evalsoc: add Zcmt table jump example for rompatch similiar case (#21)

Signed-off-by: Huaqi Fang <[email protected]>

evalsoc/zcmt_jumptable/Makefile

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+TARGET = jmp
+
+NUCLEI_SDK_ROOT = ../../..
+
+CORE ?= n300
+
+ARCH_EXT ?= _zca_zcb_zcmp_zcmt
+
+SRCDIRS = .
+
+INCDIRS = .
+
+COMMON_FLAGS := -O3
+
+include $(NUCLEI_SDK_ROOT)/Build/Makefile.base

evalsoc/zcmt_jumptable/README.md

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+# RISC-V Zcmt Jump Table Example For Nuclei SDK
+
+This example is used to demostrate how to use Zcmt extension to implement
+runtime jump function replacement, so you can do hotfix for certain functions.
+
+## Run in command line
+
+You need to download Nuclei SDK >= 0.5.0 version.
+
+~~~shell
+cd /path/to/nuclei-sdk
+cd nuclei-board-labs/evalsoc/zcmt_jumptable
+# build it
+# Assume environment is already setup, see https://doc.nucleisys.com/nuclei_sdk/quickstart.html
+# Require Nuclei Studio 2023.10
+make all
+# run on qemu
+make run_qemu
+# run on hw
+# require N300 with Zc extension bitstream
+make upload
+~~~
+
+## Run in Nuclei Studio
+
+> Nuclei Studio >= 2023.10 is required
+

evalsoc/zcmt_jumptable/main.c

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+#include "nuclei_sdk_hal.h"
+#include <stdio.h>
+
+// used for jump table index < 32, cm.jt
+// https://github.com/riscv/riscv-code-size-reduction/blob/main/Zc-specification/cm_jt.adoc
+void __attribute__ ((naked)) zcmt_cmjt(void)
+{
+    asm volatile("cm.jt 0 \n");
+}
+
+// used for jump table index >= 32, cm.jalt
+// https://github.com/riscv/riscv-code-size-reduction/blob/main/Zc-specification/cm_jalt.adoc
+void __attribute__ ((naked)) zcmt_cmjalt(void)
+{
+#if __riscv_xlen == 32
+    asm volatile(
+            "add sp,sp,-4\n"
+            "sw ra,0(sp) \n"
+            "cm.jalt 255 \n"
+            "lw ra,0(sp) \n"
+            "add sp,sp,4\n"
+            "ret");
+#else
+    asm volatile(
+            "add sp,sp,-8\n"
+            "sd ra,0(sp) \n"
+            "cm.jalt 255 \n"
+            "ld ra,0(sp) \n"
+            "add sp,sp,8\n"
+            "ret");
+#endif
+}
+
+// Test func 1
+void abc()
+{
+    printf("hello from abc\n");
+}
+
+// Test func 2
+void cdf()
+{
+    printf("hello from cdf\n");
+}
+
+// Need to align at 64bytes, required by jvt csr
+// The value in the BASE field must always be aligned on a 64-byte boundary. see https://github.com/riscv/riscv-code-size-reduction/blob/main/Zc-specification/jvt_csr.adoc
+// For this encoding to decode as cm.jalt, index>=32, otherwise it decodes as cm.jt
+// max entries are 0-255, total 256 entries
+// TODO jump table need to place in a ram where cpu instruction fetch unit and data acess unit can both access it
+static unsigned long jptbl[256] __ALIGNED(64) = {};
+
+unsigned long update_jump_table(unsigned long index, unsigned long funptr)
+{
+    unsigned long *tbptr = (unsigned long *)__RV_CSR_READ(CSR_JVT);
+
+    if (tbptr != jptbl) {
+        printf("jump table not match!\n");
+        return 1;
+    }
+    tbptr[index] = funptr;
+    // fence.i is required to flush cache if cache present
+    __FENCE_I();
+}
+
+// NOTE: About Zcmt table jump, see https://github.com/riscv/riscv-code-size-reduction/blob/main/Zc-specification/tablejump.adoc
+void main(void)
+{
+    __RV_CSR_WRITE(CSR_JVT, jptbl);
+
+    printf("Jump table located in 0x%x\n", __RV_CSR_READ(CSR_JVT));
+
+    printf("--> Test cm.jt instruction!\n");
+    // let cm.jt jump to abc
+    update_jump_table(0, (unsigned long)abc);
+    // before execute this function the jump table must be initialized
+    zcmt_cmjt();
+
+    // let cm.jt jump to cdf
+    update_jump_table(0, (unsigned long)cdf);
+    zcmt_cmjt();
+
+    printf("--> Test cm.jalt instruction!\n");
+    // let cm.jalt jump to abc
+    update_jump_table(255, (unsigned long)abc);
+    zcmt_cmjalt();
+
+    // let cm.jalt jump to cdf
+    update_jump_table(255, (unsigned long)cdf);
+    zcmt_cmjalt();
+}

evalsoc/zcmt_jumptable/npk.yml

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+## Package Base Information
+name: app_evalsoc_zcmt_jumptable
+owner: nuclei
+version: 1.0.0
+description: Nuclei Zcmt Jump Table Demo
+type: app
+keywords:
+  - nuclei board labs
+  - baremetal
+  - jump table
+category: Board Labs
+license: Apache-2.0
+homepage: https://github.com/Nuclei-Software/nuclei-board-labs/tree/master/evalsoc/zcmt_jumptable
+
+## Package Dependency
+dependencies:
+  - name: ssp-nsdk_evalsoc
+    owner: nuclei
+    version:
+
+## Package Configurations
+configuration:
+  app_commonflags:
+    value: -O3
+    type: text
+    description: Application Compile Flags
+
+setconfig:
+  - config: nuclei_core
+    value: n300
+  - config: nuclei_archext
+    value: _zca_zcb_zcmp_zcmt
+
+## Source Code Management
+codemanage:
+  copyfiles:
+    - path: ["*.c", "*.h", "*.S", "*.s", "*.C"]
+  incdirs:
+    - path: ["./"]
+  libdirs:
+  ldlibs:
+    - libs: [""]
+
+## Build Configuration
+buildconfig:
+  - type: common
+    common_flags: # flags need to be combined together across all packages
+      - flags: ${app_commonflags}
+    ldflags:
+    cflags:
+    asmflags:
+    cxxflags:
+    prebuild_steps: # could be override by app/bsp type
+      command:
+      description:
+    postbuild_steps: # could be override by app/bsp type
+      command:
+      description: