On 05/03/12 10:16, Ilija Kocho wrote: > On 05.03.2012 10:49, John Dallaway wrote: >> Hi Tomas >> >> Tomas Frydrych wrote: >> >>> On 05/03/12 08:30, Tomas Frydrych wrote: >>>> On 04/03/12 19:37, John Dallaway wrote: >>>>> However, this success was achieved using arm-eabi-gdb 6.8.50.20080706. >>>>> There does appear to be an issue with the length of the 'g' packet when >>>>> using the new arm-eabi-gdb 7.3.1: >>>>> >>>>>> (gdb) tar rem /dev/ttyS0 >>>>>> Remote debugging using /dev/ttyS0 >>>>>> Remote 'g' packet reply is too long: >>>>>> e14e000810000000000000001000000000000000000000000000000000000000000000000000000000000000fccf0d6800000000e8cf0d6895680008e24e00080000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000021 >>>>>> (gdb) >>>>> We will need to look into why the packet length has apparently changed >>>>> for Cortex-M targets. I can connect to an ARM7 target using the new GDB >>>>> without problem. >>>> This is a mismatch between the number of registers a gdb server reports >>>> and the number that gdb expects for the given architecture. In this case >>>> too many registers are being reported. IIRC, there should be 8 hex >>>> digits for a register, so the above string seems to represent 42 >>>> registers instead of the 21 that Cortex-M has. Looks like a bug in the >>>> monitor stub code, or perhaps a work around for something broken in >>>> older toolchains? >>> Done bit further digging around the sources, >>> hal/cortexm/arch/.../cortexm_stub.h:64 defines 16 gpr, 8 fp or 12 bytes >>> each and 2 ps registers; this adds up to the 336 bytes of the above output. >> Yes. It looks like the FPA registers have been dropped from the default >> register set for Cortex-M targets in recent GDB. In the longer term, we >> should add a CDL option to our GDB stub code to accommodate this change. >> In the short term, I will look at creating a GDB target description file >> that we can use to accommodate the larger register set returned by our >> stubs. > > Could the reason for this be because Cortex-M(4) uses VFP architecture > rather than FPA? > The FPU used on Cortex-M4 is FPv4-SP-d16 > http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0439c/BEHFGGGE.html
I think the original inclusion of the FP registers is to accommodate earlier version of GDB that expected any arm platform to have FP registers even though few really did -- I think it will be necessary for the gdb stubs to have a CDL option to choose which gdb incarnation to target, I don't think there is any way to do the right thing automatically. I do not know if gdb 7.3 expects any sort of fp registers on M4, if so it might be necessary for the definitions in cortexm_stubs.h to be more finely honed based on the cortex-m variant. Tomas
