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llvm-project/llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll

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hwasan: Move memory access checks into small outlined functions on aarch64. Each hwasan check requires emitting a small piece of code like this: https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html#memory-accesses The problem with this is that these code blocks typically bloat code size significantly. An obvious solution is to outline these blocks of code. In fact, this has already been implemented under the -hwasan-instrument-with-calls flag. However, as currently implemented this has a number of problems: - The functions use the same calling convention as regular C functions. This means that the backend must spill all temporary registers as required by the platform's C calling convention, even though the check only needs two registers on the hot path. - The functions take the address to be checked in a fixed register, which increases register pressure. Both of these factors can diminish the code size effect and increase the performance hit of -hwasan-instrument-with-calls. The solution that this patch implements is to involve the aarch64 backend in outlining the checks. An intrinsic and pseudo-instruction are created to represent a hwasan check. The pseudo-instruction is register allocated like any other instruction, and we allow the register allocator to select almost any register for the address to check. A particular combination of (register selection, type of check) triggers the creation in the backend of a function to handle the check for specifically that pair. The resulting functions are deduplicated by the linker. The pseudo-instruction (really the function) is specified to preserve all registers except for the registers that the AAPCS specifies may be clobbered by a call. To measure the code size and performance effect of this change, I took a number of measurements using Chromium for Android on aarch64, comparing a browser with inlined checks (the baseline) against a browser with outlined checks. Code size: Size of .text decreases from 243897420 to 171619972 bytes, or a 30% decrease. Performance: Using Chromium's blink_perf.layout microbenchmarks I measured a median performance regression of 6.24%. The fact that a perf/size tradeoff is evident here suggests that we might want to make the new behaviour conditional on -Os/-Oz. But for now I've enabled it unconditionally, my reasoning being that hwasan users typically expect a relatively large perf hit, and ~6% isn't really adding much. We may want to revisit this decision in the future, though. I also tried experimenting with varying the number of registers selectable by the hwasan check pseudo-instruction (which would result in fewer variants being created), on the hypothesis that creating fewer variants of the function would expose another perf/size tradeoff by reducing icache pressure from the check functions at the cost of register pressure. Although I did observe a code size increase with fewer registers, I did not observe a strong correlation between the number of registers and the performance of the resulting browser on the microbenchmarks, so I conclude that we might as well use ~all registers to get the maximum code size improvement. My results are below: Regs | .text size | Perf hit -----+------------+--------- ~all | 171619972 | 6.24% 16 | 171765192 | 7.03% 8 | 172917788 | 5.82% 4 | 177054016 | 6.89% Differential Revision: https://reviews.llvm.org/D56954 llvm-svn: 351920
2019-01-23 10:20:10 +08:00
; RUN: llc < %s | FileCheck %s
target triple = "aarch64--linux-android"
define i8* @f1(i8* %x0, i8* %x1) {
; CHECK: f1:
; CHECK: str x30, [sp, #-16]!
; CHECK-NEXT: .cfi_def_cfa_offset 16
; CHECK-NEXT: .cfi_offset w30, -16
; CHECK-NEXT: mov x9, x0
; CHECK-NEXT: bl __hwasan_check_x1_123
; CHECK-NEXT: mov x0, x1
; CHECK-NEXT: ldr x30, [sp], #16
; CHECK-NEXT: ret
call void @llvm.hwasan.check.memaccess(i8* %x0, i8* %x1, i32 123)
ret i8* %x1
}
define i8* @f2(i8* %x0, i8* %x1) {
; CHECK: f2:
; CHECK: str x30, [sp, #-16]!
