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With -fpatchable-function-entry (or the patchable_function_entry function attribute), we emit records of patchable entry locations to the __patchable_function_entries section. Add an additional parameter to the command line option that allows one to specify a different default section name for the records, and an identical parameter to the function attribute that allows one to override the section used. The main use case for this change is the Linux kernel using prefix NOPs for ftrace, and thus depending on__patchable_function_entries to locate traceable functions. Functions that are not traceable currently disable entry NOPs using the function attribute, but this creates a compatibility issue with -fsanitize=kcfi, which expects all indirectly callable functions to have a type hash prefix at the same offset from the function entry. Adding a section parameter would allow the kernel to distinguish between traceable and non-traceable functions by adding entry records to separate sections while maintaining a stable function prefix layout for all functions. LKML discussion: https://lore.kernel.org/lkml/Y1QEzk%2FA41PKLEPe@hirez.programming.kicks-ass.net/
114 lines
3.5 KiB
LLVM
114 lines
3.5 KiB
LLVM
; RUN: llc -mtriple=i386 %s -o - | FileCheck --check-prefixes=CHECK,X86 %s
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; RUN: llc -mtriple=x86_64 %s -o - | FileCheck --check-prefixes=CHECK,X64 %s
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; RUN: llc -mtriple=x86_64 -function-sections %s -o - | FileCheck --check-prefixes=CHECK,X64 %s
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define void @f0() "patchable-function-entry"="0" {
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; CHECK-LABEL: f0:
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; CHECK-NEXT: .Lfunc_begin0:
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; CHECK-NOT: nop
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; CHECK: ret
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; CHECK-NOT: .section __patchable_function_entries
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ret void
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}
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define void @f1() "patchable-function-entry"="1" {
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; CHECK-LABEL: f1:
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; CHECK-NEXT: .Lfunc_begin1:
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; CHECK: nop
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; CHECK-NEXT: ret
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; CHECK: .section __patchable_function_entries,"awo",@progbits,f1{{$}}
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; X86: .p2align 2
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; X86-NEXT: .long .Lfunc_begin1
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; X64: .p2align 3
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; X64-NEXT: .quad .Lfunc_begin1
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ret void
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}
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;; Without -function-sections, f2 is in the same text section as f1.
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;; They share the __patchable_function_entries section.
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;; With -function-sections, f1 and f2 are in different text sections.
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;; Use separate __patchable_function_entries.
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define void @f2() "patchable-function-entry"="2" {
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; CHECK-LABEL: f2:
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; CHECK-NEXT: .Lfunc_begin2:
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; X86: xchgw %ax, %ax
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; X64: xchgw %ax, %ax
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; CHECK-NEXT: ret
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; CHECK: .section __patchable_function_entries,"awo",@progbits,f2{{$}}
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; X86: .p2align 2
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; X86-NEXT: .long .Lfunc_begin2
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; X64: .p2align 3
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; X64-NEXT: .quad .Lfunc_begin2
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ret void
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}
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$f3 = comdat any
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define void @f3() "patchable-function-entry"="3" comdat {
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; CHECK-LABEL: f3:
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; CHECK-NEXT: .Lfunc_begin3:
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; X86: xchgw %ax, %ax
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; X86-NEXT: nop
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; X64: nopl (%rax)
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; CHECK: ret
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; CHECK: .section __patchable_function_entries,"awoG",@progbits,f3,f3,comdat{{$}}
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; X86: .p2align 2
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; X86-NEXT: .long .Lfunc_begin3
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; X64: .p2align 3
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; X64-NEXT: .quad .Lfunc_begin3
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ret void
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}
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$f5 = comdat any
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define void @f5() "patchable-function-entry"="5" comdat {
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; CHECK-LABEL: f5:
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; CHECK-NEXT: .Lfunc_begin4:
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; X86-COUNT-2: xchgw %ax, %ax
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; X86-NEXT: nop
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; X64: nopl 8(%rax,%rax)
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; CHECK-NEXT: ret
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; CHECK: .section __patchable_function_entries,"awoG",@progbits,f5,f5,comdat{{$}}
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; X86: .p2align 2
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; X86-NEXT: .long .Lfunc_begin4
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; X64: .p2align 3
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; X64-NEXT: .quad .Lfunc_begin4
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ret void
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}
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;; -fpatchable-function-entry=3,2
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;; "patchable-function-prefix" emits data before the function entry label.
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;; We emit 1-byte NOPs before the function entry, so that with a partial patch,
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;; the remaining instructions do not need to be modified.
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define void @f3_2() "patchable-function-entry"="1" "patchable-function-prefix"="2" {
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; CHECK-LABEL: .type f3_2,@function
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; CHECK-NEXT: .Ltmp0:
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; CHECK-NEXT: nop
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; CHECK-NEXT: nop
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; CHECK-NEXT: f3_2: # @f3_2
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; CHECK: # %bb.0:
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; CHECK-NEXT: nop
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; CHECK-NEXT: ret
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;; .size does not include the prefix.
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; CHECK: .Lfunc_end5:
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; CHECK-NEXT: .size f3_2, .Lfunc_end5-f3_2
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; CHECK: .section __patchable_function_entries,"awo",@progbits,f3_2{{$}}
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; X86: .p2align 2
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; X86-NEXT: .long .Ltmp0
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; X64: .p2align 3
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; X64-NEXT: .quad .Ltmp0
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%frame = alloca i8, i32 16
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ret void
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}
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define void @s1() "patchable-function-entry"="1" "patchable-function-entry-section"=".entries" {
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; CHECK-LABEL: s1:
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; CHECK-NEXT: .Lfunc_begin6:
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; CHECK: nop
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; CHECK-NEXT: ret
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; CHECK: .section .entries,"awo",@progbits,s1{{$}}
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; X86: .p2align 2
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; X86-NEXT: .long .Lfunc_begin6
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; X64: .p2align 3
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; X64-NEXT: .quad .Lfunc_begin6
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ret void
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}
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