Auto merge of rust-lang#84658 - Amanieu:reserved_regs, r=petrochenkov

Be stricter about rejecting LLVM reserved registers in asm!

LLVM will silently produce incorrect code if these registers are used as operands.

cc `@rust-lang/wg-inline-asm`

Author: bors

compiler/rustc_target/src/asm/aarch64.rs

@@ -85,8 +85,6 @@ def_regs! {
         x15: reg = ["x15", "w15"],
         x16: reg = ["x16", "w16"],
         x17: reg = ["x17", "w17"],
-        x18: reg = ["x18", "w18"],
-        x19: reg = ["x19", "w19"],
         x20: reg = ["x20", "w20"],
         x21: reg = ["x21", "w21"],
         x22: reg = ["x22", "w22"],
@@ -96,7 +94,7 @@ def_regs! {
         x26: reg = ["x26", "w26"],
         x27: reg = ["x27", "w27"],
         x28: reg = ["x28", "w28"],
-        x30: reg = ["x30", "w30", "lr"],
+        x30: reg = ["x30", "w30", "lr", "wlr"],
         v0: vreg, vreg_low16 = ["v0", "b0", "h0", "s0", "d0", "q0"],
         v1: vreg, vreg_low16 = ["v1", "b1", "h1", "s1", "d1", "q1"],
         v2: vreg, vreg_low16 = ["v2", "b2", "h2", "s2", "d2", "q2"],
@@ -129,7 +127,11 @@ def_regs! {
         v29: vreg = ["v29", "b29", "h29", "s29", "d29", "q29"],
         v30: vreg = ["v30", "b30", "h30", "s30", "d30", "q30"],
         v31: vreg = ["v31", "b31", "h31", "s31", "d31", "q31"],
-        #error = ["x29", "fp"] =>
+        #error = ["x18", "w18"] =>
+            "x18 is used as a reserved register on some targets and cannot be used as an operand for inline asm",
+        #error = ["x19", "w19"] =>
+            "x19 is used internally by LLVM and cannot be used as an operand for inline asm",
+        #error = ["x29", "w29", "fp", "wfp"] =>
             "the frame pointer cannot be used as an operand for inline asm",
         #error = ["sp", "wsp"] =>
             "the stack pointer cannot be used as an operand for inline asm",

compiler/rustc_target/src/asm/arm.rs

@@ -98,7 +98,6 @@ def_regs! {
         r5: reg, reg_thumb = ["r5", "v2"],
         r7: reg, reg_thumb = ["r7", "v4"] % frame_pointer_r7,
         r8: reg = ["r8", "v5"],
-        r9: reg = ["r9", "v6", "rfp"],
         r10: reg = ["r10", "sl"],
         r11: reg = ["r11", "fp"] % frame_pointer_r11,
         r12: reg = ["r12", "ip"],
@@ -185,6 +184,8 @@ def_regs! {
         q15: qreg = ["q15"],
         #error = ["r6", "v3"] =>
             "r6 is used internally by LLVM and cannot be used as an operand for inline asm",
+        #error = ["r9", "v6", "rfp"] =>
+            "r9 is used internally by LLVM and cannot be used as an operand for inline asm",
         #error = ["r13", "sp"] =>
             "the stack pointer cannot be used as an operand for inline asm",
         #error = ["r15", "pc"] =>

compiler/rustc_target/src/asm/hexagon.rs

@@ -60,7 +60,6 @@ def_regs! {
         r16: reg = ["r16"],
         r17: reg = ["r17"],
         r18: reg = ["r18"],
-        r19: reg = ["r19"],
         r20: reg = ["r20"],
         r21: reg = ["r21"],
         r22: reg = ["r22"],
@@ -70,6 +69,8 @@ def_regs! {
         r26: reg = ["r26"],
         r27: reg = ["r27"],
         r28: reg = ["r28"],
+        #error = ["r19"] =>
+            "r19 is used internally by LLVM and cannot be used as an operand for inline asm",
         #error = ["r29", "sp"] =>
             "the stack pointer cannot be used as an operand for inline asm",
         #error = ["r30", "fr"] =>

compiler/rustc_target/src/asm/riscv.rs

@@ -66,7 +66,6 @@ def_regs! {
         x5: reg = ["x5", "t0"],
         x6: reg = ["x6", "t1"],
         x7: reg = ["x7", "t2"],
-        x9: reg = ["x9", "s1"],
         x10: reg = ["x10", "a0"],
         x11: reg = ["x11", "a1"],
         x12: reg = ["x12", "a2"],
@@ -121,6 +120,8 @@ def_regs! {
         f29: freg = ["f29", "ft9"],
         f30: freg = ["f30", "ft10"],
         f31: freg = ["f31", "ft11"],
+        #error = ["x9", "s1"] =>
+            "s1 is used internally by LLVM and cannot be used as an operand for inline asm",
         #error = ["x8", "s0", "fp"] =>
             "the frame pointer cannot be used as an operand for inline asm",
         #error = ["x2", "sp"] =>

