diff --git a/compiler/rustc_codegen_llvm/src/va_arg.rs b/compiler/rustc_codegen_llvm/src/va_arg.rs
index e4c3e748cb5df..8baa69cefe1e2 100644
--- a/compiler/rustc_codegen_llvm/src/va_arg.rs
+++ b/compiler/rustc_codegen_llvm/src/va_arg.rs
@@ -10,6 +10,15 @@ use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
 use crate::value::Value;
 
+fn round_up_to_alignment<'ll>(
+    bx: &mut Builder<'_, 'll, '_>,
+    mut value: &'ll Value,
+    align: Align,
+) -> &'ll Value {
+    value = bx.add(value, bx.cx().const_i32(align.bytes() as i32 - 1));
+    return bx.and(value, bx.cx().const_i32(-(align.bytes() as i32)));
+}
+
 fn round_pointer_up_to_alignment<'ll>(
     bx: &mut Builder<'_, 'll, '_>,
     addr: &'ll Value,
@@ -17,8 +26,7 @@ fn round_pointer_up_to_alignment<'ll>(
     ptr_ty: &'ll Type,
 ) -> &'ll Value {
     let mut ptr_as_int = bx.ptrtoint(addr, bx.cx().type_isize());
-    ptr_as_int = bx.add(ptr_as_int, bx.cx().const_i32(align.bytes() as i32 - 1));
-    ptr_as_int = bx.and(ptr_as_int, bx.cx().const_i32(-(align.bytes() as i32)));
+    ptr_as_int = round_up_to_alignment(bx, ptr_as_int, align);
     bx.inttoptr(ptr_as_int, ptr_ty)
 }
 
@@ -270,6 +278,106 @@ fn emit_s390x_va_arg<'ll, 'tcx>(
     bx.load(val_type, val_addr, layout.align.abi)
 }
 
+fn emit_xtensa_va_arg<'ll, 'tcx>(
+    bx: &mut Builder<'_, 'll, 'tcx>,
+    list: OperandRef<'tcx, &'ll Value>,
+    target_ty: Ty<'tcx>,
+) -> &'ll Value {
+    // Implementation of va_arg for Xtensa. There doesn't seem to be an authoritative source for
+    // this, other than "what GCC does".
+    //
+    // The va_list type has three fields:
+    // struct __va_list_tag {
+    //   int32_t *va_stk; // Arguments passed on the stack
+    //   int32_t *va_reg; // Arguments passed in registers, saved to memory by the prologue.
+    //   int32_t va_ndx; // Offset into the arguments, in bytes
+    // };
+    //
+    // The first 24 bytes (equivalent to 6 registers) come from va_reg, the rest from va_stk.
+    // Thus if va_ndx is less than 24, the next va_arg *may* read from va_reg,
+    // otherwise it must come from va_stk.
+    //
+    // Primitive arguments are never split between registers and the stack. For example, if loading an 8 byte
+    // primitive value and va_ndx = 20, we instead bump the offset and read everything from va_stk.
+    let va_list_addr = list.immediate();
+    // FIXME: handle multi-field structs that split across regsave/stack?
+    let layout = bx.cx.layout_of(target_ty);
+    let from_stack = bx.append_sibling_block("va_arg.from_stack");
+    let from_regsave = bx.append_sibling_block("va_arg.from_regsave");
+    let end = bx.append_sibling_block("va_arg.end");
+
+    // (*va).va_ndx
+    let va_reg_offset = 4;
+    let va_ndx_offset = va_reg_offset + 4;
+    let offset_ptr =
+        bx.inbounds_gep(bx.type_i8(), va_list_addr, &[bx.cx.const_usize(va_ndx_offset)]);
+
+    let offset = bx.load(bx.type_i32(), offset_ptr, bx.tcx().data_layout.i32_align.abi);
+    let offset = round_up_to_alignment(bx, offset, layout.align.abi);
+
+    let slot_size = layout.size.align_to(Align::from_bytes(4).unwrap()).bytes() as i32;
+
+    // Update the offset in va_list, by adding the slot's size.
+    let offset_next = bx.add(offset, bx.const_i32(slot_size));
+
+    // Figure out where to look for our value. We do that by checking the end of our slot (offset_next).
+    // If that is within the regsave area, then load from there. Otherwise load from the stack area.
