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Commit Graph

Author	SHA1	Message	Date
Yonghong Song	048493f882	[BPF] Preserve debuginfo array/union/struct type/access index For background of BPF CO-RE project, please refer to http://vger.kernel.org/bpfconf2019.html In summary, BPF CO-RE intends to compile bpf programs adjustable on struct/union layout change so the same program can run on multiple kernels with adjustment before loading based on native kernel structures. In order to do this, we need keep track of GEP(getelementptr) instruction base and result debuginfo types, so we can adjust on the host based on kernel BTF info. Capturing such information as an IR optimization is hard as various optimization may have tweaked GEP and also union is replaced by structure it is impossible to track fieldindex for union member accesses. Three intrinsic functions, preserve_{array,union,struct}_access_index, are introducted. addr = preserve_array_access_index(base, index, dimension) addr = preserve_union_access_index(base, di_index) addr = preserve_struct_access_index(base, gep_index, di_index) here, base: the base pointer for the array/union/struct access. index: the last access index for array, the same for IR/DebugInfo layout. dimension: the array dimension. gep_index: the access index based on IR layout. di_index: the access index based on user/debuginfo types. If using these intrinsics blindly, i.e., transforming all GEPs to these intrinsics and later on reducing them to GEPs, we have seen up to 7% more instructions generated. To avoid such an overhead, a clang builtin is proposed: base = __builtin_preserve_access_index(base) such that user wraps to-be-relocated GEPs in this builtin and preserve__access_index intrinsics only apply to those GEPs. Such a buyin will prevent performance degradation if people do not use CO-RE, even for programs which use bpf_probe_read(). For example, for the following example, $ cat test.c struct sk_buff { int i; int b1:1; int b2:2; union { struct { int o1; int o2; } o; struct { char flags; char dev_id; } dev; int netid; } u[10]; }; static int (bpf_probe_read)(void dst, int size, const void unsafe_ptr) = (void ) 4; #define _(x) (__builtin_preserve_access_index(x)) int bpf_prog(struct sk_buff ctx) { char dev_id; bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id)); return dev_id; } $ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \ test.c >& log The generated IR looks like below: ... define dso_local i32 @bpf_prog(%struct.sk_buff) #0 !dbg !15 { %2 = alloca %struct.sk_buff, align 8 %3 = alloca i8, align 1 store %struct.sk_buff* %0, %struct.sk_buff %2, align 8, !tbaa !45 call void @llvm.dbg.declare(metadata %struct.sk_buff %2, metadata !43, metadata !DIExpression()), !dbg !49 call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50 call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51 %4 = load i32 (i8, i32, i8), i32 (i8, i32, i8)* @bpf_probe_read, align 8, !dbg !52, !tbaa !45 %5 = load %struct.sk_buff, %struct.sk_buff* %2, align 8, !dbg !53, !tbaa !45 %6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs( %struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19 %7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons( [10 x %union.anon]* %6, i32 1, i32 5), !dbg !53 %8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons( %union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26 %9 = bitcast %union.anon* %8 to %struct.anon.0, !dbg !53 %10 = call i8 @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s( %struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34 %11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52 %12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55 %13 = sext i8 %12 to i32, !dbg !54 call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56 ret i32 %13, !dbg !57 } !19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20) !26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27) !34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35) Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index attached to instructions to provide struct/union debuginfo type information. For &ctx->u[5].dev.dev_id, . The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout. . The "%7 = ..." represents array subscript "5". . The "%8 = ..." represents union member "dev" with index 1 for DI layout. . The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout. Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and examining all preserve_*_access_index calls, the debuginfo struct/union/array access index can be achieved. The intrinsics also contain enough information to regenerate codes for IR layout. For array and structure intrinsics, the proper GEP can be constructed. For union intrinsics, replacing all uses of "addr" with "base" should be enough. Signed-off-by: Yonghong Song <yhs@fb.com> Differential Revision: https://reviews.llvm.org/D61809 llvm-svn: 365438	2019-07-09 04:21:50 +00:00
