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llvm-project/llvm/test/CodeGen/X86/xray-attribute-instrumentat...

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[XRay] Fix machine verifier issues in X86 I'm not sure if this fix is the right thing to do, but it seemed to me that PATCHABLE_RET and PATCHABLE_TAIL_CALL don't have any defs. Running the following: ``` LLVM_ENABLE_MACHINE_VERIFIER=1 ./build/bin/llvm-lit -v -a test/CodeGen/X86/xray-* ``` results in the following tests to fail (along others): ``` LLVM :: CodeGen/X86/xray-attribute-instrumentation.ll LLVM :: CodeGen/X86/xray-custom-log.ll LLVM :: CodeGen/X86/xray-log-args.ll LLVM :: CodeGen/X86/xray-loop-detection.ll LLVM :: CodeGen/X86/xray-multiplerets-in-blocks.mir LLVM :: CodeGen/X86/xray-section-group.ll LLVM :: CodeGen/X86/xray-selective-instrumentation.ll LLVM :: CodeGen/X86/xray-tail-call-sled.ll LLVM :: CodeGen/X86/xray-typed-event-log.ll ``` The errors are: ``` *** Bad machine code: Explicit definition must be a register *** - function: fn - basic block: %bb.0 (0x7fa31a84d908) - instruction: PATCHABLE_RET 2560, $eax - operand 0: 2560 ``` and ``` *** Bad machine code: Explicit definition must be a register *** - function: caller - basic block: %bb.0 (0x7fbff3044108) - instruction: PATCHABLE_TAIL_CALL 3009, @callee, <regmask $bh $bl $bp $bph $bpl $bx $ebp $ebx $hbp $hbx $rbp $rbx $r12 $r13 $r14 $r15 $r12b $r13b $r14b $r15b $r12bh $r13bh $r14bh $r15bh $r12d $r13d $r14d $r15d $r12w $r13w $r14w $r15w $r12wh and 3 more...>, implicit $rsp, implicit $ssp, implicit $rsp, implicit $ssp, implicit $edi - operand 0: 3009 ``` Differential Revision: https://reviews.llvm.org/D49187 llvm-svn: 336906
2018-07-12 22:36:43 +08:00
; RUN: llc -verify-machineinstrs -filetype=asm -o - -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
; RUN: llc -verify-machineinstrs -filetype=asm -o - \
; RUN: -mtriple=x86_64-unknown-linux-gnu -relocation-model=pic < %s | FileCheck %s
; RUN: llc -verify-machineinstrs -filetype=asm -o - -mtriple=x86_64-darwin-unknown < %s | FileCheck %s
XRay: Add entry and exit sleds Summary: In this patch we implement the following parts of XRay: - Supporting a function attribute named 'function-instrument' which currently only supports 'xray-always'. We should be able to use this attribute for other instrumentation approaches. - Supporting a function attribute named 'xray-instruction-threshold' used to determine whether a function is instrumented with a minimum number of instructions (IR instruction counts). - X86-specific nop sleds as described in the white paper. - A machine function pass that adds the different instrumentation marker instructions at a very late stage. - A way of identifying which return opcode is considered "normal" for each architecture. There are some caveats here: 1) We don't handle PATCHABLE_RET in platforms other than x86_64 yet -- this means if IR used PATCHABLE_RET directly instead of a normal ret, instruction lowering for that platform might do the wrong thing. We think this should be handled at instruction selection time to by default be unpacked for platforms where XRay is not availble yet. 2) The generated section for X86 is different from what is described from the white paper for the sole reason that LLVM allows us to do this neatly. We're taking the opportunity to deviate from the white paper from this perspective to allow us to get richer information from the runtime library. Reviewers: sanjoy, eugenis, kcc, pcc, echristo, rnk Subscribers: niravd, majnemer, atrick, rnk, emaste, bmakam, mcrosier, mehdi_amini, llvm-commits Differential Revision: http://reviews.llvm.org/D19904 llvm-svn: 275367
2016-07-14 12:06:33 +08:00
define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always" {
[XRay] Align entry and return sleds to 2 byte boundaries This should ensure that we can atomically write two bytes (on top of the retq and the one past it) and have those two bytes not straddle cache lines. We also move the label past the alignment instruction so that we can refer to the actual first instruction, as opposed to potential padding before the aligned instruction. Update the tests to allow us to reflect the new order of assembly. Reviewers: rSerge, echristo, majnemer Subscribers: llvm-commits, mehdi_amini Differential Revision: https://reviews.llvm.org/D23101 llvm-svn: 277701
2016-08-04 15:37:28 +08:00
; CHECK: .p2align 1, 0x90
