rprichard

  # Android added %a printf starting with Android L (API 21).
  Feature(name='android-no-printf-a',
          when=lambda cfg: _isAndroid(cfg) and not _isAndroidApiAtLeast(cfg, 21) and
                           not programSucceeds(cfg, """
            #include <stdio.h>
            #include <string.h>
            int main(int, char**) {
              char buf[100];
              snprintf(buf, sizeof(buf), "%a", 0.0);

rprichard

#!/bin/bash
#
# Both the builtins archive and libc.so expose __aeabi_uidiv. Normally, when
# generating a shared library, the linker links __aeabi_uidiv from the builtins
# archive because it comes first on the linker command-line. However, when
# the only reference to __aeabi_uidiv results from LTO code generation, then the
# linker instead prefers the __aeabi_uidiv from libc.so.

set -e

rprichard

#!/bin/bash

cat >dso1.c <<EOF
#include <stdio.h>
void foo(void) {
  printf("foo");
  printf("\n");
}
EOF

rprichard

// GAS:
//   arm-linux-gnueabi-gcc -march=armv7-a -c test.s
//   GNU assembler (GNU Binutils for Debian) 2.35.2
// LLVM:
//   /x/clang12/bin/clang -target armv7-linux-androideabi -c test.s
//   clang version 12.0.0 (https://github.com/llvm/llvm-project/ b978a93635b584db380274d7c8963c73989944a1)

  .syntax unified
  .thumb

rprichard

#include <errno.h>
#include <fenv.h>
#include <float.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

const char* round_mode_to_str(int round_mode) {
  switch (round_mode) {

rprichard

The linker seems to delete the weak version of _bar because it's overridden by a strong
version, and when it does, it also deletes _foo's instructions, so calling _foo actually
calls an unrelated function, _baz.

$ ./weak-to-weak-alias.sh   

=== objdump

a.out:	file format Mach-O 64-bit x86-64

rprichard

#!/bin/bash
set -e

NDK=/x/android-ndk-r21d
LIBUNWIND=/x/llvm-upstream/unwind-arm64-21/lib/libunwind.a
CXX="$NDK/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang++ -fuse-ld=lld $LIBUNWIND"

rm -fr out
mkdir -p out

rprichard

/*

$ /x/android-ndk-r21d/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android28-clang segv_leaf_unwind.c -funwind-tables -Wl,--export-dynamic -Os

$ adb push a.out /data/local/tmp
./a.out: 1 file pushed, 0 skipped. 49.8 MB/s (119472 bytes in 0.002s)

$ adb shell /data/local/tmp/a.out
0x60e1e2f3a8 [sigsegv_handler]
0x73fcfe58c0 [__kernel_rt_sigreturn]

rprichard

#!/bin/bash -e
#
# On an older device (Galaxy Nexus S running Android 4.1.2), an executable built
# with -z,max-page-size=0x10000 has a gap of size 0x1e000 between its R+E and
# R+W segments. If a DSO is loaded into the gap, then that DSO may hit a bug in
# old versions of Android where dl_unwind_find_exidx searches the executable
# rather than the DSO.
#
# This test program runs 10 times and typically fails a few times, depending on
# whether ASLR puts a DSO into the gap. Failure looks like so:

rprichard

// https://issuetracker.google.com/147619573
// https://bugs.llvm.org/show_bug.cgi?id=43703

// The program waits for 7200 seconds, and prints the elapsed time every 10 seconds.
// It should always print an elapsed time of just over 10 seconds, but about every 1845
// seconds, it instead prints -1834.66 or so. (The performance counter frequency was 10MHz
// on Wine and the Windows 10 laptop I tested.)

#include <windows.h>