From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9065D3E2AC8 for ; Wed, 3 Jun 2026 21:40:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780522853; cv=none; b=LREcx12CYDApzBTc43ueNawWVI71j2edvHGljKjO1gMPwqrAxTAjJABa2NYawOjIP6GJPa+QjBWnEnrP+geQLPrnEkdXhO7kh7KeARVQWQPvhPMoTADMQZZkCGvmjtvsv+uyFpfwlp4J718WPqL7mdD7LVkVgZuyG71zf6vOook= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780522853; c=relaxed/simple; bh=+Pp4hUB/SVlj7OWiRtYRzUGb1BV3wYEUx3VjoAnuOx0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JQ6Vn6EzH9u/BbMlU650eeX8x5YUvaO3gmeBDKsAh8laqJa8s9espVVwyp9LBdvELr6cQYod/89En+0AzB0KXdrzkS6Gxb5E/vbKERT/+7208VJXie+z8HRlPi/9HxgTRG0WGbBE9/o4N6qlqtsO4YYGOqRMQe1tTCucbK5TUC0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=VBEuk+Oz; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="VBEuk+Oz" Message-ID: <6857c249-86ea-4402-9a91-27ea5a679e32@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780522836; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3rA91WuKfkvlPJwNgx7XY7khEbvLunqfNs1YyZTJLYY=; b=VBEuk+Oz2kZYzXX70+n8NSQEtoac5Rm2l3tIrln/NZsZSE9ctEDFaVmhAZvQHegqvOtkih EfnIkHlCR74aqKrlZRVmE/HYcx6AvyyJhAwyc4gO7/2ySoGzrcCRFCtEFR2dLGWP9BXo4d FW5+aPlzsRvwsF2U9PaXK6v5jqo8+Zs= Date: Wed, 3 Jun 2026 14:40:11 -0700 Precedence: bulk X-Mailing-List: dwarves@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PAHOLE v4 2/3] dwarf_loader: Add support for DW_TAG_GNU_annotation Content-Language: en-GB To: Vineet Gupta , dwarves@vger.kernel.org Cc: bpf@vger.kernel.org, Andrii Nakryiko , acme@kernel.org, Alan Maguire , Emil Tsalapatis , jose.marchesi@oracle.com, David Faust References: <20260602195512.1511013-1-vineet.gupta@linux.dev> <20260602195512.1511013-2-vineet.gupta@linux.dev> <9152fde6-d35c-4688-9ff1-c7fe152c9b2a@linux.dev> <27ee8637-a825-4f3f-b4ec-59dad215f4b4@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <27ee8637-a825-4f3f-b4ec-59dad215f4b4@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 6/3/26 1:54 PM, Vineet Gupta wrote: > Hi Yonghong, > > Thanks for reviewing the patches. > > On 6/3/26 1:08 PM, Yonghong Song wrote: >>> [3] >>> https://lore.kernel.org/bpf/20260601183511.594100-2-vineet.gupta@linux.dev/ >>> [2] >>> https://lore.kernel.org/bpf/20260528223616.2035618-2-vineet.gupta@linux.dev/ >>> [1] >>> https://lore.kernel.org/bpf/20260526181818.4159927-2-vineet.gupta@linux.dev/ >> I download and build gcc-16.1 which will be used for gcc compilation. >> I did some experiments with this patch set for both type tag and decl >> tag. >> See below. > > FWIW, you definitely need a fix [1] on top of gcc 16.1. > The patch explains the reasoning and did cause some missing entries in > type chain. > I haven't checked if this changes anything specific to issues you > point below. > > [1] https://gcc.gnu.org/pipermail/bpf/2026-May/000147.html Thanks for the pointer. The fix is related to type tag. So I suspect typedef and struct decl_tag support is not done yet in gcc. > > >> >> For type tag >> ============ >> >> $ cat type_tag.c >> /* btf_type_tag test cases. >>    * >>    * btf_type_tag annotates a *type* and the tag becomes part of the >> type >>    * chain in BTF (TYPE_TAG kind), e.g. used by the kernel for __user >> / __rcu >>    * / __percpu style annotations. >>    * >>    * Placement matters: the tag is written *before* the '*' so it >> annotates >>    * the pointee type.  