XRay: Add entry and exit sleds Summary: In this patch we implement the following parts of XRay: - Supporting a function attribute named 'function-instrument' which currently only supports 'xray-always'. We should be able to use this attribute for other instrumentation approaches. - Supporting a function attribute named 'xray-instruction-threshold' used to determine whether a function is instrumented with a minimum number of instructions (IR instruction counts). - X86-specific nop sleds as described in the white paper. - A machine function pass that adds the different instrumentation marker instructions at a very late stage. - A way of identifying which return opcode is considered "normal" for each architecture. There are some caveats here: 1) We don't handle PATCHABLE_RET in platforms other than x86_64 yet -- this means if IR used PATCHABLE_RET directly instead of a normal ret, instruction lowering for that platform might do the wrong thing. We think this should be handled at instruction selection time to by default be unpacked for platforms where XRay is not availble yet. 2) The generated section for X86 is different from what is described from the white paper for the sole reason that LLVM allows us to do this neatly. We're taking the opportunity to deviate from the white paper from this perspective to allow us to get richer information from the runtime library. Reviewers: sanjoy, eugenis, kcc, pcc, echristo, rnk Subscribers: niravd, majnemer, atrick, rnk, emaste, bmakam, mcrosier, mehdi_amini, llvm-commits Differential Revision: http://reviews.llvm.org/D19904 llvm-svn: 275367
2016-07-14 12:06:33 +08:00
; CHECK-LABEL: Lxray_sled_0:
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK: .ascii "\353\t"
XRay: Add entry and exit sleds Summary: In this patch we implement the following parts of XRay: - Supporting a function attribute named 'function-instrument' which currently only supports 'xray-always'. We should be able to use this attribute for other instrumentation approaches. - Supporting a function attribute named 'xray-instruction-threshold' used to determine whether a function is instrumented with a minimum number of instructions (IR instruction counts). - X86-specific nop sleds as described in the white paper. - A machine function pass that adds the different instrumentation marker instructions at a very late stage. - A way of identifying which return opcode is considered "normal" for each architecture. There are some caveats here: 1) We don't handle PATCHABLE_RET in platforms other than x86_64 yet -- this means if IR used PATCHABLE_RET directly instead of a normal ret, instruction lowering for that platform might do the wrong thing. We think this should be handled at instruction selection time to by default be unpacked for platforms where XRay is not availble yet. 2) The generated section for X86 is different from what is described from the white paper for the sole reason that LLVM allows us to do this neatly. We're taking the opportunity to deviate from the white paper from this perspective to allow us to get richer information from the runtime library. Reviewers: sanjoy, eugenis, kcc, pcc, echristo, rnk Subscribers: niravd, majnemer, atrick, rnk, emaste, bmakam, mcrosier, mehdi_amini, llvm-commits Differential Revision: http://reviews.llvm.org/D19904 llvm-svn: 275367
2016-07-14 12:06:33 +08:00
; CHECK-NEXT: nopw 512(%rax,%rax)
ret i32 0
[XRay] Align entry and return sleds to 2 byte boundaries This should ensure that we can atomically write two bytes (on top of the retq and the one past it) and have those two bytes not straddle cache lines. We also move the label past the alignment instruction so that we can refer to the actual first instruction, as opposed to potential padding before the aligned instruction. Update the tests to allow us to reflect the new order of assembly. Reviewers: rSerge, echristo, majnemer Subscribers: llvm-commits, mehdi_amini Differential Revision: https://reviews.llvm.org/D23101 llvm-svn: 277701
2016-08-04 15:37:28 +08:00
; CHECK: .p2align 1, 0x90
XRay: Add entry and exit sleds Summary: In this patch we implement the following parts of XRay: - Supporting a function attribute named 'function-instrument' which currently only supports 'xray-always'. We should be able to use this attribute for other instrumentation approaches. - Supporting a function attribute named 'xray-instruction-threshold' used to determine whether a function is instrumented with a minimum number of instructions (IR instruction counts). - X86-specific nop sleds as described in the white paper. - A machine function pass that adds the different instrumentation marker instructions at a very late stage. - A way of identifying which return opcode is considered "normal" for each architecture. There are some caveats here: 1) We don't handle