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Subject[PATCH] add syslog printing to xmon debugger.
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Hi,

This patch 'dmesg'/printk log buffer printing to xmon. I find this
useful because crashes are almost always preceeded by interesting
printk's. This patch is simple & straightforward, except for one
possibly controversial aspect: it embeds a small snippet in
kernel/printk.c to return the location of the syslog. This is
needed because kallsyms and even CONFIG_KALLSYMS_ALL is not enough
to reveal the location of log_buf. This code is about 90%
cut-n-paste of earlier code from Keith Owens.

Andrew,

Please apply at least the kernel/printk.c part of the patch,
if you are feeling at all charitable.

Signed-off-by: Linas Vepstas <linas@linas.org>
===== arch/ppc64/xmon/xmon.c 1.50 vs edited =====
--- 1.50/arch/ppc64/xmon/xmon.c Fri Jul 2 00:23:46 2004
+++ edited/arch/ppc64/xmon/xmon.c Thu Sep 16 16:49:23 2004
@@ -132,6 +132,7 @@
static void bootcmds(void);
void dump_segments(void);
static void symbol_lookup(void);
+static void xmon_show_dmesg(void);
static int emulate_step(struct pt_regs *regs, unsigned int instr);
static void xmon_print_symbol(unsigned long address, const char *mid,
const char *after);
@@ -175,6 +176,7 @@
#endif
"\
C checksum\n\
+ D show dmesg (printk) buffer\n\
d dump bytes\n\
di dump instructions\n\
df dump float values\n\
@@ -911,6 +913,9 @@
case 'd':
dump();
break;
+ case 'D':
+ xmon_show_dmesg();
+ break;
case 'l':
symbol_lookup();
break;
@@ -2452,6 +2457,58 @@
printf(" [%s]", modname);
}
printf("%s", after);
+}
+
+extern void debugger_syslog_data(char *syslog_data[4]);
+#define SYSLOG_WRAP(p) if (p < syslog_data[0]) p = syslog_data[1]-1; \
+ else if (p >= syslog_data[1]) p = syslog_data[0];
+
+static void xmon_show_dmesg(void)
+{
+ char *syslog_data[4], *start, *end, c;
+ int logsize;
+
+ /* syslog_data[0,1] physical start, end+1.
+ * syslog_data[2,3] logical start, end+1.
+ */
+ debugger_syslog_data(syslog_data);
+ if (syslog_data[2] == syslog_data[3])
+ return;
+ logsize = syslog_data[1] - syslog_data[0];
+ start = syslog_data[0] + (syslog_data[2] - syslog_data[0]) % logsize;
+ end = syslog_data[0] + (syslog_data[3] - syslog_data[0]) % logsize;
+
+ /* Do a line at a time (max 200 chars) to reduce overhead */
+ c = '\0';
+ while(1) {
+ char *p;
+ int chars = 0;
+ if (!*start) {
+ while (!*start) {
+ ++start;
+ SYSLOG_WRAP(start);
+ if (start == end)
+ break;
+ }
+ if (start == end)
+ break;
+ }
+ p = start;
+ while (*start && chars < 200) {
+ c = *start;
+ ++chars;
+ ++start;
+ SYSLOG_WRAP(start);
+ if (start == end || c == '\n')
+ break;
+ }
+ if (chars)
+ printf("%.*s", chars, p);
+ if (start == end)
+ break;
+ }
+ if (c != '\n')
+ printf("\n");
}

static void debug_trace(void)
===== kernel/printk.c 1.41 vs edited =====
--- 1.41/kernel/printk.c Mon Aug 23 03:15:11 2004
+++ edited/kernel/printk.c Thu Sep 16 15:50:59 2004
@@ -376,6 +376,21 @@
return do_syslog(type, buf, len);
}

+#ifdef CONFIG_DEBUG_KERNEL
+/* Its very handy to be able to view the syslog buffer during debug.
+ * But do_syslog() uses locks so it cannot be used during debugging.
+ * Instead, provide the start and end of the physical and logical logs.
+ * This is equivalent to do_syslog(3).
+ */
+void debugger_syslog_data(char *syslog_data[4])
+{
+ syslog_data[0] = log_buf;
+ syslog_data[1] = log_buf + __LOG_BUF_LEN;
+ syslog_data[2] = log_buf + log_end - (logged_chars < __LOG_BUF_LEN ? logged_chars : __LOG_BUF_LEN);
+ syslog_data[3] = log_buf + log_end;
+}
+#endif /* CONFIG_DEBUG_KERNEL */
+
/*
* Call the console drivers on a range of log_buf
*/
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