+    let regsave_size = bx.const_i32(24);
+    let use_regsave = bx.icmp(IntPredicate::IntULE, offset_next, regsave_size);
+    bx.cond_br(use_regsave, from_regsave, from_stack);
+
+    bx.switch_to_block(from_regsave);
+    // update va_ndx
+    bx.store(offset_next, offset_ptr, bx.tcx().data_layout.pointer_align.abi);
+
+    // (*va).va_reg
+    let regsave_area_ptr =
+        bx.inbounds_gep(bx.type_i8(), va_list_addr, &[bx.cx.const_usize(va_reg_offset)]);
+    let regsave_area =
+        bx.load(bx.type_ptr(), regsave_area_ptr, bx.tcx().data_layout.pointer_align.abi);
+    let regsave_value_ptr = bx.inbounds_gep(bx.type_i8(), regsave_area, &[offset]);
+    bx.br(end);
+
+    bx.switch_to_block(from_stack);
+
+    // The first time we switch from regsave to stack we needs to adjust our offsets a bit.
+    // va_stk is set up such that the first stack argument is always at va_stk + 32.
+    // The corrected offset is written back into the va_list struct.
+
+    // let offset_corrected = cmp::max(offset, 32);
+    let stack_offset_start = bx.const_i32(32);
+    let needs_correction = bx.icmp(IntPredicate::IntULE, offset, stack_offset_start);
+    let offset_corrected = bx.select(needs_correction, stack_offset_start, offset);
+
+    // let offset_next_corrected = offset_corrected + slot_size;
+    // va_ndx = offset_next_corrected;
+    let offset_next_corrected = bx.add(offset_next, bx.const_i32(slot_size));
+    // update va_ndx
+    bx.store(offset_next_corrected, offset_ptr, bx.tcx().data_layout.pointer_align.abi);
+
+    // let stack_value_ptr = unsafe { (*va).va_stk.byte_add(offset_corrected) };
+    let stack_area_ptr = bx.inbounds_gep(bx.type_i8(), va_list_addr, &[bx.cx.const_usize(0)]);
+    let stack_area = bx.load(bx.type_ptr(), stack_area_ptr, bx.tcx().data_layout.pointer_align.abi);
+    let stack_value_ptr = bx.inbounds_gep(bx.type_i8(), stack_area, &[offset_corrected]);
+    bx.br(end);
+
+    bx.switch_to_block(end);
+
+    // On big-endian, for values smaller than the slot size we'd have to align the read to the end
+    // of the slot rather than the start. While the ISA and GCC support big-endian, all the Xtensa
+    // targets supported by rustc are litte-endian so don't worry about it.
+
+    // if from_regsave {
+    //     unsafe { *regsave_value_ptr }
+    // } else {
+    //     unsafe { *stack_value_ptr }
+    // }
+    assert!(bx.tcx().sess.target.endian == Endian::Little);
+    let value_ptr =
+        bx.phi(bx.type_ptr(), &[regsave_value_ptr, stack_value_ptr], &[from_regsave, from_stack]);
+    return bx.load(layout.llvm_type(bx), value_ptr, layout.align.abi);
+}
+
 pub(super) fn emit_va_arg<'ll, 'tcx>(
     bx: &mut Builder<'_, 'll, 'tcx>,
     addr: OperandRef<'tcx, &'ll Value>,
@@ -302,6 +410,7 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
             let indirect: bool = target_ty_size > 8 || !target_ty_size.is_power_of_two();
             emit_ptr_va_arg(bx, addr, target_ty, indirect, Align::from_bytes(8).unwrap(), false)
         }
+        "xtensa" => emit_xtensa_va_arg(bx, addr, target_ty),
         // For all other architecture/OS combinations fall back to using
         // the LLVM va_arg instruction.