; CHECK-NEXT: .cfi_def_cfa_offset 16
; CHECK-NEXT: .cfi_offset w30, -16
; CHECK-NEXT: mov x9, x1
; CHECK-NEXT: bl __hwasan_check_x0_456
; CHECK-NEXT: ldr x30, [sp], #16
; CHECK-NEXT: ret
call void @llvm.hwasan.check.memaccess(i8* %x1, i8* %x0, i32 456)
ret i8* %x0
}
declare void @llvm.hwasan.check.memaccess(i8*, i8*, i32)
; CHECK: .section .text.hot,"axG",@progbits,__hwasan_check_x0_456,comdat
; CHECK-NEXT: .type __hwasan_check_x0_456,@function
; CHECK-NEXT: .weak __hwasan_check_x0_456
; CHECK-NEXT: .hidden __hwasan_check_x0_456
; CHECK-NEXT: __hwasan_check_x0_456:
; CHECK-NEXT: ubfx x16, x0, #4, #52
; CHECK-NEXT: ldrb w16, [x9, x16]
hwasan: Shrink outlined checks by 1 instruction. Turns out that we can save an instruction by folding the right shift into the compare. Differential Revision: https://reviews.llvm.org/D63568 llvm-svn: 363874
2019-06-20 04:40:03 +08:00
; CHECK-NEXT: cmp x16, x0, lsr #56
hwasan: Move memory access checks into small outlined functions on aarch64. Each hwasan check requires emitting a small piece of code like this: https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html#memory-accesses The problem with this is that these code blocks typically bloat code size significantly. An obvious solution is to outline these blocks of code. In fact, this has already been implemented under the -hwasan-instrument-with-calls flag. However, as currently implemented this has a number of problems: - The functions use the same calling convention as regular C functions. This means that the backend must spill all temporary registers as required by the platform's C calling convention, even though the check only needs two registers on the hot path. - The functions take the address to be checked in a fixed register, which increases register pressure. Both of these factors can diminish the code size effect and increase the performance hit of -hwasan-instrument-with-calls. The solution that this patch implements is to involve the aarch64 backend in outlining the checks. An intrinsic and pseudo-instruction are created to represent a hwasan check. The pseudo-instruction is register allocated like any other instruction, and we allow the register allocator to select almost any register for the address to check. A particular combination of (register selection, type of check) triggers the creation in the backend of a function to handle the check for specifically that pair. The resulting functions are deduplicated by the linker. The pseudo-instruction (really the function) is specified to preserve all registers except for the registers that the AAPCS specifies may be clobbered by a call. To measure the code size and performance effect of this change, I took a number of measurements using Chromium for Android on aarch64, comparing a browser with inlined checks (the baseline) against a browser with outlined checks. Code size: Size of .text decreases from 243897420 to 171619972 bytes, or a 30% decrease. Performance: Using Chromium's blink_perf.layout microbenchmarks I measured a median performance regression of 6.24%. The fact that a perf/size tradeoff is evident here suggests that we might want to make the new behaviour conditional on -Os/-Oz. But for now I've enabled it unconditionally, my reasoning being that hwasan users typically expect a relatively large perf hit, and ~6% isn't really adding much. We may want to revisit this decision in the future, though. I also tried experimenting with varying the number of registers selectable by the hwasan check pseudo-instruction (which would result in fewer variants being created), on the hypothesis that creating fewer variants of the function would expose another perf/size tradeoff by reducing icache pressure from the check functions at the cost of register pressure. Although I did observe a code size increase with fewer registers, I did not observe a strong correlation between the number of registers and the performance of the resulting browser on the microbenchmarks, so I conclude that we might as well use ~all registers to get the maximum code size improvement. My results are below: Regs | .text size | Perf hit -----+------------+--------- ~all | 171619972 | 6.24% 16 | 171765192 | 7.03% 8 | 172917788 | 5.82% 4 | 177054016 | 6.89% Differential Revision: https://reviews.llvm.org/D56954 llvm-svn: 351920
2019-01-23 10:20:10 +08:00
; CHECK-NEXT: b.ne .Ltmp0
; CHECK-NEXT: ret
; CHECK-NEXT: .Ltmp0:
