Update mmu_get... and mmu_set... (esp8266#8290)

These changes are needed to address bugs that can emerge with the improved optimization from the GCC 10.3 compiler.

Updated performance inline functions `mmu_get_uint8()`, ... and `mmu_set_uint8()`, ...  to comply with strict-aliasing rules. 
Without this change, stale data may be referenced. This issue was revealed in discussions on esp8266#8261 (comment) 

Changes to avoid over-optimization of 32-bit wide transfers from IRAM, turning into 8-bit or 16-bit transfers by the new GCC 10.3 compiler. This has been a reoccurring/tricky problem for me with the new compiler. 

So far referencing the 32-bit value loaded by way of an Extended ASM R/W output register has stopped the compiler from optimizing down to an 8-bit or 16-bit transfer.

Example:
```cpp
  uint32_t val;
  __builtin_memcpy(&val, v32, sizeof(uint32_t));
  asm volatile ("" :"+r"(val)); // inject 32-bit dependency
  ...
```

Updated example `irammem.ino`
* do a simple test of compliance to strict-aliasing rules
* For `mmu_get_uint8()`, added tests to evaluate if 32-bit wide transfers were converted to an 8-bit transfer.

cores/esp8266/mmu_iram.h

@@ -26,13 +26,24 @@
 extern "C" {
 #endif
 
-//C This turns on range checking. Is this the value you want to trigger it?
+// This turns on range checking.
 #ifdef DEBUG_ESP_CORE
 #define DEBUG_ESP_MMU
 #endif
 
 #if defined(CORE_MOCK)
 #define ets_uart_printf(...) do {} while(false)
+#define XCHAL_INSTRAM0_VADDR		0x40000000
+#define XCHAL_INSTRAM1_VADDR		0x40100000
+#define XCHAL_INSTROM0_VADDR		0x40200000
+#else
+#include <sys/config.h> // For config/core-isa.h
+/*
+  Cautiously use XCHAL_..._VADDR values where possible.
+  While XCHAL_..._VADDR values in core-isa.h may define the Xtensa processor
+  CONFIG options, they are not always an indication of DRAM, IRAM, or ROM
+  size or position in the address space.
+*/
 #endif
 
 /*
@@ -71,32 +82,34 @@ DBG_MMU_FLUSH(0)
 
 static inline __attribute__((always_inline))
 bool mmu_is_iram(const void *addr) {
-  #define IRAM_START 0x40100000UL
+  const uintptr_t iram_start = (uintptr_t)XCHAL_INSTRAM1_VADDR;
 #ifndef MMU_IRAM_SIZE
 #if defined(__GNUC__) && !defined(CORE_MOCK)
   #warning "MMU_IRAM_SIZE was undefined, setting to 0x8000UL!"
 #endif
-  #define MMU_IRAM_SIZE 0x8000UL
+  #define MMU_IRAM_SIZE 0x8000ul
 #endif
-  #define IRAM_END (IRAM_START + MMU_IRAM_SIZE)
+  const uintptr_t iram_end = iram_start + MMU_IRAM_SIZE;
 
-  return (IRAM_START <= (uintptr_t)addr && IRAM_END > (uintptr_t)addr);
+  return (iram_start <= (uintptr_t)addr && iram_end > (uintptr_t)addr);
 }
 
 static inline __attribute__((always_inline))
 bool mmu_is_dram(const void *addr) {
-  #define DRAM_START 0x3FF80000UL
-  #define DRAM_END 0x40000000UL
+  const uintptr_t dram_start = 0x3FFE8000ul;
+  // The start of the Boot ROM sits at the end of DRAM. 0x40000000ul;
+  const uintptr_t dram_end = (uintptr_t)XCHAL_INSTRAM0_VADDR;
 
