arch/risc-v/include/elf.f: Support coredump for rv32 and rv64 targets.

[g2gps]

Summary

Adds the missing elf_gregset_t type definition so pr_regs field can be resolved. Coredumps can be produced for both 32 and 64 bit targets.

Impact

Can produce coredumps for postmortem or runtime analysis.

Testing

rv-virt:nsh and rv-virt:nsh64 with:

CONFIG_BOARD_COREDUMP_SYSLOG=y
CONFIG_ELF_COREDUMP=y
CONFIG_SYSTEM_COREDUMP=y

And our custom Litex based target which also uses CONFIG_BUILD_KERNEL. Although system coredump is not available in user context.

Using the same procedure outlined in: https://nuttx.incubator.apache.org/docs/latest/guides/coredump.html

Example gdb session:

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Reading symbols from nuttx/nuttx...

warning: core file may not match specified executable file.
[New process 2]
[New LWP 1]
[New LWP 2]
Core was generated by `'.
#0  0x80006c54 in up_idle () at common/riscv_idle.c:75
75      }
[Current thread is 1 (process 2)]
(gdb) info threads
  Id   Target Id         Frame 
* 1    process 2         0x80006c54 in up_idle () at common/riscv_idle.c:75
  2    LWP 1             sys_call2 (nbr=2, parm2=2147708528, parm1=2147704744) at /workspaces/nuttx-clean/nuttx/include/arch/syscall.h:227
  3    LWP 2             elf_emit_tcb_note (cinfo=0x80037954, tcb=0x80036e70) at libelf/libelf_coredump.c:283
(gdb) thread 3
[Switching to thread 3 (LWP 2)]
#0  elf_emit_tcb_note (cinfo=0x80037954, tcb=0x80036e70) at libelf/libelf_coredump.c:283
283       if (regs != NULL)
(gdb) info reg
ra             0x80011cba       0x80011cba <elf_emit_tcb_note+278>
sp             0x80037760       0x80037760
gp             0x0      0x0
tp             0x0      0x0
t0             0x8003fee9       -2147221783
t1             0x1b     27
t2             0x2000   8192
fp             0x80037954       0x80037954
s1             0x80034000       -2147270656
a0             0x80034380       -2147269760
a1             0x80037778       -2147256456
a2             0x20     32
a3             0xde     222
a4             0x0      0
a5             0x80036e70       -2147258768
a6             0x80040074       -2147221388
a7             0x8003feeb       -2147221781
s2             0x80036f10       -2147258608
s3             0x2088   8328
s4             0x80035000       -2147266560
s5             0x80035000       -2147266560
s6             0xc      12
s7             0x70     112
s8             0x0      0
s9             0x0      0
s10            0x0      0
s11            0x0      0
t3             0x0      0
t4             0x80040074       -2147221388
t5             0x2a0000 2752512
t6             0x8003faec       -2147222804
pc             0x80011cba       0x80011cba <elf_emit_tcb_note+278>
(gdb) bt
#0  elf_emit_tcb_note (cinfo=0x80037954, tcb=0x80036e70) at libelf/libelf_coredump.c:283
#1  0x80012034 in elf_emit_stack (cinfo=0x80037954) at libelf/libelf_coredump.c:402
#2  elf_coredump (cinfo=cinfo@entry=0x80037954) at libelf/libelf_coredump.c:623
#3  0x80011150 in elf_dumpbinary (regions=<optimized out>, stream=<optimized out>, pid=<optimized out>) at elf.c:379
#4  0x800110c0 in core_dump (regions=regions@entry=0x0, stream=stream@entry=0x80037ad4, pid=pid@entry=-1) at binfmt_coredump.c:59
#5  0x80016e92 in coredump_now (filename=<optimized out>, pid=-1) at coredump.c:317
#6  coredump_main (argc=argc@entry=2, argv=argv@entry=0x80037240) at coredump.c:419
#7  0x8000455c in nxtask_startup (entrypt=0x80016d26 <coredump_main>, argc=2, argv=0x80037240) at sched/task_startup.c:70
#8  0x800016ee in nxtask_start () at task/task_start.c:112
#9  0x00000000 in ?? ()
Backtrace stopped: frame did not save the PC

I'm not sure on the wider implications of the change in g_reg_offs. On inspection it looks fine, and the three targets i've tested work.

[g2gps]

Coredumps with CONFIG_BUILD_KERNEL work, but only contain the stack of the current context. So if a coredump is triggered during a syscall, the userspace stack is not preserved.

It would be useful to also have this context saved, as it can be used to unwind the user stack as well.