From: Roman Penyaev <r.peniaev@gmail.com>

This change introduces parsing of the 'ESC ( <ch>' sequence, which is
supposed to change character set [1]. In the QEMU case, the
introduced parsing logic does not actually change the character set, but
simply parses the sequence and does not let output of a tool to be
corrupted with leftovers: `top` sends 'ESC ( B', so if character
sequence is not parsed correctly, chracter 'B' appears in the output:

  Btop - 11:08:42 up 5 min,  1 user,  load average: 0BB
  Tasks:B 158 Btotal,B  1 Brunning,B 157 Bsleeping,B   0 BsBB
  %Cpu(s):B  0.0 Bus,B  0.0 Bsy,B  0.0 Bni,B 99.8 Bid,B  0.2 BB
  MiB Mem :B   7955.6 Btotal,B   7778.6 Bfree,B     79.6 BB
  MiB Swap:B      0.0 Btotal,B      0.0 Bfree,B      0.0 BB

      PID USER      PR  NI    VIRT    RES    SHR S B
  B    735 root      20   0    9328   3540   3152 R B
  B      1 root      20   0   20084  10904   8404 S B
  B      2 root      20   0       0      0      0 S B

[1] https://vt100.net/docs/vt100-ug/chapter3.html#SCS

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20250226075913.353676-2-r.peniaev@gmail.com>
---
 ui/console-vc.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/ui/console-vc.c b/ui/console-vc.c
index fe20579832..90ff0ffda8 100644
--- a/ui/console-vc.c
+++ b/ui/console-vc.c
@@ -42,6 +42,8 @@ enum TTYState {
     TTY_STATE_NORM,
     TTY_STATE_ESC,
     TTY_STATE_CSI,
+    TTY_STATE_G0,
+    TTY_STATE_G1,
 };
 
 typedef struct QemuTextConsole {
@@ -694,6 +696,10 @@ static void vc_putchar(VCChardev *vc, int ch)
                 vc->esc_params[i] = 0;
             vc->nb_esc_params = 0;
             vc->state = TTY_STATE_CSI;
+        } else if (ch == '(') {
+            vc->state = TTY_STATE_G0;
+        } else if (ch == ')') {
+            vc->state = TTY_STATE_G1;
         } else {
             vc->state = TTY_STATE_NORM;
         }
@@ -844,6 +850,16 @@ static void vc_putchar(VCChardev *vc, int ch)
             }
             break;
         }
+        break;
+    case TTY_STATE_G0: /* set character sets */
+    case TTY_STATE_G1: /* set character sets */
+        switch (ch) {
+        case 'B':
+            /* Latin-1 map */
+            break;
+        }
+        vc->state = TTY_STATE_NORM;
+        break;
     }
 }
 
-- 
2.47.0