-  return (DRAM_START <= (uintptr_t)addr && DRAM_END > (uintptr_t)addr);
+  return (dram_start <= (uintptr_t)addr && dram_end > (uintptr_t)addr);
 }
 
 static inline __attribute__((always_inline))
 bool mmu_is_icache(const void *addr) {
-  #define ICACHE_START 0x40200000UL
-  #define ICACHE_END (ICACHE_START + 0x100000UL)
+  extern void _irom0_text_end(void);
+  const uintptr_t icache_start = (uintptr_t)XCHAL_INSTROM0_VADDR;
+  const uintptr_t icache_end = (uintptr_t)_irom0_text_end;
 
-  return (ICACHE_START <= (uintptr_t)addr && ICACHE_END > (uintptr_t)addr);
+  return (icache_start <= (uintptr_t)addr && icache_end > (uintptr_t)addr);
 }
 
 #ifdef DEBUG_ESP_MMU
@@ -127,90 +140,131 @@ bool mmu_is_icache(const void *addr) {
 static inline __attribute__((always_inline))
 uint8_t mmu_get_uint8(const void *p8) {
   ASSERT_RANGE_TEST_READ(p8);
-  uint32_t val = (*(uint32_t *)((uintptr_t)p8 & ~0x3));
-  uint32_t pos = ((uintptr_t)p8 & 0x3) * 8;
+  // https://gist.github.com/shafik/848ae25ee209f698763cffee272a58f8#how-do-we-type-pun-correctly
+  // Comply with strict-aliasing rules. Using memcpy is a Standards suggested
+  // method for type punning. The compiler optimizer will replace the memcpy
+  // with an `l32i` instruction.  Using __builtin_memcpy to ensure we get the
+  // effects of the compiler optimization and not some #define version of
+  // memcpy.
+  void *v32 = (void *)((uintptr_t)p8 & ~(uintptr_t)3u);
+  uint32_t val;
+  __builtin_memcpy(&val, v32, sizeof(uint32_t));
+  // Use an empty ASM to reference the 32-bit value. This will block the
+  // compiler from immediately optimizing to an 8-bit or 16-bit load instruction
+  // against IRAM memory. (This approach was inspired by
+  // https://github.com/esp8266/Arduino/pull/7780#discussion_r548303374)
+  // This issue was seen when using a constant address with the GCC 10.3
+  // compiler.
+  // As a general practice, I think referencing by way of Extended ASM R/W
+  // output register will stop the the compiler from reloading the value later
+  // as 8-bit load from IRAM.
+  asm volatile ("" :"+r"(val)); // inject 32-bit dependency
+  uint32_t pos = ((uintptr_t)p8 & 3u) * 8u;
   val >>= pos;
   return (uint8_t)val;
 }
 
 static inline __attribute__((always_inline))
 uint16_t mmu_get_uint16(const uint16_t *p16) {
   ASSERT_RANGE_TEST_READ(p16);
-  uint32_t val = (*(uint32_t *)((uintptr_t)p16 & ~0x3));
-  uint32_t pos = ((uintptr_t)p16 & 0x3) * 8;
+  void *v32 = (void *)((uintptr_t)p16 & ~(uintptr_t)0x3u);
+  uint32_t val;
+  __builtin_memcpy(&val, v32, sizeof(uint32_t));
+  asm volatile ("" :"+r"(val));
+  uint32_t pos = ((uintptr_t)p16 & 3u) * 8u;
   val >>= pos;
   return (uint16_t)val;
 }
 
 static inline __attribute__((always_inline))
 int16_t mmu_get_int16(const int16_t *p16) {
   ASSERT_RANGE_TEST_READ(p16);
-  uint32_t val = (*(uint32_t *)((uintptr_t)p16 & ~0x3));
-  uint32_t pos = ((uintptr_t)p16 & 0x3) * 8;
+  void *v32 = (void *)((uintptr_t)p16 & ~(uintptr_t)3u);
+  uint32_t val;
+  __builtin_memcpy(&val, v32, sizeof(uint32_t));
+  asm volatile ("" :"+r"(val));
+  uint32_t pos = ((uintptr_t)p16 & 3u) * 8u;
   val >>= pos;
   return (int16_t)val;
 }
 
