Re: [PATCH v5] RISC-V: support for vector register accesses via ptrace() in RISC-V Linux native

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, May 07, 2025 at 11:57:09AM +0000, Sameer Natu wrote:
> From: Sameer Natu <snatu@whileone.in>
> 
> Add vector registers and CSRs
> 
> Co-Authored-By: Greg Savin <greg.savin@sifive.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>

Andrew, please let us know your feedback!

- Charlie


> ---
> A v5 re-spin of the original patch. Tested with latest kernel 6.14.2 on RISCV QEMU.
> Removed Magic Numbers from v2 patch and worked on review comments of v2 patch.
> ---
>  gdb/arch/riscv.c             | 180 ++++++++++++++++++++++++++++++++++-
>  gdb/nat/riscv-linux-tdesc.c  |  68 +++++++++++++
>  gdb/nat/riscv-linux-tdesc.h  |  24 +++++
>  gdb/riscv-linux-nat.c        | 162 +++++++++++++++++++++++++++++++
>  gdb/riscv-linux-tdep.c       | 133 ++++++++++++++++++++++++++
>  gdb/riscv-tdep.c             |  49 +++++++++-
>  gdb/riscv-tdep.h             |   6 ++
>  gdbserver/linux-riscv-low.cc | 110 +++++++++++++++++++++
>  include/elf/common.h         |   1 +
>  9 files changed, 726 insertions(+), 7 deletions(-)
> 
> diff --git a/gdb/arch/riscv.c b/gdb/arch/riscv.c
> index a6188ea3a8c..f1f5d83d60a 100644
> --- a/gdb/arch/riscv.c
> +++ b/gdb/arch/riscv.c
> @@ -25,12 +25,30 @@
>  #include "../features/riscv/64bit-fpu.c"
>  #include "../features/riscv/rv32e-xregs.c"
>  
> +#include "opcode/riscv-opc.h"
> +
>  #ifndef GDBSERVER
>  #define STATIC_IN_GDB static
>  #else
>  #define STATIC_IN_GDB
>  #endif
>  
> +#ifdef GDBSERVER
> +/* Work around issue where trying to include riscv-tdep.h (to get access to canonical RISCV_V0_REGNUM declaration
> +   from that header) is problamtic for gdbserver build.  */
> +#define RISCV_V0_REGNUM 4162
> +#else
> +#include "riscv-tdep.h"
> +#include "defs.h"
> +#endif
> +
> +static int
> +create_feature_riscv_vector_from_features (struct target_desc *result,
> +					   long regnum,
> +					   const struct riscv_gdbarch_features
> +					   features);
> +
> +
>  /* See arch/riscv.h.  */
>  
>  STATIC_IN_GDB target_desc_up
> @@ -83,15 +101,169 @@ riscv_create_target_description (const struct riscv_gdbarch_features features)
>    else if (features.flen == 8)
>      regnum = create_feature_riscv_64bit_fpu (tdesc.get (), regnum);
>  
> -  /* Currently GDB only supports vector features coming from remote
> -     targets.  We don't support creating vector features on native targets
> -     (yet).  */
>    if (features.vlen != 0)
> -    error (_("unable to create vector feature"));
> +    regnum =
> +      create_feature_riscv_vector_from_features (tdesc.get (),
> +						 regnum, features);
>  
>    return tdesc;
>  }
>  
> +
> +
> +/* Usually, these target_desc instances are static for an architecture, and expressable
> +   in XML format, but this is a special case where length of a RISC-V vector register
> +   is not architecturally fixed to a constant (the maximuim width is a defined constant,
> +   but it's nice to tailor a target description the actual VLENB) */
> +static int
> +create_feature_riscv_vector_from_features (struct target_desc *result,
> +					   long regnum,
> +					   const struct riscv_gdbarch_features
> +					   features)
> +{
> +  struct tdesc_feature *feature;
> +  unsigned long bitsize;
> +
> +  feature = tdesc_create_feature (result, "org.gnu.gdb.riscv.vector");
> +  tdesc_type *element_type;
> +
> +  /* if VLENB is present (which we know it is present if execution reaches this function),
> +     then we know by definition that it is at least 4 bytes wide */
> +
> +  element_type = tdesc_named_type (feature, "uint8");
> +  tdesc_create_vector (feature, "bytes", element_type, features.vlen);
> +
> +  element_type = tdesc_named_type (feature, "uint16");
> +  tdesc_create_vector (feature, "shorts", element_type, features.vlen / 2);
> +
> +  element_type = tdesc_named_type (feature, "uint32");
> +  tdesc_create_vector (feature, "words", element_type, features.vlen / 4);
> +
> +  /* Need VLENB value checks for element chunks larger than 4 bytes */
> +
> +  if (features.vlen >= 8)
> +    {
> +      element_type = tdesc_named_type (feature, "uint64");
> +      tdesc_create_vector (feature, "longs", element_type, features.vlen / 8);
> +    }
> +
> +  /* QEMU and OpenOCD include the quads width in their target descriptions, so we're
> +     following that precedent, even if it's not particularly useful in practice, yet */
> +
> +  if (features.vlen >= 16)
> +    {
> +      element_type = tdesc_named_type (feature, "uint128");
> +      tdesc_create_vector (feature, "quads", element_type,
> +			   features.vlen / 16);
> +    }
> +
> +  tdesc_type_with_fields *type_with_fields;
> +  type_with_fields = tdesc_create_union (feature, "riscv_vector");
> +  tdesc_type *field_type;
> +
> +  if (features.vlen >= 16)
> +    {
> +      field_type = tdesc_named_type (feature, "quads");
