ddb: add support for DWARF line number decoding

This allows ddb's "trace" command to include file and line numbers:

  ddb{0}> trace
  Debugger() at Debugger+0x9 [../../../../arch/amd64/amd64/db_interface.c:405]
  ddb_sysctl() at ddb_sysctl+0x1b4 [../../../../ddb/db_usrreq.c:104]
  sys___sysctl() at sys___sysctl+0x216 [../../../../kern/kern_sysctl.c:229]
  syscall() at syscall+0x297 [../../../../sys/syscall_mi.h:84]
  --- syscall (number 202) ---
  end of kernel
  end trace frame: 0x7f7ffffcf1d7, count: -4
  acpi_pdirpa+0x4117aa:

For this to work, it requires using a new version of boot(8), and
booting a kernel with the .debug_line section present (e.g., building
with ``makeoptions DEBUG="-g"'' and then booting the bsd.gdb kernel
instead of the stripped bsd kernel).

Still a WIP, but no failure reports yet.  Committing so further
development and testing can happen in tree.

prodding deraadt, guenther, mlarkin
ok mpi

3 files changed, 74 insertions, 12 deletions

diff --git a/sys/conf/files b/sys/conf/files
index 680b077acea..7862ae70303 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -1,4 +1,4 @@
-#	$OpenBSD: files,v 1.580 2014/10/09 03:36:32 tedu Exp $
+#	$OpenBSD: files,v 1.581 2014/10/09 08:21:48 matthew Exp $
 #	$NetBSD: files,v 1.87 1996/05/19 17:17:50 jonathan Exp $
 
 #	@(#)files.newconf	7.5 (Berkeley) 5/10/93
@@ -609,6 +609,7 @@ file 	net/if_pppoe.c			pppoe	needs-flag
 file ddb/db_access.c			ddb | kgdb
 file ddb/db_break.c			ddb
 file ddb/db_command.c			ddb
+file ddb/db_dwarf.c			ddb
 file ddb/db_elf.c			ddb
 file ddb/db_examine.c			ddb
 file ddb/db_expr.c			ddb
diff --git a/sys/ddb/db_elf.c b/sys/ddb/db_elf.c
index 277488a80aa..9ccb5f3fb98 100644
--- a/sys/ddb/db_elf.c
+++ b/sys/ddb/db_elf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: db_elf.c,v 1.11 2014/09/14 14:17:24 jsg Exp $	*/
+/*	$OpenBSD: db_elf.c,v 1.12 2014/10/09 08:21:48 matthew Exp $	*/
 /*	$NetBSD: db_elf.c,v 1.13 2000/07/07 21:55:18 jhawk Exp $	*/
 
 /*-
@@ -32,12 +32,14 @@
  */
 
 #include <sys/types.h>
+#include <sys/stdint.h>
 #include <sys/param.h>
 #include <sys/systm.h>  
 #include <sys/exec.h>
 
 #include <machine/db_machdep.h>
 
+#include <ddb/db_dwarf.h>
 #include <ddb/db_sym.h>
 #include <ddb/db_output.h>
 #include <ddb/db_extern.h>
@@ -45,6 +47,7 @@
 #include <sys/exec_elf.h>
 
 static char *db_elf_find_strtab(db_symtab_t *);
+static char *db_elf_find_linetab(db_symtab_t *, size_t *);
 
 #define	STAB_TO_SYMSTART(stab)	((Elf_Sym *)((stab)->start))
 #define	STAB_TO_SYMEND(stab)	((Elf_Sym *)((stab)->end))
@@ -110,10 +113,10 @@ db_elf_sym_init(int symsize, void *symtab, void *esymtab, const char *name)
 	 *	. . .
 	 *	. . .
 	 *	last section header
-	 *	first symbol or string table section
+	 *	first symbol, string, or line table section
 	 *	. . .
 	 *	. . .
-	 *	last symbol or string table section
+	 *	last symbol, string, or line table section
 	 */
 
 	/*
@@ -232,6 +235,30 @@ db_elf_find_strtab(db_symtab_t *stab)
 }
 
 /*
+ * Internal helper function - return a pointer to the line table
+ * for the current symbol table.
+ */
+static char *
+db_elf_find_linetab(db_symtab_t *stab, size_t *size)
+{
+	Elf_Ehdr *elf = STAB_TO_EHDR(stab);
+	Elf_Shdr *shp = STAB_TO_SHDR(stab, elf);
+	char *shstrtab;
+	int i;
+
+	shstrtab = (char *)elf + shp[elf->e_shstrndx].sh_offset;
+	for (i = 0; i < elf->e_shnum; i++) {
+		if ((shp[i].sh_flags & SHF_ALLOC) != 0 &&
+		    strcmp(".debug_line", shstrtab+shp[i].sh_name) == 0) {
+			*size = shp[i].sh_size;
+			return ((char *)elf + shp[i].sh_offset);
+		}
+	}
+
+	return (NULL);
+}
+
+/*
  * Lookup the symbol with the given name.
  */
 db_sym_t
@@ -350,11 +377,25 @@ boolean_t
 db_elf_line_at_pc(db_symtab_t *symtab, db_sym_t cursym, char **filename,
     int *linenum, db_expr_t off)
 {
+	const char *linetab;
+	size_t linetab_size;
 