         // https://llvm.org/docs/LangRef.html#va-arg-instruction
diff --git a/compiler/rustc_target/src/spec/targets/armv4t_unknown_linux_gnueabi.rs b/compiler/rustc_target/src/spec/targets/armv4t_unknown_linux_gnueabi.rs
index 3a2fb753ba147..7ca2babffe9fc 100644
--- a/compiler/rustc_target/src/spec/targets/armv4t_unknown_linux_gnueabi.rs
+++ b/compiler/rustc_target/src/spec/targets/armv4t_unknown_linux_gnueabi.rs
@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
             description: Some("Armv4T Linux".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),
diff --git a/compiler/rustc_target/src/spec/targets/armv5te_unknown_linux_uclibceabi.rs b/compiler/rustc_target/src/spec/targets/armv5te_unknown_linux_uclibceabi.rs
index e0bc1936e221c..154103c36f79c 100644
--- a/compiler/rustc_target/src/spec/targets/armv5te_unknown_linux_uclibceabi.rs
+++ b/compiler/rustc_target/src/spec/targets/armv5te_unknown_linux_uclibceabi.rs
@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
             description: Some("Armv5TE Linux with uClibc".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),
diff --git a/compiler/rustc_target/src/spec/targets/m68k_unknown_linux_gnu.rs b/compiler/rustc_target/src/spec/targets/m68k_unknown_linux_gnu.rs
index 1515d8fe00abc..47c6d80548359 100644
--- a/compiler/rustc_target/src/spec/targets/m68k_unknown_linux_gnu.rs
+++ b/compiler/rustc_target/src/spec/targets/m68k_unknown_linux_gnu.rs
@@ -12,7 +12,7 @@ pub(crate) fn target() -> Target {
             description: Some("Motorola 680x0 Linux".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "E-m:e-p:32:16:32-i8:8:8-i16:16:16-i32:16:32-n8:16:32-a:0:16-S16".into(),
diff --git a/compiler/rustc_target/src/spec/targets/mips64_openwrt_linux_musl.rs b/compiler/rustc_target/src/spec/targets/mips64_openwrt_linux_musl.rs
index b7415bf683de2..cc288e042d987 100644
--- a/compiler/rustc_target/src/spec/targets/mips64_openwrt_linux_musl.rs
+++ b/compiler/rustc_target/src/spec/targets/mips64_openwrt_linux_musl.rs
@@ -17,7 +17,7 @@ pub(crate) fn target() -> Target {
             description: Some("MIPS64 for OpenWrt Linux musl 1.2.3".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "E-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/mipsisa32r6_unknown_linux_gnu.rs b/compiler/rustc_target/src/spec/targets/mipsisa32r6_unknown_linux_gnu.rs
index 2ff06dc6669bb..3ef0988d23570 100644
--- a/compiler/rustc_target/src/spec/targets/mipsisa32r6_unknown_linux_gnu.rs
+++ b/compiler/rustc_target/src/spec/targets/mipsisa32r6_unknown_linux_gnu.rs
@@ -8,7 +8,7 @@ pub(crate) fn target() -> Target {
             description: Some("32-bit MIPS Release 6 Big Endian".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "E-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".into(),
diff --git a/compiler/rustc_target/src/spec/targets/mipsisa32r6el_unknown_linux_gnu.rs b/compiler/rustc_target/src/spec/targets/mipsisa32r6el_unknown_linux_gnu.rs
index 05b246698482a..c75023385c220 100644
--- a/compiler/rustc_target/src/spec/targets/mipsisa32r6el_unknown_linux_gnu.rs
+++ b/compiler/rustc_target/src/spec/targets/mipsisa32r6el_unknown_linux_gnu.rs
@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
             description: Some("32-bit MIPS Release 6 Little Endian".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64".into(),
diff --git a/compiler/rustc_target/src/spec/targets/mipsisa64r6_unknown_linux_gnuabi64.rs b/compiler/rustc_target/src/spec/targets/mipsisa64r6_unknown_linux_gnuabi64.rs
index c5948b745ff59..d0d0ed1acc3f0 100644
--- a/compiler/rustc_target/src/spec/targets/mipsisa64r6_unknown_linux_gnuabi64.rs
+++ b/compiler/rustc_target/src/spec/targets/mipsisa64r6_unknown_linux_gnuabi64.rs
@@ -8,7 +8,7 @@ pub(crate) fn target() -> Target {
             description: Some("64-bit MIPS Release 6 Big Endian".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "E-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/powerpc64_unknown_linux_musl.rs b/compiler/rustc_target/src/spec/targets/powerpc64_unknown_linux_musl.rs
index 5da891cc13f6d..62c30aebc518e 100644
--- a/compiler/rustc_target/src/spec/targets/powerpc64_unknown_linux_musl.rs
+++ b/compiler/rustc_target/src/spec/targets/powerpc64_unknown_linux_musl.rs
@@ -14,7 +14,7 @@ pub(crate) fn target() -> Target {
             description: Some("64-bit PowerPC Linux with musl 1.2.3".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "E-m:e-Fn32-i64:64-n32:64-S128-v256:256:256-v512:512:512".into(),
diff --git a/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_freebsd.rs b/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_freebsd.rs
index e194f5f8a36f3..0c1218bd05939 100644
--- a/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_freebsd.rs
+++ b/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_freebsd.rs
@@ -12,8 +12,8 @@ pub(crate) fn target() -> Target {
         metadata: crate::spec::TargetMetadata {
             description: Some("PPC64LE FreeBSD".into()),
             tier: Some(3),
-            host_tools: Some(false),
-            std: Some(false),
+            host_tools: Some(true),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-Fn32-i64:64-n32:64".into(),
diff --git a/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_linux_musl.rs b/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_linux_musl.rs
index e2921aa17fe64..50946ae4ce66d 100644
--- a/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_linux_musl.rs
+++ b/compiler/rustc_target/src/spec/targets/powerpc64le_unknown_linux_musl.rs
@@ -13,7 +13,7 @@ pub(crate) fn target() -> Target {
