Re: [Qemu-devel] [RFC PATCH] vl.c: add -semihosting-config "arg" sub-argument

[Leon Alrae]

On 02/04/2015 17:47, Liviu Ionescu wrote:
> 
>> On 02 Apr 2015, at 17:27, Matthew Fortune <address@hidden> wrote:
>>
>> Liviu Ionescu <address@hidden> writes:
>>> for completeness:
>>>
>>> ilg-mbp:gnuarmeclipse-qemu.git ilg$ "/Applications/GNU ARM
>>> Eclipse/QEMU/2.2.91-201504021111-dev/bin/qemu-system-gnuarmeclipse" -
>>> verbose -machine STM32-H103 -gdb tcp::1234 -semihosting-config
>>> enable=on,target=native,cmdline='n "1 a" 2 3'
>>
>> I see here that you have switched quotes because you know that you are
>> providing a double quoted argument within the string.
> 
> my code works both ways symmetrically:
> 
> ilg-mbp:~ ilg$ "/Applications/GNU ARM 
> Eclipse"/QEMU/2.2.91-201504021111-dev/bin/qemu-system-gnuarmeclipse -verbose 
> -machine STM32-H103 -gdb tcp::1234 -semihosting-config 
> enable=on,target=native,cmdline="name 1 '2 a' 3"
> 
> GNU ARM Eclipse QEMU v2.2.91 (qemu-system-gnuarmeclipse).
> Board: 'STM32-H103' (Olimex Header Board for STM32F103RBT6 (Experimental)).
> Device: 'STM32F103RB' (cortex-m3, MPU), Flash: 128 KB, RAM: 20 KB.
> Command line: 'name 1 '2 a' 3' (14 bytes).
> GDB Server listening on: 'tcp::1234'...
> ... connection accepted from 127.0.0.1.
> 
> Execute 'mon system_reset'.
> main(argc=4, argv=["name", "1", "2 a", "3"]);
> Hello ARM World!
> 
> in other words, after being delivered by SYS_GET_CMDLINE to the application, 
> the startup parser uses either single or double quotes to split the string 
> into arguments, similarly to a real life shell.
> 
>> The root of all
>> argument passing issues tends to boil down to how to quote and or escape
>> characters appropriately. Because you know the arguments you can quote
>> correctly but for an unknown user-provided set of arguments (where they
>> do not know how their arguments will flow down to an application) then
>> the appropriate quoting and escaping becomes harder.
>>
>> The problem characters are obviously single and double quotes. Having
>> different quoting rules for any of the layers between a user and
>> the emulated program is always going to cause some confusion so when
>> quoting is necessary I have always found that following the standard
>> argument passing rules of the native application is the least
>> problematic.
> 
> I guess you are generally right, but in this case any quoting is perfectly 
> fine.
> 
>> qemu-system... -semihosting-config "arg=foo bar" -semihosting-config 
>> "arg=second"
>>
>> This should give an argv of ["foo bar", "second"]
> 
> yes, but for the casual user the above syntax is already not natural and even 
> more confusing: should I use "arg=foo bar" or arg="foo bar"? should I repeat 
> -semihosting-config for each argument, or I can group all together 
> (-semihosting-config arg="foo bar",arg="second")?
> 
> 
> if for your use cases this syntax is acceptable, ok, go for it.

Hmm... the -semihosting-config group would be indeed unusual comparing
to the other groups, but on the other hand this would solve also the
double-comma problem. For simple cases the casual user can just stick to
the cmdline.

> 
> 
> my first use of qemu is as a background GDB server started by an Eclipse 
> plug-in. the plug-in will have a single edit field, where the user can enter 
> the semihosting command line args. for args that include spaces, the user 
> should use either single or double quotes, as in any other field.
> 
> my preferred implemention for this would be the original -semihosting-cmdline 
> "some string".
> 
> both proposed implementations (-semihosting-config cmdline="some-string") and 
> even worse for the multiple (-semihosting-config arg=some-string), are way 
> more complicated to use in my Eclipse plug-in, requiring special precautions 
> for passing single/double quotes, commas and possibly equals.
> 
> with the -semihosting-cmdline some-string, the only thing I have to do is to 
> pass [-semihosting-cmdline] in one string array element, and the unmodified 
> [some-string], regardless the quoting used, as the next string array element, 
> and call exec().
> 
> given the above reasons, there are good chances that in my qemu fork (GNU ARM 
> Eclipse QEMU) I'll have to use the separate -semihosting-cmdline option; if 
> you'll accept my patches in the main trunk, ok, if not... no problem; 
> 
> as a conclusion, if you like arg=, go for it, but just be aware that this 
> solution does not cover all use cases properly.

I wasn't focussing on a specific use case, I just thought that having
only one flexible command line option used for passing input arguments
regardless of semi-hosting interface would be ideal. I do understand
however that in your particular case cmdline is more convenient, thus I
personally don’t mind having both options: the user-friendly cmdline and
more flexible arg.

Leon