Re: [PATCH 4/8] bfd/riscv: prepare to handle bare metal core dump creation

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

* Jim Wilson <jimw@sifive.com> [2020-12-02 15:24:41 -0800]:

> On Wed, Dec 2, 2020 at 9:39 AM Andrew Burgess <andrew.burgess@embecosm.com>
> wrote:
> 
> > +/* Write PRSTATUS note into core file.  This will be called before the
> > +   generic code in elf.c.  By checking the compiler defines we only
> > perform
> > +   any action here if the generic code would otherwise not be able to help
> > +   us.  The intention is that bare metal core dumps (where the
> > prstatus32_t
> > +   might not be available) will use this code, while non bare metal tools
> > +   will use the generic elf code.  */
> >
> 
> The reference to prstatus32_t is a little confusing, as that appears to be
> an x64_64 specific type.  I think that should be prstatus_t.
> 
> The function handles both PRSTATUS and PRPSINFO but the comment only
> mentions PRSTATUS.  Maybe it should mention both?
> 
> Otherwise this looks OK to me, with a minor comment clarification.

I updated the comment and posted the revised patch below.

Thanks,
Andrew

---

commit 00f409a72ba183ef0f80b5874f7d0c6464d85073
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Mon Nov 30 12:14:38 2020 +0000

    bfd/riscv: prepare to handle bare metal core dump creation
    
    When creating a core file GDB will call the function
    elfcore_write_prstatus to write out the general purpose registers
    along with the pid/tid for the thread.
    
    However, for a bare metal RISC-V tool chain the prstatus*_t types are
    not defined so the elfcore_write_prstatus function will return NULL,
    preventing core file creation.
    
    This commit provides the `elf_backend_write_core_note' hook and uses
    the provided function to write out the ptstatus information.
    
    In order to keep changes in the non bare metal tools to a minimum, the
    provided backend function will itself return NULL when the prstatus*_t
    types are available, the consequence of this is that the generic code
    in elfcore_write_prstatus will be used just as before.  But, when
    prstatus*_t is not available, the new backend function will write out
    the prstatus information using predefined offsets.
    
    This new functionality will be used by a later GDB commit that will
    add bare metal core dumps for RISC-V.
    
    bfd/ChangeLog:
    
            * elfnn-riscv.c (riscv_write_core_note): New function.
            (elf_backend_write_core_note): Define.

diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index 20944c8109f..29cccf06e67 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -4874,6 +4874,77 @@ _bfd_riscv_relax_section (bfd *abfd, asection *sec,
 # define PRPSINFO_OFFSET_PR_PSARGS	56
 #endif
 
+/* Write PRSTATUS and PRPSINFO note into core file.  This will be called
+   before the generic code in elf.c.  By checking the compiler defines we
+   only perform any action here if the generic code would otherwise not be
+   able to help us.  The intention is that bare metal core dumps (where the
+   prstatus_t and/or prpsinfo_t might not be available) will use this code,
+   while non bare metal tools will use the generic elf code.  */
+
+static char *
+riscv_write_core_note (bfd *abfd ATTRIBUTE_UNUSED,
+                       char *buf ATTRIBUTE_UNUSED,
+                       int *bufsiz ATTRIBUTE_UNUSED,
+                       int note_type ATTRIBUTE_UNUSED, ...)
+{
+  switch (note_type)
+    {
+    default:
+      return NULL;
+
+#if !defined (HAVE_PRPSINFO_T)
+    case NT_PRPSINFO:
+      {
+	char data[PRPSINFO_SIZE] ATTRIBUTE_NONSTRING;
+	va_list ap;
+
+	va_start (ap, note_type);
+	memset (data, 0, sizeof (data));
+	strncpy (data + PRPSINFO_OFFSET_PR_FNAME, va_arg (ap, const char *), 16);
+#if GCC_VERSION == 8000 || GCC_VERSION == 8001
+	DIAGNOSTIC_PUSH;
+	/* GCC 8.0 and 8.1 warn about 80 equals destination size with
+	   -Wstringop-truncation:
+	   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85643
+	 */
+	DIAGNOSTIC_IGNORE_STRINGOP_TRUNCATION;
+#endif
+	strncpy (data + PRPSINFO_OFFSET_PR_PSARGS, va_arg (ap, const char *), 80);
+#if GCC_VERSION == 8000 || GCC_VERSION == 8001
+	DIAGNOSTIC_POP;
+#endif
+	va_end (ap);
+	return elfcore_write_note (abfd, buf, bufsiz,
+				   "CORE", note_type, data, sizeof (data));
+      }
+#endif /* !HAVE_PRPSINFO_T */
+
+#if !defined (HAVE_PRSTATUS_T)
+    case NT_PRSTATUS:
+      {
+        char data[PRSTATUS_SIZE];
+        va_list ap;
+        long pid;
+        int cursig;
+        const void *greg;
+
+        va_start (ap, note_type);
+        memset (data, 0, sizeof(data));
+        pid = va_arg (ap, long);
+        bfd_put_32 (abfd, pid, data + PRSTATUS_OFFSET_PR_PID);
+        cursig = va_arg (ap, int);
+        bfd_put_16 (abfd, cursig, data + PRSTATUS_OFFSET_PR_CURSIG);
+        greg = va_arg (ap, const void *);
+        memcpy (data + PRSTATUS_OFFSET_PR_REG, greg,
+                PRSTATUS_SIZE - PRSTATUS_OFFSET_PR_REG - ARCH_SIZE / 8);
+        va_end (ap);
+        return elfcore_write_note (abfd, buf, bufsiz,
+                                   "CORE", note_type, data, sizeof (data));
+      }
+#endif /* !HAVE_PRSTATUS_T */
+    }
+}
+
 /* Support for core dump NOTE sections.  */
 
 static bfd_boolean
@@ -4984,6 +5055,8 @@ riscv_elf_obj_attrs_arg_type (int tag)
 #define elf_backend_grok_prstatus	     riscv_elf_grok_prstatus
 #define elf_backend_grok_psinfo		     riscv_elf_grok_psinfo
 #define elf_backend_object_p		     riscv_elf_object_p
+#undef  elf_backend_write_core_note
+#define elf_backend_write_core_note          riscv_write_core_note
 #define elf_info_to_howto_rel		     NULL
 #define elf_info_to_howto		     riscv_info_to_howto_rela
 #define bfd_elfNN_bfd_relax_section	     _bfd_riscv_relax_section