> +      tdesc_add_field (type_with_fields, "q", field_type);
> +    }
> +  if (features.vlen >= 8)
> +    {
> +      field_type = tdesc_named_type (feature, "longs");
> +      tdesc_add_field (type_with_fields, "l", field_type);
> +    }
> +
> +  /* Again, we know vlenb is >= 4, so no if guards needed for words/shorts/bytes */
> +
> +  field_type = tdesc_named_type (feature, "words");
> +  tdesc_add_field (type_with_fields, "w", field_type);
> +
> +  field_type = tdesc_named_type (feature, "shorts");
> +  tdesc_add_field (type_with_fields, "s", field_type);
> +
> +  field_type = tdesc_named_type (feature, "bytes");
> +  tdesc_add_field (type_with_fields, "b", field_type);
> +
> +  /* Register vector and CSR definitions using stable magic regnums to
> +     ensure compatibility across GDB and gdbserver builds.  */
> +  tdesc_create_reg (feature, "vstart", regnum++, 1, NULL, features.xlen * 8, "int");
> +  tdesc_create_reg (feature, "vxsat", regnum++, 1, NULL, features.xlen * 8, "int");
> +  tdesc_create_reg (feature, "vxrm", regnum++, 1, NULL, features.xlen * 8, "int");
> +  tdesc_create_reg (feature, "vcsr", regnum++, 1, NULL, features.xlen * 8, "int");
> +  tdesc_create_reg (feature, "vl", regnum++, 1, NULL, features.xlen * 8, "int");
> +  tdesc_create_reg (feature, "vtype", regnum++, 1, NULL, features.xlen * 8, "int");
> +  tdesc_create_reg (feature, "vlenb", regnum++, 1, NULL, features.xlen * 8, "int");
> +
> +  bitsize = features.vlen * 8;
> +  tdesc_create_reg (feature, "v0", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v1", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v2", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v3", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v4", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v5", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v6", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v7", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v8", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v9", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v10", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v11", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v12", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v13", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v14", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v15", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v16", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v17", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v18", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v19", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v20", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v21", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v22", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v23", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v24", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v25", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v26", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v27", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v28", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v29", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v30", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +  tdesc_create_reg (feature, "v31", regnum++, 1, NULL, bitsize,
> +		    "riscv_vector");
> +
> +
> +  return regnum;
> +}
> +
> +
>  #ifndef GDBSERVER
>  
>  /* Wrapper used by std::unordered_map to generate hash for feature set.  */
> diff --git a/gdb/nat/riscv-linux-tdesc.c b/gdb/nat/riscv-linux-tdesc.c
> index 254a25ccefe..80d1ca64ba9 100644
> --- a/gdb/nat/riscv-linux-tdesc.c
> +++ b/gdb/nat/riscv-linux-tdesc.c
> @@ -22,14 +22,18 @@
>  #include "elf/common.h"
>  #include "nat/gdb_ptrace.h"
>  #include "nat/riscv-linux-tdesc.h"
> +#include "gdbsupport/gdb_setjmp.h"
>  
>  #include <sys/uio.h>
> +#include <signal.h>
>  
>  /* Work around glibc header breakage causing ELF_NFPREG not to be usable.  */
>  #ifndef NFPREG
>  # define NFPREG 33
>  #endif
>  
> +static unsigned long safe_read_vlenb ();
> +
>  /* See nat/riscv-linux-tdesc.h.  */
>  
>  struct riscv_gdbarch_features
> @@ -78,5 +82,69 @@ riscv_linux_read_features (int tid)
>        break;
>      }
>  
> +  features.vlen = safe_read_vlenb ();
> +
>    return features;
>  }
> +
> +static SIGJMP_BUF sigill_guard_jmp_buf;
> +
> +static void
> +sigill_guard (int sig)
> +{
> +  /* this will gets us back to caller deeper in the call stack, with an indication that
> +     an illegal instruction condition was encountered */
> +  SIGLONGJMP (sigill_guard_jmp_buf, -1);
> +
> +  /* control won't get here */
> +}
> +
> +
> +
> +static unsigned long
> +safe_read_vlenb ()
> +{
> +  /* Surrounding the attempt here to read VLENB CSR to have a signal handler set up
> +     to trap illegal instruction condition (SIGILL), and if a trap happens during this call,
> +     get control back within this function and return 0 in that case.