             description: Some("64-bit PowerPC Linux with musl 1.2.3, Little Endian".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-Fn32-i64:64-n32:64-S128-v256:256:256-v512:512:512".into(),
diff --git a/compiler/rustc_target/src/spec/targets/powerpc_unknown_freebsd.rs b/compiler/rustc_target/src/spec/targets/powerpc_unknown_freebsd.rs
index 393946980f8b3..9cfc2153ac170 100644
--- a/compiler/rustc_target/src/spec/targets/powerpc_unknown_freebsd.rs
+++ b/compiler/rustc_target/src/spec/targets/powerpc_unknown_freebsd.rs
@@ -17,7 +17,7 @@ pub(crate) fn target() -> Target {
             description: Some("PowerPC FreeBSD".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "E-m:e-p:32:32-Fn32-i64:64-n32".into(),
diff --git a/compiler/rustc_target/src/spec/targets/powerpc_unknown_linux_musl.rs b/compiler/rustc_target/src/spec/targets/powerpc_unknown_linux_musl.rs
index 9859e8ced4f46..5372a83e29a22 100644
--- a/compiler/rustc_target/src/spec/targets/powerpc_unknown_linux_musl.rs
+++ b/compiler/rustc_target/src/spec/targets/powerpc_unknown_linux_musl.rs
@@ -13,7 +13,7 @@ pub(crate) fn target() -> Target {
             description: Some("PowerPC Linux with musl 1.2.3".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "E-m:e-p:32:32-Fn32-i64:64-n32".into(),
diff --git a/compiler/rustc_target/src/spec/targets/powerpc_unknown_openbsd.rs b/compiler/rustc_target/src/spec/targets/powerpc_unknown_openbsd.rs
index a8254af9736c0..7aedc2d0665cb 100644
--- a/compiler/rustc_target/src/spec/targets/powerpc_unknown_openbsd.rs
+++ b/compiler/rustc_target/src/spec/targets/powerpc_unknown_openbsd.rs
@@ -13,7 +13,7 @@ pub(crate) fn target() -> Target {
             description: None,
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "E-m:e-p:32:32-Fn32-i64:64-n32".into(),
diff --git a/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_gnu.rs b/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_gnu.rs
index 8b0a140c9ade5..e9c57b99b9279 100644
--- a/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_gnu.rs
+++ b/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_gnu.rs
@@ -9,7 +9,7 @@ pub(crate) fn target() -> Target {
             description: Some("RISC-V Linux (kernel 5.4, glibc 2.33)".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-i64:64-n32-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_musl.rs b/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_musl.rs
index 212de791e499a..08871d9d72bfb 100644
--- a/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_musl.rs
+++ b/compiler/rustc_target/src/spec/targets/riscv32gc_unknown_linux_musl.rs
@@ -11,7 +11,7 @@ pub(crate) fn target() -> Target {
             ),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-i64:64-n32-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs b/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs
index 8b5d4751a5733..f694a1cb60dd2 100644
--- a/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs
+++ b/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs
@@ -9,7 +9,7 @@ pub(crate) fn target() -> Target {
             description: Some("RISC-V 64-bit Android".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_freebsd.rs b/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_freebsd.rs
index d1b0d801fd60b..905bed76db4d0 100644
--- a/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_freebsd.rs
+++ b/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_freebsd.rs
@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
             description: Some("RISC-V FreeBSD".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_fuchsia.rs b/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_fuchsia.rs
index 6de51f9b07e2a..7a887b604c507 100644
--- a/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_fuchsia.rs
+++ b/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_fuchsia.rs
@@ -7,7 +7,7 @@ pub(crate) fn target() -> Target {
             description: Some("RISC-V Fuchsia".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_linux_musl.rs b/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_linux_musl.rs
index 2e6fce91d4c75..397c202ec1a57 100644
--- a/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_linux_musl.rs
+++ b/compiler/rustc_target/src/spec/targets/riscv64gc_unknown_linux_musl.rs
@@ -9,7 +9,7 @@ pub(crate) fn target() -> Target {
             description: Some("RISC-V Linux (kernel 4.20, musl 1.2.3)".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
diff --git a/compiler/rustc_target/src/spec/targets/s390x_unknown_linux_musl.rs b/compiler/rustc_target/src/spec/targets/s390x_unknown_linux_musl.rs
index 4bde0fb729c75..7a78004927b10 100644
--- a/compiler/rustc_target/src/spec/targets/s390x_unknown_linux_musl.rs
+++ b/compiler/rustc_target/src/spec/targets/s390x_unknown_linux_musl.rs
@@ -19,7 +19,7 @@ pub(crate) fn target() -> Target {
             description: Some("S390x Linux (kernel 3.2, musl 1.2.3)".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: Some(false),
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout: "E-m:e-i1:8:16-i8:8:16-i64:64-f128:64-v128:64-a:8:16-n32:64".into(),
diff --git a/compiler/rustc_target/src/spec/targets/thumbv7neon_unknown_linux_musleabihf.rs b/compiler/rustc_target/src/spec/targets/thumbv7neon_unknown_linux_musleabihf.rs
index 5c43ca69bd852..2f539f4f6004d 100644
--- a/compiler/rustc_target/src/spec/targets/thumbv7neon_unknown_linux_musleabihf.rs
+++ b/compiler/rustc_target/src/spec/targets/thumbv7neon_unknown_linux_musleabihf.rs
@@ -16,7 +16,7 @@ pub(crate) fn target() -> Target {
             description: Some("Thumb2-mode ARMv7-A Linux with NEON, musl 1.2.3".into()),
             tier: Some(3),
             host_tools: Some(false),
-            std: None, // ?
