diff --git a/src/doc/rustc/src/platform-support/arm-none-eabi.md b/src/doc/rustc/src/platform-support/arm-none-eabi.md
index de0ef322fa6..9732df4be7f 100644
--- a/src/doc/rustc/src/platform-support/arm-none-eabi.md
+++ b/src/doc/rustc/src/platform-support/arm-none-eabi.md
@@ -42,16 +42,15 @@ their own document.
There are two 32-bit instruction set architectures (ISAs) defined by Arm:
- The [*A32 ISA*][a32-isa], with fixed-width 32-bit instructions. Previously
- known as the *Arm* ISA, this originated with the original Arm1 of 1985 and has
+ known as the *Arm* ISA, this originated with the original ARM1 of 1985 and has
been updated by various revisions to the architecture specifications ever
since.
- The [*T32 ISA*][t32-isa], with a mix of 16-bit and 32-bit width instructions.
Note that this term includes both the original 16-bit width *Thumb* ISA
introduced with the Armv4T architecture in 1994, and the later 16/32-bit sized
- *Thumb-2* ISA introduced with the Armv6T2 architecture in 2003.
-
-Again, these ISAs have been revised by subsequent revisions to the relevant Arm
-architecture specifications.
+ *Thumb-2* ISA introduced with the Armv6T2 architecture in 2003. Again, these
+ ISAs have been revised by subsequent revisions to the relevant Arm
+ architecture specifications.
There is also a 64-bit ISA with fixed-width 32-bit instructions called the *A64
ISA*, but targets which implement that instruction set generally start with
@@ -106,10 +105,14 @@ features you do not have available, leaving you with the optimized instruction
scheduling and support for the features you do have. More details are available
in the detailed target-specific documentation.
-**Note:** Many target-features are currently unstable and subject to change, and
+
+
+Many target-features are currently unstable and subject to change, and
if you use them you should disassemble the compiler output and manually inspect
it to ensure only appropriate instructions for your CPU have been generated.
+
+
If you wish to use the *target-cpu* and *target-feature* options, you can add
them to your `.cargo/config.toml` file alongside any other flags your project
uses (likely linker related ones):
diff --git a/src/doc/rustc/src/platform-support/thumbv7em-none-eabi.md b/src/doc/rustc/src/platform-support/thumbv7em-none-eabi.md
index f25ef0383b1..11c9486cb76 100644
--- a/src/doc/rustc/src/platform-support/thumbv7em-none-eabi.md
+++ b/src/doc/rustc/src/platform-support/thumbv7em-none-eabi.md
@@ -35,9 +35,9 @@ to use these flags.
| CPU | FPU | DSP | Target CPU | Target Features |
| ---------- | --- | --- | ----------- | --------------- |
| Any | No | Yes | None | None |
-| Cortex-M4 | No | Yes | `cortex-m4` | `+soft-float` |
+| Cortex-M4 | No | Yes | `cortex-m4` | `-fpregs` |
| Cortex-M4F | SP | Yes | `cortex-m4` | None |
-| Cortex-M7 | No | Yes | `cortex-m7` | `+soft-float` |
+| Cortex-M7 | No | Yes | `cortex-m7` | `-fpregs` |
| Cortex-M7F | SP | Yes | `cortex-m7` | `-fp64` |
| Cortex-M7F | DP | Yes | `cortex-m7` | None |
@@ -50,6 +50,13 @@ to use these flags.
| Cortex-M7F | SP | Yes | `cortex-m7` | `-fp64` |
| Cortex-M7F | DP | Yes | `cortex-m7` | None |
+
+
+Never use the `-fpregs` *target-feature* with the `thumbv7em-none-eabihf` target
+as it will cause compilation units to have different ABIs, which is unsound.
+
+
+
### Arm Cortex-M4 and Arm Cortex-M4F
The target CPU is `cortex-m4`.
@@ -59,7 +66,7 @@ The target CPU is `cortex-m4`.
* enabled by default with this *target*
* Cortex-M4F has a single precision FPU
* support is enabled by default with this *target-cpu*
- * disable support using the `+soft-float` feature (`eabi` only)
+ * disable support using the `-fpregs` *target-feature* (`eabi` only)
### Arm Cortex-M7 and Arm Cortex-M7F
@@ -71,4 +78,4 @@ The target CPU is `cortex-m7`.
* Cortex-M7F have either a single-precision or double-precision FPU
* double-precision support is enabled by default with this *target-cpu*
* opt-out by using the `-f64` *target-feature*
- * disable support entirely using the `+soft-float` feature (`eabi` only)
+ * disable support entirely using the `-fpregs` *target-feature* (`eabi` only)
diff --git a/src/doc/rustc/src/platform-support/thumbv8m.main-none-eabi.md b/src/doc/rustc/src/platform-support/thumbv8m.main-none-eabi.md
index 4e696f9c304..82fdc5b21cf 100644
--- a/src/doc/rustc/src/platform-support/thumbv8m.main-none-eabi.md
+++ b/src/doc/rustc/src/platform-support/thumbv8m.main-none-eabi.md
@@ -39,22 +39,22 @@ to use these flags.