> +   */
> +  unsigned long vlenb = 0;
> +  struct sigaction our_action = { 0 };
> +  struct sigaction original_action;
> +  int sysresult;
> +
> +
> +  our_action.sa_handler = sigill_guard;
> +
> +  sysresult = sigaction (SIGILL, &our_action, &original_action);
> +  if (sysresult != 0)
> +    {
> +      perror
> +	("Error installing temporary SIGILL handler in safe_read_vlenb()");
> +    }
> +
> +  if (SIGSETJMP (sigill_guard_jmp_buf, 1) == 0)
> +    {
> +    asm ("csrr %0, vlenb":"=r" (vlenb));
> +    }
> +  else
> +    {
> +      /* Must've generated an illegal instruction condition; we'll figure this means
> +         no vector unit is present */
> +      vlenb = 0;
> +    }
> +
> +
> +  if (sysresult == 0)
> +    {
> +      /* re-install former handler */
> +      sysresult = sigaction (SIGILL, &original_action, NULL);
> +      if (sysresult != 0)
> +	{
> +	  perror
> +	    ("Error re-installing original SIGILL handler in safe_read_vlenb()");
> +	}
> +
> +    }
> +  return vlenb;
> +}
> diff --git a/gdb/nat/riscv-linux-tdesc.h b/gdb/nat/riscv-linux-tdesc.h
> index de10d91caae..76f8d2f0cdd 100644
> --- a/gdb/nat/riscv-linux-tdesc.h
> +++ b/gdb/nat/riscv-linux-tdesc.h
> @@ -20,9 +20,33 @@
>  #define GDB_NAT_RISCV_LINUX_TDESC_H
>  
>  #include "arch/riscv.h"
> +#include "asm/ptrace.h"
>  
>  /* Determine XLEN and FLEN for the LWP identified by TID, and return a
>     corresponding features object.  */
>  struct riscv_gdbarch_features riscv_linux_read_features (int tid);
>  
> +#define RISCV_MAX_VLENB (8192)
> +
> +/* Some branches and/or commits of linux kernel named this "struct __riscv_v_state",
> +   and later it was changed to "struct __riscv_v_ext_state",
> +   so using a macro to stand-in for that struct type to make it easier to modify
> +   in a single place, if compiling against one of those older Linux kernel commits */
> +#ifndef RISCV_VECTOR_STATE_T
> +#define RISCV_VECTOR_STATE_T struct __riscv_v_ext_state
> +#endif
> +
> +/* Struct for use in ptrace() calls for vector CSRs/registers */
> +struct __riscv_vregs
> +{
> +  RISCV_VECTOR_STATE_T vstate;
> +  gdb_byte data[RISCV_MAX_VLENB * 32]; /* data will arrive packed, VLENB bytes per element, not necessarily RISCV_MAX_VLENB bytes per element */
> +};
> +
> +#define VCSR_MASK_VXSAT 0x1
> +#define VCSR_POS_VXSAT 0
> +#define VCSR_MASK_VXRM 0x3
> +#define VCSR_POS_VXRM 1
> +
> +
>  #endif /* GDB_NAT_RISCV_LINUX_TDESC_H */
> diff --git a/gdb/riscv-linux-nat.c b/gdb/riscv-linux-nat.c
> index 8846329afc6..a8dcc1e637a 100644
> --- a/gdb/riscv-linux-nat.c
> +++ b/gdb/riscv-linux-nat.c
> @@ -21,6 +21,7 @@
>  #include "linux-nat.h"
>  #include "riscv-tdep.h"
>  #include "inferior.h"
> +#include "regset.h"
>  
>  #include "elf/common.h"
>  
> @@ -124,6 +125,113 @@ supply_fpregset_regnum (struct regcache *regcache, const prfpregset_t *fpregs,
>      }
>  }
>  
> +#define MEMBER_SIZE(type, member) sizeof(((type *) 0)->member)
> +
> +static const regcache_map_entry riscv_linux_vregmap[] =
> +{
> +  { 1, RISCV_CSR_VSTART_REGNUM, MEMBER_SIZE(struct __riscv_vregs, vstate.vstart) },
> +  { 1, RISCV_CSR_VL_REGNUM, MEMBER_SIZE(struct __riscv_vregs, vstate.vl) },
> +  { 1, RISCV_CSR_VTYPE_REGNUM, MEMBER_SIZE(struct __riscv_vregs, vstate.vtype) },
> +  { 1, RISCV_CSR_VCSR_REGNUM, MEMBER_SIZE(struct __riscv_vregs, vstate.vcsr) },
> +  /* struct __riscv_vregs member "datap" is a pointer that doesn't correspond
> +     to a register value.  In the context of ptrace(), member is always zero,
> +     with V0..V31 values inline after that.  So, skipping datap */
> +  { 1, REGCACHE_MAP_SKIP, MEMBER_SIZE(struct __riscv_vregs, vstate.datap) },
> +  /* Here's V0..V31.  Specifying 0 as size leads to a call to register_size()
> +     for size determination */
> +  { 32, RISCV_V0_REGNUM, 0 },
> +  { 0 },  /* count==0 represents termination of entries */
> +};
> +
> +/* Define the vector register regset.  */
> +
> +static const struct regset riscv_linux_vregset =
> +{
> +  riscv_linux_vregmap,
> +  regcache_supply_regset /* Other RISC-V regsets use riscv_supply_regset here; not sure that'd be correct for this case */,
> +  regcache_collect_regset
> +};
> +
> +
> +/* Supply RISC-V vector register values (including inferred CSRs) to the GDB regcache.  */
> +
> +static void
> +supply_vregset_regnum (struct regcache *regcache,
> +		       const struct __riscv_vregs *vregs, int regnum)