+            std: Some(true),
         },
         pointer_width: 32,
         data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_unknown_linux_none.rs b/compiler/rustc_target/src/spec/targets/x86_64_unknown_linux_none.rs
index 91eb7b53fea8a..900dbed205c8e 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_unknown_linux_none.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_unknown_linux_none.rs
@@ -14,7 +14,7 @@ pub(crate) fn target() -> Target {
             description: None,
             tier: None,
             host_tools: None,
-            std: None,
+            std: Some(true),
         },
         pointer_width: 64,
         data_layout:
diff --git a/library/core/Cargo.toml b/library/core/Cargo.toml
index cace4582b489a..46c55c437cce5 100644
--- a/library/core/Cargo.toml
+++ b/library/core/Cargo.toml
@@ -43,6 +43,7 @@ check-cfg = [
     'cfg(bootstrap)',
     'cfg(no_fp_fmt_parse)',
     'cfg(stdarch_intel_sde)',
+    'cfg(target_arch, values("xtensa"))',
     # core use #[path] imports to portable-simd `core_simd` crate
     # and to stdarch `core_arch` crate which messes-up with Cargo list
     # of declared features, we therefor expect any feature cfg
diff --git a/library/core/src/ffi/va_list.rs b/library/core/src/ffi/va_list.rs
index 3a224e4d8fe5f..f67c592d8d8f7 100644
--- a/library/core/src/ffi/va_list.rs
+++ b/library/core/src/ffi/va_list.rs
@@ -15,6 +15,7 @@ use crate::ops::{Deref, DerefMut};
         not(target_arch = "aarch64"),
         not(target_arch = "powerpc"),
         not(target_arch = "s390x"),
+        not(target_arch = "xtensa"),
         not(target_arch = "x86_64")
     ),
     all(target_arch = "aarch64", target_vendor = "apple"),
@@ -37,6 +38,7 @@ pub struct VaListImpl<'f> {
         not(target_arch = "aarch64"),
         not(target_arch = "powerpc"),
         not(target_arch = "s390x"),
+        not(target_arch = "xtensa"),
         not(target_arch = "x86_64")
     ),
     all(target_arch = "aarch64", target_vendor = "apple"),
@@ -113,6 +115,18 @@ pub struct VaListImpl<'f> {
     _marker: PhantomData<&'f mut &'f c_void>,
 }
 
+/// Xtensa ABI implementation of a `va_list`.