Yonghong Song	e085b40e9c	Revert "[BPF] Preserve debuginfo array/union/struct type/access index" This reverts commit r365435. Forgot adding the Differential Revision link. Will add to the commit message and resubmit. llvm-svn: 365436	2019-07-09 04:15:12 +00:00
Yonghong Song	f21eeafcd9	[BPF] Preserve debuginfo array/union/struct type/access index For background of BPF CO-RE project, please refer to http://vger.kernel.org/bpfconf2019.html In summary, BPF CO-RE intends to compile bpf programs adjustable on struct/union layout change so the same program can run on multiple kernels with adjustment before loading based on native kernel structures. In order to do this, we need keep track of GEP(getelementptr) instruction base and result debuginfo types, so we can adjust on the host based on kernel BTF info. Capturing such information as an IR optimization is hard as various optimization may have tweaked GEP and also union is replaced by structure it is impossible to track fieldindex for union member accesses. Three intrinsic functions, preserve_{array,union,struct}_access_index, are introducted. addr = preserve_array_access_index(base, index, dimension) addr = preserve_union_access_index(base, di_index) addr = preserve_struct_access_index(base, gep_index, di_index) here, base: the base pointer for the array/union/struct access. index: the last access index for array, the same for IR/DebugInfo layout. dimension: the array dimension. gep_index: the access index based on IR layout. di_index: the access index based on user/debuginfo types. If using these intrinsics blindly, i.e., transforming all GEPs to these intrinsics and later on reducing them to GEPs, we have seen up to 7% more instructions generated. To avoid such an overhead, a clang builtin is proposed: base = __builtin_preserve_access_index(base) such that user wraps to-be-relocated GEPs in this builtin and preserve__access_index intrinsics only apply to those GEPs. Such a buyin will prevent performance degradation if people do not use CO-RE, even for programs which use bpf_probe_read(). For example, for the following example, $ cat test.c struct sk_buff { int i; int b1:1; int b2:2; union { struct { int o1; int o2; } o; struct { char flags; char dev_id; } dev; int netid; } u[10]; }; static int (bpf_probe_read)(void dst, int size, const void unsafe_ptr) = (void ) 4; #define _(x) (__builtin_preserve_access_index(x)) int bpf_prog(struct sk_buff ctx) { char dev_id; bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id)); return dev_id; } $ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \ test.c >& log The generated IR looks like below: ... define dso_local i32 @bpf_prog(%struct.sk_buff) #0 !dbg !15 { %2 = alloca %struct.sk_buff, align 8 %3 = alloca i8, align 1 store %struct.sk_buff* %0, %struct.sk_buff %2, align 8, !tbaa !45 call void @llvm.dbg.declare(metadata %struct.sk_buff %2, metadata !43, metadata !DIExpression()), !dbg !49 call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50 call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51 %4 = load i32 (i8, i32, i8), i32 (i8, i32, i8)* @bpf_probe_read, align 8, !dbg !52, !tbaa !45 %5 = load %struct.sk_buff, %struct.sk_buff* %2, align 8, !dbg !53, !tbaa !45 %6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs( %struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19 %7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons( [10 x %union.anon]* %6, i32 1, i32 5), !dbg !53 %8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons( %union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26 %9 = bitcast %union.anon* %8 to %struct.anon.0, !dbg !53 %10 = call i8 @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s( %struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34 %11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52 %12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55 %13 = sext i8 %12 to i32, !dbg !54 call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56 ret i32 %13, !dbg !57 } !19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20) !26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27) !34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35) Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index attached to instructions to provide struct/union debuginfo type information. For &ctx->u[5].dev.dev_id, . The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout. . The "%7 = ..." represents array subscript "5". . The "%8 = ..." represents union member "dev" with index 1 for DI layout. . The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout. Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and examining all preserve_*_access_index calls, the debuginfo struct/union/array access index can be achieved. The intrinsics also contain enough information to regenerate codes for IR layout. For array and structure intrinsics, the proper GEP can be constructed. For union intrinsics, replacing all uses of "addr" with "base" should be enough. Signed-off-by: Yonghong Song <yhs@fb.com> llvm-svn: 365435	2019-07-09 04:04:21 +00:00