[HWASan] Save + print registers when tag mismatch occurs in AArch64. Summary: This change change the instrumentation to allow users to view the registers at the point at which tag mismatch occured. Most of the heavy lifting is done in the runtime library, where we save the registers to the stack and emit unwind information. This allows us to reduce the overhead, as very little additional work needs to be done in each __hwasan_check instance. In this implementation, the fast path of __hwasan_check is unmodified. There are an additional 4 instructions (16B) emitted in the slow path in every __hwasan_check instance. This may increase binary size somewhat, but as most of the work is done in the runtime library, it's manageable. The failure trace now contains a list of registers at the point of which the failure occured, in a format similar to that of Android's tombstones. It currently has the following format: Registers where the failure occurred (pc 0x0055555561b4): x0 0000000000000014 x1 0000007ffffff6c0 x2 1100007ffffff6d0 x3 12000056ffffe025 x4 0000007fff800000 x5 0000000000000014 x6 0000007fff800000 x7 0000000000000001 x8 12000056ffffe020 x9 0200007700000000 x10 0200007700000000 x11 0000000000000000 x12 0000007fffffdde0 x13 0000000000000000 x14 02b65b01f7a97490 x15 0000000000000000 x16 0000007fb77376b8 x17 0000000000000012 x18 0000007fb7ed6000 x19 0000005555556078 x20 0000007ffffff768 x21 0000007ffffff778 x22 0000000000000001 x23 0000000000000000 x24 0000000000000000 x25 0000000000000000 x26 0000000000000000 x27 0000000000000000 x28 0000000000000000 x29 0000007ffffff6f0 x30 00000055555561b4 ... and prints after the dump of memory tags around the buggy address. Every register is saved exactly as it was at the point where the tag mismatch occurs, with the exception of x16/x17. These registers are used in the tag mismatch calculation as scratch registers during __hwasan_check, and cannot be saved without affecting the fast path. As these registers are designated as scratch registers for linking, there should be no important information in them that could aid in debugging. Reviewers: pcc, eugenis Reviewed By: pcc, eugenis Subscribers: srhines, kubamracek, mgorny, javed.absar, krytarowski, kristof.beyls, hiraditya, jdoerfert, llvm-commits, #sanitizers Tags: #sanitizers, #llvm Differential Revision: https://reviews.llvm.org/D58857 llvm-svn: 355738
2019-03-09 05:22:35 +08:00
; CHECK-NEXT: stp x0, x1, [sp, #-256]!
; CHECK-NEXT: stp x29, x30, [sp, #232]
hwasan: Move memory access checks into small outlined functions on aarch64. Each hwasan check requires emitting a small piece of code like this: https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html#memory-accesses The problem with this is that these code blocks typically bloat code size significantly. An obvious solution is to outline these blocks of code. In fact, this has already been implemented under the -hwasan-instrument-with-calls flag. However, as currently implemented this has a number of problems: - The functions use the same calling convention as regular C functions. This means that the backend must spill all temporary registers as required by the platform's C calling convention, even though the check only needs two registers on the hot path. - The functions take the address to be checked in a fixed register, which increases register pressure. Both of these factors can diminish the code size effect and increase the performance hit of -hwasan-instrument-with-calls. The solution that this patch implements is to involve the aarch64 backend in outlining the checks. An intrinsic and pseudo-instruction are created to represent a hwasan check. The pseudo-instruction is register allocated like any other instruction, and we allow the register allocator to select almost any register for the address to check. A particular combination of (register selection, type of check) triggers the creation in the backend of a function to handle the check for specifically that pair. The resulting functions are deduplicated by the linker. The pseudo-instruction (really the function) is specified to preserve all registers except for the registers that the AAPCS specifies may be clobbered by a call. To measure the code size and performance effect of this change, I took a number of measurements using Chromium for Android on aarch64, comparing a browser with inlined checks (the baseline) against a browser with outlined checks. Code size: Size of .text decreases from 243897420 to 171619972 bytes, or a 30% decrease. Performance: Using Chromium's blink_perf.layout microbenchmarks I measured a median performance regression of 6.24%. The fact that a perf/size tradeoff is evident here suggests that we might want to make the new