On Fri, 2024-11-29 at 09:59 +0000, Alex Bennée wrote: > Yanfeng <yfliu2...@qq.com> writes: > > > On Thu, 2024-11-28 at 14:21 +0000, Alex Bennée wrote: > > > Yanfeng Liu <yfliu2...@qq.com> writes: > > > > > > > This adds `virt` virtual register on debug interface so that users > > > > can access current virtualization mode for debugging purposes. > > > > > > > > Signed-off-by: Yanfeng Liu <yfliu2...@qq.com> > > > > --- > > > > gdb-xml/riscv-32bit-virtual.xml | 1 + > > > > gdb-xml/riscv-64bit-virtual.xml | 1 + > > > > target/riscv/gdbstub.c | 18 ++++++++++++------ > > > > 3 files changed, 14 insertions(+), 6 deletions(-) > > > > > > > > diff --git a/gdb-xml/riscv-32bit-virtual.xml b/gdb-xml/riscv-32bit- > > > > virtual.xml > > > > index 905f1c555d..d44b6ca2dc 100644 > > > > --- a/gdb-xml/riscv-32bit-virtual.xml > > > > +++ b/gdb-xml/riscv-32bit-virtual.xml > > > > @@ -8,4 +8,5 @@ > > > > <!DOCTYPE feature SYSTEM "gdb-target.dtd"> > > > > <feature name="org.gnu.gdb.riscv.virtual"> > > > > <reg name="priv" bitsize="32"/> > > > > + <reg name="virt" bitsize="32"/> > > > > </feature> > > > > diff --git a/gdb-xml/riscv-64bit-virtual.xml b/gdb-xml/riscv-64bit- > > > > virtual.xml > > > > index 62d86c237b..7c9b63d5b6 100644 > > > > --- a/gdb-xml/riscv-64bit-virtual.xml > > > > +++ b/gdb-xml/riscv-64bit-virtual.xml > > > > @@ -8,4 +8,5 @@ > > > > <!DOCTYPE feature SYSTEM "gdb-target.dtd"> > > > > <feature name="org.gnu.gdb.riscv.virtual"> > > > > <reg name="priv" bitsize="64"/> > > > > + <reg name="virt" bitsize="64"/> > > > > </feature> > > > > > > I assume these are mirrored in gdb not a QEMU only extension? > > > > So far I think it is a QEMU extension and the `gdb-multiarch` doesn't treat > > is > > specially. My tests shows it basically works: > > > > ``` > > (gdb) ir virt > > priv 0x3 prv:3 [Machine] > > virt 0x0 0 > > (gdb) set $priv = 2 > > (gdb) ir virt > > priv 0x1 prv:1 [Supervisor] > > virt 0x0 0 > > (gdb) set $virt = 1 > > (gdb) ir virt > > priv 0x1 prv:1 [Supervisor] > > virt 0x1 1 > > (gdb) set $virt = 0 > > (gdb) ir virt > > priv 0x1 prv:1 [Supervisor] > > virt 0x0 0 > > (gdb) set $virt = 1 > > (gdb) ir virt > > priv 0x1 prv:1 [Supervisor] > > virt 0x1 1 > > (gdb) set $priv = 3 > > (gdb) ir virt > > priv 0x3 prv:3 [Machine] > > virt 0x0 0 > > ``` > > A gdbstub test case would be useful for this although I don't know if > the RiscV check-tcg tests switch mode at all. > > > > > As I am rather new to QEMU, please teach how we can add it as a QEMU only > > extension. > > You don't need to extend the XML from GDB, you can build a specific one > for QEMU extensions. For example: > > gdb_feature_builder_init(¶m.builder, > &cpu->dyn_sysreg_feature.desc, > "org.qemu.gdb.arm.sys.regs", > "system-registers.xml", > base_reg); > > This exports all the system registers QEMU knows about and GDB can > access generically. Note the id is org.qemu..., indicating its our > schema not gdbs. Thanks for teaching, I need time to digest. I guess more feature builder APIs are needed (like append_reg) and the getter/setter callbacks might be at a different place.
BTW, compared to adding virtual register `virt`, how do you think if we share the V bit as part of existing `priv` register? Or maybe we shall talk to GDB community to get their opinions? If they agree to add a few words about V bit here https://sourceware.org/gdb/current/onlinedocs/gdb.html/RISC_002dV-Features.html, then it saves us a lot. >
