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4e2ce228ae
This is a resubmission for the previous reverted commit
9434360401 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
37 lines
1.1 KiB
C
37 lines
1.1 KiB
C
// REQUIRES: bpf-registered-target
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// RUN: %clang -target bpf -emit-llvm -S -g %s -o - | FileCheck %s
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#define __reloc__ __attribute__((preserve_access_index))
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// chain of records, all with attributes
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struct s1;
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struct s2;
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struct s3;
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struct s1 {
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int c;
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} __reloc__;
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typedef struct s1 __s1;
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struct s2 {
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union {
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__s1 b[3];
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};
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} __reloc__;
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typedef struct s2 __s2;
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struct s3 {
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__s2 a;
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} __reloc__;
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typedef struct s3 __s3;
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int test(__s3 *arg) {
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return arg->a.b[2].c;
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}
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// CHECK: call %struct.s2* @llvm.preserve.struct.access.index.p0s_struct.s2s.p0s_struct.s3s(%struct.s3* %{{[0-9a-z]+}}, i32 0, i32 0)
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// CHECK: call %union.anon* @llvm.preserve.struct.access.index.p0s_union.anons.p0s_struct.s2s(%struct.s2* %{{[0-9a-z]+}}, i32 0, i32 0)
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// CHECK: call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(%union.anon* %{{[0-9a-z]+}}, i32 0)
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// CHECK: call %struct.s1* @llvm.preserve.array.access.index.p0s_struct.s1s.p0a3s_struct.s1s([3 x %struct.s1]* %{{[0-9a-z]+}}, i32 1, i32 2)
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// CHECK: call i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.s1s(%struct.s1* %{{[0-9a-z]+}}, i32 0, i32 0)
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