common/syscalls: Moved all the system calls implementations into thei…

…r own file

src/platforms/common/Makefile.inc

@@ -27,4 +27,5 @@ SRC += \
  usb.c \
  usb_serial.c \
  usb_dfu_stub.c \
- aux_serial.c
+ aux_serial.c \
+ syscalls.c

src/platforms/common/meson.build

@@ -37,6 +37,7 @@ platform_common_sources = files(
  'usb.c',
  'usb_dfu_stub.c',
  'usb_serial.c',
+ 'syscalls.c',
 )
 
 platform_common = declare_dependency(

src/platforms/common/syscalls.c

@@ -0,0 +1,192 @@
+/*
+ * This file is part of the Black Magic Debug project.
+ *
+ * Copyright (C) 2024 1BitSquared <[email protected]>
+ * Written by Rachel Mant <[email protected]>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "general.h"
+#include "platform.h"
+#include "usb_serial.h"
+#if ENABLE_DEBUG != 1
+#include <sys/stat.h>
+#include <string.h>
+
+typedef struct stat stat_s;
+#endif
+#include <errno.h>
+
+extern uint8_t heap_start;
+extern uint8_t heap_end;
+static uint8_t *heap_current = NULL;
+
+#if ENABLE_DEBUG == 1
+/*
+ * newlib defines _write as a weak link'd function for user code to override.
+ *
+ * This function forms the root of the implementation of a variety of functions
+ * that can write to stdout/stderr, including printf().
+ *
+ * The result of this function is the number of bytes written.
+ */
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) int _write(const int file, const void *const ptr, const size_t len)
+{
+ (void)file;
+#ifdef PLATFORM_HAS_DEBUG
+ if (debug_bmp)
+ return debug_serial_debug_write(ptr, len);
+#else
+ (void)ptr;
+#endif
+ return len;
+}
+
+/*
+ * newlib defines isatty as a weak link'd function for user code to override.
+ *
+ * The result of this function is always 'true'.
+ */
+__attribute__((used)) int isatty(const int file)
+{
+ (void)file;
+ return true;
+}
+
+#define RDI_SYS_OPEN 0x01U
+
+typedef struct ex_frame {
+ uint32_t r0;
+ const uint32_t *params;
+ uint32_t r2;
+ uint32_t r3;
+ uint32_t r12;
+ uintptr_t lr;
+ uintptr_t return_address;
+} ex_frame_s;
+
+/*
+ * This implements the other half of the newlib syscall puzzle.
+ * When newlib is built for ARM, various calls that do file IO
+ * such as printf end up calling [_swiwrite](https://github.com/mirror/newlib-cygwin/blob/master/newlib/libc/sys/arm/syscalls.c#L317)
+ * and other similar low-level implementation functions. These
+ * generate `swi` instructions for the "RDI Monitor" and that lands us.. here.
+ *
+ * The RDI calling convention sticks the file number in r0, the buffer pointer in r1, and length in r2.
+ * ARMv7-M's SWI (SVC) instruction then takes all that and maps it into an exception frame on the stack.
+ */
+void debug_monitor_handler(void)
+{
+ ex_frame_s *frame;
+ __asm__("mov %[frame], sp" : [frame] "=r"(frame));
+
+ /* Make sure to return to the instruction after the SWI/BKPT */
+ frame->return_address += 2U;
+
+ switch (frame->r0) {
+ case RDI_SYS_OPEN:
+ frame->r0 = 1;
+ break;
+ default:
+ frame->r0 = UINT32_MAX;
+ }
+ __asm__("bx lr");
+}
+#else
+/* This defines stubs for the newlib fake file IO layer for compatibility with GCC 12 `-specs=nosys.specs` */
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) int _write(const int file, const void *const buffer, const size_t length)
+{
+ (void)file;
+ (void)buffer;
+ return length;
+}
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) int _read(const int file, void *const buffer, const size_t length)
+{
+ (void)file;
+ (void)buffer;
+ return length;
+}
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) off_t _lseek(const int file, const off_t offset, const int direction)
+{
+ (void)file;
+ (void)offset;
+ (void)direction;
+ return 0;
+}
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) int _fstat(const int file, stat_s *stats)
+{
+ (void)file;
+ memset(stats, 0, sizeof(*stats));
+ return 0;
+}
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) int _isatty(const int file)
+{
+ (void)file;
+ return true;
+}
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) int _close(const int file)
+{
+ (void)file;
+ return 0;
+}
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) pid_t _getpid(void)
+{
+ return 1;
+}
+
+/* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
+__attribute__((used)) int _kill(const int pid, const int signal)
+{
+ (void)pid;
+ (void)signal;
+ return 0;
+}
+#endif
+
+__attribute__((used)) void *_sbrk(const ptrdiff_t alloc_size)
+{
+ /* If we've not yet made any heap allocations, set the heap pointer up */
+ if (heap_current == NULL)
+ heap_current = &heap_start;
+
+ /* Check if this allocation would exhaust the heap */
+ if (heap_current + alloc_size > &heap_end) {
+ errno = ENOMEM;
+ return (void *)-1;
+ }
+
+ /*
+ * Everything is ok, so make a copy of the heap pointer to return then add the
+ * allocation to the heap pointer
+ */
+ void *const result = heap_current;
+ heap_current += alloc_size;
+ return result;
+}