Credits to @drinkcat for reporting it.

- 3300bfb#r154209904

… `<component_name> version=<name> org=<name> project=<name>` format

…tdout of parent and log them to original stderr of child, otherwise they would get captured in `output` of parent and compared with `output_regex`

…ORTED` define

…`ExecVP` and `ExecVPE` tests by setting `file` to `NULL`

…e by setting `expectedExitCode` to `-1`

This is needed for running specific commands whose exit code can vary on different Android versions, like when getting help output of system executables.

…to override init function of child process that runs the test

…g a non-regular file instead of `Is a directory (EISDIR)` for a directory

Despite `EISDIR` being more appropriate if trying to execute a directory, considering even `bash` and `sh` return the same, `execve` expects `EACCES` as per its  man page.

> EACCES The file or a script interpreter is not a regular file.

- https://man7.org/linux/man-pages/man2/execve.2.html

```
~ $ TERMUX_EXEC__LOG_LEVEL=4 env .
28077 E termux  : TERMUX_EXEC__VERSION: '1:2.1.0+direct-ld-preload'
28077 E termux.exec: <----- execve() intercepted ----->
28077 E termux.exec: executable = '/data/data/com.termux/files/usr/bin/env'
28077 E termux.exec:    argv[0] = 'env'
28077 E termux.exec:    argv[1] = '.'
28077 E termux.exec: Intercepting execve
28077 E termux.exec: read_file_header: '1'
28077 E termux.ld-preload: system_linker_exec_mode: '1'
28077 E termux.ld-preload: android_build_version_sdk: '30'
28077 E termux.ld-preload: se_process_context_from_file: 'u:r:untrusted_app_27:s0:c212,c256,c512,c768'
28077 E termux.ld-preload: app_data_file_exec_exempted: '1'
28077 E termux.ld-preload: system_linker_exec_enabled: '0'
28077 E termux.exec: unset_ld_vars_from_env: '0'
28077 E termux.exec: modify_env: '0'
28077 E termux.exec: modify_args: '0'
28077 E termux.exec: Calling syscall execve
28077 E termux.exec: executable = '/data/data/com.termux/files/usr/bin/env'
28077 E termux.exec:    argv[0] = 'env'
28077 E termux.exec:    argv[1] = '.'
28077 E termux  : TERMUX_EXEC__VERSION: '1:2.1.0+direct-ld-preload'
28077 E termux.exec: <----- execvp() intercepted ----->
28077 E termux.exec: executable = '/data/data/com.termux/files/usr/bin/.'
28077 E termux.exec:    argv[0] = '.'
28077 E termux.exec: Intercepting execve
28077 E termux.exec: normalized_executable: '/data/data/com.termux/files/usr/bin'
28077 E termux.exec: read_file_header: '1'
28077 E termux.exec: Failed to read executable path '/data/data/com.termux/files/usr/bin' for file header: Is a directory
28077 E termux.exec: <----- execve() failed ----->
env: ‘.’: Is a directory

~ $ bash -c './'
bash: line 1: ./: Is a directory

~ $ /system/bin/sh -c './'
/system/bin/sh: ./: can't execute: Is a directory
```

Related commit termux/termux-core-package@1779618b

Closes #33

…running commands with empty `$LD_PRELOAD` variable, like `LD_PRELOAD= <command>` will fail with `CANNOT LINK EXECUTABLE` errors with a random environment variable `<name=value>` pair or `DT_RUNPATH` directory loaded as a library

```
$ LD_DEBUG=3 LD_PRELOAD= bash
CANNOT LINK EXECUTABLE "bash": can't read file "/data/data/com.termux/files/usr/lib": Is a directory
[ Android dynamic linker (64-bit) ]
W  [ LD_PRELOAD set to "" ]
I  name /data/data/com.termux/files/usr/bin/bash: allocated soinfo @ 0x7f97a24010
W  [ Linking "/data/data/com.termux/files/usr/bin/bash" ]
I  [ "" find_loaded_library_by_soname failed (*candidate=n/a@0x0). Trying harder...]
I  [ opening  ]
I  name /data/data/com.termux/files/usr/lib: allocated soinfo @ 0x7f97a24240
D  DEBUG: can't read file "/data/data/com.termux/files/usr/lib": Is a directory
I  name /data/data/com.termux/files/usr/lib: freeing soinfo @ 0x7f97a24240
A  CANNOT LINK EXECUTABLE "bash": can't read file "/data/data/com.termux/files/usr/lib": Is a directory

$ LD_PRELOAD="" /system/bin/sh
CANNOT LINK EXECUTABLE "/system/bin/sh": cant read file "/system/lib64": Is a directory
```

```
$ LD_DEBUG=3 LD_PRELOAD= bash
CANNOT LINK EXECUTABLE: library "SHELL=/data/data/com.termux/files/usr/bin/bash" not found
page record for 0x7f6384688050 was not found (block_size=64)
W  [ android linker & debugger ]
I  name bash: allocated soinfo @ 0x7fa61e09b008
W  [ linking bash ]
I  [ 'SHELL=/data/data/com.termux/files/usr/bin/bash' find_loaded_library_by_soname returned false (*candidate=n/a@0x0). Trying harder...]
I  [ opening SHELL=/data/data/com.termux/files/usr/bin/bash ]
D  DEBUG: library "SHELL=/data/data/com.termux/files/usr/bin/bash" not found

 $ LD_PRELOAD= /system/bin/sh
CANNOT LINK EXECUTABLE: library "_=/system/bin/sh" not found

$ LD_PRELOAD= /system/bin/pm
CANNOT LINK EXECUTABLE: library "_=/system/bin/pm" not found
```