 static inline __attribute__((always_inline))
 uint8_t mmu_set_uint8(void *p8, const uint8_t val) {
   ASSERT_RANGE_TEST_WRITE(p8);
-  uint32_t pos = ((uintptr_t)p8 & 0x3) * 8;
+  uint32_t pos = ((uintptr_t)p8 & 3u) * 8u;
   uint32_t sval = val << pos;
-  uint32_t valmask =  0x0FF << pos;
+  uint32_t valmask =  0x0FFu << pos;
+
+  void *v32 = (void *)((uintptr_t)p8 & ~(uintptr_t)3u);
+  uint32_t ival;
+  __builtin_memcpy(&ival, v32, sizeof(uint32_t));
+  asm volatile ("" :"+r"(ival));
 
-  uint32_t *p32 = (uint32_t *)((uintptr_t)p8 & ~0x3);
-  uint32_t ival = *p32;
   ival &= (~valmask);
   ival |= sval;
-  *p32 = ival;
+  /*
+    This 32-bit dependency injection does not appear to be needed with the
+    current GCC 10.3; however, that could change in the future versions. Or, I
+    may not have the right test for it to fail.
+  */
+  asm volatile ("" :"+r"(ival));
+  __builtin_memcpy(v32, &ival, sizeof(uint32_t));
   return val;
 }
 
 static inline __attribute__((always_inline))
 uint16_t mmu_set_uint16(uint16_t *p16, const uint16_t val) {
   ASSERT_RANGE_TEST_WRITE(p16);
-  uint32_t pos = ((uintptr_t)p16 & 0x3) * 8;
+  uint32_t pos = ((uintptr_t)p16 & 3u) * 8u;
   uint32_t sval = val << pos;
-  uint32_t valmask =  0x0FFFF << pos;
+  uint32_t valmask =  0x0FFFFu << pos;
+
+  void *v32 = (void *)((uintptr_t)p16 & ~(uintptr_t)3u);
+  uint32_t ival;
+  __builtin_memcpy(&ival, v32, sizeof(uint32_t));
+  asm volatile ("" :"+r"(ival));
 
-  uint32_t *p32 = (uint32_t *)((uintptr_t)p16 & ~0x3);
-  uint32_t ival = *p32;
   ival &= (~valmask);
   ival |= sval;
-  *p32 = ival;
+  asm volatile ("" :"+r"(ival));
+  __builtin_memcpy(v32, &ival, sizeof(uint32_t));
   return val;
 }
 
 static inline __attribute__((always_inline))
 int16_t mmu_set_int16(int16_t *p16, const int16_t val) {
   ASSERT_RANGE_TEST_WRITE(p16);
   uint32_t sval = (uint16_t)val;
-  uint32_t pos = ((uintptr_t)p16 & 0x3) * 8;
+  uint32_t pos = ((uintptr_t)p16 & 3u) * 8u;
   sval <<= pos;
-  uint32_t valmask =  0x0FFFF << pos;
+  uint32_t valmask =  0x0FFFFu << pos;
+
+  void *v32 = (void *)((uintptr_t)p16 & ~(uintptr_t)3u);
+  uint32_t ival;
+  __builtin_memcpy(&ival, v32, sizeof(uint32_t));
+  asm volatile ("" :"+r"(ival));
 
-  uint32_t *p32 = (uint32_t *)((uintptr_t)p16 & ~0x3);
-  uint32_t ival = *p32;
   ival &= (~valmask);
   ival |= sval;
-  *p32 = ival;
+  asm volatile ("" :"+r"(ival));
+  __builtin_memcpy(v32, &ival, sizeof(uint32_t));
   return val;
 }
 
