[PATCH 2/2] lib: utils/serial: add semihosting support
Kautuk Consul
kconsul at ventanamicro.com
Thu Sep 8 01:42:39 PDT 2022
We add RISC-V semihosting based serial console for JTAG based early
debugging.
The RISC-V semihosting specification is available at:
https://github.com/riscv/riscv-semihosting-spec/blob/main/riscv-semihosting-spec.adoc
Signed-off-by: Anup Patel <apatel at ventanamicro.com>
Signed-off-by: Kautuk Consul <kconsul at ventanamicro.com>
---
include/sbi_utils/serial/semihosting.h | 47 +++++++
lib/utils/serial/Kconfig | 4 +
lib/utils/serial/objects.mk | 1 +
lib/utils/serial/semihosting.c | 176 +++++++++++++++++++++++++
platform/generic/configs/defconfig | 1 +
platform/generic/platform.c | 11 +-
6 files changed, 239 insertions(+), 1 deletion(-)
create mode 100644 include/sbi_utils/serial/semihosting.h
create mode 100644 lib/utils/serial/semihosting.c
diff --git a/include/sbi_utils/serial/semihosting.h b/include/sbi_utils/serial/semihosting.h
new file mode 100644
index 0000000..8cc4a86
--- /dev/null
+++ b/include/sbi_utils/serial/semihosting.h
@@ -0,0 +1,47 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2022 Ventana Micro Systems Inc.
+ *
+ * Authors:
+ * Anup Patel <apatel at ventanamicro.com>
+ * Kautuk Consul <kconsul at ventanamicro.com>
+ */
+
+#ifndef __SERIAL_SEMIHOSTING_H__
+#define __SERIAL_SEMIHOSTING_H__
+
+#include <sbi/sbi_types.h>
+
+/**
+ * enum semihosting_open_mode - Numeric file modes for use with semihosting_open()
+ * MODE_READ: 'r'
+ * MODE_BINARY: 'b'
+ * MODE_PLUS: '+'
+ * MODE_WRITE: 'w'
+ * MODE_APPEND: 'a'
+ *
+ * These modes represent the mode string used by fopen(3) in a form which can
+ * be passed to semihosting_open(). These do NOT correspond directly to %O_RDONLY,
+ * %O_CREAT, etc; see fopen(3) for details. In particular, @MODE_PLUS
+ * effectively results in adding %O_RDWR, and @MODE_WRITE will add %O_TRUNC.
+ * For compatibility, @MODE_BINARY should be added when opening non-text files
+ * (such as images).
+ */
+enum semihosting_open_mode {
+ MODE_READ = 0x0,
+ MODE_BINARY = 0x1,
+ MODE_PLUS = 0x2,
+ MODE_WRITE = 0x4,
+ MODE_APPEND = 0x8,
+};
+
+#ifdef CONFIG_SERIAL_SEMIHOSTING
+int semihosting_init(void);
+int semihosting_enabled(void);
+#else
+static inline int semihosting_init(void) { return SBI_ENODEV; }
+static inline int semihosting_enabled(void) { return 0; }
+#endif
+
+#endif
diff --git a/lib/utils/serial/Kconfig b/lib/utils/serial/Kconfig
index 6e425f2..da549a7 100644
--- a/lib/utils/serial/Kconfig
+++ b/lib/utils/serial/Kconfig
@@ -79,4 +79,8 @@ config SERIAL_XILINX_UARTLITE
bool "Xilinx UART Lite support"
default n
+config SERIAL_SEMIHOSTING
+ bool "Semihosting support"
+ default n
+
endmenu
diff --git a/lib/utils/serial/objects.mk b/lib/utils/serial/objects.mk
index efb1d9e..98f3f9a 100644
--- a/lib/utils/serial/objects.mk
+++ b/lib/utils/serial/objects.mk
@@ -41,3 +41,4 @@ libsbiutils-objs-$(CONFIG_SERIAL_SIFIVE) += serial/sifive-uart.o
libsbiutils-objs-$(CONFIG_SERIAL_LITEX) += serial/litex-uart.o
libsbiutils-objs-$(CONFIG_SERIAL_UART8250) += serial/uart8250.o
libsbiutils-objs-$(CONFIG_SERIAL_XILINX_UARTLITE) += serial/xlnx-uartlite.o
+libsbiutils-objs-$(CONFIG_SERIAL_SEMIHOSTING) += serial/semihosting.o
diff --git a/lib/utils/serial/semihosting.c b/lib/utils/serial/semihosting.c
new file mode 100644
index 0000000..aa1bb16
--- /dev/null
+++ b/lib/utils/serial/semihosting.c
@@ -0,0 +1,176 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2022 Ventana Micro Systems Inc.