PATCHABLE_RET in platforms other than x86_64 yet -- this means if IR used PATCHABLE_RET directly instead of a normal ret, instruction lowering for that platform might do the wrong thing. We think this should be handled at instruction selection time to by default be unpacked for platforms where XRay is not availble yet. 2) The generated section for X86 is different from what is described from the white paper for the sole reason that LLVM allows us to do this neatly. We're taking the opportunity to deviate from the white paper from this perspective to allow us to get richer information from the runtime library. Reviewers: sanjoy, eugenis, kcc, pcc, echristo, rnk Subscribers: niravd, majnemer, atrick, rnk, emaste, bmakam, mcrosier, mehdi_amini, llvm-commits Differential Revision: http://reviews.llvm.org/D19904 llvm-svn: 275367
2016-07-14 12:06:33 +08:00
; CHECK-LABEL: Lxray_sled_1:
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK: retq
XRay: Add entry and exit sleds Summary: In this patch we implement the following parts of XRay: - Supporting a function attribute named 'function-instrument' which currently only supports 'xray-always'. We should be able to use this attribute for other instrumentation approaches. - Supporting a function attribute named 'xray-instruction-threshold' used to determine whether a function is instrumented with a minimum number of instructions (IR instruction counts). - X86-specific nop sleds as described in the white paper. - A machine function pass that adds the different instrumentation marker instructions at a very late stage. - A way of identifying which return opcode is considered "normal" for each architecture. There are some caveats here: 1) We don't handle PATCHABLE_RET in platforms other than x86_64 yet -- this means if IR used PATCHABLE_RET directly instead of a normal ret, instruction lowering for that platform might do the wrong thing. We think this should be handled at instruction selection time to by default be unpacked for platforms where XRay is not availble yet. 2) The generated section for X86 is different from what is described from the white paper for the sole reason that LLVM allows us to do this neatly. We're taking the opportunity to deviate from the white paper from this perspective to allow us to get richer information from the runtime library. Reviewers: sanjoy, eugenis, kcc, pcc, echristo, rnk Subscribers: niravd, majnemer, atrick, rnk, emaste, bmakam, mcrosier, mehdi_amini, llvm-commits Differential Revision: http://reviews.llvm.org/D19904 llvm-svn: 275367
2016-07-14 12:06:33 +08:00
; CHECK-NEXT: nopw %cs:512(%rax,%rax)
}
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK-LABEL: xray_instr_map
[XRay] Reduce synthetic references emitted by XRay Summary: When we're building with XRay instrumentation, we use a trick that preserves references from the function to a function sled index. This index table lives in a separate section, and without this trick the linker is free to garbage-collect this section and all the segments it refers to. Until we're able to tell the linkers to preserve these sections, we use this reference trick to keep around both the index and the entries in the instrumentation map. Before this change we emitted both a synthetic reference to the label in the instrumentation map, and to the entry in the function map index. This change removes the first synthetic reference and only emits one synthetic reference to the index -- the index entry has the references to the labels in the instrumentation map, so the linker will still preserve those if the function itself is preserved. This reduces the amount of synthetic references we emit from 16 bytes to just 8 bytes in x86_64, and similarly to other platforms. Reviewers: dblaikie Subscribers: javed.absar, kpw, pelikan, llvm-commits Differential Revision: https://reviews.llvm.org/D34340 llvm-svn: 305880
2017-06-21 14:39:42 +08:00
; CHECK-LABEL: Lxray_sleds_start0:
[xray] Add XRay support for Mach-O in CodeGen Currently, XRay only supports emitting the XRay table (xray_instr_map) on ELF binaries. Let's add Mach-O support. Differential Revision: https://reviews.llvm.org/D26983 llvm-svn: 287734
2016-11-23 10:07:04 +08:00
; CHECK: .quad {{.*}}xray_sled_0
; CHECK: .quad {{.*}}xray_sled_1