-	/*
-	 * XXX We don't support this (yet).
-	 */
-	return (FALSE);
+	linetab = db_elf_find_linetab(symtab, &linetab_size);
+	if (linetab == NULL)
+		return (FALSE);
+
+	const char *dirname, *basename;
+	if (!db_dwarf_line_at_pc(linetab, linetab_size, off,
+	    &dirname, &basename, linenum))
+		return (FALSE);
+
+	static char path[PATH_MAX];
+	if (dirname == NULL)
+		strlcpy(path, basename, sizeof(path));
+	else
+		snprintf(path, sizeof(path), "%s/%s", dirname, basename);
+	*filename = path;
+	return (TRUE);
 }
 
 /*
diff --git a/sys/lib/libsa/loadfile_elf.c b/sys/lib/libsa/loadfile_elf.c
index e9ee42440de..42d3adcb216 100644
--- a/sys/lib/libsa/loadfile_elf.c
+++ b/sys/lib/libsa/loadfile_elf.c
@@ -1,5 +1,5 @@
 /* $NetBSD: loadfile.c,v 1.10 2000/12/03 02:53:04 tsutsui Exp $ */
-/* $OpenBSD: loadfile_elf.c,v 1.8 2014/02/25 21:40:39 miod Exp $ */
+/* $OpenBSD: loadfile_elf.c,v 1.9 2014/10/09 08:21:48 matthew Exp $ */
 
 /*-
  * Copyright (c) 1997 The NetBSD Foundation, Inc.
@@ -76,7 +76,7 @@ ELFNAME(exec)(int fd, Elf_Ehdr *elf, u_long *marks, int flags)
 	int i;
 	size_t sz;
 	int first;
-	int havesyms;
+	int havesyms, havelines;
 	paddr_t minp = ~0, maxp = 0, pos = 0;
 	paddr_t offset = marks[MARK_START], shpp, elfp;
 
@@ -199,6 +199,21 @@ ELFNAME(exec)(int fd, Elf_Ehdr *elf, u_long *marks, int flags)
 		shpp = maxp;
 		maxp += roundup(sz, sizeof(Elf_Addr));
 
+		size_t shstrsz = shp[elf->e_shstrndx].sh_size;
+		char *shstr = ALLOC(shstrsz);
+		if (lseek(fd, (off_t)shp[elf->e_shstrndx].sh_offset, SEEK_SET) == -1) {
+			WARN(("lseek section header string table"));
+			FREE(shstr, shstrsz);
+			FREE(shp, sz);
+			return 1;
+		}
+		if (READ(fd, shstr, shstrsz) != shstrsz) {
+			WARN(("read section header string table"));
+			FREE(shstr, shstrsz);
+			FREE(shp, sz);
+			return 1;
+		}
+
 		/*
 		 * Now load the symbol sections themselves. Make sure the
 		 * sections are aligned. Don't bother with string tables if
@@ -206,25 +221,28 @@ ELFNAME(exec)(int fd, Elf_Ehdr *elf, u_long *marks, int flags)
 		 */
 		off = roundup((sizeof(Elf_Ehdr) + sz), sizeof(Elf_Addr));
 
-		for (havesyms = i = 0; i < elf->e_shnum; i++)
+		for (havesyms = havelines = i = 0; i < elf->e_shnum; i++)
 			if (shp[i].sh_type == SHT_SYMTAB)
 				havesyms = 1;
 
 		for (first = 1, i = 0; i < elf->e_shnum; i++) {
 			if (shp[i].sh_type == SHT_SYMTAB ||
-			    shp[i].sh_type == SHT_STRTAB) {
+			    shp[i].sh_type == SHT_STRTAB ||
+			    !strcmp(shstr + shp[i].sh_name, ".debug_line")) {
 				if (havesyms && (flags & LOAD_SYM)) {
 					PROGRESS(("%s%ld", first ? " [" : "+",
 					    (u_long)shp[i].sh_size));
 					if (lseek(fd, (off_t)shp[i].sh_offset,
 					    SEEK_SET) == -1) {
 						WARN(("lseek symbols"));
+						FREE(shstr, shstrsz);
 						FREE(shp, sz);
 						return 1;
 					}
 					if (READ(fd, maxp, shp[i].sh_size) !=
 					    shp[i].sh_size) {
 						WARN(("read symbols"));
+						FREE(shstr, shstrsz);
 						FREE(shp, sz);
 						return 1;
 					}
@@ -232,6 +250,7 @@ ELFNAME(exec)(int fd, Elf_Ehdr *elf, u_long *marks, int flags)
 				maxp += roundup(shp[i].sh_size,
 				    sizeof(Elf_Addr));
 				shp[i].sh_offset = off;
+				shp[i].sh_flags |= SHF_ALLOC;
 				off += roundup(shp[i].sh_size, sizeof(Elf_Addr));
 				first = 0;
 			}
@@ -242,6 +261,7 @@ ELFNAME(exec)(int fd, Elf_Ehdr *elf, u_long *marks, int flags)
 			if (havesyms && first == 0)
 				PROGRESS(("]"));
 		}
+		FREE(shstr, shstrsz);
 		FREE(shp, sz);
 	}