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

Andrew Burgess
2020-12-07T14:39:51Z

* 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