Add offsetof() #2579

Rtoax · 2023-04-25T06:15:02Z

Add the offsetof() function, the syntax follows the kernel offsetof() macro definition, and currently only supports single-member format parameters such as offsetof(struct task_struct, comm). The function returns a long integer with the output format '%ld'.

This is the second PR for offsetof(), v1[0] and v2[1] was not merged, and the discussion of offsetof() can be found in [0][1].

Basic use:

    struct Foo {
        int a;
        long b;
        char c;
        struct {
            int d;
        };
        struct {
            int a;
        } e;
    }
    struct offsetof {
        int bswap;
	int comm;
	int kstack;
	int ustack;
	int pid;
	int ctx;
	int arg;
    }

    BEGIN {
        printf("%ld\n", offsetof(struct Foo, c));
        printf("%ld\n", offsetof(struct Foo, d));

        printf("%ld\n", offsetof(struct offsetof, bswap));

        printf("%ld\n", offsetof(struct task_struct, comm));
        printf("%ld\n", offsetof(*curtask, comm));

        exit();
    }

Get offset:

[0] v1: #2216
[1] v2: #2565

src/ast/ast.cpp

@@ -272,6 +279,16 @@
 {
 }

+Offsetof::Offsetof(SizedType record, std::string &field, location loc)


viktormalik

Looks mostly good, thanks! I'd just like to see a few more tests and highlighted a couple of nits below.

src/ast/passes/semantic_analyser.cpp

tests/codegen/call_offsetof.cpp

tests/mocks.cpp

tests/semantic_analyser.cpp

src/parser.yy

viktormalik · 2023-04-25T08:01:07Z

cc @lenticularis39

src/ast/passes/semantic_analyser.cpp

tests/semantic_analyser.cpp

viktormalik

LGTM, thanks!

danobi

thanks for getting this through!

docs/reference_guide.md

man/adoc/bpftrace.adoc

Add the offsetof() function, the syntax follows the kernel offsetof() macro definition, and currently only supports single-member format parameters such as offsetof(struct task_struct, comm). The function returns a long integer with the output format '%ld'. This is the third PR for offsetof(), v1[0] and v2[1] was not merged, and the discussion of offsetof() can be found in [0][1]. Basic use: struct Foo { int a; long b; char c; struct { int d; }; struct { int a; } e; } struct offsetof { int bswap; int comm; int kstack; int ustack; int pid; int ctx; int arg; } BEGIN { printf("%ld\n", offsetof(struct Foo, c)); printf("%ld\n", offsetof(struct Foo, d)); printf("%ld\n", offsetof(struct offsetof, bswap)); printf("%ld\n", offsetof(struct task_struct, comm)); printf("%ld\n", offsetof(*curtask, comm)); exit(); } Get offset: 16 20 0 3240 3240 [0] v1: bpftrace#2216 [1] v2: bpftrace#2565 Signed-off-by: Rong Tao <rongtao@cestc.cn>

Rtoax · 2023-04-28T13:18:42Z

@lenticularis39 Fixed the description of offsetof() in docs/reference_guide.md and man/adoc/bpftrace.adoc, and rebase to master. please review.

Since bpftrace PR [1] support offsetof() function. As previously discussed [2], the current offsetof() does not support sub-fields, and this PR implements offsetof(struct foo, a.b.c). Example: struct Foo { struct e { int a; int b; struct c { int a, b, c; } c; } e; } struct offsetof { struct { int comm; int ustack; } kstack; } BEGIN { printf("struct Foo e.b offset %ld\n", offsetof(struct Foo, e.b)); printf("struct Foo e.c offset %ld\n", offsetof(struct Foo, e.c)); printf("struct Foo e.c.b offset %ld\n", offsetof(struct Foo, e.c.b)); printf("struct offsetof kstack.ustack offset %ld\n", offsetof(struct offsetof, kstack.ustack)); exit(); } Link: bpftrace#2579 [1] merged Link: bpftrace#2216 [2] Signed-off-by: Rong Tao <rongtao@cestc.cn>