This produces  PTR -> TYPE_TAG 'x' -> . >>    * >>    * Build:  clang -O2 -g -target bpf -c type_tag.c -o type_tag.o >>    *         /home/yhs/work/gcc-build/opt/gcc-16.1/bin/gcc -O2 -gbtf >> -g -c type_tag.c -o type_tag.o >>    * Dump:   bpftool btf dump file type_tag.o >>    */ >> >> #define __type_tag(x) __attribute__((btf_type_tag(x))) >> >> /* a single type tag on a pointer's pointee */ >> int __type_tag("user") *user_ptr_var; >> >> /* stacked type tags: the chain is preserved, outermost first */ >> int __type_tag("tag1") __type_tag("tag2") *stacked_var; >> >> /* type tags inside struct members */ >> struct bar { >>           char __type_tag("rcu") *name; >>           int  __type_tag("percpu") *counter; >> }; >> >> /* type tag on a function parameter's pointee */ >> int read_user(int __type_tag("user") *p) >> { >>           return *p; >> } >> >> /* keep things referenced */ >> int use(struct bar *b) >> { >>           return read_user(user_ptr_var) + (stacked_var ? >> *stacked_var : 0) + >>                  (b->counter ? *b->counter : 0); >> } >> >> $ /home/yhs/work/gcc-build/opt/gcc-16.1/bin/gcc -O2 -gbtf -g -c >> type_tag.c -o type_tag.o >> $ bpftool btf dump file type_tag.o >> [1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED >> [2] PTR '(anon)' type_id=15 >> [3] PTR '(anon)' type_id=17 >> [4] STRUCT 'bar' size=16 vlen=2 >>           'name' type_id=6 bits_offset=0 >>           'counter' type_id=7 bits_offset=64 >> [5] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED >> [6] PTR '(anon)' type_id=18 >> [7] PTR '(anon)' type_id=19 >> [8] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1 >>           'b' type_id=9 >> [9] PTR '(anon)' type_id=4 >> [10] FUNC_PROTO '(anon)' ret_type_id=1 vlen=1 >>           'p' type_id=2 >> [11] VAR 'stacked_var' type_id=3, linkage=global >> [12] VAR 'user_ptr_var' type_id=2, linkage=global >> [13] FUNC 'use' type_id=8 linkage=global >> [14] FUNC 'read_user' type_id=10 linkage=global >> [15] TYPE_TAG 'user' type_id=1 >> [16] TYPE_TAG 'tag1' type_id=1 >> [17] TYPE_TAG 'tag2' type_id=16 >> [18] TYPE_TAG 'rcu' type_id=5 >> [19] TYPE_TAG 'percpu' type_id=1 >> [20] DATASEC '.bss' size=0 vlen=2 >>           type_id=11 offset=0 size=8 (VAR 'stacked_var') >>           type_id=12 offset=0 size=8 (VAR 'user_ptr_var') >> $ >> >> $ clang -O2 -g -target bpf -c type_tag.c -o type_tag.o >> $ bpftool btf dump file type_tag.o >> [1] TYPE_TAG 'user' type_id=3 >> [2] PTR '(anon)' type_id=1 >> [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED >> [4] FUNC_PROTO '(anon)' ret_type_id=3 vlen=1 >>           'p' type_id=2 >> [5] FUNC 'read_user' type_id=4 linkage=global >> [6] PTR '(anon)' type_id=7 >> [7] STRUCT 'bar' size=16 vlen=2 >>           'name' type_id=9 bits_offset=0 >>           'counter' type_id=12 bits_offset=64 >> [8] TYPE_TAG 'rcu' type_id=10 >> [9] PTR '(anon)' type_id=8 >> [10] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED >> [11] TYPE_TAG 'percpu' type_id=3 >> [12] PTR '(anon)' type_id=11 >> [13] FUNC_PROTO '(anon)' ret_type_id=3 vlen=1 >>           'b' type_id=6 >> [14] FUNC 'use' type_id=13 