Add demo for shell (FISH) script

demos/fish/.gitignore

@@ -0,0 +1,4 @@
+ncurses/
+fish-shell/
+busybox/
+occlum-context/

demos/fish/Occlum.json

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+{
+    "vm": {
+        "user_space_size": "512MB"
+    },
+    "process": {
+        "default_stack_size": "4MB",
+        "default_heap_size": "32MB",
+        "default_mmap_size": "80MB"
+    },
+    "env": {
+        "default": [
+            "OCCLUM=yes",
+            "HOME=/root"
+        ],
+        "untrusted": [
+        ]
+    },
+    "entry_points": [
+        "/bin"
+    ],
+    "mount": [
+        {
+            "target": "/",
+            "type": "sefs",
+            "source": "./image",
+            "options": {
+                "integrity_only": true
+            }
+        },
+        {
+            "target": "/root",
+            "type": "sefs"
+        },
+        {
+            "target": "/host",
+            "type": "hostfs",
+            "source": "."
+        },
+        {
+            "target": "/tmp",
+            "type": "ramfs"
+        }
+    ]
+}

demos/fish/README.md

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+# Run FISH script on Occlum
+
+This demo will show Occlum's support in shell script.
+
+Occlum now only supports FISH (the friendly interactive shell, https://github.com/fish-shell/fish-shell) for now
+because FISH initially use `posix_spawn()` to create process.
+
+This shell script works with BusyBox (the Swiss army knife of embedded Linux, https://busybox.net/).
+BusyBox combines tiny versions of many common UNIX utilities into a single small executable. It provides replacements
+for most of the utilities you usually find in GNU fileutils, shellutils, etc.
+
+This shell script contains executable binaries, pipe symbols and output redirection like this:
+```
+busybox echo "Hello-world-from-fish" | busybox awk '$1=$1' FS="-" OFS=" " > /root/output.txt
+```
+
+which is defined in `fish_script.sh`. `awk` will replace `-` to `space` and should output result
+string `Hello world from fish` and store in `/root/output.txt` of Occlum SEFS and can only be read
+inside Occlum.
+
+## Step 1:
+Downlaod FISH and busybox and build them with Occlum tool chain:
+```
+./download_and_build.sh
+```
+
+## Step 2:
+Prepare environment by running:
+```
+./env_setup.sh
+```
+
+If user wants to run this demo on non-SGX platform, run command:
+```
+SGX_MODE=SIM ./env_setup.sh
+```
+
+## Step 3:
+Run command to execute script:
+```
+cd occlum-context && occlum run /bin/fish /fish_script.sh
+```
+
+## Step 4:
+Go to `occlum-context` and check result by running:
+```
+occlum run /bin/busybox cat /root/output.txt
+```
+
+And you should see `Hello world from fish`.

demos/fish/download_and_build.sh

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+#!/bin/bash
+set -e
+
+# download and install ncurses
+git clone -b v6.1 --depth 1 https://github.com/mirror/ncurses.git
+cd ncurses
+CC=occlum-gcc CXX=occlum-g++ CFLAGS="-O2 -fPIC" CXXFLAGS="-O2 -fPIC" LDFLAGS="-pie"  \
+./configure --without-shared --without-cxx-shared --prefix=/usr/local/occlum --enable-overwrite
+make && make install
+cd ..
+
+# download and build FISH
+git clone -b 3.1.2 --depth 1 https://github.com/fish-shell/fish-shell.git
+cd fish-shell
+git apply ../fish.patch
+mkdir build && cd build
+cmake ../  -DCMAKE_BUILD_TYPE=Debug -DCURSES_LIBRARY=/opt/occlum/toolchains/gcc/lib/libcurses.a \
+-DCMAKE_C_COMPILER=occlum-gcc -DCMAKE_CXX_COMPILER=occlum-g++ \
+-DCMAKE_CXX_COMPILER_AR=/usr/local/occlum/bin/occlum-ar \
+-DCMAKE_CXX_COMPILER_RANLIB=/usr/local/occlum/bin/occlum-ranlib \
+-DCMAKE_C_COMPILER_AR=/usr/local/occlum/bin/occlum-ar \
+-DCMAKE_C_COMPILER_RANLIB=/usr/local/occlum/bin/occlum-ranlib \
+-DCMAKE_LINKER=/usr/local/occlum/bin/occlum-ld -DCMAKE_C_FLAGS="-I/usr/local/occlum/include -fpic -pie" \
+-DCMAKE_CXX_FLAGS="-I/usr/local/occlum/include -fpic -pie"
+make
+cd ../../
+
+# download and build busybox
+git clone -b 1_31_1 --depth 1 https://github.com/mirror/busybox.git
+cd busybox
+CROSS_COMPILE=/opt/occlum/toolchains/gcc/bin/occlum-
+make CROSS_COMPILE="$CROSS_COMPILE" defconfig
+cp ../.config .
+make CROSS_COMPILE="$CROSS_COMPILE"

demos/fish/env_setup.sh

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+#!/bin/bash
+set -e
+
+#
+rm -rf occlum-context
+mkdir occlum-context && cd occlum-context
+occlum init
+cp ../Occlum.json .
+cp ../fish-shell/build/fish image/bin
+cp ../busybox/busybox image/bin
+cp ../fish_script.sh image
+
+occlum build

demos/fish/fish.patch

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+diff --git a/src/exec.cpp b/src/exec.cpp
+index 1557caf0b..254dd0e2e 100644
+--- a/src/exec.cpp
++++ b/src/exec.cpp
+@@ -565,7 +565,7 @@ static bool exec_external_command(parser_t &parser, const std::shared_ptr<job_t>
+ 
+ #if FISH_USE_POSIX_SPAWN
+     // Prefer to use posix_spawn, since it's faster on some systems like OS X.
+-    bool use_posix_spawn = g_use_posix_spawn && can_use_posix_spawn_for_job(j, dup2s);
++    bool use_posix_spawn = g_use_posix_spawn; //&& can_use_posix_spawn_for_job(j, dup2s);
+     if (use_posix_spawn) {
+         s_fork_count++;  // spawn counts as a fork+exec
+         // Create posix spawn attributes and actions.

demos/fish/fish_script.sh

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+#! /bin/fish
+busybox echo "Hello-world-from-fish" | busybox awk '$1=$1' FS="-" OFS=" " > /root/output.txt

tools/toolchains/gcc/build.sh

@@ -70,3 +70,5 @@ chmod +x ${INSTALL_DIR}/bin/occlum-ld
 # Make symbolic links
 ln -sf ${INSTALL_DIR}/${TARGET}/lib/libc.so /lib/ld-musl-x86_64.so.1
 ln -sf ${INSTALL_DIR} /usr/local/occlum
+ln -sf ${INSTALL_DIR}/bin/x86_64-linux-musl-gcc-ar ${INSTALL_DIR}/bin/occlum-ar
+ln -sf ${INSTALL_DIR}/bin/x86_64-linux-musl-strip ${INSTALL_DIR}/bin/occlum-strip