+#[cfg(target_arch = "xtensa")]
+#[repr(C)]
+#[derive(Debug)]
+#[lang = "va_list"]
+pub struct VaListImpl<'f> {
+    stk: *mut i32,
+    reg: *mut i32,
+    ndx: i32,
+    _marker: PhantomData<&'f mut &'f c_void>,
+}
+
 /// A wrapper for a `va_list`
 #[repr(transparent)]
 #[derive(Debug)]
@@ -124,6 +138,7 @@ pub struct VaList<'a, 'f: 'a> {
             not(target_arch = "s390x"),
             not(target_arch = "x86_64")
         ),
+        target_arch = "xtensa",
         all(target_arch = "aarch64", target_vendor = "apple"),
         target_family = "wasm",
         target_os = "uefi",
@@ -138,6 +153,7 @@ pub struct VaList<'a, 'f: 'a> {
             target_arch = "s390x",
             target_arch = "x86_64"
         ),
+        not(target_arch = "xtensa"),
         any(not(target_arch = "aarch64"), not(target_vendor = "apple")),
         not(target_family = "wasm"),
         not(target_os = "uefi"),
@@ -155,6 +171,7 @@ pub struct VaList<'a, 'f: 'a> {
         not(target_arch = "s390x"),
         not(target_arch = "x86_64")
     ),
+    target_arch = "xtensa",
     all(target_arch = "aarch64", target_vendor = "apple"),
     target_family = "wasm",
     target_os = "uefi",
@@ -173,8 +190,10 @@ impl<'f> VaListImpl<'f> {
         target_arch = "aarch64",
         target_arch = "powerpc",
         target_arch = "s390x",
+        target_arch = "xtensa",
         target_arch = "x86_64"
     ),
+    not(target_arch = "xtensa"),
     any(not(target_arch = "aarch64"), not(target_vendor = "apple")),
     not(target_family = "wasm"),
     not(target_os = "uefi"),
diff --git a/library/core/src/intrinsics/simd.rs b/library/core/src/intrinsics/simd.rs
index 0d24b0558c594..f80a60d471c04 100644
--- a/library/core/src/intrinsics/simd.rs
+++ b/library/core/src/intrinsics/simd.rs
@@ -619,7 +619,8 @@ extern "rust-intrinsic" {
     /// set has support for a fused operation, and that the fused operation is more efficient
     /// than the equivalent, separate pair of mul and add instructions. It is unspecified
     /// whether or not a fused operation is selected, and that may depend on optimization
-    /// level and context, for example.
+    /// level and context, for example. It may even be the case that some SIMD lanes get fused
+    /// and others do not.
     ///
     /// `T` must be a vector of floats.
     #[cfg(not(bootstrap))]
diff --git a/library/std/src/sys/backtrace.rs b/library/std/src/sys/backtrace.rs
index 4d939e175cf2e..efa6a896dad8f 100644
--- a/library/std/src/sys/backtrace.rs
+++ b/library/std/src/sys/backtrace.rs
@@ -58,8 +58,8 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
     let mut res = Ok(());
     let mut omitted_count: usize = 0;
     let mut first_omit = true;
-    // Start immediately if we're not using a short backtrace.
-    let mut start = print_fmt != PrintFmt::Short;
+    // If we're using a short backtrace, ignore all frames until we're told to start printing.
+    let mut print = print_fmt != PrintFmt::Short;
     set_image_base();
     // SAFETY: we roll our own locking in this town
     unsafe {
@@ -72,27 +72,25 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
             backtrace_rs::resolve_frame_unsynchronized(frame, |symbol| {
                 hit = true;
 
-                // Any frames between `__rust_begin_short_backtrace` and `__rust_end_short_backtrace`
-                // are omitted from the backtrace in short mode, `__rust_end_short_backtrace` will be
-                // called before the panic hook, so we won't ignore any frames if there is no
-                // invoke of `__rust_begin_short_backtrace`.
+                // `__rust_end_short_backtrace` means we are done hiding symbols
+                // for now. Print until we see `__rust_begin_short_backtrace`.
                 if print_fmt == PrintFmt::Short {
                     if let Some(sym) = symbol.name().and_then(|s| s.as_str()) {
-                        if start && sym.contains("__rust_begin_short_backtrace") {
-                            start = false;
+                        if sym.contains("__rust_end_short_backtrace") {
+                            print = true;
                             return;
                         }
-                        if sym.contains("__rust_end_short_backtrace") {
-                            start = true;
+                        if print && sym.contains("__rust_begin_short_backtrace") {
+                            print = false;
                             return;
                         }
-                        if !start {
+                        if !print {
                             omitted_count += 1;
                         }
                     }
                 }
 
-                if start {
+                if print {
                     if omitted_count > 0 {
                         debug_assert!(print_fmt == PrintFmt::Short);
                         // only print the message between the middle of frames
@@ -112,7 +110,7 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
             });
             #[cfg(target_os = "nto")]
             if libc::__my_thread_exit as *mut libc::c_void == frame.ip() {
-                if !hit && start {
+                if !hit && print {
                     use crate::backtrace_rs::SymbolName;
                     res = bt_fmt.frame().print_raw(
                         frame.ip(),
@@ -123,7 +121,7 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
                 }
                 return false;
             }
-            if !hit && start {
+            if !hit && print {
