Peer review fixes (thanks Copilot)

hal/stm32g4.c:
- hal_flash_write unaligned path: rebase the aligned doubleword on
  (address + i), not the initial address; index as dst[0]/dst[1].
  The old form skipped to the wrong DW once i advanced past 8 with
  an unaligned starting address.
- hal_flash_erase: end_address was address + len - 1 paired with a
  strict less-than, which dropped the last page when len straddled a
  page boundary by one byte. Use address + len.
- flash_clear_errors / EOP clear at end of hal_flash_write: FLASH_SR
  bits are W1C. Read-modify-write via |= can clear unrelated W1C
  bits that happen to be set. Write the mask directly.
- uart_write: cast through uint8_t before promoting to uint32_t so
  high-bit chars do not sign-extend into TDR.

hal/stm32g4.h:
- DMB/ISB/DSB: add the "memory" clobber so the compiler also treats
  them as scheduling barriers, not just hardware-level fences.

hal/stm32g4.ld:
- Rename the output section .edidx to .ARM.exidx to match the
  input-section pattern and standard Cortex-M linker scripts.

Author: dgarske

hal/stm32g4.c

@@ -36,10 +36,13 @@ static RAMFUNCTION void flash_wait_complete(void)
 
 static void RAMFUNCTION flash_clear_errors(void)
 {
-    FLASH_SR |= (FLASH_SR_OPERR | FLASH_SR_PROGERR | FLASH_SR_WRPERR |
-                 FLASH_SR_PGAERR | FLASH_SR_SIZERR | FLASH_SR_PGSERR |
-                 FLASH_SR_MISERR | FLASH_SR_FASTERR | FLASH_SR_RDERR |
-                 FLASH_SR_OPTVERR);
+    /* FLASH_SR error/EOP bits are write-1-to-clear. Assign the mask
+     * directly so a read-modify-write doesn't accidentally clear any
+     * other W1C bits that happen to be set. */
+    FLASH_SR = (FLASH_SR_OPERR | FLASH_SR_PROGERR | FLASH_SR_WRPERR |
+                FLASH_SR_PGAERR | FLASH_SR_SIZERR | FLASH_SR_PGSERR |
+                FLASH_SR_MISERR | FLASH_SR_FASTERR | FLASH_SR_RDERR |
+                FLASH_SR_OPTVERR);
 }
 
 int RAMFUNCTION hal_flash_write(uint32_t address, const uint8_t *data, int len)
@@ -63,21 +66,21 @@ int RAMFUNCTION hal_flash_write(uint32_t address, const uint8_t *data, int len)
         } else {
             uint32_t val[2];
             uint8_t *vbytes = (uint8_t *)(val);
-            int off = (address + i) - (((address + i) >> 3) << 3);
-            uint32_t base_addr = address & (~0x07); /* aligned to 64 bit */
-            int u32_idx = (i >> 2);
+            uint32_t base_addr = (address + i) & ~0x7u; /* DW we touch */
+            int off = (address + i) & 0x7;              /* byte in DW */
             dst = (uint32_t *)(base_addr);
-            val[0] = dst[u32_idx];
-            val[1] = dst[u32_idx + 1];
+            val[0] = dst[0];
+            val[1] = dst[1];
             while ((off < 8) && (i < len))
                 vbytes[off++] = data[i++];
-            dst[u32_idx] = val[0];
-            dst[u32_idx + 1] = val[1];
+            flash_wait_complete();
+            dst[0] = val[0];
+            dst[1] = val[1];
             flash_wait_complete();
         }
     }
-    if ((FLASH_SR & FLASH_SR_EOP) == FLASH_SR_EOP)
-        FLASH_SR |= FLASH_SR_EOP;
+    /* W1C: assign directly; no RMW. Harmless if EOP isn't set. */
+    FLASH_SR = FLASH_SR_EOP;
     FLASH_CR &= ~FLASH_CR_PG;
     return 0;
 }
@@ -113,7 +116,7 @@ int RAMFUNCTION hal_flash_erase(uint32_t address, int len)
     if (len == 0)
         return -1;
     address -= FLASHMEM_ADDRESS_SPACE;
-    end_address = address + len - 1;
+    end_address = address + len;
     for (p = address; p < end_address; p += FLASH_PAGE_SIZE) {
         flash_wait_complete();
         flash_clear_errors();
@@ -258,7 +261,7 @@ void uart_write(const char *buf, unsigned int len)
     for (i = 0; i < len; i++) {
         while ((LPUART1_ISR & USART_ISR_TXE) == 0)
             ;
-        LPUART1_TDR = (uint32_t)buf[i];
+        LPUART1_TDR = (uint32_t)(uint8_t)buf[i];
     }
 }
 

hal/stm32g4.h

@@ -30,10 +30,12 @@
 
 #include <stdint.h>
 
-/* Assembly helpers */
-#define DMB() __asm__ volatile ("dmb")
-#define ISB() __asm__ volatile ("isb")
-#define DSB() __asm__ volatile ("dsb")
+/* Assembly helpers. The "memory" clobber tells the compiler not to
+ * reorder loads/stores across the barrier; without it the asm only
+ * orders hardware accesses, not the compiler's own scheduling. */
+#define DMB() __asm__ volatile ("dmb" ::: "memory")
+#define ISB() __asm__ volatile ("isb" ::: "memory")
+#define DSB() __asm__ volatile ("dsb" ::: "memory")
 
 
 /* -------- RCC (AHB1 + 0x1000 = 0x40021000) -------- RM0440 - 7.4 -------- */

hal/stm32g4.ld

@@ -16,7 +16,7 @@ SECTIONS
         _end_text = .;
     } > FLASH
 
-    .edidx :
+    .ARM.exidx :
     {
         . = ALIGN(4);
         *(.ARM.exidx*)