behaviour conditional on -Os/-Oz. But for now I've enabled it unconditionally, my reasoning being that hwasan users typically expect a relatively large perf hit, and ~6% isn't really adding much. We may want to revisit this decision in the future, though. I also tried experimenting with varying the number of registers selectable by the hwasan check pseudo-instruction (which would result in fewer variants being created), on the hypothesis that creating fewer variants of the function would expose another perf/size tradeoff by reducing icache pressure from the check functions at the cost of register pressure. Although I did observe a code size increase with fewer registers, I did not observe a strong correlation between the number of registers and the performance of the resulting browser on the microbenchmarks, so I conclude that we might as well use ~all registers to get the maximum code size improvement. My results are below: Regs | .text size | Perf hit -----+------------+--------- ~all | 171619972 | 6.24% 16 | 171765192 | 7.03% 8 | 172917788 | 5.82% 4 | 177054016 | 6.89% Differential Revision: https://reviews.llvm.org/D56954 llvm-svn: 351920
2019-01-23 10:20:10 +08:00
; CHECK-NEXT: mov x1, #456
[HWASan] Save + print registers when tag mismatch occurs in AArch64. Summary: This change change the instrumentation to allow users to view the registers at the point at which tag mismatch occured. Most of the heavy lifting is done in the runtime library, where we save the registers to the stack and emit unwind information. This allows us to reduce the overhead, as very little additional work needs to be done in each __hwasan_check instance. In this implementation, the fast path of __hwasan_check is unmodified. There are an additional 4 instructions (16B) emitted in the slow path in every __hwasan_check instance. This may increase binary size somewhat, but as most of the work is done in the runtime library, it's manageable. The failure trace now contains a list of registers at the point of which the failure occured, in a format similar to that of Android's tombstones. It currently has the following format: Registers where the failure occurred (pc 0x0055555561b4): x0 0000000000000014 x1 0000007ffffff6c0 x2 1100007ffffff6d0 x3 12000056ffffe025 x4 0000007fff800000 x5 0000000000000014 x6 0000007fff800000 x7 0000000000000001 x8 12000056ffffe020 x9 0200007700000000 x10 0200007700000000 x11 0000000000000000 x12 0000007fffffdde0 x13 0000000000000000 x14 02b65b01f7a97490 x15 0000000000000000 x16 0000007fb77376b8 x17 0000000000000012 x18 0000007fb7ed6000 x19 0000005555556078 x20 0000007ffffff768 x21 0000007ffffff778 x22 0000000000000001 x23 0000000000000000 x24 0000000000000000 x25 0000000000000000 x26 0000000000000000 x27 0000000000000000 x28 0000000000000000 x29 0000007ffffff6f0 x30 00000055555561b4 ... and prints after the dump of memory tags around the buggy address. Every register is saved exactly as it was at the point where the tag mismatch occurs, with the exception of x16/x17. These registers are used in the tag mismatch calculation as scratch registers during __hwasan_check, and cannot be saved without affecting the fast path. As these registers are designated as scratch registers for linking, there should be no important information in them that could aid in debugging. Reviewers: pcc, eugenis Reviewed By: pcc, eugenis Subscribers: srhines, kubamracek, mgorny, javed.absar, krytarowski, kristof.beyls, hiraditya, jdoerfert, llvm-commits, #sanitizers Tags: #sanitizers, #llvm Differential Revision: https://reviews.llvm.org/D58857 llvm-svn: 355738
2019-03-09 05:22:35 +08:00
; CHECK-NEXT: adrp x16, :got:__hwasan_tag_mismatch
; CHECK-NEXT: ldr x16, [x16, :got_lo12:__hwasan_tag_mismatch]
; CHECK-NEXT: br x16
hwasan: Move memory access checks into small outlined functions on aarch64. Each hwasan check requires emitting a small piece of code like this: https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html#memory-accesses The problem with this is that these code blocks typically bloat code size significantly. An obvious solution is to outline these blocks of code. In fact, this has already been implemented under the -hwasan-instrument-with-calls flag. However, as currently implemented this has a number of problems: - The functions use the same calling convention as regular C functions. This means that the backend must spill all temporary registers as required by the platform's C calling convention, even though the check only needs two registers on the hot path. - The functions take the address to be checked in