                 res = bt_fmt.frame().print_raw(frame.ip(), None, None, None);
             }
 
diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 762f4e653e91b..9ef9ccec1937f 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -1184,6 +1184,8 @@ def bootstrap(args):
     args = [build.bootstrap_binary()]
     args.extend(sys.argv[1:])
     env = os.environ.copy()
+    # The Python process ID is used when creating a Windows job object
+    # (see src\bootstrap\src\utils\job.rs)
     env["BOOTSTRAP_PARENT_ID"] = str(os.getpid())
     env["BOOTSTRAP_PYTHON"] = sys.executable
     run(args, env=env, verbose=build.verbose, is_bootstrap=True)
diff --git a/src/bootstrap/src/core/build_steps/setup.rs b/src/bootstrap/src/core/build_steps/setup.rs
index 3a8f9e48c0da2..7ed01f25c94b2 100644
--- a/src/bootstrap/src/core/build_steps/setup.rs
+++ b/src/bootstrap/src/core/build_steps/setup.rs
@@ -452,24 +452,26 @@ pub struct Hook;
 impl Step for Hook {
     type Output = ();
     const DEFAULT: bool = true;
+
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
         run.alias("hook")
     }
+
     fn make_run(run: RunConfig<'_>) {
-        if run.builder.config.dry_run() {
-            return;
-        }
         if let [cmd] = &run.paths[..] {
             if cmd.assert_single_path().path.as_path().as_os_str() == "hook" {
                 run.builder.ensure(Hook);
             }
         }
     }
+
     fn run(self, builder: &Builder<'_>) -> Self::Output {
         let config = &builder.config;
-        if config.dry_run() {
+
+        if config.dry_run() || !config.rust_info.is_managed_git_subrepository() {
             return;
         }
+
         t!(install_git_hook_maybe(builder, config));
     }
 }
diff --git a/src/bootstrap/src/utils/job.rs b/src/bootstrap/src/utils/job.rs
index c5e892450c4c5..fb69d331d27e1 100644
--- a/src/bootstrap/src/utils/job.rs
+++ b/src/bootstrap/src/utils/job.rs
@@ -15,11 +15,12 @@ pub unsafe fn setup(build: &mut crate::Build) {
 ///
 /// Most of the time when you're running a build system (e.g., make) you expect
 /// Ctrl-C or abnormal termination to actually terminate the entire tree of
-/// process in play, not just the one at the top. This currently works "by
+/// processes in play. This currently works "by
 /// default" on Unix platforms because Ctrl-C actually sends a signal to the
-/// *process group* rather than the parent process, so everything will get torn
-/// down. On Windows, however, this does not happen and Ctrl-C just kills the
-/// parent process.
+/// *process group* so everything will get torn
+/// down. On Windows, however, Ctrl-C is only sent to processes in the same console.
+/// If a process is detached or attached to another console, it won't receive the
+/// signal.
 ///
 /// To achieve the same semantics on Windows we use Job Objects to ensure that
 /// all processes die at the same time. Job objects have a mode of operation
@@ -87,15 +88,7 @@ mod for_windows {
         );
         assert!(r.is_ok(), "{}", io::Error::last_os_error());
 
-        // Assign our process to this job object. Note that if this fails, one very
-        // likely reason is that we are ourselves already in a job object! This can
-        // happen on the build bots that we've got for Windows, or if just anyone
-        // else is instrumenting the build. In this case we just bail out
-        // immediately and assume that they take care of it.
-        //
-        // Also note that nested jobs (why this might fail) are supported in recent
-        // versions of Windows, but the version of Windows that our bots are running
-        // at least don't support nested job objects.
+        // Assign our process to this job object.
         let r = AssignProcessToJobObject(job, GetCurrentProcess());
         if r.is_err() {
             CloseHandle(job).ok();
@@ -124,14 +117,19 @@ mod for_windows {
                 // (only when wrongly setting the environmental variable),
                 // it might be better to improve the experience of the second case
                 // when users have interrupted the parent process and we haven't finish
-                // duplicating the handle yet. We just need close the job object if that occurs.
-                CloseHandle(job).ok();
+                // duplicating the handle yet.
                 return;
             }
         };
 
         let mut parent_handle = HANDLE::default();
-        let r = DuplicateHandle(
+        // If this fails, well at least we tried! An example of DuplicateHandle
+        // failing in the past has been when the wrong python2 package spawned this
+        // build system (e.g., the `python2` package in MSYS instead of
+        // `mingw-w64-x86_64-python2`). Not sure why it failed, but the "failure
+        // mode" here is that we only clean everything up when the build system
+        // dies, not when the python parent does, so not too bad.
+        let _ = DuplicateHandle(
             GetCurrentProcess(),
             job,
             parent,
@@ -140,15 +138,6 @@ mod for_windows {
             false,
             DUPLICATE_SAME_ACCESS,
         );
-
-        // If this failed, well at least we tried! An example of DuplicateHandle
-        // failing in the past has been when the wrong python2 package spawned this
-        // build system (e.g., the `python2` package in MSYS instead of
-        // `mingw-w64-x86_64-python2`). Not sure why it failed, but the "failure
-        // mode" here is that we only clean everything up when the build system
-        // dies, not when the python parent does, so not too bad.
