MachineFunction: -fsanitize={function,kcfi}: ensure 4-byte alignment

Fix https://github.com/llvm/llvm-project/issues/63579
```
% cat a.c
void foo() {}
% clang --target=arm-none-eabi -mthumb -mno-una

MachineFunction: -fsanitize={function,kcfi}: ensure 4-byte alignment

Fix https://github.com/llvm/llvm-project/issues/63579
```
% cat a.c
void foo() {}
% clang --target=arm-none-eabi -mthumb -mno-unaligned-access -fsanitize=kcfi a.c -S -o - | grep p2align
.p2align 1
% clang --target=armv6m-none-eabi -fsanitize=function a.c -S -o - | grep p2align
.p2align 1
```

Ensure that -fsanitize={function,kcfi} instrumented functions are aligned by at
least 4, so that loading the type hash before the function label will not cause
a misaligned access. This is especially important for -mno-unaligned-access
configurations that don't set `setMinFunctionAlignment` to 4 or greater.

With this patch, the generated assembly for the examples above will contain `.p2align 2`
before the type hash.

If `__attribute__((aligned(N)))` or `-falign-functions=N` is specified, the
larger alignment will be used.

Reviewed By: simon_tatham, samitolvanen

Differential Revision: https://reviews.llvm.org/D154125

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[RISCV] Implement KCFI operand bundle lowering

With `-fsanitize=kcfi` (Kernel Control-Flow Integrity), Clang emits
"kcfi" operand bundles to indirect call instructions. Similarly to
the target-speci

[RISCV] Implement KCFI operand bundle lowering

With `-fsanitize=kcfi` (Kernel Control-Flow Integrity), Clang emits
"kcfi" operand bundles to indirect call instructions. Similarly to
the target-specific lowering added in D119296, implement KCFI operand
bundle lowering for RISC-V.

This patch disables the generic KCFI pass for RISC-V in Clang, and
adds the KCFI machine function pass in `RISCVPassConfig::addPreSched`
to emit target-specific `KCFI_CHECK` pseudo instructions before calls
that have KCFI operand bundles. The machine function pass also bundles
the instructions to ensure we emit the checks immediately before the
calls, which is not possible with the generic pass.

`KCFI_CHECK` instructions are lowered in `RISCVAsmPrinter` to a
contiguous code sequence that traps if the expected hash in the
operand bundle doesn't match the hash before the target function
address. This patch emits an `ebreak` instruction for error handling
to match the Linux kernel's `BUG()` implementation. Just like for X86,
we also emit trap locations to a `.kcfi_traps` section to support
error handling, as we cannot embed additional information to the trap
instruction itself.

Relands commit 62fa708ceb027713b386c7e0efda994f8bdc27e2 with fixed
tests.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D148385

show more ...

[RISCV] Implement KCFI operand bundle lowering

With `-fsanitize=kcfi` (Kernel Control-Flow Integrity), Clang emits
"kcfi" operand bundles to indirect call instructions. Similarly to
the target-speci

[RISCV] Implement KCFI operand bundle lowering

With `-fsanitize=kcfi` (Kernel Control-Flow Integrity), Clang emits
"kcfi" operand bundles to indirect call instructions. Similarly to
the target-specific lowering added in D119296, implement KCFI operand
bundle lowering for RISC-V.

This patch disables the generic KCFI pass for RISC-V in Clang, and
adds the KCFI machine function pass in `RISCVPassConfig::addPreSched`
to emit target-specific `KCFI_CHECK` pseudo instructions before calls
that have KCFI operand bundles. The machine function pass also bundles
the instructions to ensure we emit the checks immediately before the
calls, which is not possible with the generic pass.

`KCFI_CHECK` instructions are lowered in `RISCVAsmPrinter` to a
contiguous code sequence that traps if the expected hash in the
operand bundle doesn't match the hash before the target function
address. This patch emits an `ebreak` instruction for error handling
to match the Linux kernel's `BUG()` implementation. Just like for X86,
we also emit trap locations to a `.kcfi_traps` section to support
error handling, as we cannot embed additional information to the trap
instruction itself.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D148385

show more ...