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Date: Sun, 21 Nov 1999 01:14:03 -0500 (EST)
From: vns@delta.odessa.ua
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Subject: kern/15014: DDB can't find symbol for address in kernel loadable modules.
Sender: owner-freebsd-bugs@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.org


>Number:         15014
>Category:       kern
>Synopsis:       DDB can't find symbol for address in kernel loadable modules.
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Nov 20 22:20:00 PST 1999
>Closed-Date:
>Last-Modified:
>Originator:     Vladimir N. Silyaev
>Release:        FreeBSD 4.0-CURRENT i386
>Organization:
>Environment:

	FreeBSD 4.0-CURRENT i386

	ELF kernel
	ELF KLD

>Description:

	DDB can't locate names to stack frame, when frames include pointer
        from kernel loadable module

>How-To-Repeat:

- Build kernel with DDB support.
- Load linux KLD (launch linux command).

Throw to DDB, then 
db> b linux_open
db> c

Run any linux command, for example:
> /compat/linux/bin/bash

Breakpoint at   linux_open:     pushl   %ebp
db> trace
_end(c4324280,c45f3f80,28051dc6,3,28054a10) at 0xc06ef344
syscall(2f,2f,2f,28054a10,3) at syscall+0x119
Xint0x80_syscall() at Xint0x80_syscall+0x26
db> c


>Fix:

Apply the following patch.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
--- /sys/kern/link_elf.c.orig	Fri Oct 29 18:12:02 1999
+++ /sys/kern/link_elf.c	Sat Nov 20 17:51:16 1999
@@ -958,17 +958,19 @@
 	const Elf_Sym* es;
 	const Elf_Sym* best = 0;
 	int i;
+	u_long st_value;
 
 	for (i = 0, es = ef->ddbsymtab; i < ef->ddbsymcnt; i++, es++) {
 		if (es->st_name == 0)
 			continue;
-		if (off >= es->st_value) {
-			if (off - es->st_value < diff) {
-				diff = off - es->st_value;
+		st_value = es->st_value + (u_long)ef->address;
+		if (off >= st_value) {
+			if (off - st_value < diff) {
+				diff = off - st_value;
 				best = es;
 				if (diff == 0)
 					break;
-			} else if (off - es->st_value == diff) {
+			} else if (off - st_value == diff) {
 				best = es;
 			}
 		}
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

After applying this patch, in the same circumstance, trace will be printing:
db> trace
linux_open(c4324280,c45f3f80,28051dc6,3,28054a10) at linux_open
syscall(2f,2f,2f,28054a10,3) at syscall+0x119
Xint0x80_syscall() at Xint0x80_syscall+0x26


P.S. It's looks like that the /sys/kern/link_aout.c have the same kind
of problem.


>Release-Note:
>Audit-Trail:
>Unformatted:


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