-        if r.is_err() {
-            CloseHandle(job).ok();
-        }
+        CloseHandle(parent).ok();
     }
 }
diff --git a/src/doc/rustc/src/platform-support.md b/src/doc/rustc/src/platform-support.md
index 243cb3b2fc832..3b82d123276d9 100644
--- a/src/doc/rustc/src/platform-support.md
+++ b/src/doc/rustc/src/platform-support.md
@@ -344,15 +344,15 @@ target | std | host | notes
 [`powerpc-wrs-vxworks-spe`](platform-support/vxworks.md) | ✓ |  |
 [`powerpc-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
 `powerpc64-unknown-freebsd` | ✓ | ✓ | PPC64 FreeBSD (ELFv1 and ELFv2)
-`powerpc64le-unknown-freebsd` |   |   | PPC64LE FreeBSD
-`powerpc-unknown-freebsd` |   |   | PowerPC FreeBSD
+`powerpc64le-unknown-freebsd` | ✓ | ✓ | PPC64LE FreeBSD
+`powerpc-unknown-freebsd` | ? |   | PowerPC FreeBSD
 `powerpc64-unknown-linux-musl` | ? |  | 64-bit PowerPC Linux with musl 1.2.3
 [`powerpc64-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
 `powerpc64le-unknown-linux-musl` | ? |  | 64-bit PowerPC Linux with musl 1.2.3, Little Endian
 [`powerpc64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/powerpc64
 [`powerpc64-ibm-aix`](platform-support/aix.md) | ? |  | 64-bit AIX (7.2 and newer)
-`riscv32gc-unknown-linux-gnu` |   |   | RISC-V Linux (kernel 5.4, glibc 2.33)
-`riscv32gc-unknown-linux-musl` |   |   | RISC-V Linux (kernel 5.4, musl 1.2.3 + RISCV32 support patches)
+`riscv32gc-unknown-linux-gnu` | ✓ |   | RISC-V Linux (kernel 5.4, glibc 2.33)
+`riscv32gc-unknown-linux-musl` | ? |   | RISC-V Linux (kernel 5.4, musl 1.2.3 + RISCV32 support patches)
 [`riscv32im-risc0-zkvm-elf`](platform-support/riscv32im-risc0-zkvm-elf.md) | ? |  | RISC Zero's zero-knowledge Virtual Machine (RV32IM ISA)
 [`riscv32ima-unknown-none-elf`](platform-support/riscv32-unknown-none-elf.md) | * |  | Bare RISC-V (RV32IMA ISA)
 [`riscv32imac-unknown-xous-elf`](platform-support/riscv32imac-unknown-xous-elf.md) | ? |  | RISC-V Xous (RV32IMAC ISA)
@@ -361,13 +361,13 @@ target | std | host | notes
 [`riscv32imafc-esp-espidf`](platform-support/esp-idf.md) | ✓ |  | RISC-V ESP-IDF
 [`riscv32-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
 [`riscv64gc-unknown-hermit`](platform-support/hermit.md) | ✓ |   | RISC-V Hermit
-`riscv64gc-unknown-freebsd` |   |   | RISC-V FreeBSD
-`riscv64gc-unknown-fuchsia` |   |   | RISC-V Fuchsia
+`riscv64gc-unknown-freebsd` | ? |   | RISC-V FreeBSD
+`riscv64gc-unknown-fuchsia` | ? |   | RISC-V Fuchsia
 [`riscv64gc-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | RISC-V NetBSD
 [`riscv64gc-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/riscv64
-[`riscv64-linux-android`](platform-support/android.md) |   |   | RISC-V 64-bit Android
+[`riscv64-linux-android`](platform-support/android.md) | ? |   | RISC-V 64-bit Android
 [`riscv64-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
-[`s390x-unknown-linux-musl`](platform-support/s390x-unknown-linux-musl.md) |  |  | S390x Linux (kernel 3.2, musl 1.2.3)
+[`s390x-unknown-linux-musl`](platform-support/s390x-unknown-linux-musl.md) | ✓ |  | S390x Linux (kernel 3.2, musl 1.2.3)
 `sparc-unknown-linux-gnu` | ✓ |  | 32-bit SPARC Linux
 [`sparc-unknown-none-elf`](./platform-support/sparc-unknown-none-elf.md) | * |  | Bare 32-bit SPARC V7+
 [`sparc64-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/sparc64