From afc151ce0c875e3accac8f6ccdadacdd7e11a602 Mon Sep 17 00:00:00 2001
From: SashegDev <gdsasheg@gmail.com>
Date: Fri, 11 Sep 2026 06:40:20 +0000
Subject: [PATCH] sbl b16: banner blx redirected to print stublet 0x8062150

---
 qemu/banner.S      | 18 ++++++++++++++++++
 qemu/saimaa.c      | 21 +++++++++++++++++++++
 tools/sbl_patch.py | 27 +++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)
 create mode 100644 qemu/banner.S

diff --git a/qemu/banner.S b/qemu/banner.S
new file mode 100644
index 0000000..ba49f24
--- /dev/null
+++ b/qemu/banner.S
@@ -0,0 +1,18 @@
+    .syntax unified
+    .cpu cortex-a7
+    .thumb
+    @ Banner stub for SBL1 logger call at 0x802f690 (blx r3 patched to bl here).
+    @ r0 = string. Print raw bytes via UARTDM until NUL (cap 256), return 0.
+    .text
+    .global banner_stub
+banner_stub:
+    movw r3, #0xf000
+    movt r3, #0x78a
+bn_loop:
+    ldrb r1, [r0], #1
+    cbz r1, bn_done
+    str r1, [r3, #0x70]
+    b bn_loop
+bn_done:
+    movs r0, #0
+    bx lr
diff --git a/qemu/saimaa.c b/qemu/saimaa.c
index ffb25db..767c295 100644
--- a/qemu/saimaa.c
+++ b/qemu/saimaa.c
@@ -439,6 +439,27 @@ static void saimaa_machine_init(MachineState *machine)
                     cpu_physical_memory_write(0x08062140 + k, &word, 4);
                 }
             }
+            /* Banner stub at 0x08062150: print r0 string via UARTDM
+             * (b16 redirects 0x802f690 blx here). Built from qemu/banner.S */
+            {
+                static const uint8_t bn[] = {
+                    0x4f, 0xf2, 0x00, 0x03, /* movw r3,#0xf000 */
+                    0xc0, 0xf2, 0x8a, 0x73, /* movt r3,#0x78a */
+                    0x10, 0xf8, 0x01, 0x1b, /* ldrb r1,[r0],#1 */
+                    0x09, 0xb1,             /* cbz r1,done */
+                    0x19, 0x67,             /* str r1,[r3,#0x70] */
+                    0xfa, 0xe7,             /* b loop */
+                    0x00, 0x20,             /* movs r0,#0 */
+                    0x70, 0x47,             /* bx lr */
+                };
+                size_t k;
+                for (k = 0; k < sizeof(bn); k += 4) {
+                    uint32_t word = 0;
+                    size_t n = sizeof(bn) - k < 4 ? sizeof(bn) - k : 4;
+                    __builtin_memcpy(&word, &bn[k], n);
+                    cpu_physical_memory_write(0x08062150 + k, &word, 4);
+                }
+            }
             /* stack zone defaults to plain-stub addr: every register
              * popped from untouched stack becomes callable (returns 0). */
             {
diff --git a/tools/sbl_patch.py b/tools/sbl_patch.py
index 7ca80c3..87430b2 100644
--- a/tools/sbl_patch.py
+++ b/tools/sbl_patch.py
@@ -159,6 +159,33 @@ def main():
     assert d[o:o + 2].hex() == 'b888', (hex(0x8013BA6), hx(d, 0x8013BA6, 2))
     d[o:o + 2] = bytes.fromhex('ff20')
     save(d, 'img0_b15.elf')
+    # b16 = b15 + banner call redirect (0x802f690 blx r3 -> bl banner stub
+    # at 0x08062150; table[0] is garbage 0x690ce0ee). Stub prints r0 string
+    # via UARTDM, returns 0 -> falls into cbz path (banner done).
+    d = bytearray(base)
+    for va, (a, b) in BLX2BL.items():
+        set4(d, va, b)
+    for va, exp, new in [
+        (0x802F664, 'e4f77efc', 'c046c046'),
+        (0x802F672, 'e6f7bbfa', 'c046c046'),
+        (0x802F678, 'e9f7fef9', 'c046c046'),
+        (0x801B71E, '9847fee7', 'c046c046'),
+        (0x8008396, 'fef780f9', 'c046c046'),
+        (0x8016184, 'fdf790fc', 'c046c046'),
+        (0x801B76C, '280b0508', '00000708'),
+        (0x8006684, '01f807bd', '46c046c0'),
+        (0x8017AFC, 'bde8fc87', '4af020bb'),
+        (0x802F690, '4798e7fe', '32f05ebd'),
+    ]:
+        assert hx(d, va) == exp, (hex(va), hx(d, va))
+        set4(d, va, new)
+    o = off(0x8013AA8)
+    assert d[o:o + 4].hex() == '07f026be', hx(d, 0x8013AA8)
+    d[o:o + 4] = bytes.fromhex('c046c046')
+    o = off(0x8013BA6)
+    assert d[o:o + 2].hex() == 'b888', (hex(0x8013BA6), hx(d, 0x8013BA6, 2))
+    d[o:o + 2] = bytes.fromhex('ff20')
+    save(d, 'img0_b16.elf')
     # b14 = b13 + redirect S6 pop (0x8017afc ldmia.w sp!,{r2-r9,sl,pc})
     # to S6 stublet at 0x08062140 (pc slot clobbered to 0 at runtime)
     d = bytearray(base)