+ *
+ * Authors:
+ * Anup Patel <apatel at ventanamicro.com>
+ * Kautuk Consul <kconsul at ventanamicro.com>
+ */
+
+#include <sbi/sbi_console.h>
+#include <limits.h>
+#include <sbi/sbi_string.h>
+#include <sbi/sbi_error.h>
+#include <sbi_utils/serial/semihosting.h>
+
+#define SYSOPEN 0x01
+#define SYSWRITEC 0x03
+#define SYSREAD 0x06
+#define SYSREADC 0x07
+#define SYSERRNO 0x13
+
+/*
+ * Note: This function is intentionally noinline and 256 bytes aligned to
+ * ensure that semihosting instruction sequence is within same 4K page.
+ */
+static __noinline __aligned(256) long semihosting_trap(int sysnum, void *addr)
+{
+ register int ret asm ("a0") = sysnum;
+ register void *param0 asm ("a1") = addr;
+
+ asm volatile (
+ "\t.option push\n"
+ "\t.option norvc\n"
+ "\tslli zero, zero, 0x1f\n"
+ "\tebreak\n"
+ "\tsrai zero, zero, 7\n"
+ "\t.option pop\n"
+ : "+r" (ret) : "r" (param0) : "memory");
+
+ return ret;
+}
+
+static bool _semihosting_enabled = true;
+static bool try_semihosting = true;
+
+bool __aligned(256) semihosting_enabled(void)
+{
+ register int ret asm ("a0") = SYSERRNO;
+ register void *param0 asm ("a1") = NULL;
+ unsigned long tmp = 0;
+
+ if (!try_semihosting)
+ return _semihosting_enabled;
+
+ asm volatile (
+ "\t.option push\n"
+ "\t.option norvc\n"
+
+ "\tj _semihost_test_vector_next\n"
+ "\t.align 4\n"
+ "\t_semihost_test_vector:\n"
+ "\t\tcsrr %[en], mepc\n"
+ "\t\taddi %[en], %[en], 4\n"
+ "\t\tcsrw mepc, %[en]\n"
+ "\t\tadd %[en], zero, zero\n"
+ "\t\tmret\n"
+ "\t_semihost_test_vector_next:\n"
+
+ "\tla %[tmp], _semihost_test_vector\n"
+ "\tcsrrw %[tmp], mtvec, %[tmp]\n"
+ "\tslli zero, zero, 0x1f\n"
+ "\tebreak\n"
+ "\tsrai zero, zero, 7\n"
+ "\tcsrw mtvec, %[tmp]\n"
+
+ "\t.option pop\n"
+ : [tmp] "+r" (tmp), [en] "+r" (_semihosting_enabled),
+ [ret] "+r" (ret)
+ : "r" (param0) : "memory");
+
+ try_semihosting = false;
+ return _semihosting_enabled;
+}
+
+static int semihosting_errno(void)
+{
+ long ret = semihosting_trap(SYSERRNO, NULL);
+
+ if (ret > 0 && ret < INT_MAX)
+ return -ret;
+ return SBI_EIO;
+}
+
+static int infd = SBI_ENODEV;
+
+static long semihosting_open(const char *fname, enum semihosting_open_mode mode)
+{
+ long fd;
+ struct semihosting_open_s {
+ const char *fname;
+ unsigned long mode;
+ size_t len;
+ } open;
+
+ open.fname = fname;
+ open.len = sbi_strlen(fname);
+ open.mode = mode;
+
+ /* Open the file on the host */
+ fd = semihosting_trap(SYSOPEN, &open);
+ if (fd == -1)
+ return semihosting_errno();
+ return fd;
+}
+
+/**
+ * struct semihosting_rdwr_s - Arguments for read and write
+ * @fd: A file descriptor returned from semihosting_open()
