Change in coreboot[master]: libpayload: cbmem_console: Drop loglevel markers from snapshot

[Julius Werner (Code Review)]

Attention is currently required from: Raul Rangel, Yu-Ping Wu.
Hello Raul Rangel, Yu-Ping Wu,

I'd like you to do a code review. Please visit

https://review.coreboot.org/c/coreboot/+/62506

to review the following change.

Change subject: libpayload: cbmem_console: Drop loglevel markers from snapshot
......................................................................

libpayload: cbmem_console: Drop loglevel markers from snapshot

coreboot recently introduced non-printable loglevel markers in the CBMEM
console. Payloads were generally unaffected since they don't use log
levels and it is still legal to append lines without a marker to the
log. However, payloads using cbmem_console_snapshot() to display
existing logs from coreboot have started seeing '?' characters in place
of the markers. This patch fixes the issue by filtering out marker
characters.

BUG=b:221909874

Signed-off-by: Julius Werner 
Change-Id: I4a9e5d464508320cf43ea572d62896d38c2a128d
---
M payloads/libpayload/drivers/cbmem_console.c
1 file changed, 24 insertions(+), 12 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/06/62506/1

diff --git a/payloads/libpayload/drivers/cbmem_console.c b/payloads/libpayload/drivers/cbmem_console.c
index 22d5312..df40ad0 100644
--- a/payloads/libpayload/drivers/cbmem_console.c
+++ b/payloads/libpayload/drivers/cbmem_console.c
@@ -80,11 +80,28 @@
    do_write(buffer, count);
 }

+static void snapshot_putc(char *console, uint32_t *cursor, char c)
+{
+	/* This is BIOS_LOG_IS_MARKER() from coreboot. Due to stupid
+	   licensing restrictions, we can't use it directly. */
+	if (c >= 0x10 && c <= 0x18)
+		return;
+
+	/* Slight memory corruption may occur between reboots and give us a few
+	   unprintable characters like '\0'. Replace them with '?' on output. */
+	if (!isprint(c) && !isspace(c))
+		console[*cursor] = '?';
+	else
+		console[*cursor] = c;
+
+	*cursor += 1;
+}
+
 char *cbmem_console_snapshot(void)
 {
    const struct cbmem_console *const console_p = phys_to_virt(cbmem_console_p);
    char *console_c;
-	uint32_t size, cursor, overflow;
+	uint32_t size, cursor, overflow, newc, oldc;

if (!console_p) {
    	printf("ERROR: No cbmem console found in coreboot table\n");
@@ -104,24 +121,19 @@
    	       size);
    	return NULL;
    }
-	console_c[size] = '\0';

+	newc = 0;
    if (overflow) {
    	if (cursor >= size) {
    		printf("ERROR: CBMEM console struct is corrupted\n");
    		return NULL;
    	}
-		memcpy(console_c, console_p->body + cursor, size - cursor);
-		memcpy(console_c + size - cursor, console_p->body, cursor);
-	} else {
-		memcpy(console_c, console_p->body, size);
+		for (oldc = cursor; oldc < size; oldc++)
+			snapshot_putc(console_c, &newc, console_p->body[oldc]);
    }
-
-	/* Slight memory corruption may occur between reboots and give us a few
-	   unprintable characters like '\0'. Replace them with '?' on output. */
-	for (cursor = 0; cursor < size; cursor++)
-		if (!isprint(console_c[cursor]) && !isspace(console_c[cursor]))
-			console_c[cursor] = '?';
+	for (oldc = 0; oldc < size && oldc < cursor; oldc++)
+		snapshot_putc(console_c, &newc, console_p->body[oldc]);
+	console_c[newc] = '\0';

return console_c;
 }