SITL: dumpstack/dumpcore do not run if PWD is not in the repository and sh != bash

[durka]

Bug report

Issue details

There is a comment here:

ardupilot/libraries/AP_HAL_SITL/system.cpp

Line 58 in a480c0a

const char *command_filepath = commandname; // if we can't find it trust in PATH

Unfortunately, trusting in $PATH is a hazardous course of action! This function uses sh to invoke the program. On my system (Ubuntu 18.04), sh is symlinked to dash, which does NOT search $PATH when given a command that doesn't include a slash.

The man page makes it sound like it does, but it doesn't.

Path Search
 When locating a command, the shell first looks to see if it has a shell function by that name.  Then it looks for a builtin command by that name.  If a builtin command is not found, one of two things happen:
 1.   Command names containing a slash are simply executed without performing any searches.
 2.   The shell searches each entry in PATH in turn for the command.  The value of the PATH variable should be a series of entries separated by colons.  Each entry consists of a directory name.  The current directory may be indicated implicitly by an empty directory name, or explicitly by a single period.

$ mkdir test
$ echo -e '#!/bin/sh\necho $0 "$@"\n' >test/test.sh
$ PATH=$PWD/test:$PATH bash test.sh 1 2 3
test.sh 1 2 3
$ PATH=$PWD/test:$PATH dash test.sh 1 2 3
dash: 0: cannot open test.sh: No such file

Here are a couple of workarounds:

1. Use bash instead of sh
2. Use sh -c, but note that in that case the full command needs to be in quotes, i.e. sh -c "dumpstack.sh PID" or sh -c "dumpstack.sh $0" PID
3. If the command isn't found in one of the canned search directories, find it from $PATH using which, then pass that to sh

Version
4.2.3

Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Submarine
[x] SITL

Airframe type
N/A

Hardware type
N/A

Logs
N/A

[peterbarker]

We can remove any hack required for this when this sequence of commands results in something sensible:

pbarker@fx:~/rc/ardupilot(master)$ ls ~/bin/bin2elf.sh 
/home/pbarker/bin/bin2elf.sh
pbarker@fx:~/rc/ardupilot(master)$ bash bin2elf.sh
Usage: bin2elf.sh BINFILE ELFFILE ADDRESS
pbarker@fx:~/rc/ardupilot(master)$ dash bin2elf.sh
dash: 0: cannot open bin2elf.sh: No such file
pbarker@fx:~/rc/ardupilot(master)$ 

[peterbarker]

@durka OK, you've obviously got a slightly weird setup where it can't find the thing in the path it is expecting, but that you are adding that scripts directory to the path.

I'm uncomfortable changing that code for everyone, but please see the PR I just created (#27742) to give people some sort of an option, at least.

Look reasonable to you?

[durka]

I'll comment over in there, we can close this if it's not the desired approach