> +{
> +  const gdb_byte *buf;
> +  int vlenb = register_size (regcache->arch (), RISCV_V0_REGNUM);
> +
> +  regcache_supply_regset (&riscv_linux_vregset, regcache, regnum, vregs, sizeof(*vregs));
> +
> +  if (regnum == -1 || regnum == RISCV_CSR_VLENB_REGNUM)
> +    {
> +      /* we already have a local copy above, use that (widened for XLEN padding) */
> +      uint64_t xlen_safe_vlenb = vlenb;
> +      buf = (gdb_byte *) & xlen_safe_vlenb;
> +      regcache->raw_supply (RISCV_CSR_VLENB_REGNUM, buf);
> +    }
> +
> +  if (regnum == -1 || regnum == RISCV_CSR_VXSAT_REGNUM)
> +    {
> +      /*  this CSR is not part of vregs->vstate literally, but we can infer a value from vcsr */
> +      uint64_t vxsat = ((vregs->vstate.vcsr >> VCSR_POS_VXSAT) & VCSR_MASK_VXSAT);
> +      buf = (gdb_byte *) & vxsat;
> +      regcache->raw_supply (RISCV_CSR_VXSAT_REGNUM, buf);
> +    }
> +
> +  if (regnum == -1 || regnum == RISCV_CSR_VXRM_REGNUM)
> +    {
> +      /*  this CSR is not part of vregs->vstate literally, but we can infer a value from vcsr */
> +      uint64_t vxrm = ((vregs->vstate.vcsr >> VCSR_POS_VXRM) & VCSR_MASK_VXRM);
> +      buf = (gdb_byte *) & vxrm;
> +      regcache->raw_supply (RISCV_CSR_VXRM_REGNUM, buf);
> +    }
> +}
> +
> +/* Collect RISC-V vector register values (including inferred CSRs) from the GDB regcache.  */
> +static void
> +fill_vregset (const struct regcache *regcache, struct __riscv_vregs *vregs,
> +	      int regnum)
> +{
> +  regcache_collect_regset (&riscv_linux_vregset, regcache, regnum, vregs, sizeof(*vregs));
> +
> +  if (regnum == -1 || regnum == RISCV_CSR_VCSR_REGNUM || regnum == RISCV_CSR_VXSAT_REGNUM
> +      || regnum == RISCV_CSR_VXRM_REGNUM)
> +    {
> +      uint64_t vxsat_from_regcache;
> +      uint64_t vxrm_from_regcache;
> +
> +      if ( ! (regnum == -1 || regnum == RISCV_CSR_VCSR_REGNUM) )
> +	{
> +	  /* We don't already have the VCSR value, from the earlier regcache_collect_regset call, so let's get it now.  */
> +	  regcache_collect_regset (&riscv_linux_vregset, regcache, RISCV_CSR_VCSR_REGNUM, vregs, sizeof(*vregs));
> +	}
> +
> +      if (regnum == RISCV_CSR_VXSAT_REGNUM)
> +	{
> +	  /* Overwrite VCSR with the VXSAT bit here.  */
> +          gdb_byte *buf = (gdb_byte *) &vxsat_from_regcache;
> +	  regcache->raw_collect (RISCV_CSR_VXSAT_REGNUM, buf);
> +	  vregs->vstate.vcsr &= ~((uint64_t) VCSR_MASK_VXSAT << VCSR_POS_VXSAT);
> +	  vregs->vstate.vcsr |= ((vxsat_from_regcache & VCSR_MASK_VXSAT) << VCSR_POS_VXSAT);
> +	}
> +
> +      if (regnum == RISCV_CSR_VXRM_REGNUM)
> +	{
> +	  /* Overwrite VCSR with the VXRM bit here.  */
> +          gdb_byte *buf = (gdb_byte *) &vxsat_from_regcache;
> +	  regcache->raw_collect (RISCV_CSR_VXRM_REGNUM, buf);
> +	  vregs->vstate.vcsr &= ~((uint64_t) VCSR_MASK_VXRM << VCSR_POS_VXRM);
> +	  vregs->vstate.vcsr |= ((vxrm_from_regcache & VCSR_MASK_VXRM) << VCSR_POS_VXRM);
> +	}
> +    }
> +
> +  /* VLENB register is not writable, so that's why nothing is collected here for that register.  */
> +
> +}
> +
> +
>  /* Copy all floating point registers from regset FPREGS into REGCACHE.  */
>  
>  void
> @@ -254,6 +362,31 @@ riscv_linux_nat_target::fetch_registers (struct regcache *regcache, int regnum)
>  	supply_fpregset_regnum (regcache, &regs, regnum);
>      }
>  
> +  /* if Linux kernel was not configured to support RISC-V vectors, then
> +     the ptrace call will return -1, and we just won't get vector registers,
> +     but in that case it wouldn't be an error that needs user attention.
> +   */
> +  if ((regnum >= RISCV_V0_REGNUM && regnum <= RISCV_V31_REGNUM)
> +      || (regnum == RISCV_CSR_VSTART_REGNUM)
> +      || (regnum == RISCV_CSR_VL_REGNUM)
> +      || (regnum == RISCV_CSR_VTYPE_REGNUM)
> +      || (regnum == RISCV_CSR_VCSR_REGNUM)
> +      || (regnum == RISCV_CSR_VLENB_REGNUM)
> +      || (regnum == RISCV_CSR_VXSAT_REGNUM)
> +      || (regnum == RISCV_CSR_VXRM_REGNUM)
> +      || (regnum == -1))
> +    {
> +      struct iovec iov;
> +      struct __riscv_vregs vregs;
> +
> +      iov.iov_base = &vregs;
> +      iov.iov_len = sizeof (vregs);
> +
> +      if (ptrace (PTRACE_GETREGSET, tid, NT_RISCV_VECTOR,
> +		  (PTRACE_TYPE_ARG3) & iov) == 0)
> +	supply_vregset_regnum (regcache, &vregs, regnum);
> +    }
> +
>    if ((regnum == RISCV_CSR_MISA_REGNUM)
>        || (regnum == -1))
