Update note about eh_personality

Author: lights0123

src/custom-target.md

@@ -51,8 +51,8 @@ You can pretty much copy that output into your file. Start with a few modificati
 - Remove `"is-builtin": true`
 - Fill `llvm-target` with [the triple that LLVM expects][llvm-target-triple]
 - Decide on a panicking strategy. A bare metal implementation will likely use
-  `"panic-strategy": "abort"`. If you decide not to `abort` on panicking, even if you [tell Cargo
-  to][aborting-on-panic], you must define an [eh_personality] function.
+  `"panic-strategy": "abort"`. If you decide not to `abort` on panicking, unless you [tell Cargo
+  to][eh_personality], you must define an [eh_personality] function.
 - Configure atomics. Pick the first option that describes your target:
   - I have a single-core processor, no threads, no interrupts, or any way for multiple things to be
     happening in parallel: if you are **sure** that is the case, such as WASM (for now), you may set
@@ -166,6 +166,7 @@ exclude `std` when compiling for bare-metal. To do so, specify the crated you'd
 ### language item required, but not found: `eh_personality`
 
 Either add `"panic-strategy": "abort"` to your target file, or define an [eh_personality] function.
+Alternatively, [tell Cargo to ignore it][eh_personality].
 
 ### undefined reference to `__sync_val_compare_and_swap_#`
 

src/smallest-no-std.md

@@ -108,11 +108,24 @@ $ cat .cargo/config
 
 ## eh_personality
 
-If your [target][custom-target] does not contain `"panic-strategy": "abort"`, which most targets for
-full operating systems don't, then you must add an `eh_personality` function, which requires a
-nightly compiler. [Here is Rust's documentation about it][more-about-lang-items], and [here is some
-discussion about it][til-why-eh-personality]. A simple implementation that does not do anything
-special when unwinding is as follows:
+If your configuration does not unconditionally abort on panic, which most targets for full operating
+systems don't (or if your [custom target][custom-target] does not contain
+`"panic-strategy": "abort"`), then you must tell Cargo to do so or add an `eh_personality` function,
+which requires a nightly compiler. [Here is Rust's documentation about it][more-about-lang-items],
+and [here is some discussion about it][til-why-eh-personality].
+
+In your Cargo.toml, add:
+
+``` toml
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+panic = "abort"
+```
+
+Alternatively, declare the `eh_personality` function. A simple implementation that does not do
+anything special when unwinding is as follows:
 
 ``` rust
 #![feature(lang_items)]
@@ -121,6 +134,9 @@ special when unwinding is as follows:
 extern "C" fn eh_personality() {}
 ```
 
+You will receive the error `language item required, but not found: 'eh_personality'` if not
+included.
+
 [custom-target]: ./custom-target.md
 [more-about-lang-items]:
   https://doc.rust-lang.org/unstable-book/language-features/lang-items.html#more-about-the-language-items