Improve support for XSAVE with debuggers.

- Dump an NT_X86_XSTATE note if XSAVE is in use. This note is designed
  to match what Linux does in that 1) it dumps the entire XSAVE area
  including the fxsave state, and 2) it stashes a copy of the current
  xsave mask in the unused padding between the fxsave state and the
  xstate header at the same location used by Linux.
- Teach readelf() to recognize NT_X86_XSTATE notes.
- Change PT_GET/SETXSTATE to take the entire XSAVE state instead of
  only the extra portion. This avoids having to always make two
  ptrace() calls to get or set the full XSAVE state.
- Add a PT_GET_XSTATE_INFO which returns the length of the current
  XSTATE save area (so the size of the buffer needed for PT_GETXSTATE)
  and the current XSAVE mask (%xcr0).

Differential Revision:	https://reviews.freebsd.org/D1193
Reviewed by:	kib
MFC after:	2 weeks

1 files changed, 35 insertions, 0 deletions

diff --git a/usr.bin/gcore/elfcore.c b/usr.bin/gcore/elfcore.c
index 037854c34d03..fb3bf5067e47 100644
--- a/usr.bin/gcore/elfcore.c
+++ b/usr.bin/gcore/elfcore.c
@@ -47,6 +47,7 @@ __FBSDID("$FreeBSD$");
 #include <err.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -101,6 +102,9 @@ static void *elf_note_fpregset(void *, size_t *);
 static void *elf_note_prpsinfo(void *, size_t *);
 static void *elf_note_prstatus(void *, size_t *);
 static void *elf_note_thrmisc(void *, size_t *);
+#if defined(__i386__) || defined(__amd64__)
+static void *elf_note_x86_xstate(void *, size_t *);
+#endif
 static void *elf_note_procstat_auxv(void *, size_t *);
 static void *elf_note_procstat_files(void *, size_t *);
 static void *elf_note_procstat_groups(void *, size_t *);
@@ -341,6 +345,9 @@ elf_putnotes(pid_t pid, struct sbuf *sb, size_t *sizep)
 		elf_putnote(NT_PRSTATUS, elf_note_prstatus, tids + i, sb);
 		elf_putnote(NT_FPREGSET, elf_note_fpregset, tids + i, sb);
 		elf_putnote(NT_THRMISC, elf_note_thrmisc, tids + i, sb);
+#if defined(__i386__) || defined(__amd64__)
+		elf_putnote(NT_X86_XSTATE, elf_note_x86_xstate, tids + i, sb);
+#endif
 	}
 
 #ifndef ELFCORE_COMPAT_32
@@ -615,6 +622,34 @@ elf_note_thrmisc(void *arg, size_t *sizep)
 	return (thrmisc);
 }
 
+#if defined(__i386__) || defined(__amd64__)
+static void *
+elf_note_x86_xstate(void *arg, size_t *sizep)
+{
+	lwpid_t tid;
+	char *xstate;
+	static bool xsave_checked = false;
+	static struct ptrace_xstate_info info;
+
+	tid = *(lwpid_t *)arg;
+	if (!xsave_checked) {
+		if (ptrace(PT_GETXSTATE_INFO, tid, (void *)&info,
+		    sizeof(info)) != 0)
+			info.xsave_len = 0;
+		xsave_checked = true;
+	}
+	if (info.xsave_len == 0) {
+		*sizep = 0;
+		return (NULL);
+	}
+	xstate = calloc(1, info.xsave_len);
+	ptrace(PT_GETXSTATE, tid, xstate, 0);
+	*(uint64_t *)(xstate + X86_XSTATE_XCR0_OFFSET) = info.xsave_mask;
+	*sizep = info.xsave_len;
+	return (xstate);
+}
+#endif
+
 static void *
 procstat_sysctl(void *arg, int what, size_t structsz, size_t *sizep)
 {