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[BPF] Add preserve_access_index attribute for record definition This is a resubmission for the previous reverted commit 943436040121 with the same subject. This commit fixed the segfault issue and addressed additional review comments. This patch introduced a new bpf specific attribute which can be added to struct or union definition. For example, struct s { ... } __attribute__((preserve_access_index)); union u { ... } __attribute__((preserve_access_index)); The goal is to simplify user codes for cases where preserve access index happens for certain struct/union, so user does not need to use clang __builtin_preserve_access_index for every members. The attribute has no effect if -g is not specified. When the attribute is specified and -g is specified, any member access defined by that structure or union, including array subscript access and inner records, will be preserved through __builtin_preserve_{array,struct,union}_access_index() IR intrinsics, which will enable relocation generation in bpf backend. The following is an example to illustrate the usage: -bash-4.4$ cat t.c #define __reloc__ __attribute__((preserve_access_index)) struct s1 { int c; } __reloc__; struct s2 { union { struct s1 b[3]; }; } __reloc__; struct s3 { struct s2 a; } __reloc__; int test(struct s3 *arg) { return arg->a.b[2].c; } -bash-4.4$ clang -target bpf -g -S -O2 t.c A relocation with access string "0:0:0:0:2:0" will be generated representing access offset of arg->a.b[2].c. forward declaration with attribute is also handled properly such that the attribute is copied and populated in real record definition. Differential Revision: https://reviews.llvm.org/D69759
2019-11-02 13:16:59 +08:00
// REQUIRES: bpf-registered-target
BPF: move AbstractMemberAccess and PreserveDIType passes to EP_EarlyAsPossible Move abstractMemberAccess and PreserveDIType passes as early as possible, right after clang code generation. Currently, compiler may transform the above code p1 = llvm.bpf.builtin.preserve.struct.access(base, 0, 0); p2 = llvm.bpf.builtin.preserve.struct.access(p1, 1, 2); a = llvm.bpf.builtin.preserve_field_info(p2, EXIST); if (a) { p1 = llvm.bpf.builtin.preserve.struct.access(base, 0, 0); p2 = llvm.bpf.builtin.preserve.struct.access(p1, 1, 2); bpf_probe_read(buf, buf_size, p2); } to p1 = llvm.bpf.builtin.preserve.struct.access(base, 0, 0); p2 = llvm.bpf.builtin.preserve.struct.access(p1, 1, 2); a = llvm.bpf.builtin.preserve_field_info(p2, EXIST); if (a) { bpf_probe_read(buf, buf_size, p2); } and eventually assembly code looks like reloc_exist = 1; reloc_member_offset = 10; //calculate member offset from base p2 = base + reloc_member_offset; if (reloc_exist) { bpf_probe_read(bpf, buf_size, p2); } if during libbpf relocation resolution, reloc_exist is actually resolved to 0 (not exist), reloc_member_offset relocation cannot be resolved and will be patched with illegal instruction. This will cause verifier failure. This patch attempts to address this issue by do chaining analysis and replace chains with special globals right after clang code gen. This will remove the cse possibility described in the above. The IR typically looks like %6 = load @llvm.sk_buff:0:50$0:0:0:2:0 %7 = bitcast %struct.sk_buff* %2 to i8* %8 = getelementptr i8, i8* %7, %6 for a particular address computation relocation. But this transformation has another consequence, code sinking may happen like below: PHI = <possibly different @preserve_*_access_globals> %7 = bitcast %struct.sk_buff* %2 to i8* %8 = getelementptr i8, i8* %7, %6 For such cases, we will not able to generate relocations since multiple relocations are merged into one. This patch introduced a passthrough builtin to prevent such optimization. Looks like inline assembly has more impact for optimizaiton, e.g., inlining. Using passthrough has less impact on optimizations. A new IR pass is introduced at the beginning of target-dependent IR optimization, which does: - report fatal error if any reloc global in PHI nodes - remove all bpf passthrough builtin functions Changes for existing CORE tests: - for clang tests, add "-Xclang -disable-llvm-passes" flags to avoid builtin->reloc_global transformation so the test is still able to check correctness for clang generated IR. - for llvm CodeGen/BPF tests, add "opt -O2 <ir_file> | llvm-dis" command before "llc" command since "opt" is needed to call newly-placed builtin->reloc_global transformation. Add target triple in the IR file since "opt" requires it. - Since target triple is added in IR file, if a test may produce different results for different endianness, two tests will be created, one for bpfeb and another for bpfel, e.g., some tests for relocation of lshift/rshift of bitfields. - field-reloc-bitfield-1.ll has different relocations compared to old codes. This is because for the structure in the test, new code returns struct layout alignment 4 while old code is 8. Align 8 is more precise and permits double load. With align 4, the new mechanism uses 4-byte load, so generating different relocations. - test intrinsic-transforms.ll is removed. This is used to test cse on intrinsics so we do not lose metadata. Now metadata is attached to global and not instruction, it won't get lost with cse. Differential Revision: https://reviews.llvm.org/D87153
2020-09-03 13:56:41 +08:00
// RUN: %clang -target bpf -emit-llvm -S -g -Xclang -disable-llvm-passes %s -o - | FileCheck %s