a fixed register, which increases register pressure. Both of these factors can diminish the code size effect and increase the performance hit of -hwasan-instrument-with-calls. The solution that this patch implements is to involve the aarch64 backend in outlining the checks. An intrinsic and pseudo-instruction are created to represent a hwasan check. The pseudo-instruction is register allocated like any other instruction, and we allow the register allocator to select almost any register for the address to check. A particular combination of (register selection, type of check) triggers the creation in the backend of a function to handle the check for specifically that pair. The resulting functions are deduplicated by the linker. The pseudo-instruction (really the function) is specified to preserve all registers except for the registers that the AAPCS specifies may be clobbered by a call. To measure the code size and performance effect of this change, I took a number of measurements using Chromium for Android on aarch64, comparing a browser with inlined checks (the baseline) against a browser with outlined checks. Code size: Size of .text decreases from 243897420 to 171619972 bytes, or a 30% decrease. Performance: Using Chromium's blink_perf.layout microbenchmarks I measured a median performance regression of 6.24%. The fact that a perf/size tradeoff is evident here suggests that we might want to make the new behaviour conditional on -Os/-Oz. But for now I've enabled it unconditionally, my reasoning being that hwasan users typically expect a relatively large perf hit, and ~6% isn't really adding much. We may want to revisit this decision in the future, though. I also tried experimenting with varying the number of registers selectable by the hwasan check pseudo-instruction (which would result in fewer variants being created), on the hypothesis that creating fewer variants of the function would expose another perf/size tradeoff by reducing icache pressure from the check functions at the cost of register pressure. Although I did observe a code size increase with fewer registers, I did not observe a strong correlation between the number of registers and the performance of the resulting browser on the microbenchmarks, so I conclude that we might as well use ~all registers to get the maximum code size improvement. My results are below: Regs | .text size | Perf hit -----+------------+--------- ~all | 171619972 | 6.24% 16 | 171765192 | 7.03% 8 | 172917788 | 5.82% 4 | 177054016 | 6.89% Differential Revision: https://reviews.llvm.org/D56954 llvm-svn: 351920
2019-01-23 10:20:10 +08:00
; CHECK: .section .text.hot,"axG",@progbits,__hwasan_check_x1_123,comdat
; CHECK-NEXT: .type __hwasan_check_x1_123,@function
; CHECK-NEXT: .weak __hwasan_check_x1_123
; CHECK-NEXT: .hidden __hwasan_check_x1_123
; CHECK-NEXT: __hwasan_check_x1_123:
; CHECK-NEXT: ubfx x16, x1, #4, #52
; CHECK-NEXT: ldrb w16, [x9, x16]
hwasan: Shrink outlined checks by 1 instruction. Turns out that we can save an instruction by folding the right shift into the compare. Differential Revision: https://reviews.llvm.org/D63568 llvm-svn: 363874
2019-06-20 04:40:03 +08:00
; CHECK-NEXT: cmp x16, x1, lsr #56
hwasan: Move memory access checks into small outlined functions on aarch64. Each hwasan check requires emitting a small piece of code like this: https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html#memory-accesses The problem with this is that these code blocks typically bloat code size significantly. An obvious solution is to outline these blocks of code. In fact, this has already been implemented under the -hwasan-instrument-with-calls flag. However, as currently implemented this has a number of problems: - The functions use the same calling convention as regular C functions. This means that the backend must spill all temporary registers as required by the platform's C calling convention, even though the check only needs two registers on the hot path. - The functions take the address to be checked in a fixed register, which increases register pressure. Both of these factors can diminish the code size effect and increase the performance hit of -hwasan-instrument-with-calls. The solution that this patch implements is to involve the aarch64 backend in outlining the checks. An intrinsic and pseudo-instruction are created to represent a hwasan check. The pseudo-instruction is register allocated like any other instruction, and we allow the register allocator to select almost any register for the address to check. A particular combination of (register