[XRay] Reduce synthetic references emitted by XRay Summary: When we're building with XRay instrumentation, we use a trick that preserves references from the function to a function sled index. This index table lives in a separate section, and without this trick the linker is free to garbage-collect this section and all the segments it refers to. Until we're able to tell the linkers to preserve these sections, we use this reference trick to keep around both the index and the entries in the instrumentation map. Before this change we emitted both a synthetic reference to the label in the instrumentation map, and to the entry in the function map index. This change removes the first synthetic reference and only emits one synthetic reference to the index -- the index entry has the references to the labels in the instrumentation map, so the linker will still preserve those if the function itself is preserved. This reduces the amount of synthetic references we emit from 16 bytes to just 8 bytes in x86_64, and similarly to other platforms. Reviewers: dblaikie Subscribers: javed.absar, kpw, pelikan, llvm-commits Differential Revision: https://reviews.llvm.org/D34340 llvm-svn: 305880
2017-06-21 14:39:42 +08:00
; CHECK-LABEL: Lxray_sleds_end0:
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK-LABEL: xray_fn_idx
[XRay] Reduce synthetic references emitted by XRay Summary: When we're building with XRay instrumentation, we use a trick that preserves references from the function to a function sled index. This index table lives in a separate section, and without this trick the linker is free to garbage-collect this section and all the segments it refers to. Until we're able to tell the linkers to preserve these sections, we use this reference trick to keep around both the index and the entries in the instrumentation map. Before this change we emitted both a synthetic reference to the label in the instrumentation map, and to the entry in the function map index. This change removes the first synthetic reference and only emits one synthetic reference to the index -- the index entry has the references to the labels in the instrumentation map, so the linker will still preserve those if the function itself is preserved. This reduces the amount of synthetic references we emit from 16 bytes to just 8 bytes in x86_64, and similarly to other platforms. Reviewers: dblaikie Subscribers: javed.absar, kpw, pelikan, llvm-commits Differential Revision: https://reviews.llvm.org/D34340 llvm-svn: 305880
2017-06-21 14:39:42 +08:00
; CHECK: .quad {{.*}}xray_sleds_start0
; CHECK-NEXT: .quad {{.*}}xray_sleds_end0
[XRay] Create an Index of sleds per function Summary: This change adds a new section to the xray-instrumented binary that stores an index into ranges of the instrumentation map, where sleds associated with the same function can be accessed as an array. At runtime, we can get access to this index by function ID offset allowing for selective patching and unpatching by function ID. Each entry in this new section (xray_fn_idx) will include two pointers indicating the start and one past the end of the sleds associated with the same function. These entries will be 16 bytes long on x86 and aarch64. On arm, we align to 16 bytes anyway so the runtime has to take that into consideration. __{start,stop}_xray_fn_idx will be the symbols that the runtime will look for when we implement the selective patching/unpatching by function id APIs. Because XRay synthesizes the function id's in a monotonically increasing manner at runtime now, implementations (and users) can use this table to look up the sleds associated with a specific function. This is useful in implementations that want to do things like: - Implement coverage mode for functions by patching everything pre-main, then as functions are encountered, the installed handler can unpatch the function that's been encountered after recording that it's been called. - Do "learning mode", so that the implementation can figure out some statistical information about function calls by function id for a time being, and then determine which functions are worth uninstrumenting at runtime. - Do "selective instrumentation" where an implementation can specifically instrument only certain function id's at runtime (either based on some external data, or through some other heuristics) instead of patching all the instrumented functions at runtime. Reviewers: dblaikie, echristo, chandlerc, javed.absar Subscribers: pelikan, aemerson, kpw, llvm-commits, rengolin Differential Revision: https://reviews.llvm.org/D32693 llvm-svn: 302109
2017-05-04 11:37:57 +08:00
[XRay] Support multiple return instructions in a single basic block Add a .mir test to catch this case, and fix the xray-instrumentation pass to handle it appropriately. llvm-svn: 280192
2016-08-31 13:20:08 +08:00
; We test multiple returns in a single function to make sure we're getting all
; of them with XRay instrumentation.
