.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
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  3. compiler.h: add macros to add symbol version info to shared library 

    Add the SYMVER_GP131() and SYMVER_COMPAT_GP11() macros to help define
versioned symbols for functions when building shared libraries.

- SYMVER_GP131(foo) associates version GP_1.3.1 to symbol foo and
  makes it the default version, that is, the version that is recorded
  by the linker when a TA links against the shared library and references
  foo. Such a symbol is shown as foo@@GP_1.3.1 by the command:
    readelf -W --dyn-syms libname.so
  The undefined symbol created in the application by linking against
  this entry is displayed as foo@GP_1.3.1.
  Symbol foo (unversioned) is removed from the linker output.
- SYMVER_COMPAT_GP11(foo) defines symbol foo with version GP_1.1
  and makes it the same as the unversioned symbol __GP11_foo.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
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  4. [WIP] libutee: add symbol versioning for shared library 

    Add the required macros and version script to associate version numbers
with TEE API functions when libutee is built as a shared library
(CFG_ULIBS_SHARED=y).

The version script lib/libutee/libutee.ver declares two versions: GP_1.1
and GP_1.3.1. All symbols matching the glob pattern "TEE_[A-Z]*" are
tagged with default version GP_1.1 (TEE_foo@@GP_1.1), unless version
GP_1.3.1 is explicitly assigned in the source code via SYMVER_GP131().
In this case the default version symbol is GP_1.3.1 (TEE_foo@@GP_1.3.1).
All GP1.3.1 function have a compatibility inplementation called __GP11_*()
which is globally visible as an unversioned symbol (otherwise TAs that
use the __OPTEE_CORE_API_COMPAT_1_1 mechanism would not work) and also as
a versioned TEE_foo symbol with non-default version GP_1.1
(TEE_foo@GP_1.1).

The UUID of libutee is reverted to the one it had before the GP 1.3.1
update since the library is now compatible with the old one.

FIXME: THIS CAN NOT WORK until ldelf can resolve versioned symbols.
Test case: xtest 4002. There is an infinite loop as follows:
  __utee_entry()
    entry_open_session()
      init_instance()
        get_memtag_implementation
          TEE_GetPropertyAsU32()
            TEE_CheckMemoryAccessRights()
            /*
             * That should call 1.3.1 but due to ldelf not knowing
             * about versions, __GP11_TEE_CheckMemoryAccessRights()
             * is called instead, which is supposed to call
             * TEE_CheckMemoryAccessRights() 1.3.1 => infinite loop
             */

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
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    jforissier committed Feb 20, 2023
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