[Qemu-devel] qemu-arm: Make commandline args available to semihosting

[Wolfgang Schildbach]

Hello list,

ARM ADS/RVCT compiler generated executables by default use "semihosting" 
to communicate with the host, including retrieval of a commandline. The 
semihosting implementation up to now did not implement this functionality; 
this patch adds the SYS_GET_CMDLINE semihosting call, such that 
semihosting executables get a command line when executed through qemu-arm.

This is a reworked patch an earlier version of which can be found at 
http://lists.gnu.org/archive/html/qemu-devel/2006-06/msg00323.html . The 
old version contained a bug which effectively limited the commandline to 
128 bytes.

(quoted from that earlier mail:)

The patch below implements the SYS_GET_CMDLINE semihosting call, by 
keeping a global pointer to the user space commandline arguments, and by 
re-building a space-separated command line in the guest side supplied 
buffer. This patch has two shortcomings, which I would love to see 
feedback on:

- I am keeping a global pointer in order to have a handle on the command 
line arguments inside do_arm_semihosting. Is there a better place to keep 
this?
- The ARM (guest) side supplied buffer is only 256 bytes long; if the user 

supplied command line is larger, the semihosting call will fail 
(gracefully). A better strategy may be to build the string on the initial 
guest stack (similar to loader_build_argptgr()) and then hand that pointer 

to the guest.

I am not quite sure whether the ARGS[] array should be locked before 
access (then again, none of the functions in do_arm_semihosting() do 
this).

This is tested with both big- and littleendian emulation (i.e. qemu-arm 
and qemu-armeb).

All comments welcome.

--
Wolfgang Schildbach, Senior Research Engineer
Coding Technologies GmbH

arm_semihosting_commandline.diff
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