| CPU | FPU | DSP | MVE | Target CPU | Target Features |
| ----------- | --- | --- | --------- | ------------- | --------------------- |
| Unspecified | No | No | No | None | None |
-| Cortex-M33 | No | No | No | `cortex-m33` | `+soft-float,-dsp` |
-| Cortex-M33 | No | Yes | No | `cortex-m33` | `+soft-float` |
+| Cortex-M33 | No | No | No | `cortex-m33` | `-fpregs,-dsp` |
+| Cortex-M33 | No | Yes | No | `cortex-m33` | `-fpregs` |
| Cortex-M33 | SP | No | No | `cortex-m33` | `-dsp` |
| Cortex-M33 | SP | Yes | No | `cortex-m33` | None |
-| Cortex-M35P | No | No | No | `cortex-m35p` | `+soft-float,-dsp` |
-| Cortex-M35P | No | Yes | No | `cortex-m35p` | `+soft-float` |
+| Cortex-M35P | No | No | No | `cortex-m35p` | `-fpregs,-dsp` |
+| Cortex-M35P | No | Yes | No | `cortex-m35p` | `-fpregs` |
| Cortex-M35P | SP | No | No | `cortex-m35p` | `-dsp` |
| Cortex-M35P | SP | Yes | No | `cortex-m35p` | None |
-| Cortex-M55 | No | Yes | No | `cortex-m55` | `+soft-float,-mve` |
+| Cortex-M55 | No | Yes | No | `cortex-m55` | `-fpregs,-mve` |
| Cortex-M55 | DP | Yes | No | `cortex-m55` | `-mve` |
-| Cortex-M55 | No | Yes | Int | `cortex-m55` | `+soft-float,-mve.fp` |
+| Cortex-M55 | No | Yes | Int | `cortex-m55` | `-fpregs,-mve.fp,+mve`|
| Cortex-M55 | DP | Yes | Int | `cortex-m55` | `-mve.fp` |
| Cortex-M55 | DP | Yes | Int+Float | `cortex-m55` | None |
-| Cortex-M85 | No | Yes | No | `cortex-m85` | `+soft-float,-mve` |
+| Cortex-M85 | No | Yes | No | `cortex-m85` | `-fpregs,-mve` |
| Cortex-M85 | DP | Yes | No | `cortex-m85` | `-mve` |
-| Cortex-M85 | No | Yes | Int | `cortex-m85` | `+soft-float,-mve.fp` |
+| Cortex-M85 | No | Yes | Int | `cortex-m85` | `-fpregs,-mve.fp,+mve`|
| Cortex-M85 | DP | Yes | Int | `cortex-m85` | `-mve.fp` |
| Cortex-M85 | DP | Yes | Int+Float | `cortex-m85` | None |
@@ -74,6 +74,19 @@ to use these flags.
| Cortex-M85 | DP | Yes | Int | `cortex-m85` | `-mve.fp` |
| Cortex-M85 | DP | Yes | Int+Float | `cortex-m85` | None |
+*Technically* you can use this hard-float ABI on a CPU which has no FPU but does
+have Integer MVE, because MVE provides the same set of registers as the FPU
+(including `s0` and `d0`). The particular set of flags that might enable this
+unusual scenario are currently not recorded here.
+
+
+
+Never use the `-fpregs` *target-feature* with the `thumbv8m.main-none-eabihf`
+target as it will cause compilation units to have different ABIs, which is
+unsound.
+
+
+
### Arm Cortex-M33
The target CPU is `cortex-m33`.
@@ -83,7 +96,7 @@ The target CPU is `cortex-m33`.
* enabled by default with this *target-cpu*
* Has an optional single precision FPU
* support is enabled by default with this *target-cpu*
- * disable support using the `+soft-float` feature (`eabi` only)
+ * disable support using the `-fpregs` *target-feature* (`eabi` only)
### Arm Cortex-M35P
@@ -94,7 +107,7 @@ The target CPU is `cortex-m35p`.
* enabled by default with this *target-cpu*
* Has an optional single precision FPU
* support is enabled by default with this *target-cpu*
- * disable support using the `+soft-float` feature (`eabi` only)
+ * disable support using the `-fpregs` *target-feature* (`eabi` only)
### Arm Cortex-M55
@@ -106,7 +119,7 @@ The target CPU is `cortex-m55`.
* Has an optional double-precision FPU that also supports half-precision FP16
values
* support is enabled by default with this *target-cpu*
- * disable support using the `+soft-float` feature (`eabi` only)
+ * disable support using the `-fpregs` *target-feature* (`eabi` only)
* Has optional support for M-Profile Vector Extensions
* Also known as *Helium Technology*
* Available with only integer support, or both integer/float support
@@ -125,7 +138,7 @@ The target CPU is `cortex-m85`.
* Has an optional double-precision FPU that also supports half-precision FP16
values
* support is enabled by default with this *target-cpu*
- * disable support using the `+soft-float` feature (`eabi` only)
+ * disable support using the `-fpregs` *target-feature* (`eabi` only)
* Has optional support for M-Profile Vector Extensions
* Also known as *Helium Technology*
* Available with only integer support, or both integer/float support