Author

SHA1

Message

Date

Yonghong Song

048493f882

[BPF] Preserve debuginfo array/union/struct type/access index

For background of BPF CO-RE project, please refer to
  http://vger.kernel.org/bpfconf2019.html
In summary, BPF CO-RE intends to compile bpf programs
adjustable on struct/union layout change so the same
program can run on multiple kernels with adjustment
before loading based on native kernel structures.

In order to do this, we need keep track of GEP(getelementptr)
instruction base and result debuginfo types, so we
can adjust on the host based on kernel BTF info.
Capturing such information as an IR optimization is hard
as various optimization may have tweaked GEP and also
union is replaced by structure it is impossible to track
fieldindex for union member accesses.

Three intrinsic functions, preserve_{array,union,struct}_access_index,
are introducted.
  addr = preserve_array_access_index(base, index, dimension)
  addr = preserve_union_access_index(base, di_index)
  addr = preserve_struct_access_index(base, gep_index, di_index)
here,
  base: the base pointer for the array/union/struct access.
  index: the last access index for array, the same for IR/DebugInfo layout.
  dimension: the array dimension.
  gep_index: the access index based on IR layout.
  di_index: the access index based on user/debuginfo types.

If using these intrinsics blindly, i.e., transforming all GEPs
to these intrinsics and later on reducing them to GEPs, we have
seen up to 7% more instructions generated. To avoid such an overhead,
a clang builtin is proposed:
  base = __builtin_preserve_access_index(base)
such that user wraps to-be-relocated GEPs in this builtin
and preserve_*_access_index intrinsics only apply to
those GEPs. Such a buyin will prevent performance degradation
if people do not use CO-RE, even for programs which use
bpf_probe_read().

For example, for the following example,
  $ cat test.c
  struct sk_buff {
     int i;
     int b1:1;
     int b2:2;
     union {
       struct {
         int o1;
         int o2;
       } o;
       struct {
         char flags;
         char dev_id;
       } dev;
       int netid;
     } u[10];
  };

  static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr)
      = (void *) 4;

  #define _(x) (__builtin_preserve_access_index(x))

  int bpf_prog(struct sk_buff *ctx) {
    char dev_id;
    bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id));
    return dev_id;
  }
  $ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \
    test.c >& log

The generated IR looks like below:
  ...
  define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 {
    %2 = alloca %struct.sk_buff*, align 8
    %3 = alloca i8, align 1
    store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45
    call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49
    call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50
    call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51
    %4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45
    %5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45
    %6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs(
         %struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19
    %7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons(
         [10 x %union.anon]* %6, i32 1, i32 5), !dbg !53
    %8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(
         %union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26
    %9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53
    %10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s(
         %struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34
    %11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52
    %12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55
    %13 = sext i8 %12 to i32, !dbg !54
    call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56
    ret i32 %13, !dbg !57
  }

  !19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20)
  !26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27)
  !34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35)

Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index
attached to instructions to provide struct/union debuginfo type information.

For &ctx->u[5].dev.dev_id,
  . The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout.
  . The "%7 = ..." represents array subscript "5".
  . The "%8 = ..." represents union member "dev" with index 1 for DI layout.
  . The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout.

Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and
examining all preserve_*_access_index calls, the debuginfo struct/union/array access index
can be achieved.

The intrinsics also contain enough information to regenerate codes for IR layout.
For array and structure intrinsics, the proper GEP can be constructed.
For union intrinsics, replacing all uses of "addr" with "base" should be enough.

