Re: [PATCHv2 6/9] bfd/binutils: add support for RISC-V CSRs in core files

[Andrew Burgess <andrew.burgess@embecosm.com>]

Here is an update version of this patch.

In this patch I have placed the CSRs into a note named "GDB".  This
should protect us if, in the future, the note type number I have used
is reused by some other core file producer (Linux / FreeBSD) and given
a different meaning.

Any feedback?

Thanks,
Andrew


---

commit 15bcb460981a000e74b2d3dc4f59f0f06bc0cd52
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Fri Nov 27 14:04:16 2020 +0000

    bfd/binutils: add support for RISC-V CSRs in core files
    
    Adds support for including RISC-V control and status registers into
    core files.
    
    The value for the define NT_RISCV_CSR is set to 0x900, this
    corresponds to a patch I have proposed for the Linux kernel here:
    
      http://lists.infradead.org/pipermail/linux-riscv/2020-December/003910.html
    
    As I have not yet heard if the above patch will be accepted into the
    kernel or not I have set the note name string to "GDB", and the note
    type to NT_RISCV_CSR.
    
    This means that if the above patch is rejected from the kernel, and
    the note type number 0x900 is assigned to some other note type, we
    will still be able to distinguish between the GDB produced
    NT_RISCV_CSR, and the kernel produced notes, where the name would be
    set to "CORE".
    
    bfd/ChangeLog:
    
            * elf-bfd.h (elfcore_write_riscv_csr): Declare.
            * elf.c (elfcore_grok_riscv_csr): New function.
            (elfcore_grok_note): Handle NT_RISCV_CSR.
            (elfcore_write_riscv_csr): New function.
            (elfcore_write_register_note): Handle '.reg-riscv-csr'.
    
    binutils/ChangeLog:
    
            * readelf.c (get_note_type): Handle NT_RISCV_CSR.
    
    include/ChangeLog:
    
            * elf/common.h (NT_RISCV_CSR): Define.

diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index 779acc745bc..5b7eb8897c8 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -2797,6 +2797,8 @@ extern char *elfcore_write_aarch_pauth
   (bfd *, char *, int *, const void *, int);
 extern char *elfcore_write_arc_v2
   (bfd *, char *, int *, const void *, int);
+extern char *elfcore_write_riscv_csr
+  (bfd *, char *, int *, const void *, int);
 extern char *elfcore_write_gdb_tdesc
   (bfd *, char *, int *, const void *, int);
 extern char *elfcore_write_lwpstatus
diff --git a/bfd/elf.c b/bfd/elf.c
index c6cf7fe2d6e..d1fd29f380a 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -9912,6 +9912,12 @@ elfcore_grok_arc_v2 (bfd *abfd, Elf_Internal_Note *note)
   return elfcore_make_note_pseudosection (abfd, ".reg-arc-v2", note);
 }
 
+static bfd_boolean
+elfcore_grok_riscv_csr (bfd *abfd, Elf_Internal_Note *note)
+{
+  return elfcore_make_note_pseudosection (abfd, ".reg-riscv-csr", note);
+}
+
 static bfd_boolean
 elfcore_grok_gdb_tdesc (bfd *abfd, Elf_Internal_Note *note)
 {
@@ -10583,6 +10589,13 @@ elfcore_grok_note (bfd *abfd, Elf_Internal_Note *note)
       else
         return TRUE;
 
+    case NT_RISCV_CSR:
+      if (note->namesz == 4
+          && strcmp (note->namedata, "GDB") == 0)
+        return elfcore_grok_riscv_csr (abfd, note);
+      else
+	return TRUE;
+
     case NT_PRPSINFO:
     case NT_PSINFO:
       if (bed->elf_backend_grok_psinfo)
@@ -11964,6 +11977,18 @@ elfcore_write_arc_v2 (bfd *abfd,
 			     note_name, NT_ARC_V2, arc_v2, size);
 }
 
+char *
+elfcore_write_riscv_csr (bfd *abfd,
+                         char *buf,
+                         int *bufsiz,
+                         const void *csrs,
+                         int size)
+{
+  const char *note_name = "GDB";
+  return elfcore_write_note (abfd, buf, bufsiz,
+			     note_name, NT_RISCV_CSR, csrs, size);
+}
+
 char *
 elfcore_write_gdb_tdesc (bfd *abfd,
 			 char *buf,
@@ -12062,6 +12087,8 @@ elfcore_write_register_note (bfd *abfd,
     return elfcore_write_arc_v2 (abfd, buf, bufsiz, data, size);
   if (strcmp (section, ".gdb-tdesc") == 0)
     return elfcore_write_gdb_tdesc (abfd, buf, bufsiz, data, size);
+  if (strcmp (section, ".reg-riscv-csr") == 0)
+    return elfcore_write_riscv_csr (abfd, buf, bufsiz, data, size);
   return NULL;
 }
 
diff --git a/binutils/readelf.c b/binutils/readelf.c
index feb458877c8..807eccfb026 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -18374,6 +18374,8 @@ get_note_type (Filedata * filedata, unsigned e_type)
 	return _("NT_ARM_HW_WATCH (AArch hardware watchpoint registers)");
       case NT_ARC_V2:
 	return _("NT_ARC_V2 (ARC HS accumulator/extra registers)");
+      case NT_RISCV_CSR:
+	return _("NT_RISCV_CSR (RISC-V control and status registers)");
       case NT_PSTATUS:
 	return _("NT_PSTATUS (pstatus structure)");
       case NT_FPREGS:
diff --git a/include/elf/common.h b/include/elf/common.h
index e6e9c278faa..4cb3748e4fd 100644
--- a/include/elf/common.h
+++ b/include/elf/common.h
@@ -674,6 +674,8 @@
 					/*   note name must be "LINUX".  */
 #define NT_ARC_V2	0x600		/* ARC HS accumulator/extra registers.  */
 					/*   note name must be "LINUX".  */
+#define NT_RISCV_CSR    0x900		/* RISC-V Control and Status Registers */
+					/*   note name must be "CORE".  */
 #define NT_SIGINFO	0x53494749	/* Fields of siginfo_t.  */
 #define NT_FILE		0x46494c45	/* Description of mapped files.  */