[PATCH] [PATCH v3] RISC-V: support for vector register accesses via ptrace() in RISC-V Linux native

[snatu@whileone.in]

From: Sameer Natu <snatu@whileone.in>

A v3 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             | 188 ++++++++++++++++++++++++++++++++++-
 gdb/nat/riscv-linux-tdesc.c  |  68 +++++++++++++
 gdb/nat/riscv-linux-tdesc.h  |  24 +++++
 gdb/riscv-linux-nat.c        | 163 ++++++++++++++++++++++++++++++
 gdb/riscv-linux-tdep.c       | 133 +++++++++++++++++++++++++
 gdb/riscv-tdep.c             |  49 ++++++++-
 gdb/riscv-tdep.h             |  14 +++
 gdbserver/linux-riscv-low.cc | 110 ++++++++++++++++++++
 include/elf/common.h         |   1 +
 9 files changed, 743 insertions(+), 7 deletions(-)

diff --git a/gdb/arch/riscv.c b/gdb/arch/riscv.c
index a6188ea3a8c..14fc85631e3 100644
--- a/gdb/arch/riscv.c
+++ b/gdb/arch/riscv.c
@@ -25,12 +25,38 @@
 #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.  */
+//#include "riscv-tdep.h"
+#define RISCV_VSTART 73
+#define RISCV_VXSAT 74
+#define RISCV_VXRM 75
+#define RISCV_VCSR 80
+#define RISCV_VL 3169 
+#define RISCV_VTYPE 3170
+#define RISCV_VLENB 3171
+#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 +109,169 @@ 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 (),
+						 RISCV_V0_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", RISCV_VSTART, 1, NULL, features.xlen * 8, "int");
+  tdesc_create_reg (feature, "vxsat", RISCV_VXSAT, 1, NULL, features.xlen * 8, "int");
+  tdesc_create_reg (feature, "vxrm", RISCV_VXRM, 1, NULL, features.xlen * 8, "int");  
+  tdesc_create_reg (feature, "vcsr", RISCV_VCSR, 1, NULL, features.xlen * 8, "int");
+  tdesc_create_reg (feature, "vl", RISCV_VL, 1, NULL, features.xlen * 8, "int");
+  tdesc_create_reg (feature, "vtype", RISCV_VTYPE, 1, NULL, features.xlen * 8, "int");
+  tdesc_create_reg (feature, "vlenb", RISCV_VLENB, 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..000a9de8abf 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 +125,114 @@ 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 +363,31 @@ 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 +457,35 @@ 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 4c0c65c1457..44c7d7c8115 100644
--- a/gdb/riscv-linux-tdep.c
+++ b/gdb/riscv-linux-tdep.c
@@ -31,6 +31,10 @@
 
 #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.  */
@@ -119,8 +123,123 @@ 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,
@@ -131,6 +250,7 @@ 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;
@@ -154,6 +274,19 @@ 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 91f6dffebe1..eb276d55f80 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"
@@ -650,6 +651,14 @@ 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" } },
     };
   }
 
@@ -681,10 +690,16 @@ 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;
       }
 
@@ -694,6 +709,12 @@ 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)
 	  {
@@ -816,6 +837,16 @@ 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
@@ -1467,7 +1498,19 @@ 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 ad1e9596b83..7b41dfbdcbc 100644
--- a/gdb/riscv-tdep.h
+++ b/gdb/riscv-tdep.h
@@ -46,6 +46,15 @@ enum
   RISCV_LAST_FP_REGNUM = 64,	/* Last Floating Point Register */
 
   RISCV_FIRST_CSR_REGNUM = 65,  /* First CSR */
+
+  RISCV_VSTART = 73,    /* Vector start position.  */
+  RISCV_VXSAT = 74,     /* Fixed-Point Saturate Flag.  */
+  RISCV_VXRM = 75,      /* Fixed-Point Rounding Mode.  */  
+  RISCV_VCSR = 80,      /* Vector control and status register.  */
+  RISCV_VL = 3169,      /* Vector length.  */
+  RISCV_VTYPE = 3170,    /* Vector data type register.  */
+  RISCV_VLENB = 3171,    /* VLEN/8 (vector register length in bytes) */
+
 #define DECLARE_CSR(name, num, class, define_version, abort_version) \
   RISCV_ ## num ## _REGNUM = RISCV_FIRST_CSR_REGNUM + num,
 #include "opcode/riscv-opc.h"
@@ -150,6 +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..ac83d6b0808 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