>      {
> @@ -323,6 +456,35 @@ riscv_linux_nat_target::store_registers (struct regcache *regcache, int regnum)
>  	}
>      }
>  
> +  /* VLENB isn't writable, so we'll skip considering that one, if it's being
> +     specified alone */
> +  if ((regnum >= RISCV_V0_REGNUM && regnum <= RISCV_V31_REGNUM)
> +      || (regnum == RISCV_CSR_VSTART_REGNUM)
> +      || (regnum == RISCV_CSR_VL_REGNUM)
> +      || (regnum == RISCV_CSR_VTYPE_REGNUM)
> +      || (regnum == RISCV_CSR_VCSR_REGNUM)
> +      || (regnum == RISCV_CSR_VXSAT_REGNUM)
> +      || (regnum == RISCV_CSR_VXRM_REGNUM)
> +      || (regnum == -1))
> +    {
> +      struct iovec iov;
> +      struct __riscv_vregs vregs;
> +
> +      iov.iov_base = &vregs;
> +      iov.iov_len = sizeof (vregs);
> +
> +      if (ptrace (PTRACE_GETREGSET, tid, NT_RISCV_VECTOR,
> +		  (PTRACE_TYPE_ARG3) & iov) == 0)
> +	{
> +	  fill_vregset (regcache, &vregs, regnum);
> +
> +	  if (ptrace (PTRACE_SETREGSET, tid, NT_RISCV_VECTOR,
> +		      (PTRACE_TYPE_ARG3) & iov) == -1)
> +	    perror_with_name (_("Couldn't set vector registers"));
> +	}
> +    }
> +
> +
>    /* Access to CSRs has potential security issues, don't support them for
>       now.  */
>  }
> diff --git a/gdb/riscv-linux-tdep.c b/gdb/riscv-linux-tdep.c
> index e1ea6158a45..e9531094de5 100644
> --- a/gdb/riscv-linux-tdep.c
> +++ b/gdb/riscv-linux-tdep.c
> @@ -38,6 +38,10 @@ extern unsigned int record_debug;
>  
>  #define RISCV_NR_rt_sigreturn 139
>  
> +/* Magic number written to the head.magic field of struct __sc_riscv_v_state that kernel
> +   places in the reserved area of struct sigcontext.  Comes from <asm/sigcontext.h> */
> +#define RVV_MAGIC 0x53465457
> +
>  /* Define the general register mapping.  The kernel puts the PC at offset 0,
>     gdb puts it at offset 32.  Register x0 is always 0 and can be ignored.
>     Registers x1 to x31 are in the same place.  */
> @@ -126,8 +130,123 @@ static const struct tramp_frame riscv_linux_sigframe = {
>       mcontext_t uc_mcontext;
>     }; */
>  
> +
> +/* Read RVV magic and size fields from address REGS_BASE and return true if a valid
> +   RISC-V vector context header is found, otherwise return false. THIS_FRAME is used
> +   for the architecture and byte-order when reading memory. VLEN and XLEN are the
> +   v-register and x-register sizes (in bytes) and are used for validation.  */
> +
> +static bool
> +riscv_linux_vector_sigframe_header_check (frame_info_ptr this_frame,
> +					  int vlen, int xlen,
> +					  CORE_ADDR regs_base)
> +{
> +  uint32_t rvv_magic;
> +  uint32_t rvv_size;
> +  bool info_good = false;
> +
> +  /* If vector information is available, then we should see this structure at this address:
> +     struct __riscv_ctx_hdr {
> +     __u32 magic;  (RVV_MAGIC).
> +     __u32 size;   (size of struct __sc_riscv_v_state + vector register data size (32*VLENB))
> +     } head;
> +   */
> +
> +  rvv_magic =
> +    get_frame_memory_unsigned (this_frame, regs_base, sizeof (rvv_magic));
> +  regs_base += sizeof (rvv_magic);
> +  rvv_size =
> +    get_frame_memory_unsigned (this_frame, regs_base, sizeof (rvv_magic));
> +  regs_base += sizeof (rvv_size);
> +
> +
> +  info_good = (rvv_magic == RVV_MAGIC);
> +  if (!info_good)
> +    {
> +      /* Not an error, because kernels can be configured without CONFIG_VECTOR, but worth noting if frame debug
> +         setting is turned on */
> +      frame_debug_printf
> +        ("Did not find RISC-V vector information in ucontext (kernel not built with CONFIG_VECTOR?)");
> +
> +      return false;
> +    }
> +
> +  if (frame_debug)
> +    {
> +      uint32_t expected_rvv_size;
> +
> +      frame_debug_printf
> +	("Located RISC-V vector information in signal frame ucontext (info size %u)",
> +	 rvv_size);
> +
> +      /* sanity check the reported size; should be sizeof(uint32_t) + sizeof(uint32_t) + 5 * XLENB + 32 * vlen */
> +      expected_rvv_size = sizeof (uint32_t) /* magic */  +
> +	sizeof (uint32_t) /* size */  +
> +	5 * xlen /* vstart, vl, vtype, vcsr, and datap */  +
> +	32 * vlen;		/* v0..v31 values */
> +
> +      if (rvv_size != expected_rvv_size)
> +	{
> +          warning (_("Size in RISC-V vector information header in ucontext (%u) differs from expected size (%u)."),
> +             rvv_size, expected_rvv_size);
> +
> +          /* Additional debug details if frame_debug is on.  */
