commit	e8c76b7a30b57ec1b9858353bb32bfceda285f4b	[log] [tgz]
author	Goran Ferenc <goran.ferenc@imgtec.com>	Tue Feb 21 16:24:51 2017 +0100
committer	Goran Ferenc <goran.ferenc@imgtec.com>	Fri Oct 13 12:08:30 2017 +0200
tree	e7d9cee9965a7c5a66aaaf38508616208a34d19b
parent	ddd6436df2adef2e195cf45634750a31c3e03bd1 [diff]

MIPS: Fix MIPS linker VDSO issues

This patch resolves two issues:
(1) AOSP MIPS linker crash with SIGSEGV while relocating VDSO GOT
(2) Missing of MIPS_ABI_FP_ANY flag while ckecking & adjusting MIPS FP modes

(1): AOSP MIPS linker crash with SIGSEGV while relocating VDSO GOT

During bringup and testing of the kernel VDSO support on the emulator we
encountered an issue where all userspace processes were crashing due to
linker crash with SIGSEGV during VDSO GOT relocation.

The mentioned scenario will trigger SIGSEGV in the linker only if the kernel
code base contains VDSO implementation introduced with the following commits:

a7f4df4 MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime()
c0a9f72 irqchip: irq-mips-gic: Provide function to map GIC user section
ebb5e78 MIPS: Initial implementation of a VDSO

Another prerequisite is that the linker contains the following commit from AOSP:
https://android-review.googlesource.com/#/c/264857/

The above commit introduces auxvec.h header containing definition of
AT_SYSINFO_EHDR in:
https://android.googlesource.com/platform/bionic/+/master/libc/kernel/uapi/asm-mips/asm/auxvec.h,
which in turn activates VDSO GOT relocations in mips_relocate_got():
https://android.googlesource.com/platform/bionic/+/master/linker/linker_mips.cpp#149

Since VDSO is mapped as a RO region, writing anything to its page will result
in SIGSEGV.

Removing this 0xdeadbeef cookies writes to the got[0]/got[1] solved SIGSEGV issue.
We also compared with the glibc linker code and we haven't seen anything similar
like writing some cookie values into GOT entries.

(2): Missing of MIPS_ABI_FP_ANY flag while checking & adjusting MIPS FP modes

This issue was found during testing of the patch:
https://android-review.googlesource.com/#/c/platform/bionic/+/494440/

This patch adds a bionic dlfcn.dlopen_vdso test which tries to open "linux-vdso.so.1"
(virtual ELF shared library) and expects to succeed.

dlopen fails in the mips linker part due to the following error:
"Unsupported MIPS32 FloatPt ABI 0 found in linux.vdso.so.1"

According to:
https://dmz-portal.imgtec.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#A.2._O32_FPXX_code_calling_FPXX,
ABI 0 is:
Val_GNU_MIPS_ABI_FP_ANY = 0 /* Not tagged or not using any ABIs affected by the differences.  */

The issue appeared because MIPS_ABI_FP_ANY is not supposed to be checked as
a possible FP ABI-variant compatibility flag.

This patch adds logic to MIPS linker to handle this case appropriately,
after which dlfcn.dlopen_vdso test passes.

Test:
* bionic-unit-tests --gtest_filter=dlfcn.dlopen_vdso
* Boot android in emulator with kernel which supports VDSO optimizations

Change-Id: Icbcd9879beea1b38fbe8d97b3b205058eaa861f4
Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com>

linker/linker_mips.cpp[diff]

1 file changed

tree: e7d9cee9965a7c5a66aaaf38508616208a34d19b

README.md

Using bionic

See the additional documentation.

Working on bionic

What are the big pieces of bionic?

libc/ --- libc.so, libc.a

The C library. Stuff like fopen(3) and kill(2).

libm/ --- libm.so, libm.a

The math library. Traditionally Unix systems kept stuff like sin(3) and cos(3) in a separate library to save space in the days before shared libraries.

libdl/ --- libdl.so

The dynamic linker interface library. This is actually just a bunch of stubs that the dynamic linker replaces with pointers to its own implementation at runtime. This is where stuff like dlopen(3) lives.

libstdc++/ --- libstdc++.so

The C++ ABI support functions. The C++ compiler doesn't know how to implement thread-safe static initialization and the like, so it just calls functions that are supplied by the system. Stuff like __cxa_guard_acquire and __cxa_pure_virtual live here.

linker/ --- /system/bin/linker and /system/bin/linker64

The dynamic linker. When you run a dynamically-linked executable, its ELF file has a DT_INTERP entry that says "use the following program to start me". On Android, that's either linker or linker64 (depending on whether it's a 32-bit or 64-bit executable). It's responsible for loading the ELF executable into memory and resolving references to symbols (so that when your code tries to jump to fopen(3), say, it lands in the right place).

tests/ --- unit tests

The tests/ directory contains unit tests. Roughly arranged as one file per publicly-exported header file.

benchmarks/ --- benchmarks

The benchmarks/ directory contains benchmarks, with its own documentation.

What's in libc/?