Signed-off-by: Yonghong Song <yhs@fb.com>

Differential Revision: https://reviews.llvm.org/D61809

llvm-svn: 365438

2019-07-09 04:21:50 +00:00

Yonghong Song

e085b40e9c

Revert "[BPF] Preserve debuginfo array/union/struct type/access index"

This reverts commit r365435.

Forgot adding the Differential Revision link. Will add to the
commit message and resubmit.

llvm-svn: 365436

2019-07-09 04:15:12 +00:00

Yonghong Song

f21eeafcd9

[BPF] Preserve debuginfo array/union/struct type/access index

For background of BPF CO-RE project, please refer to
  http://vger.kernel.org/bpfconf2019.html
In summary, BPF CO-RE intends to compile bpf programs
adjustable on struct/union layout change so the same
program can run on multiple kernels with adjustment
before loading based on native kernel structures.

In order to do this, we need keep track of GEP(getelementptr)
instruction base and result debuginfo types, so we
can adjust on the host based on kernel BTF info.
Capturing such information as an IR optimization is hard
as various optimization may have tweaked GEP and also
union is replaced by structure it is impossible to track
fieldindex for union member accesses.

Three intrinsic functions, preserve_{array,union,struct}_access_index,
are introducted.
  addr = preserve_array_access_index(base, index, dimension)
  addr = preserve_union_access_index(base, di_index)
  addr = preserve_struct_access_index(base, gep_index, di_index)
here,
  base: the base pointer for the array/union/struct access.
  index: the last access index for array, the same for IR/DebugInfo layout.
  dimension: the array dimension.
  gep_index: the access index based on IR layout.
  di_index: the access index based on user/debuginfo types.

If using these intrinsics blindly, i.e., transforming all GEPs
to these intrinsics and later on reducing them to GEPs, we have
seen up to 7% more instructions generated. To avoid such an overhead,
a clang builtin is proposed:
  base = __builtin_preserve_access_index(base)
such that user wraps to-be-relocated GEPs in this builtin
and preserve_*_access_index intrinsics only apply to
those GEPs. Such a buyin will prevent performance degradation
if people do not use CO-RE, even for programs which use
bpf_probe_read().

For example, for the following example,
  $ cat test.c
  struct sk_buff {
     int i;
     int b1:1;
     int b2:2;
     union {
       struct {
         int o1;
         int o2;
       } o;
       struct {
         char flags;
         char dev_id;
       } dev;
       int netid;
     } u[10];
  };

  static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr)
      = (void *) 4;

  #define _(x) (__builtin_preserve_access_index(x))

  int bpf_prog(struct sk_buff *ctx) {
    char dev_id;
    bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id));
    return dev_id;
  }
  $ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \
    test.c >& log

The generated IR looks like below:
  ...
  define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 {
    %2 = alloca %struct.sk_buff*, align 8
    %3 = alloca i8, align 1
    store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45
    call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49
    call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50
    call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51
    %4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45
    %5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45
    %6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs(
         %struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19
    %7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons(
         [10 x %union.anon]* %6, i32 1, i32 5), !dbg !53
    %8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(
         %union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26
    %9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53
    %10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s(
         %struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34
    %11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52
    %12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55
    %13 = sext i8 %12 to i32, !dbg !54
    call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56
    ret i32 %13, !dbg !57
  }

  !19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20)
  !26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27)
  !34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35)

Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index
attached to instructions to provide struct/union debuginfo type information.

For &ctx->u[5].dev.dev_id,
  . The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout.
  . The "%7 = ..." represents array subscript "5".
  . The "%8 = ..." represents union member "dev" with index 1 for DI layout.
  . The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout.

Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and
examining all preserve_*_access_index calls, the debuginfo struct/union/array access index
can be achieved.

The intrinsics also contain enough information to regenerate codes for IR layout.
For array and structure intrinsics, the proper GEP can be constructed.
For union intrinsics, replacing all uses of "addr" with "base" should be enough.

Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 365435

2019-07-09 04:04:21 +00:00

3 Commits