> +	  frame_debug_printf ("Detailed size mismatch: expected %u based on VLEN=%d and XLEN=%d",
> +             expected_rvv_size, vlen, xlen);
> +	}
> +    }
> +
> +  return info_good;
> +}
> +
> +static CORE_ADDR
> +riscv_linux_sigframe_vector_init (frame_info_ptr this_frame,
> +				  struct trad_frame_cache *this_cache,
> +				  CORE_ADDR regs_base, int xlen, int vlen)
> +{
> +  int vfieldidx;
> +  CORE_ADDR p_datap;
> +  CORE_ADDR datap;
> +
> +  /* vstart, vl, vtype, vcsr, and datap are XLEN sized fields (unsigned long) from this point.  */
> +  vfieldidx = 0;
> +  trad_frame_set_reg_addr (this_cache, RISCV_CSR_VSTART_REGNUM,
> +			   regs_base + (vfieldidx * xlen));
> +  vfieldidx++;
> +  trad_frame_set_reg_addr (this_cache, RISCV_CSR_VL_REGNUM,
> +			   regs_base + (vfieldidx * xlen));
> +
> +  vfieldidx++;
> +  trad_frame_set_reg_addr (this_cache, RISCV_CSR_VTYPE_REGNUM,
> +			   regs_base + (vfieldidx * xlen));
> +
> +  vfieldidx++;
> +  trad_frame_set_reg_addr (this_cache, RISCV_CSR_VCSR_REGNUM,
> +			   regs_base + (vfieldidx * xlen));
> +
> +  /* for the datap member, there is one level of memory indirection to get the address of
> +     the block of values for v0..v31 */
> +  vfieldidx++;
> +  p_datap = regs_base + (vfieldidx * xlen);
> +  datap = get_frame_memory_unsigned (this_frame, p_datap, xlen);
> +  regs_base = datap;
> +  for (int i = 0; i < 32; i++)
> +    {
> +      trad_frame_set_reg_addr (this_cache, RISCV_V0_REGNUM + i,
> +			       regs_base + (i * vlen));
> +    }
> +  regs_base += 32 * vlen;
> +
> +  return regs_base;
> +}
> +
> +
>  #define SIGFRAME_SIGINFO_SIZE		128
>  #define UCONTEXT_MCONTEXT_OFFSET	176
> +#define MCONTEXT_VECTOR_OFFSET		784	/* offset of struct mcontext's __reserved field,
> +						   which is where the struct __sc_riscv_v_state is overlaid */
> +#define RISCV_CONTEXT_HEADER_SIZE	8	/* size of struct __riscv_ctx_hdr {__u32 magic;  __u32 size; } */
> +
>  
>  static void
>  riscv_linux_sigframe_init (const struct tramp_frame *self,
> @@ -138,6 +257,7 @@ riscv_linux_sigframe_init (const struct tramp_frame *self,
>    struct gdbarch *gdbarch = get_frame_arch (this_frame);
>    int xlen = riscv_isa_xlen (gdbarch);
>    int flen = riscv_isa_flen (gdbarch);
> +  int vlen = riscv_isa_vlen (gdbarch);
>    CORE_ADDR frame_sp = get_frame_sp (this_frame);
>    CORE_ADDR mcontext_base;
>    CORE_ADDR regs_base;
> @@ -161,6 +281,19 @@ riscv_linux_sigframe_init (const struct tramp_frame *self,
>    regs_base += 32 * flen;
>    trad_frame_set_reg_addr (this_cache, RISCV_CSR_FCSR_REGNUM, regs_base);
>  
> +  /* Handle the vector registers, if present. */
> +  if (vlen > 0)
> +    {
> +      regs_base = mcontext_base + MCONTEXT_VECTOR_OFFSET;
> +      if (riscv_linux_vector_sigframe_header_check
> +	  (this_frame, vlen, xlen, regs_base))
> +	{
> +	  regs_base += RISCV_CONTEXT_HEADER_SIZE;	/* advance past the header */
> +	  riscv_linux_sigframe_vector_init (this_frame, this_cache, regs_base,
> +					    xlen, vlen);
> +	}
> +    }
> +
>    /* Choice of the bottom of the sigframe is somewhat arbitrary.  */
>    trad_frame_set_id (this_cache, frame_id_build (frame_sp, func));
>  }
> diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
> index a735c095b0d..f61a3429b70 100644
> --- a/gdb/riscv-tdep.c
> +++ b/gdb/riscv-tdep.c
> @@ -47,6 +47,7 @@
>  #include "remote.h"
>  #include "target-descriptions.h"
>  #include "dwarf2/frame.h"
> +#include "dwarf2/expr.h"
>  #include "user-regs.h"
>  #include "valprint.h"
>  #include "opcode/riscv-opc.h"
> @@ -653,6 +654,14 @@ struct riscv_vector_feature : public riscv_register_feature
>        { RISCV_V0_REGNUM + 29, { "v29" } },
>        { RISCV_V0_REGNUM + 30, { "v30" } },
>        { RISCV_V0_REGNUM + 31, { "v31" } },
> +      /* vector CSRs */
> +      { RISCV_CSR_VSTART_REGNUM, { "vstart" } },
> +      { RISCV_CSR_VXSAT_REGNUM, { "vxsat" } },
> +      { RISCV_CSR_VXRM_REGNUM, { "vxrm" } },
> +      { RISCV_CSR_VL_REGNUM, { "vl" } },
> +      { RISCV_CSR_VTYPE_REGNUM, { "vtype" } },
> +      { RISCV_CSR_VCSR_REGNUM, { "vcsr" } },
> +      { RISCV_CSR_VLENB_REGNUM, { "vlenb" } },
>      };
>    }
>  
> @@ -684,10 +693,16 @@ struct riscv_vector_feature : public riscv_register_feature
>  	return true;
>        }
>  
> -    /* Check all of the vector registers are present.  */