Adding system calls

Adding a system call usually involves:

Add entries to SYSCALLS.TXT. See SYSCALLS.TXT itself for documentation on the format.
Run the gensyscalls.py script.
Add constants (and perhaps types) to the appropriate header file. Note that you should check to see whether the constants are already in kernel uapi header files, in which case you just need to make sure that the appropriate POSIX header file in libc/include/ includes the relevant file or files.
Add function declarations to the appropriate header file.
Add the function name to the correct section in libc/libc.map.txt and run ./libc/tools/genversion-scripts.py.
Add at least basic tests. Even a test that deliberately supplies an invalid argument helps check that we're generating the right symbol and have the right declaration in the header file, and that you correctly updated the maps in step 5. (You can use strace(1) to confirm that the correct system call is being made.)

Updating kernel header files

As mentioned above, this is currently a two-step process:

Use generate_uapi_headers.sh to go from a Linux source tree to appropriate contents for external/kernel-headers/.
Run update_all.py to scrub those headers and import them into bionic.

Note that if you're actually just trying to expose device-specific headers to build your device drivers, you shouldn't modify bionic. Instead use TARGET_DEVICE_KERNEL_HEADERS and friends described in config.mk.

Updating tzdata

This is fully automated (and these days handled by the libcore team, because they own icu, and that needs to be updated in sync with bionic):

Run update-tzdata.py in external/icu/tools/.

Verifying changes

If you make a change that is likely to have a wide effect on the tree (such as a libc header change), you should run make checkbuild. A regular make will not build the entire tree; just the minimum number of projects that are required for the device. Tests, additional developer tools, and various other modules will not be built. Note that make checkbuild will not be complete either, as make tests covers a few additional modules, but generally speaking make checkbuild is enough.

Running the tests

The tests are all built from the tests/ directory.

Device tests

$ mma # In $ANDROID_ROOT/bionic.
$ adb root && adb remount && adb sync
$ adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests32
$ adb shell \
    /data/nativetest/bionic-unit-tests-static/bionic-unit-tests-static32
# Only for 64-bit targets
$ adb shell /data/nativetest64/bionic-unit-tests/bionic-unit-tests64
$ adb shell \
    /data/nativetest64/bionic-unit-tests-static/bionic-unit-tests-static64

Note that we use our own custom gtest runner that offers a superset of the options documented at https://github.com/google/googletest/blob/master/googletest/docs/AdvancedGuide.md#running-test-programs-advanced-options, in particular for test isolation and parallelism (both on by default).

Device tests via CTS

Most of the unit tests are executed by CTS. By default, CTS runs as a non-root user, so the unit tests must also pass when not run as root. Some tests cannot do any useful work unless run as root. In this case, the test should check getuid() == 0 and do nothing otherwise (typically we log in this case to prevent accidents!). Obviously, if the test can be rewritten to not require root, that's an even better solution.

Currently, the list of bionic CTS tests is generated at build time by running a host version of the test executable and dumping the list of all tests. In order for this to continue to work, all architectures must have the same number of tests, and the host version of the executable must also have the same number of tests.

Running the gtests directly is orders of magnitude faster than using CTS, but in cases where you really have to run CTS:

$ make cts # In $ANDROID_ROOT.
$ adb unroot # Because real CTS doesn't run as root.
# This will sync any *test* changes, but not *code* changes:
$ cts-tradefed \
    run singleCommand cts --skip-preconditions -m CtsBionicTestCases

Host tests

The host tests require that you have lunched either an x86 or x86_64 target. Note that due to ABI limitations (specifically, the size of pthread_mutex_t), 32-bit bionic requires PIDs less than 65536. To enforce this, set /proc/sys/kernel/pid_max to 65536.

$ ./tests/run-on-host.sh 32
$ ./tests/run-on-host.sh 64   # For x86_64-bit *targets* only.

You can supply gtest flags as extra arguments to this script.

Against glibc

As a way to check that our tests do in fact test the correct behavior (and not just the behavior we think is correct), it is possible to run the tests against the host's glibc.

$ ./tests/run-on-host.sh glibc

Gathering test coverage

For either host or target coverage, you must first:

$ export NATIVE_COVERAGE=true
- Note that the build system is ignorant to this flag being toggled, i.e. if you change this flag, you will have to manually rebuild bionic.
Set bionic_coverage=true in libc/Android.mk and libm/Android.mk.

Coverage from device tests

$ mma
$ adb sync
$ adb shell \
    GCOV_PREFIX=/data/local/tmp/gcov \
    GCOV_PREFIX_STRIP=`echo $ANDROID_BUILD_TOP | grep -o / | wc -l` \
    /data/nativetest/bionic-unit-tests/bionic-unit-tests32
$ acov

acov will pull all coverage information from the device, push it to the right directories, run lcov, and open the coverage report in your browser.

Coverage from host tests

First, build and run the host tests as usual (see above).

$ croot
$ lcov -c -d $ANDROID_PRODUCT_OUT -o coverage.info
$ genhtml -o covreport coverage.info # or lcov --list coverage.info

The coverage report is now available at covreport/index.html.

Attaching GDB to the tests

Bionic's test runner will run each test in its own process by default to prevent tests failures from impacting other tests. This also has the added benefit of running them in parallel, so they are much faster.

However, this also makes it difficult to run the tests under GDB. To prevent each test from being forked, run the tests with the flag --no-isolate.

32-bit ABI bugs

See 32-bit ABI bugs.