Since bpftrace PR [1] support offsetof() function. As previously discussed [2], the current offsetof() does not support sub-fields, and this PR implements offsetof(struct foo, a.b.c), implement [1] unfinished features. Example: struct Foo { struct e { int a; int b; struct c { int a, b, c; } c; } e; } struct offsetof { struct { int comm; int ustack; } kstack; } BEGIN { printf("struct Foo e.b offset %ld\n", offsetof(struct Foo, e.b)); printf("struct Foo e.c offset %ld\n", offsetof(struct Foo, e.c)); printf("struct Foo e.c.b offset %ld\n", offsetof(struct Foo, e.c.b)); printf("struct offsetof kstack.ustack offset %ld\n", offsetof(struct offsetof, kstack.ustack)); exit(); } Link: bpftrace#2579 [1] merged Link: bpftrace#2216 [2] Signed-off-by: Rong Tao <rongtao@cestc.cn>

Since bpftrace PR [1] support offsetof() function. As previously discussed [2], the current offsetof() does not support sub-fields, and this PR implements offsetof(struct foo, a.b.c), implement [1] unfinished features. Example: struct Foo { struct e { int a; int b; struct c { int a, b, c; } c; } e; } struct offsetof { struct { int comm; int ustack; } kstack; } BEGIN { printf("struct Foo e.b offset %ld\n", offsetof(struct Foo, e.b)); printf("struct Foo e.c offset %ld\n", offsetof(struct Foo, e.c)); printf("struct Foo e.c.b offset %ld\n", offsetof(struct Foo, e.c.b)); printf("struct offsetof kstack.ustack offset %ld\n", offsetof(struct offsetof, kstack.ustack)); exit(); } Link: #2579 [1] merged Link: #2216 [2] Signed-off-by: Rong Tao <rongtao@cestc.cn>

Rtoax requested review from ajor, viktormalik, danobi and fbs as code owners April 25, 2023 06:15

Rtoax mentioned this pull request Apr 25, 2023

Add offsetof() builtin #2565

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Rtoax force-pushed the patch-44-offsetof-v4 branch 4 times, most recently from 198d9ea to ba6222d Compare April 25, 2023 06:37

github-advanced-security bot found potential problems Apr 25, 2023

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src/ast/ast.cpp

@@ -272,6 +279,16 @@

{

}

Offsetof::Offsetof(SizedType record, std::string &field, location loc)

Check notice

Code scanning / CodeQL

Large object passed by value

This parameter of type [SizedType](1) is 136 bytes - consider passing a const pointer/reference instead.

Rtoax force-pushed the patch-44-offsetof-v4 branch 2 times, most recently from a47adff to 5babd76 Compare April 25, 2023 07:57

viktormalik reviewed Apr 25, 2023

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Rtoax force-pushed the patch-44-offsetof-v4 branch from 5babd76 to 817461f Compare April 25, 2023 08:23

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Rtoax force-pushed the patch-44-offsetof-v4 branch from 817461f to cf0aab7 Compare April 25, 2023 09:49

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Rtoax force-pushed the patch-44-offsetof-v4 branch 2 times, most recently from 00c9afe to 8068c20 Compare April 25, 2023 11:18

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Rtoax force-pushed the patch-44-offsetof-v4 branch from 8068c20 to a1aae77 Compare April 28, 2023 13:14

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viktormalik merged commit a7c2c35 into bpftrace:master May 2, 2023

Rtoax mentioned this pull request Feb 1, 2025

offsetof: Support sub-field #3761

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Add offsetof() #2579

Add offsetof() #2579

Rtoax commented Apr 25, 2023 •

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Rtoax commented Apr 28, 2023

Add offsetof() #2579

Add offsetof() #2579

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Rtoax commented Apr 25, 2023 •

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