 #if (MMU_IRAM_SIZE > 32*1024) && !defined(MMU_SEC_HEAP)
-extern void _text_end(void);
 #define MMU_SEC_HEAP mmu_sec_heap()
 #define MMU_SEC_HEAP_SIZE mmu_sec_heap_size()
 
 static inline __attribute__((always_inline))
 void *mmu_sec_heap(void) {
-  uint32_t sec_heap = (uint32_t)_text_end + 32;
-  return (void *)(sec_heap &= ~7);
+  extern void _text_end(void);
+  uintptr_t sec_heap = (uintptr_t)_text_end + (uintptr_t)32u;
+  return (void *)(sec_heap &= ~(uintptr_t)7u);
 }
 
 static inline __attribute__((always_inline))
 size_t mmu_sec_heap_size(void) {
-  return (size_t)0xC000UL - ((size_t)mmu_sec_heap() - 0x40100000UL);
+  return (size_t)0xC000ul - ((uintptr_t)mmu_sec_heap() - (uintptr_t)XCHAL_INSTRAM1_VADDR);
 }
 #endif
 

libraries/esp8266/examples/IramReserve/IramReserve.ino

@@ -17,6 +17,12 @@
 #include <umm_malloc/umm_malloc.h>
 #if defined(UMM_HEAP_IRAM)
 
+#if defined(CORE_MOCK)
+#define XCHAL_INSTRAM1_VADDR		0x40100000
+#else
+#include <sys/config.h> // For config/core-isa.h
+#endif
+
 // durable - as in long life, persisting across reboots.
 struct durable {
   uint32_t bootCounter;
@@ -30,7 +36,7 @@ struct durable {
 #define IRAM_RESERVE_SZ ((sizeof(struct durable) + 7UL) & ~7UL)
 
 // Position its address just above the reduced 2nd Heap.
-#define IRAM_RESERVE (0x40100000UL + 0xC000UL - IRAM_RESERVE_SZ)
+#define IRAM_RESERVE ((uintptr_t)XCHAL_INSTRAM1_VADDR + 0xC000UL - IRAM_RESERVE_SZ)
 
 // Define a reference with the right properties to make access easier.
 #define DURABLE ((struct durable *)IRAM_RESERVE)
@@ -100,9 +106,9 @@ extern "C" void umm_init_iram(void) {
     adjustments and checksums. These can affect the persistence of data across
     reboots.
   */
-  uint32_t sec_heap = (uint32_t)_text_end + 32;
+  uintptr_t sec_heap = (uintptr_t)_text_end + 32;
   sec_heap &= ~7;
-  size_t sec_heap_sz = 0xC000UL - (sec_heap - 0x40100000UL);
+  size_t sec_heap_sz = 0xC000UL - (sec_heap - (uintptr_t)XCHAL_INSTRAM1_VADDR);
   sec_heap_sz -= IRAM_RESERVE_SZ; // Shrink IRAM heap
   if (0xC000UL > sec_heap_sz) {
 

libraries/esp8266/examples/MMU48K/MMU48K.ino

@@ -3,6 +3,12 @@
 #include <umm_malloc/umm_malloc.h>
 #include <umm_malloc/umm_heap_select.h>
 
+#if defined(CORE_MOCK)
+#define XCHAL_INSTRAM1_VADDR		0x40100000
+#else
+#include <sys/config.h> // For config/core-isa.h
+#endif
+
 uint32_t timed_byte_read(char *pc, uint32_t * o);
 uint32_t timed_byte_read2(char *pc, uint32_t * o);
 int divideA_B(int a, int b);
@@ -102,7 +108,7 @@ void print_mmu_status(Print& oStream) {
 #ifdef MMU_IRAM_SIZE
   oStream.printf_P(PSTR("  IRAM Size:               %u"), MMU_IRAM_SIZE);
   oStream.println();
-  const uint32_t iram_free = MMU_IRAM_SIZE - (uint32_t)((uintptr_t)_text_end - 0x40100000UL);
+  const uint32_t iram_free = MMU_IRAM_SIZE - (uint32_t)((uintptr_t)_text_end - (uintptr_t)XCHAL_INSTRAM1_VADDR);
   oStream.printf_P(PSTR("  IRAM free:               %u"), iram_free);
   oStream.println();
 #endif