define i32 @bar(i32 %i) nounwind noinline uwtable "function-instrument"="xray-always" {
; CHECK: .p2align 1, 0x90
; CHECK-LABEL: Lxray_sled_2:
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK: .ascii "\353\t"
[XRay] Support multiple return instructions in a single basic block Add a .mir test to catch this case, and fix the xray-instrumentation pass to handle it appropriately. llvm-svn: 280192
2016-08-31 13:20:08 +08:00
; CHECK-NEXT: nopw 512(%rax,%rax)
Test:
%cond = icmp eq i32 %i, 0
br i1 %cond, label %IsEqual, label %NotEqual
IsEqual:
ret i32 0
; CHECK: .p2align 1, 0x90
; CHECK-LABEL: Lxray_sled_3:
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK: retq
[XRay] Support multiple return instructions in a single basic block Add a .mir test to catch this case, and fix the xray-instrumentation pass to handle it appropriately. llvm-svn: 280192
2016-08-31 13:20:08 +08:00
; CHECK-NEXT: nopw %cs:512(%rax,%rax)
NotEqual:
ret i32 1
; CHECK: .p2align 1, 0x90
; CHECK-LABEL: Lxray_sled_4:
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK: retq
[XRay] Support multiple return instructions in a single basic block Add a .mir test to catch this case, and fix the xray-instrumentation pass to handle it appropriately. llvm-svn: 280192
2016-08-31 13:20:08 +08:00
; CHECK-NEXT: nopw %cs:512(%rax,%rax)
}
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK-LABEL: xray_instr_map
[XRay] Reduce synthetic references emitted by XRay Summary: When we're building with XRay instrumentation, we use a trick that preserves references from the function to a function sled index. This index table lives in a separate section, and without this trick the linker is free to garbage-collect this section and all the segments it refers to. Until we're able to tell the linkers to preserve these sections, we use this reference trick to keep around both the index and the entries in the instrumentation map. Before this change we emitted both a synthetic reference to the label in the instrumentation map, and to the entry in the function map index. This change removes the first synthetic reference and only emits one synthetic reference to the index -- the index entry has the references to the labels in the instrumentation map, so the linker will still preserve those if the function itself is preserved. This reduces the amount of synthetic references we emit from 16 bytes to just 8 bytes in x86_64, and similarly to other platforms. Reviewers: dblaikie Subscribers: javed.absar, kpw, pelikan, llvm-commits Differential Revision: https://reviews.llvm.org/D34340 llvm-svn: 305880
2017-06-21 14:39:42 +08:00
; CHECK-LABEL: Lxray_sleds_start1:
[xray] Add XRay support for Mach-O in CodeGen Currently, XRay only supports emitting the XRay table (xray_instr_map) on ELF binaries. Let's add Mach-O support. Differential Revision: https://reviews.llvm.org/D26983 llvm-svn: 287734
2016-11-23 10:07:04 +08:00
; CHECK: .quad {{.*}}xray_sled_2
; CHECK: .quad {{.*}}xray_sled_3
; CHECK: .quad {{.*}}xray_sled_4
[XRay] Reduce synthetic references emitted by XRay Summary: When we're building with XRay instrumentation, we use a trick that preserves references from the function to a function sled index. This index table lives in a separate section, and without this trick the linker is free to garbage-collect this section and all the segments it refers to. Until we're able to tell the linkers to preserve these sections, we use this reference trick to keep around both the index and the entries in the instrumentation map. Before this change we emitted both a synthetic reference to the label in the instrumentation map, and to the entry in the function map index. This change removes the first synthetic reference and only emits one synthetic reference to the index -- the index entry has the references to the labels in the instrumentation map, so the linker will still preserve those if the function itself is preserved. This reduces the amount of synthetic references we emit from 16 bytes to just 8 bytes in x86_64, and similarly to other platforms. Reviewers: dblaikie Subscribers: javed.absar, kpw, pelikan, llvm-commits Differential Revision: https://reviews.llvm.org/D34340 llvm-svn: 305880
2017-06-21 14:39:42 +08:00
; CHECK-LABEL: Lxray_sleds_end1:
[XRay][CodeGen] Use PIC-friendly code in XRay sleds and remove synthetic references in .text Summary: This is a re-roll of D36615 which uses PLT relocations in the back-end to the call to __xray_CustomEvent() when building in -fPIC and -fxray-instrument mode. Reviewers: pcc, djasper, bkramer Subscribers: sdardis, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D37373 llvm-svn: 312466
2017-09-04 13:34:58 +08:00
; CHECK-LABEL: xray_fn_idx
[XRay] Reduce synthetic references emitted by XRay Summary: When we're building with XRay instrumentation, we use a trick that preserves references from the function to a function sled index. This index table lives in a separate section, and without this trick the linker is free to garbage-collect this section and all the segments it refers to. Until we're able to tell the linkers to preserve these sections, we use this reference trick to keep around both the index and the entries in the instrumentation map. Before this change we emitted both a synthetic reference to the label in the instrumentation map, and to the entry in the function map index. This change removes the first synthetic reference and only emits one synthetic reference to the index -- the index entry has the references to the labels in the instrumentation map, so the linker will still preserve those if the function itself is preserved. This reduces the amount of synthetic references we emit from 16 bytes to just 8 bytes in x86_64, and similarly to other platforms. Reviewers: dblaikie Subscribers: javed.absar, kpw, pelikan, llvm-commits Differential Revision: https://reviews.llvm.org/D34340 llvm-svn: 305880
2017-06-21 14:39:42 +08:00
; CHECK: .quad {{.*}}xray_sleds_start1
; CHECK-NEXT: .quad {{.*}}xray_sleds_end1