Cause is unknown, but related changes in linker for empty LD_PRELOAD are at:
- https://cs.android.com/android/_/android/platform/bionic/+/d799b2bb
- https://cs.android.com/android/_/android/platform/bionic/+/44f6e189

Was found locally before on Android 6 while testing, but ignored. Reported again by @robertkirkman at following:
- #31 (comment)

…ExecutableUnderSystemDir()`

…ables if executed with `fexecve()` or fd path, and their file header being read instead of skipped as per 3300bfb

File descriptor executable paths are in the format `/proc/self/fd/<num>` or `/proc/<pid>/fd/<num>`, normally for `fexecve()`, but can be passed manually by callers. For such paths, checks would fail for if the path is under system directories with `isExecutableUnderSystemDir()` or if `LD_VARS` should be unset with `shouldUnsetLDVarsFromEnv()`, as path would start with `/proc` instead of one of the system directories. Now we find the real path before any checks are done by calling `readlink()` via `getRegularFileFdRealPath()` on the fd path.

Note that `fexecve()` is only supported for Android `>= 9` and `CANNOT LINK EXECUTABLE` errors due to `LD_VARS` being set like `LD_LIBRARY_PATH=/data/data/com.termux/files/usr/lib` when calling system binaries only seem to occur on older Android versions. So we simulate `fexecve()` for tests by opening a system executable, generating fd path manually and then executing it.

Following are examples of errors caused by `LD_LIBRARY_PATH` being set. Termux app only exports it for Android `5` and `6` though.

```
$ LD_PRELOAD= bash

$ LD_LIBRARY_PATH=/data/data/com.termux/files/usr/lib PATH=/system/bin /system/bin/{am,pm}
CANNOT LINK EXECUTABLE: could not load library "libandroid_runtime.so" needed by "app_process"; caused by could not load library "libhwui.so" needed by "libandroid_runtime.so"; caused by could not load library "libRS.so" needed by "libhwui.so"; caused by could not load library "libbcc.so" needed by "libRS.so"; caused by could not load library "libbcinfo.so" needed by "libbcc.so"; caused by cannot locate symbol "_ZNK4llvm6MDNode10getOperandEj" referenced by "libbcinfo.so"...

$ LD_LIBRARY_PATH=/data/data/com.termux/files/usr/lib PATH=/system/bin /system/bin/dalvikvm
Aborted
dlopen("libjavacore.so", RTLD_LAZY) failed: dlopen failed: cannot locate symbol "bn_expand2" referenced by "libjavacore.so"...

LD_LIBRARY_PATH=/data/data/com.termux/files/usr/lib PATH=/system/bin /system/bin/{am,pm}
CANNOT LINK EXECUTABLE: cannot locate symbol "u_charMirror_55" referenced by "/system/lib64/libandroid_runtime.so"...

$ LD_LIBRARY_PATH=/data/data/com.termux/files/usr/lib PATH=/system/bin /system/bin/dalvikvm
Aborted
art/runtime/runtime.cc:1149] LoadNativeLibrary failed for "libjavacore.so": dlopen failed: cannot locate symbol "_ZTVN6icu_5513UnicodeStringE" referenced by "/system/lib64/libjavacore.so"...

~ $ LD_LIBRARY_PATH=/data/data/com.termux/files/usr/lib PATH=/system/bin /system/bin/{am,pm}
CANNOT LINK EXECUTABLE "app_process": cannot locate symbol "glTexGenxvOES" referenced by "/system/lib64/libandroid_runtime.so"...
Aborted
$ LD_LIBRARY_PATH=/data/data/com.termux/files/usr/lib PATH=/system/bin /system/bin/dalvikvm
Failed to initialize JNI invocation API from (null)
Failed to dlopen libart.so: dlopen failed: cannot locate symbol "XzUnpacker_Construct" referenced by "/system/lib64/libunwind.so"...
```

…er_exec` in `v2.0.0` release notes

Seems like changes to `src/termux-exec.c` accidentally got removed while rebasing 2fe4775 due to file path changes. So add link to older commit that had the file changes for credits and historical reason.

5ea25ee was modified version of 38a51829 and ecad16fd

…put synchronous if `stdout` and `stderr` streams are captured separately as other log entries are being sent to `stdout`

The existence of `stderr` being set can also be considered a failure by clients.

…ec_nos_c/tre` and `termux/api/termux_exec/ld_preload` sources to `termux/api/termux_exec/service/ld_preload` stage 1

…ec_nos_c/tre` and `api/termux_exec/ld_preload` sources to `api/termux_exec/service/ld_preload` stage 2

The Termux Runtime Environment `tre` is a variant of the `termux-exec_nos_c` library and so its sources should be under the `tre` sub directory to be consistent with the library naming and directory hierarchy convention. For example, for a `foo_jvm_java` library with the Android App Runtime Environment `aare` and Java Runtime Environment `jre` variants that share common code, the directory hierarchy would be `lib/foo_jvm_java/{share,aare,jre}`, where `share` sub directory contains the common code.

The API service code must exist under the `service` directory like `api/<host>/service/<service_name>` as other directories like `config`/`utils` could exist that are shared between different API services, as they would otherwise conflict with the service name directory.