SBRK Wrapper

vcu118/Makefile

@@ -37,6 +37,7 @@ C_SRCS = init.c \
 				 wrap/puts.c \
 				 wrap/read.c \
 				 wrap/write.c \
+				 wrap/sbrk.c \
 			   xilinx/common/xbasic_types.c \
 				 xilinx/common/xil_io.c \
 				 xilinx/common/xil_assert.c \

vcu118/bsp.h

@@ -24,4 +24,8 @@
 #define XPAR_UARTNS550_1_BASEADDR (0x62340000ULL)
 #define XPAR_UARTNS550_1_CLOCK_HZ CPU_CLOCK_HZ
 
+static const volatile uint32_t* const PEX_MB = (uint32_t*)0x10080;
+static volatile uint32_t* const AP_MB = (uint32_t*)0x10090;
+static volatile uint32_t* const MB_IRQ = (uint32_t*)0x100a0;
+
 #endif /* RISCV_P1_BSP_H */

vcu118/wrap/sbrk.c

@@ -0,0 +1,47 @@
+#include <stdint.h>
+#include "bsp.h"
+
+#include "weak_under_alias.h"
+
+#define SBRK_REQ 1
+
+extern uintptr_t _heap_end;
+static void* program_break = &_heap_end;
+static const volatile uintptr_t sbrk_zero = 0;
+
+void* __wrap_sbrk(intptr_t increment)
+{
+  // If increment is zero, just return the fake program break
+  if (increment == 0)
+    return program_break;
+
+  // Ensure the new program break always aligns to pointer size
+  increment = (increment + sizeof(uintptr_t) - 1)/sizeof(uintptr_t)*sizeof(uintptr_t);
+
+  // Move the fake program break
+  AP_MB[1] = (uint32_t)program_break;
+  void* temp = program_break;
+  program_break += increment;
+  AP_MB[2] = (uint32_t)program_break;
+
+  if (increment > 0) {
+    // Interrupt the PEX to tell it the AP might want to allocate a new memory region
+    AP_MB[0] = SBRK_REQ;
+    uint32_t pex = PEX_MB[0];
+    *MB_IRQ = 1;
+    while (PEX_MB[0] == pex); // Wait for the PEX to finish processing the request
+  }
+
+  // Update tags for newly-allocated or deallocated memory
+  uintptr_t size = increment > 0 ? increment : -increment;
+  volatile uintptr_t* to_tag = (uintptr_t*)(increment > 0 ? temp : program_break);
+  for (intptr_t i = 0; i < size/sizeof(uintptr_t); i++)
+    to_tag[i] = sbrk_zero;
+
+  return temp;
+}
+
+void* __wrap__sbrk(intptr_t increment)
+{
+  return __wrap_sbrk(increment);
+}