selection, type of check) triggers the creation in the backend of a function to handle the check for specifically that pair. The resulting functions are deduplicated by the linker. The pseudo-instruction (really the function) is specified to preserve all registers except for the registers that the AAPCS specifies may be clobbered by a call. To measure the code size and performance effect of this change, I took a number of measurements using Chromium for Android on aarch64, comparing a browser with inlined checks (the baseline) against a browser with outlined checks. Code size: Size of .text decreases from 243897420 to 171619972 bytes, or a 30% decrease. Performance: Using Chromium's blink_perf.layout microbenchmarks I measured a median performance regression of 6.24%. The fact that a perf/size tradeoff is evident here suggests that we might want to make the new behaviour conditional on -Os/-Oz. But for now I've enabled it unconditionally, my reasoning being that hwasan users typically expect a relatively large perf hit, and ~6% isn't really adding much. We may want to revisit this decision in the future, though. I also tried experimenting with varying the number of registers selectable by the hwasan check pseudo-instruction (which would result in fewer variants being created), on the hypothesis that creating fewer variants of the function would expose another perf/size tradeoff by reducing icache pressure from the check functions at the cost of register pressure. Although I did observe a code size increase with fewer registers, I did not observe a strong correlation between the number of registers and the performance of the resulting browser on the microbenchmarks, so I conclude that we might as well use ~all registers to get the maximum code size improvement. My results are below: Regs | .text size | Perf hit -----+------------+--------- ~all | 171619972 | 6.24% 16 | 171765192 | 7.03% 8 | 172917788 | 5.82% 4 | 177054016 | 6.89% Differential Revision: https://reviews.llvm.org/D56954 llvm-svn: 351920
2019-01-23 10:20:10 +08:00
; CHECK-NEXT: b.ne .Ltmp1
; CHECK-NEXT: ret
; CHECK-NEXT: .Ltmp1:
[HWASan] Save + print registers when tag mismatch occurs in AArch64. Summary: This change change the instrumentation to allow users to view the registers at the point at which tag mismatch occured. Most of the heavy lifting is done in the runtime library, where we save the registers to the stack and emit unwind information. This allows us to reduce the overhead, as very little additional work needs to be done in each __hwasan_check instance. In this implementation, the fast path of __hwasan_check is unmodified. There are an additional 4 instructions (16B) emitted in the slow path in every __hwasan_check instance. This may increase binary size somewhat, but as most of the work is done in the runtime library, it's manageable. The failure trace now contains a list of registers at the point of which the failure occured, in a format similar to that of Android's tombstones. It currently has the following format: Registers where the failure occurred (pc 0x0055555561b4): x0 0000000000000014 x1 0000007ffffff6c0 x2 1100007ffffff6d0 x3 12000056ffffe025 x4 0000007fff800000 x5 0000000000000014 x6 0000007fff800000 x7 0000000000000001 x8 12000056ffffe020 x9 0200007700000000 x10 0200007700000000 x11 0000000000000000 x12 0000007fffffdde0 x13 0000000000000000 x14 02b65b01f7a97490 x15 0000000000000000 x16 0000007fb77376b8 x17 0000000000000012 x18 0000007fb7ed6000 x19 0000005555556078 x20 0000007ffffff768 x21 0000007ffffff778 x22 0000000000000001 x23 0000000000000000 x24 0000000000000000 x25 0000000000000000 x26 0000000000000000 x27 0000000000000000 x28 0000000000000000 x29 0000007ffffff6f0 x30 00000055555561b4 ... and prints after the dump of memory tags around the buggy address. Every register is saved exactly as it was at the point where the tag mismatch occurs, with the exception of x16/x17. These registers are used in the tag mismatch calculation as scratch registers during __hwasan_check, and cannot be saved without affecting the fast path. As these registers are designated as scratch registers for linking, there should be no important information in them that could aid in debugging. Reviewers: pcc, eugenis Reviewed By: pcc, eugenis Subscribers: srhines, kubamracek, mgorny, javed.absar, krytarowski, kristof.beyls, hiraditya, jdoerfert, llvm-commits, #sanitizers Tags: #sanitizers, #llvm Differential Revision: https://reviews.llvm.org/D58857 llvm-svn: 355738
2019-03-09 05:22:35 +08:00
; CHECK-NEXT: stp x0, x1, [sp, #-256]!