compiler/rustc_target/src/asm/x86.rs

@@ -152,13 +152,41 @@ fn high_byte(
     }
 }
 
+fn rbx_reserved(
+    arch: InlineAsmArch,
+    _has_feature: impl FnMut(&str) -> bool,
+    _target: &Target,
+) -> Result<(), &'static str> {
+    match arch {
+        InlineAsmArch::X86 => Ok(()),
+        InlineAsmArch::X86_64 => {
+            Err("rbx is used internally by LLVM and cannot be used as an operand for inline asm")
+        }
+        _ => unreachable!(),
+    }
+}
+
+fn esi_reserved(
+    arch: InlineAsmArch,
+    _has_feature: impl FnMut(&str) -> bool,
+    _target: &Target,
+) -> Result<(), &'static str> {
+    match arch {
+        InlineAsmArch::X86 => {
+            Err("esi is used internally by LLVM and cannot be used as an operand for inline asm")
+        }
+        InlineAsmArch::X86_64 => Ok(()),
+        _ => unreachable!(),
+    }
+}
+
 def_regs! {
     X86 X86InlineAsmReg X86InlineAsmRegClass {
         ax: reg, reg_abcd = ["ax", "eax", "rax"],
-        bx: reg, reg_abcd = ["bx", "ebx", "rbx"],
+        bx: reg, reg_abcd = ["bx", "ebx", "rbx"] % rbx_reserved,
         cx: reg, reg_abcd = ["cx", "ecx", "rcx"],
         dx: reg, reg_abcd = ["dx", "edx", "rdx"],
-        si: reg = ["si", "esi", "rsi"],
+        si: reg = ["si", "esi", "rsi"] % esi_reserved,
         di: reg = ["di", "edi", "rdi"],
         r8: reg = ["r8", "r8w", "r8d"] % x86_64_only,
         r9: reg = ["r9", "r9w", "r9d"] % x86_64_only,

library/std/src/sys/sgx/ext/arch.rs

@@ -32,9 +32,12 @@ pub fn egetkey(request: &Align512<[u8; 512]>) -> Result<Align16<[u8; 16]>, u32>
         let error;
 
         asm!(
+            // rbx is reserved by LLVM
+            "xchg {0}, rbx",
             "enclu",
+            "mov rbx, {0}",
+            inout(reg) request => _,
             inlateout("eax") ENCLU_EGETKEY => error,
-            in("rbx") request,
             in("rcx") out.as_mut_ptr(),
             options(nostack),
         );
@@ -60,9 +63,12 @@ pub fn ereport(
         let mut report = MaybeUninit::uninit();
 
         asm!(
+            // rbx is reserved by LLVM
+            "xchg {0}, rbx",
             "enclu",
+            "mov rbx, {0}",
+            inout(reg) targetinfo => _,
             in("eax") ENCLU_EREPORT,
-            in("rbx") targetinfo,
             in("rcx") reportdata,
             in("rdx") report.as_mut_ptr(),
             options(preserves_flags, nostack),

src/doc/unstable-book/src/library-features/asm.md

@@ -535,20 +535,20 @@ Here is the list of currently supported register classes:
 
 | Architecture | Register class | Registers | LLVM constraint code |
 | ------------ | -------------- | --------- | -------------------- |
-| x86 | `reg` | `ax`, `bx`, `cx`, `dx`, `si`, `di`, `r[8-15]` (x86-64 only) | `r` |
+| x86 | `reg` | `ax`, `bx`, `cx`, `dx`, `si`, `di`, `bp`, `r[8-15]` (x86-64 only) | `r` |
 | x86 | `reg_abcd` | `ax`, `bx`, `cx`, `dx` | `Q` |
 | x86-32 | `reg_byte` | `al`, `bl`, `cl`, `dl`, `ah`, `bh`, `ch`, `dh` | `q` |
-| x86-64 | `reg_byte`\* | `al`, `bl`, `cl`, `dl`, `sil`, `dil`, `r[8-15]b` | `q` |
+| x86-64 | `reg_byte`\* | `al`, `bl`, `cl`, `dl`, `sil`, `dil`, `bpl`, `r[8-15]b` | `q` |
 | x86 | `xmm_reg` | `xmm[0-7]` (x86) `xmm[0-15]` (x86-64) | `x` |
 | x86 | `ymm_reg` | `ymm[0-7]` (x86) `ymm[0-15]` (x86-64) | `x` |
 | x86 | `zmm_reg` | `zmm[0-7]` (x86) `zmm[0-31]` (x86-64) | `v` |
 | x86 | `kreg` | `k[1-7]` | `Yk` |
-| AArch64 | `reg` | `x[0-28]`, `x30` | `r` |
+| AArch64 | `reg` | `x[0-30]` | `r` |
 | AArch64 | `vreg` | `v[0-31]` | `w` |
 | AArch64 | `vreg_low16` | `v[0-15]` | `x` |
-| ARM | `reg` | `r[0-5]` `r7`\*, `r[8-10]`, `r11`\*, `r12`, `r14` | `r` |
+| ARM | `reg` | `r[0-12]`, `r14` | `r` |
 | ARM (Thumb) | `reg_thumb` | `r[0-r7]` | `l` |
-| ARM (ARM) | `reg_thumb` | `r[0-r10]`, `r12`, `r14` | `l` |
+| ARM (ARM) | `reg_thumb` | `r[0-r12]`, `r14` | `l` |
 | ARM | `sreg` | `s[0-31]` | `t` |
 | ARM | `sreg_low16` | `s[0-15]` | `x` |
 | ARM | `dreg` | `d[0-31]` | `w` |
@@ -573,9 +573,7 @@ Here is the list of currently supported register classes:
 >
 > Note #3: NVPTX doesn't have a fixed register set, so named registers are not supported.
 >
-> Note #4: On ARM the frame pointer is either `r7` or `r11` depending on the platform.
->
-> Note #5: WebAssembly doesn't have registers, so named registers are not supported.
+> Note #4: WebAssembly doesn't have registers, so named registers are not supported.
 
