Fix issue with -Os compilation

You get the following problem when using `-Os`:

          = note: rust-lld: error: undefined symbol: __gnu_thumb1_case_uhi
                  >>> referenced by DAP.c:1653 (CMSIS_5/CMSIS/DAP/Firmware/Source/DAP.c:1653)
                  >>>               DAP.o:(DAP_ProcessCommand) in archive /tmp/rustctmyFes/librp2040_selfdebug-254aa1d1b314f83f
        .rlib

                  rust-lld: error: undefined symbol: __gnu_thumb1_case_uqi
                  >>> referenced by DAP.c:90 (CMSIS_5/CMSIS/DAP/Firmware/Source/DAP.c:90)
                  >>>               DAP.o:(DAP_ProcessCommand) in archive /tmp/rustctmyFes/librp2040_selfdebug-254aa1d1b314f83f
        .rlib

                  rust-lld: error: undefined symbol: strcpy
                  >>> referenced by DAP_config.h:201 (CMSIS_Config/DAP_config.h:201)
                  >>>               DAP.o:(DAP_ProcessCommand) in archive /tmp/rustctmyFes/librp2040_selfdebug-254aa1d1b314f83f
        .rlib
                  >>> referenced by DAP_config.h:218 (CMSIS_Config/DAP_config.h:218)
                  >>>               DAP.o:(DAP_ProcessCommand) in archive /tmp/rustctmyFes/librp2040_selfdebug-254aa1d1b314f83f
        .rlib
                  >>> referenced by DAP_config.h:235 (CMSIS_Config/DAP_config.h:235)
                  >>>               DAP.o:(DAP_ProcessCommand) in archive /tmp/rustctmyFes/librp2040_selfdebug-254aa1d1b314f83f
        .rlib
                  >>> referenced 1 more times

- This fixes the issue of `strcpy` by just using `memcpy`
- This fixes the issue of __gnu_thumb1_case_uhi/__gnu_thumb1_case_uqi
  which are defined in `libgcc.a` by adding the libgcc path to the
  linker search path, you might optionally need to add

          "-C", "link-args=-lgcc"

  to your .cargo/config.toml

  - We are not using `cargo:rustc-link-lib=static:+verbatim={}`
    as that had problems with libgcc being doubly-linked so there being
    duplicate symbols.

CMSIS_Config/DAP_config.h

@@ -198,8 +198,8 @@ __STATIC_INLINE uint8_t DAP_GetTargetDeviceVendorString (char *str) {
 #if TARGET_FIXED != 0
   uint8_t len;
 
-  strcpy(str, TargetDeviceVendor);
-  len = (uint8_t)(strlen(TargetDeviceVendor) + 1U);
+  len = (uint8_t)sizeof(TargetDeviceVendor);
+  memcpy(str, TargetDeviceVendor, len);
   return (len);
 #else
   (void)str;
@@ -215,8 +215,8 @@ __STATIC_INLINE uint8_t DAP_GetTargetDeviceNameString (char *str) {
 #if TARGET_FIXED != 0
   uint8_t len;
 
-  strcpy(str, TargetDeviceName);
-  len = (uint8_t)(strlen(TargetDeviceName) + 1U);
+  len = (uint8_t)sizeof(TargetDeviceName);
+  memcpy(str, TargetDeviceName, len);
   return (len);
 #else
   (void)str;
@@ -232,8 +232,8 @@ __STATIC_INLINE uint8_t DAP_GetTargetBoardVendorString (char *str) {
 #if TARGET_FIXED != 0
   uint8_t len;
 
-  strcpy(str, TargetBoardVendor);
-  len = (uint8_t)(strlen(TargetBoardVendor) + 1U);
+  len = (uint8_t)sizeof(TargetBoardVendor);
+  memcpy(str, TargetBoardVendor, len);
   return (len);
 #else
   (void)str;
@@ -249,8 +249,8 @@ __STATIC_INLINE uint8_t DAP_GetTargetBoardNameString (char *str) {
 #if TARGET_FIXED != 0
   uint8_t len;
 
-  strcpy(str, TargetBoardName);
-  len = (uint8_t)(strlen(TargetBoardName) + 1U);
+  len = (uint8_t)sizeof(TargetBoardName);
+  memcpy(str, TargetBoardName, len);
   return (len);
 #else
   (void)str;

README.md

@@ -49,6 +49,32 @@ If you want to configure something else (see the file
 [CMSIS_Config/DAP_config.h](CMSIS_Config/DAP_config.h) for more configuration
 options), feel free to make a PR, or just use this repository as an example.
 