> +    /* Check all of the vector registers are present.  We also
> +       check that the vector CSRs are present too, though if these
> +       are missing this is not fatal.  */
>      for (const auto &reg : m_registers)
>        {
> -	if (!reg.check (tdesc_data, feature_vector, aliases))
> +       bool found = reg.check (tdesc_data, feature_vector, aliases);
> +
> +       bool is_ctrl_reg_p = !(reg.regnum >= RISCV_V0_REGNUM && reg.regnum <= RISCV_V31_REGNUM);
> +
> +       if (!found && !is_ctrl_reg_p)
>  	  return false;
>        }
>  
> @@ -697,6 +712,12 @@ struct riscv_vector_feature : public riscv_register_feature
>      int vector_bitsize = -1;
>      for (const auto &reg : m_registers)
>        {
> +
> +	bool is_ctrl_reg_p = !(reg.regnum >= RISCV_V0_REGNUM && reg.regnum <= RISCV_V31_REGNUM);	
> +
> +	if (is_ctrl_reg_p)
> +	  continue;
> +
>  	int reg_bitsize = -1;
>  	for (const char *name : reg.names)
>  	  {
> @@ -819,6 +840,16 @@ riscv_abi_embedded (struct gdbarch *gdbarch)
>    return tdep->abi_features.embedded;
>  }
>  
> +/* See riscv-tdep.h.  */
> +
> +int
> +riscv_isa_vlen (struct gdbarch *gdbarch)
> +{
> +  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
> +  return tdep->isa_features.vlen;
> +}
> +
> +
>  /* Return true if the target for GDBARCH has floating point hardware.  */
>  
>  static bool
> @@ -1470,7 +1501,19 @@ riscv_register_reggroup_p (struct gdbarch  *gdbarch, int regnum,
>        return 0;
>      }
>    else if (reggroup == vector_reggroup)
> -    return (regnum >= RISCV_V0_REGNUM && regnum <= RISCV_V31_REGNUM);
> +    {
> +      if (regnum >= RISCV_V0_REGNUM && regnum <= RISCV_V31_REGNUM)
> +	return 1;
> +      if (regnum == RISCV_CSR_VSTART_REGNUM
> +	  || regnum == RISCV_CSR_VXSAT_REGNUM
> +	  || regnum == RISCV_CSR_VXRM_REGNUM
> +	  || regnum == RISCV_CSR_VL_REGNUM
> +	  || regnum == RISCV_CSR_VTYPE_REGNUM
> +	  || regnum == RISCV_CSR_VCSR_REGNUM
> +	  || regnum == RISCV_CSR_VLENB_REGNUM)
> +	return 1;
> +      return 0;
> +    }
>    else
>      return 0;
>  }
> diff --git a/gdb/riscv-tdep.h b/gdb/riscv-tdep.h
> index 2903aefd007..82213f820f3 100644
> --- a/gdb/riscv-tdep.h
> +++ b/gdb/riscv-tdep.h
> @@ -50,6 +50,7 @@ enum
>    RISCV_LAST_FP_REGNUM = 64,	/* Last Floating Point Register */
>  
>    RISCV_FIRST_CSR_REGNUM = 65,  /* First CSR */
> +
>  #define DECLARE_CSR(name, num, class, define_version, abort_version) \
>    RISCV_ ## num ## _REGNUM = RISCV_FIRST_CSR_REGNUM + num,
>  #include "opcode/riscv-opc.h"
> @@ -158,6 +159,11 @@ extern int riscv_abi_flen (struct gdbarch *gdbarch);
>     argument registers.  */
>  extern bool riscv_abi_embedded (struct gdbarch *gdbarch);
>  
> +/* Return the width in bytes of the hardware vector registers for
> +   GDBARCH.  If this architecture has no vector registers, then
> +   return 0.  */
> +extern int riscv_isa_vlen (struct gdbarch *gdbarch);
> +
>  /* Single step based on where the current instruction will take us.  */
>  extern std::vector<CORE_ADDR> riscv_software_single_step
>    (struct regcache *regcache);
> diff --git a/gdbserver/linux-riscv-low.cc b/gdbserver/linux-riscv-low.cc
> index 8c742f406a2..face971a5e7 100644
> --- a/gdbserver/linux-riscv-low.cc
> +++ b/gdbserver/linux-riscv-low.cc
> @@ -161,6 +161,113 @@ riscv_store_fpregset (struct regcache *regcache, const void *buf)
>    supply_register_by_name (regcache, "fcsr", regbuf);
>  }
>  
> +/* Collect vector registers from REGCACHE into BUF.  */
> +
> +static void
> +riscv_fill_vregset (struct regcache *regcache, void *buf)
> +{
> +  const struct target_desc *tdesc = regcache->tdesc;
> +  int regno = find_regno (tdesc, "v0");
> +  int vlenb = register_size (regcache->tdesc, regno);
> +  uint64_t u64_vlenb = vlenb;	/* pad to max XLEN for buffer conversion */
> +  uint64_t u64_vxsat = 0;
> +  uint64_t u64_vxrm = 0;
> +  uint64_t u64_vcsr = 0;
> +  gdb_byte *regbuf;
> +  int i;
> +
> +  /* Since vxsat and equivalent bits in vcsr are aliases (and same for vxrm), we have a dilemma.
> +     For this gdb -> gdbserver topology, if the aliased pairs have values that disagree, then
> +     which value should take precedence?  We don't know which alias was most
> +     recently assigned.  We're just getting a block of register values including vxsat, vxrm,
> +     and vcsr.  We have to impose some kind of rule for predictable resolution to resolve any inconsistency.
> +     For now, let's say that vxsat and vxrm take precedence, and those values will be applied to the
> +     corresponding fields in vcsr.  Reconcile these 3 interdependent registers now:
> +  */
> +  regbuf = (gdb_byte *) & u64_vcsr;
> +  collect_register_by_name (regcache, "vcsr", regbuf);
> +  regbuf = (gdb_byte *) & u64_vxsat;
> +  collect_register_by_name (regcache, "vxsat", regbuf);
> +  regbuf = (gdb_byte *) & u64_vxrm;
> +  collect_register_by_name (regcache, "vxrm", regbuf);
> +
> +  u64_vcsr &= ~((uint64_t)VCSR_MASK_VXSAT << VCSR_POS_VXSAT);
> +  u64_vcsr |= ((u64_vxsat & VCSR_MASK_VXSAT) << VCSR_POS_VXSAT);
> +  u64_vcsr &= ~((uint64_t)VCSR_MASK_VXRM << VCSR_POS_VXRM);
> +  u64_vcsr |= ((u64_vxrm & VCSR_MASK_VXRM) << VCSR_POS_VXRM);
> +
> +  /* Replace the original vcsr value with the "cooked" value */
> +  regbuf = (gdb_byte *) & u64_vcsr;
> +  supply_register_by_name (regcache, "vcsr", regbuf);
> +
> +  /* Now stage the ptrace buffer (it'll receive the cooked vcsr value) */
> +
> +  regbuf = (gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vstart);
> +  collect_register_by_name (regcache, "vstart", regbuf);
> +  regbuf = (gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vl);
> +  collect_register_by_name (regcache, "vl", regbuf);
> +  regbuf = (gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vtype);
> +  collect_register_by_name (regcache, "vtype", regbuf);
> +  regbuf = (gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vcsr);
> +  collect_register_by_name (regcache, "vcsr", regbuf);
> +  regbuf = (gdb_byte *) & u64_vlenb;
> +  collect_register_by_name (regcache, "vlenb", regbuf);
> +
> +
> +  regbuf = (gdb_byte *) buf + offsetof (struct __riscv_vregs, data);
> +  for (i = 0; i < 32; i++, regbuf += vlenb)
> +    collect_register (regcache, regno + i, regbuf);
> +}
> +
> +/* Supply vector registers from BUF into REGCACHE.  */
> +
> +static void
> +riscv_store_vregset (struct regcache *regcache, const void *buf)
> +{
> +  const struct target_desc *tdesc = regcache->tdesc;
> +  int regno = find_regno (tdesc, "v0");
> +  int vlenb = register_size (regcache->tdesc, regno);
> +  uint64_t u64_vlenb = vlenb;	/* pad to max XLEN for buffer conversion */
> +  uint64_t vcsr;
> +  uint64_t vxsat;
> +  uint64_t vxrm;
> +  const gdb_byte *regbuf;
> +  int i;
> +
> +  regbuf =
> +    (const gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vstart);
> +  supply_register_by_name (regcache, "vstart", regbuf);
> +  regbuf =
> +    (const gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vl);
> +  supply_register_by_name (regcache, "vl", regbuf);
> +  regbuf =
> +    (const gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vtype);
> +  supply_register_by_name (regcache, "vtype", regbuf);
> +  regbuf =
> +    (const gdb_byte *) buf + offsetof (struct __riscv_vregs, vstate.vcsr);
> +  supply_register_by_name (regcache, "vcsr", regbuf);
> +  /* also store off a non-byte-wise copy of vcsr, to derive values for vxsat and vxrm */
> +  vcsr = *(uint64_t*)regbuf;
> +  /* vlenb isn't part of vstate, but we have already inferred its value by running code on this
> +     hart, and we're assuming homogeneous VLENB if it's an SMP system */
> +  regbuf = (gdb_byte *) & u64_vlenb;
> +  supply_register_by_name (regcache, "vlenb", regbuf);
> +
> +  /* vxsat and vxrm, are not part of vstate, so we have to extract from VCSR
> +     value */
> +  vxsat = ((vcsr >> VCSR_POS_VXSAT) & VCSR_MASK_VXSAT);
> +  regbuf = (gdb_byte *) &vxsat;
> +  supply_register_by_name (regcache, "vxsat", regbuf);
> +  vxrm = ((vcsr >> VCSR_POS_VXRM) & VCSR_MASK_VXRM);
> +  regbuf = (gdb_byte *) &vxrm;
> +  supply_register_by_name (regcache, "vxrm", regbuf);
> +
> +  /* v0..v31 */
> +  regbuf = (const gdb_byte *) buf + offsetof (struct __riscv_vregs, data);
> +  for (i = 0; i < 32; i++, regbuf += vlenb)
> +    supply_register (regcache, regno + i, regbuf);
> +}
> +
>  /* RISC-V/Linux regsets.  FPRs are optional and come in different sizes,
>     so define multiple regsets for them marking them all as OPTIONAL_REGS
>     rather than FP_REGS, so that "regsets_fetch_inferior_registers" picks
> @@ -178,6 +285,9 @@ static struct regset_info riscv_regsets[] = {
>    { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_FPREGSET,
>      sizeof (struct __riscv_mc_f_ext_state), OPTIONAL_REGS,
>      riscv_fill_fpregset, riscv_store_fpregset },
> +  { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_RISCV_VECTOR,
> +    sizeof (struct __riscv_vregs), OPTIONAL_REGS,
> +    riscv_fill_vregset, riscv_store_vregset },
>    NULL_REGSET
>  };
>  
> diff --git a/include/elf/common.h b/include/elf/common.h
> index fd032d1e03e..7003f987b94 100644
> --- a/include/elf/common.h
> +++ b/include/elf/common.h
> @@ -758,6 +758,7 @@
>  					/*   note name must be "LINUX".  */
>  #define NT_RISCV_CSR    0x900		/* RISC-V Control and Status Registers */
>  					/*   note name must be "LINUX".  */
> +#define NT_RISCV_VECTOR 0x901           /* RISC-V Vector Registers.  */
>  #define NT_SIGINFO	0x53494749	/* Fields of siginfo_t.  */
>  #define NT_FILE		0x46494c45	/* Description of mapped files.  */
>  
> -- 
> 2.43.0
>