[BPF] Add preserve_access_index attribute for record definition This is a resubmission for the previous reverted commit 943436040121 with the same subject. This commit fixed the segfault issue and addressed additional review comments. This patch introduced a new bpf specific attribute which can be added to struct or union definition. For example, struct s { ... } __attribute__((preserve_access_index)); union u { ... } __attribute__((preserve_access_index)); The goal is to simplify user codes for cases where preserve access index happens for certain struct/union, so user does not need to use clang __builtin_preserve_access_index for every members. The attribute has no effect if -g is not specified. When the attribute is specified and -g is specified, any member access defined by that structure or union, including array subscript access and inner records, will be preserved through __builtin_preserve_{array,struct,union}_access_index() IR intrinsics, which will enable relocation generation in bpf backend. The following is an example to illustrate the usage: -bash-4.4$ cat t.c #define __reloc__ __attribute__((preserve_access_index)) struct s1 { int c; } __reloc__; struct s2 { union { struct s1 b[3]; }; } __reloc__; struct s3 { struct s2 a; } __reloc__; int test(struct s3 *arg) { return arg->a.b[2].c; } -bash-4.4$ clang -target bpf -g -S -O2 t.c A relocation with access string "0:0:0:0:2:0" will be generated representing access offset of arg->a.b[2].c. forward declaration with attribute is also handled properly such that the attribute is copied and populated in real record definition. Differential Revision: https://reviews.llvm.org/D69759
2019-11-02 13:16:59 +08:00
#define __reloc__ __attribute__((preserve_access_index))
// chain of records, all with attributes
struct s1 {
int c;
} __reloc__;
typedef struct s1 __s1;
struct s2 {
union {
__s1 b[3];
};
} __reloc__;
typedef struct s2 __s2;
struct s3 {
__s2 a;
} __reloc__;
typedef struct s3 __s3;
int test(__s3 *arg) {
return arg->a.b[2].c;
}
[BPF] Use elementtype attribute for preserve.array/struct.index intrinsics Use the elementtype attribute introduced in D105407 for the llvm.preserve.array/struct.index intrinsics. It carries the element type of the GEP these intrinsics effectively encode. This patch: * Adds a verifier check that the attribute is required. * Adds it in the IRBuilder methods for these intrinsics. * Autoupgrades old bitcode without the attribute. * Updates the lowering code to use the attribute rather than the pointer element type. * Updates lots of tests to specify the attribute. * Adds -force-opaque-pointers to the intrinsic-array.ll test to demonstrate they work now. https://reviews.llvm.org/D106184
2021-07-17 02:26:40 +08:00
// CHECK: call %struct.s2* @llvm.preserve.struct.access.index.p0s_struct.s2s.p0s_struct.s3s(%struct.s3* elementtype(%struct.s3) %{{[0-9a-z]+}}, i32 0, i32 0)
// CHECK: call %union.anon* @llvm.preserve.struct.access.index.p0s_union.anons.p0s_struct.s2s(%struct.s2* elementtype(%struct.s2) %{{[0-9a-z]+}}, i32 0, i32 0)
[BPF] Add preserve_access_index attribute for record definition This is a resubmission for the previous reverted commit 943436040121 with the same subject. This commit fixed the segfault issue and addressed additional review comments. This patch introduced a new bpf specific attribute which can be added to struct or union definition. For example, struct s { ... } __attribute__((preserve_access_index)); union u { ... } __attribute__((preserve_access_index)); The goal is to simplify user codes for cases where preserve access index happens for certain struct/union, so user does not need to use clang __builtin_preserve_access_index for every members. The attribute has no effect if -g is not specified. When the attribute is specified and -g is specified, any member access defined by that structure or union, including array subscript access and inner records, will be preserved through __builtin_preserve_{array,struct,union}_access_index() IR intrinsics, which will enable relocation generation in bpf backend. The following is an example to illustrate the usage: -bash-4.4$ cat t.c #define __reloc__ __attribute__((preserve_access_index)) struct s1 { int c; } __reloc__; struct s2 { union { struct s1 b[3]; }; } __reloc__; struct s3 { struct s2 a; } __reloc__; int test(struct s3 *arg) { return arg->a.b[2].c; } -bash-4.4$ clang -target bpf -g -S -O2 t.c A relocation with access string "0:0:0:0:2:0" will be generated representing access offset of arg->a.b[2].c. forward declaration with attribute is also handled properly such that the attribute is copied and populated in real record definition. Differential Revision: https://reviews.llvm.org/D69759
2019-11-02 13:16:59 +08:00
// CHECK: call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(%union.anon* %{{[0-9a-z]+}}, i32 0)
[BPF] Use elementtype attribute for preserve.array/struct.index intrinsics Use the elementtype attribute introduced in D105407 for the llvm.preserve.array/struct.index intrinsics. It carries the element type of the GEP these intrinsics effectively encode. This patch: * Adds a verifier check that the attribute is required. * Adds it in the IRBuilder methods for these intrinsics. * Autoupgrades old bitcode without the attribute. * Updates the lowering code to use the attribute rather than the pointer element type. * Updates lots of tests to specify the attribute. * Adds -force-opaque-pointers to the intrinsic-array.ll test to demonstrate they work now. https://reviews.llvm.org/D106184
2021-07-17 02:26:40 +08:00
// CHECK: call %struct.s1* @llvm.preserve.array.access.index.p0s_struct.s1s.p0a3s_struct.s1s([3 x %struct.s1]* elementtype([3 x %struct.s1]) %{{[0-9a-z]+}}, i32 1, i32 2)
// CHECK: call i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.s1s(%struct.s1* elementtype(%struct.s1) %{{[0-9a-z]+}}, i32 0, i32 0)