+## Known problems
+### `rust-lld: error: undefined symbol: __gnu_thumb1_case_uhi`
+The issue here is that with the `-Os` optimisation GCC is using a "compact
+switch" which requires helper functions/tables
+(https://chromium.googlesource.com/chromiumos/platform/ec/+/refs/heads/master/core/cortex-m0/thumb_case.S),
+but `libgcc.a` isn't getting linked. To combat this, the `libgcc.a` directory
+is added to the linker search paths (see [build.rs](build.rs)) but you have to
+add `-lgcc` to your linker, e.g. put the following into `.cargo/config.toml`
+
+```diff
+@@ -1,11 +1,12 @@
+ [target.'cfg(all(target_arch = "arm", target_os = "none"))']
+ # runner = "elf2uf2-rs -d"
+ runner = "probe-rs run --chip RP2040 --probe 2E8A:000C"
+
+ rustflags = [
+   "-C", "link-arg=-Tlink.x",
+   "-C", "link-arg=-Tdefmt.x",
++  "-C", "link-args=-lgcc"
+ ]
+
+ [build]
+ target = "thumbv6m-none-eabi"
+```
+
+
 ## TODOs
 - Test flashing core-1 apps. This might require compiling two separate
   binaries, the CMSIS-DAP one first, and then the core 1 application, linked

build.rs

@@ -12,6 +12,7 @@ use std::env;
 use std::fs::File;
 use std::io::Write;
 use std::path::PathBuf;
+use std::process::Command;
 
 fn main() {
     // Put `memory.x` in our output directory and ensure it's
@@ -36,9 +37,9 @@ fn main() {
     // -- This value is used to calculate the SWD/JTAG clock speed.
     // -- (Specifies the CPU Clock in Hz.)
     let cpu_clock = match env::var("CARGO_CFG_CMSIS_DAP_CPU_CLOCK") {
-        Ok(s) => s
-            .parse()
-            .expect("Rustc cfg CMSIS_DAP_CPU_CLOCK cannot be parsed as a u32 integer"),
+        Ok(s) => s.parse().expect(
+            "Rustc cfg CMSIS_DAP_CPU_CLOCK cannot be parsed as a u32 integer",
+        ),
         Err(env::VarError::NotPresent) => 120_000_000u32,
         Err(env::VarError::NotUnicode(os_str)) => {
             panic!("Rustc cfg CMSIS_DAP_CPU_CLOCK not unicode: {:?}", os_str)
@@ -95,7 +96,8 @@ fn main() {
     }
 
     // - Building the CMSIS DAP library
-    cc::Build::new()
+    let mut cmsis_dap_build = cc::Build::new();
+    cmsis_dap_build
         .compiler("arm-none-eabi-gcc")
         .file("CMSIS_5/CMSIS/DAP/Firmware/Source/DAP.c")
         .file("CMSIS_5/CMSIS/DAP/Firmware/Source/SW_DP.c")
@@ -105,8 +107,21 @@ fn main() {
             dap_default_swj_clock.to_string().as_ref(),
         )
         .define("DAP_PACKET_COUNT", dap_packet_count.to_string().as_ref())
-        .includes(includes)
-        .compile("cmsis_dap");
+        .includes(includes);
+    cmsis_dap_build.compile("cmsis_dap");
 
-    println!("cargo:rustc-link-lib=cmsis_dap");
+    if cmsis_dap_build.get_compiler().is_like_gnu() {
+        let libgcc_file_name_out =
+            Command::new(cmsis_dap_build.get_compiler().path())
+                .args(["-print-libgcc-file-name"])
+                .output()
+                .unwrap();
+        let libgcc_file_name =
+            String::from_utf8(libgcc_file_name_out.stdout).unwrap();
+        let path = PathBuf::from(&libgcc_file_name);
+        println!(
+            "cargo:rustc-link-search={}",
+            path.parent().unwrap().to_str().unwrap()
+        )
+    }
 }