; CHECK-NEXT: stp x29, x30, [sp, #232]
hwasan: Move memory access checks into small outlined functions on aarch64. Each hwasan check requires emitting a small piece of code like this: https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html#memory-accesses The problem with this is that these code blocks typically bloat code size significantly. An obvious solution is to outline these blocks of code. In fact, this has already been implemented under the -hwasan-instrument-with-calls flag. However, as currently implemented this has a number of problems: - The functions use the same calling convention as regular C functions. This means that the backend must spill all temporary registers as required by the platform's C calling convention, even though the check only needs two registers on the hot path. - The functions take the address to be checked in a fixed register, which increases register pressure. Both of these factors can diminish the code size effect and increase the performance hit of -hwasan-instrument-with-calls. The solution that this patch implements is to involve the aarch64 backend in outlining the checks. An intrinsic and pseudo-instruction are created to represent a hwasan check. The pseudo-instruction is register allocated like any other instruction, and we allow the register allocator to select almost any register for the address to check. A particular combination of (register selection, type of check) triggers the creation in the backend of a function to handle the check for specifically that pair. The resulting functions are deduplicated by the linker. The pseudo-instruction (really the function) is specified to preserve all registers except for the registers that the AAPCS specifies may be clobbered by a call. To measure the code size and performance effect of this change, I took a number of measurements using Chromium for Android on aarch64, comparing a browser with inlined checks (the baseline) against a browser with outlined checks. Code size: Size of .text decreases from 243897420 to 171619972 bytes, or a 30% decrease. Performance: Using Chromium's blink_perf.layout microbenchmarks I measured a median performance regression of 6.24%. The fact that a perf/size tradeoff is evident here suggests that we might want to make the new behaviour conditional on -Os/-Oz. But for now I've enabled it unconditionally, my reasoning being that hwasan users typically expect a relatively large perf hit, and ~6% isn't really adding much. We may want to revisit this decision in the future, though. I also tried experimenting with varying the number of registers selectable by the hwasan check pseudo-instruction (which would result in fewer variants being created), on the hypothesis that creating fewer variants of the function would expose another perf/size tradeoff by reducing icache pressure from the check functions at the cost of register pressure. Although I did observe a code size increase with fewer registers, I did not observe a strong correlation between the number of registers and the performance of the resulting browser on the microbenchmarks, so I conclude that we might as well use ~all registers to get the maximum code size improvement. My results are below: Regs | .text size | Perf hit -----+------------+--------- ~all | 171619972 | 6.24% 16 | 171765192 | 7.03% 8 | 172917788 | 5.82% 4 | 177054016 | 6.89% Differential Revision: https://reviews.llvm.org/D56954 llvm-svn: 351920
2019-01-23 10:20:10 +08:00
; CHECK-NEXT: mov x0, x1
; CHECK-NEXT: mov x1, #123
[HWASan] Save + print registers when tag mismatch occurs in AArch64. Summary: This change change the instrumentation to allow users to view the registers at the point at which tag mismatch occured. Most of the heavy lifting is done in the runtime library, where we save the registers to the stack and emit unwind information. This allows us to reduce the overhead, as very little additional work needs to be done in each __hwasan_check instance. In this implementation, the fast path of __hwasan_check is unmodified. There are an additional 4 instructions (16B) emitted in the slow path in every __hwasan_check instance. This may increase binary size somewhat, but as most of the work is done in the runtime library, it's manageable. The failure trace now contains a list of registers at the point of which the failure occured, in a format similar to that of Android's tombstones. It currently has the following format: Registers where the failure occurred (pc 0x0055555561b4): x0 0000000000000014 x1 0000007ffffff6c0 x2 1100007ffffff6d0 x3 12000056ffffe025 x4 0000007fff800000 x5 0000000000000014 x6 0000007fff800000 x7 0000000000000001 x8 12000056ffffe020 x9 0200007700000000 x10 0200007700000000 x11 0000000000000000 x12 0000007fffffdde0 x13 0000000000000000 x14 02b65b01f7a97490 x15 0000000000000000 x16 0000007fb77376b8 x17 0000000000000012 x18 0000007fb7ed6000 x19 0000005555556078 x20 0000007ffffff768 x21 0000007ffffff778 x22 0000000000000001 x23 0000000000000000 x24 0000000000000000 x25 0000000000000000 x26 0000000000000000 x27 0000000000000000 x28 0000000000000000 x29 0000007ffffff6f0 x30 00000055555561b4 ... and prints after the dump of memory tags around the buggy address. Every register is saved exactly as it was at the point where the tag mismatch occurs, with the exception of x16/x17. These registers are used in the tag mismatch calculation as scratch registers during __hwasan_check, and cannot be saved without affecting the fast path. As these registers are designated as scratch registers for linking, there should be no important information in them that could aid in debugging. Reviewers: pcc, eugenis Reviewed By: pcc, eugenis Subscribers: srhines, kubamracek, mgorny, javed.absar, krytarowski, kristof.beyls, hiraditya, jdoerfert, llvm-commits, #sanitizers Tags: #sanitizers, #llvm Differential Revision: https://reviews.llvm.org/D58857 llvm-svn: 355738
2019-03-09 05:22:35 +08:00
; CHECK-NEXT: adrp x16, :got:__hwasan_tag_mismatch
; CHECK-NEXT: ldr x16, [x16, :got_lo12:__hwasan_tag_mismatch]
; CHECK-NEXT: br x16