 Additional register classes may be added in the future based on demand (e.g. MMX, x87, etc).
 
@@ -677,13 +675,14 @@ Some registers cannot be used for input or output operands:
 | All | `sp` | The stack pointer must be restored to its original value at the end of an asm code block. |
 | All | `bp` (x86), `x29` (AArch64), `x8` (RISC-V), `fr` (Hexagon), `$fp` (MIPS) | The frame pointer cannot be used as an input or output. |
 | ARM | `r7` or `r11` | On ARM the frame pointer can be either `r7` or `r11` depending on the target. The frame pointer cannot be used as an input or output. |
-| ARM | `r6` | `r6` is used internally by LLVM as a base pointer and therefore cannot be used as an input or output. |
+| All | `si` (x86-32), `bx` (x86-64), `r6` (ARM), `x19` (AArch64), `r19` (Hexagon), `x9` (RISC-V) | This is used internally by LLVM as a "base pointer" for functions with complex stack frames. |
 | x86 | `k0` | This is a constant zero register which can't be modified. |
 | x86 | `ip` | This is the program counter, not a real register. |
 | x86 | `mm[0-7]` | MMX registers are not currently supported (but may be in the future). |
 | x86 | `st([0-7])` | x87 registers are not currently supported (but may be in the future). |
 | AArch64 | `xzr` | This is a constant zero register which can't be modified. |
 | ARM | `pc` | This is the program counter, not a real register. |
+| ARM | `r9` | This is a reserved register on some ARM targets. |
 | MIPS | `$0` or `$zero` | This is a constant zero register which can't be modified. |
 | MIPS | `$1` or `$at` | Reserved for assembler. |
 | MIPS | `$26`/`$k0`, `$27`/`$k1` | OS-reserved registers. |
@@ -693,9 +692,10 @@ Some registers cannot be used for input or output operands:
 | RISC-V | `gp`, `tp` | These registers are reserved and cannot be used as inputs or outputs. |
 | Hexagon | `lr` | This is the link register which cannot be used as an input or output. |
 
-In some cases LLVM will allocate a "reserved register" for `reg` operands even though this register cannot be explicitly specified. Assembly code making use of reserved registers should be careful since `reg` operands may alias with those registers. Reserved registers are:
-- The frame pointer on all architectures.
-- `r6` on ARM.
+In some cases LLVM will allocate a "reserved register" for `reg` operands even though this register cannot be explicitly specified. Assembly code making use of reserved registers should be careful since `reg` operands may alias with those registers. Reserved registers are the frame pointer and base pointer
+- The frame pointer and LLVM base pointer on all architectures.
+- `r9` on ARM.
+- `x18` on AArch64.
 
 ## Template modifiers
 

src/test/codegen/asm-multiple-options.rs

@@ -10,7 +10,7 @@
 #[no_mangle]
 pub unsafe fn pure(x: i32) {
     let y: i32;
-    asm!("", out("ax") y, in("bx") x, options(pure), options(nomem));
+    asm!("", out("ax") y, in("cx") x, options(pure), options(nomem));
 }
 
 pub static mut VAR: i32 = 0;

src/test/codegen/asm-options.rs

@@ -10,7 +10,7 @@
 #[no_mangle]
 pub unsafe fn pure(x: i32) {
     let y: i32;
-    asm!("", out("ax") y, in("bx") x, options(pure, nomem));
+    asm!("", out("ax") y, in("cx") x, options(pure, nomem));
 }
 
 // CHECK-LABEL: @noreturn

src/test/pretty/asm.pp

@@ -21,7 +21,7 @@
         asm!("{0}", out(reg) a);
         asm!("{0}", inout(reg) b);
         asm!("{0} {1}", out(reg) _, inlateout(reg) b => _);
-        asm!("", out("al") _, lateout("rbx") _);
+        asm!("", out("al") _, lateout("rcx") _);
         asm!("inst1\ninst2");
         asm!("inst1 {0}, 42\ninst2 {1}, 24", in(reg) a, out(reg) b);
         asm!("inst2 {1}, 24\ninst1 {0}, 42", in(reg) a, out(reg) b);