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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/
42 lines
2.1 KiB
C
42 lines
2.1 KiB
C
// RUN: %clang_cc1 -triple aarch64 -emit-llvm %s -o - | FileCheck --check-prefixes=COMMON,NODEFAULT %s
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// RUN: %clang_cc1 -triple x86_64 -emit-llvm %s -fpatchable-function-entry=1 -fpatchable-function-entry-section=__default_section -o - | FileCheck --check-prefixes=COMMON,DEFAULT %s
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// COMMON: define{{.*}} void @f0() #0
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__attribute__((patchable_function_entry(0))) void f0(void) {}
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// COMMON: define{{.*}} void @f00() #0
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__attribute__((patchable_function_entry(0, 0, "__unused_section"))) void f00(void) {}
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// COMMON: define{{.*}} void @f2() #1
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__attribute__((patchable_function_entry(2))) void f2(void) {}
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// COMMON: define{{.*}} void @f20() #2
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__attribute__((patchable_function_entry(2, 0, "__attr_section"))) void f20(void) {}
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// COMMON: define{{.*}} void @f44() #3
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__attribute__((patchable_function_entry(4, 4))) void f44(void) {}
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// COMMON: define{{.*}} void @f52() #4
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__attribute__((patchable_function_entry(5, 2, "__attr_section"))) void f52(void) {}
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// OPT: define{{.*}} void @f() #5
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void f(void) {}
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/// No need to emit "patchable-function-entry" and thus also "patchable-function-entry-section"
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// COMMON: attributes #0 = { {{.*}}
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// COMMON-NOT: "patchable-function-entry-section"
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// NODEFAULT: attributes #1 = { {{.*}} "patchable-function-entry"="2"
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// NODEFAULT-NOT: "patchable-function-entry-section"
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// DEFAULT: attributes #1 = { {{.*}} "patchable-function-entry"="2" "patchable-function-entry-section"="__default_section"
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// COMMON: attributes #2 = { {{.*}} "patchable-function-entry"="2" "patchable-function-entry-section"="__attr_section"
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// NODEFAULT: attributes #3 = { {{.*}} "patchable-function-entry"="0" "patchable-function-prefix"="4"
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// NODEFAULT-NOT: "patchable-function-entry-section"
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// DEFAULT: attributes #3 = { {{.*}} "patchable-function-entry"="0" "patchable-function-entry-section"="__default_section" "patchable-function-prefix"="4"
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// COMMON: attributes #4 = { {{.*}} "patchable-function-entry"="3" "patchable-function-entry-section"="__attr_section" "patchable-function-prefix"="2"
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// DEFAULT: attributes #5 = { {{.*}} "patchable-function-entry"="1" "patchable-function-entry-section"="__default_section"
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