Standalone executable symlink

[danmasta]

When running a standalone executable from a symlink in PATH, qjs seems to only execute the qjs runtime, instead of the packaged bytecode

Example:
First install a package that was compiled with qjs

brew install danmasta/tap/envstr

which envstr
/home/linuxbrew/.linuxbrew/bin/envstr

Then if we try and execute the package, we get the qjs help menu:

envstr -v

qjs: unknown option '-v'
QuickJS-ng version 0.9.0
usage: qjs [options] [file [args]]
-h  --help         list options
-e  --eval EXPR    evaluate EXPR
-i  --interactive  go to interactive mode
-m  --module       load as ES6 module (default=autodetect)
    --script       load as ES6 script (default=autodetect)
-I  --include file include an additional file
    --std          make 'std', 'os' and 'bjson' available to script
-T  --trace        trace memory allocation
-d  --dump         dump the memory usage stats
-D  --dump-flags   flags for dumping debug data (see DUMP_* defines)
-c  --compile FILE compile the given JS file as a standalone executable
-o  --out FILE     output file for standalone executables
    --exe          select the executable to use as the base, defaults to the current one
    --memory-limit n       limit the memory usage to 'n' Kbytes
    --stack-size n         limit the stack size to 'n' Kbytes
-q  --quit         just instantiate the interpreter and quit

However, if we check the symlink and run using the absolute path

ls -la /home/linuxbrew/.linuxbrew/bin/envstr
lrwxrwxrwx 1 user user 33 Mar 30 18:35 /home/linuxbrew/.linuxbrew/bin/envstr -> ../Cellar/envstr/0.0.1/bin/envstr

It works as expected

/home/linuxbrew/.linuxbrew/bin/envstr -v
0.0.1

/home/linuxbrew/.linuxbrew/Cellar/envstr/0.0.1/bin/envstr -v
0.0.1

I verified this behavior by symlinking the locally compiled binary to /usr/local/bin as well:

ln -s /home/user/projects/envstr/build/bin/envstr-linux-x64 /usr/local/bin/envstr

which envstr
/usr/local/bin/envstr

Calling with the file name fails:

envstr -v

qjs: unknown option '-v'
QuickJS-ng version 0.9.0
usage: qjs [options] [file [args]]
-h  --help         list options
-e  --eval EXPR    evaluate EXPR
-i  --interactive  go to interactive mode
-m  --module       load as ES6 module (default=autodetect)
    --script       load as ES6 script (default=autodetect)
-I  --include file include an additional file
    --std          make 'std', 'os' and 'bjson' available to script
-T  --trace        trace memory allocation
-d  --dump         dump the memory usage stats
-D  --dump-flags   flags for dumping debug data (see DUMP_* defines)
-c  --compile FILE compile the given JS file as a standalone executable
-o  --out FILE     output file for standalone executables
    --exe          select the executable to use as the base, defaults to the current one
    --memory-limit n       limit the memory usage to 'n' Kbytes
    --stack-size n         limit the stack size to 'n' Kbytes
-q  --quit         just instantiate the interpreter and quit

But the absolute path works again:

/usr/local/bin/envstr -v
0.0.1

I tested this behavior on linux and mac, it was the same for both systems.

Do you think this is a bug, or am I missing some compile option?

[saghul]

I think the problem is when we read the executable we don't do realpath to get the actual location.

Thanks for the report!

[danmasta]

I tried making a patch for this using realpath, by updating the is_standalone function:

#include <limits.h>

static bool is_standalone(const char *exe)
{
    char exe_r[PATH_MAX];
    FILE *exe_f = fopen(realpath(exe, exe_r), "rb");
    ...
}

But it doesn't work. It seems like realpath only resolves from CWD. If I print the paths, during build we get:

EXE: /home/user/projects/quickjs/build/qjs
REALPATH: /mnt/wsl/projects/quickjs/build/qjs

And if we execute the symlink:

envstr -v

EXE: envstr
REALPATH: (null)
REALPATH ERROR: No such file or directory

And if we execute the full path:

/usr/local/bin/envstr -v

EXE: /usr/local/bin/envstr
REALPATH: /mnt/wsl/projects/envstr/build/envstr

It works as expected. So it seems like we're not able to resolve the file name from $PATH currently.

I found a method called execlp() which does what we want, except it executes the file instead of returning the path. Do you know if there is any std method to search for a file in $PATH?

I think we need to add the logic:

• Get realpath of exe (argv[0])
• If realpath is null, search $PATH

What do you think?

[saghul]

I think the problem is also in the JS side since it opens the executable to read the ancillary data, you would need to realpath there too.

[danmasta]

I see what you mean. I tested that too in standalone.js, but the issue is argv0 is incorrect in both qjs.c and standlone.js.

When you run the exe from a symlink in PATH, argv0 is just the filename: eg envstr. And realpath does not resolve the filename, it only recognizes it as a relative path.

If you use the full symlink path: eg /usr/local/bin/envstr then realpath is able to resolve that link. But with just the filename it fails.

So if argv0 is just the filename from a symlink, we need to iterate through PATH to try and find the real file path. With linux we could do readlink /proc/self/exe, but that isn't portable.

[saghul]

We can take uv_exepath from libuv

[saghul]

PR: #1029

[danmasta]

Tested the PR in linux, it works great now. Thank you!