+ * @memp: Pointer to a buffer of memory of at least @len bytes
+ * @len: The number of bytes to read or write
+ */
+struct semihosting_rdwr_s {
+ long fd;
+ void *memp;
+ size_t len;
+};
+
+static long semihosting_read(long fd, void *memp, size_t len)
+{
+ long ret;
+ struct semihosting_rdwr_s read;
+
+ read.fd = fd;
+ read.memp = memp;
+ read.len = len;
+
+ ret = semihosting_trap(SYSREAD, &read);
+ if (ret < 0)
+ return semihosting_errno();
+ return len - ret;
+}
+
+/* clang-format on */
+
+static void semihosting_putc(char ch)
+{
+ semihosting_trap(SYSWRITEC, &ch);
+}
+
+static int semihosting_getc(void)
+{
+ char ch = 0;
+
+ if (infd < 0)
+ return semihosting_trap(SYSREADC, NULL);
+
+ semihosting_read(infd, &ch, sizeof(ch));
+
+ return ch;
+}
+
+static struct sbi_console_device semihosting_console = {
+ .name = "semihosting",
+ .console_putc = semihosting_putc,
+ .console_getc = semihosting_getc
+};
+
+int semihosting_init(void)
+{
+ infd = semihosting_open(":tt", MODE_READ);
+
+ sbi_console_set_device(&semihosting_console);
+
+ return 0;
+}
diff --git a/platform/generic/configs/defconfig b/platform/generic/configs/defconfig
index e324173..c95b7fa 100644
--- a/platform/generic/configs/defconfig
+++ b/platform/generic/configs/defconfig
@@ -28,3 +28,4 @@ CONFIG_FDT_SERIAL_UART8250=y
CONFIG_FDT_SERIAL_XILINX_UARTLITE=y
CONFIG_FDT_TIMER=y
CONFIG_FDT_TIMER_MTIMER=y
+CONFIG_SERIAL_SEMIHOSTING=y
diff --git a/platform/generic/platform.c b/platform/generic/platform.c
index cc3620f..bf51aba 100644
--- a/platform/generic/platform.c
+++ b/platform/generic/platform.c
@@ -23,6 +23,7 @@
#include <sbi_utils/timer/fdt_timer.h>
#include <sbi_utils/ipi/fdt_ipi.h>
#include <sbi_utils/reset/fdt_reset.h>
+#include <sbi_utils/serial/semihosting.h>
/* List of platform override modules generated at compile time */
extern const struct platform_override *platform_override_modules[];
@@ -242,6 +243,14 @@ static uint64_t generic_pmu_xlate_to_mhpmevent(uint32_t event_idx,
return evt_val;
}
+static int generic_console_init(void)
+{
+ if (semihosting_enabled())
+ return semihosting_init();
+ else
+ return fdt_serial_init();
+}
+
const struct sbi_platform_operations platform_ops = {
.nascent_init = generic_nascent_init,
.early_init = generic_early_init,
@@ -249,7 +258,7 @@ const struct sbi_platform_operations platform_ops = {
.early_exit = generic_early_exit,
.final_exit = generic_final_exit,
.domains_init = generic_domains_init,
- .console_init = fdt_serial_init,
+ .console_init = generic_console_init,
.irqchip_init = fdt_irqchip_init,
.irqchip_exit = fdt_irqchip_exit,
.ipi_init = fdt_ipi_init,
--
2.34.1
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