linkage=global >> [15] VAR 'user_ptr_var' type_id=2, linkage=global >> [16] TYPE_TAG 'tag1' type_id=3 >> [17] TYPE_TAG 'tag2' type_id=16 >> [18] PTR '(anon)' type_id=17 >> [19] VAR 'stacked_var' type_id=18, linkage=global >> [20] DATASEC '.bss' size=0 vlen=2 >>           type_id=15 offset=0 size=8 (VAR 'user_ptr_var') >>           type_id=19 offset=0 size=8 (VAR 'stacked_var') >> $ >> >> So type tag matches between clang and gcc. > > Nice, thanks for cross-checking and confirming. > > >> For decl tag >> ============ >> >> $ cat decl_tag.c >> /* btf_decl_tag test cases. >>    * >>    * btf_decl_tag can be attached to: >>    *   - global (incl. static) variables >>    *   - functions >>    *   - function parameters >>    *   - struct/union types and their members >>    *   - typedefs >>    * >>    * Build:  clang -O2 -target bpf -g -c decl_tag.c -o decl_tag.o >>    *         /home/yhs/work/gcc-build/opt/gcc-16.1/bin/gcc -O2 -gbtf >> -g -c decl_tag.c -o decl_tag.o >>    * Dump:   bpftool btf dump file decl_tag.o >>    */ >> >> #define __tag(x) __attribute__((btf_decl_tag(x))) >> >> /* tag on a global variable */ >> int global_var __tag("global_var_tag"); >> >> /* tag on a static variable */ >> static int static_var __tag("static_var_tag"); >> >> /* multiple tags on one declaration */ >> int multi_tag_var __tag("tag_a") __tag("tag_b"); >> >> /* tag on struct type and its members */ >> struct foo { >>           int a __tag("member_a_tag"); >>           int b __tag("member_b_tag"); >> } __tag("struct_foo_tag"); >> >> /* tag on a typedef */ >> typedef struct foo foo_t1 __tag("typedef_foo_tag"); >> typedef struct {int foo2;} foo_t2 __tag("typedef_foo2_tag"); >> >> /* tag on a function and its parameters */ >> __tag("func_add_tag") >> int add(int x __tag("param_x_tag"), int y __tag("param_y_tag")) >> { >>           return x + y; >> } >> >> /* keep the globals/types alive so they land in BTF */ >> int use(foo_t1 *f, foo_t2 *g) >> { >>           return add(global_var + static_var + multi_tag_var, f->a + >> g->foo2); >> } >> >> $ /home/yhs/work/gcc-build/opt/gcc-16.1/bin/gcc -O2 -gbtf -g -c >> decl_tag.c -o decl_tag.o >> decl_tag.c:30:1: warning: ‘btf_decl_tag’ attribute does not apply to >> types [-Wattributes] >>      30 | } __tag("struct_foo_tag"); >>         | ^ >> >> $ bpftool btf dump file decl_tag.o >> [1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED >> [2] STRUCT 'foo' size=8 vlen=2 >>           'a' type_id=1 bits_offset=0 >>           'b' type_id=1 bits_offset=32 >> [3] TYPEDEF 'foo_t1' type_id=2 >> [4] STRUCT '(anon)' size=4 vlen=1 >>           'foo2' type_id=1 bits_offset=0 >> [5] TYPEDEF 'foo_t2' type_id=4 >> [6] FUNC_PROTO '(anon)' ret_type_id=1 vlen=2 >>           'f' type_id=7 >>           'g' type_id=8 >> [7] PTR '(anon)' type_id=3 >> [8] PTR '(anon)' type_id=5 >> [9] FUNC_PROTO '(anon)' ret_type_id=1 vlen=2 >>           'x' type_id=1 >>           'y' type_id=1 >> [10] VAR 'multi_tag_var' type_id=1, linkage=global >> [11] VAR 'global_var' type_id=1, linkage=global >> [12] FUNC 'use' type_id=6 linkage=global >> [13] FUNC 'add' type_id=9 linkage=global >> [14] DECL_TAG 'global_var_tag' type_id=11 component_idx=-1 >> [15] DECL_TAG 'static_var_tag' type_id=0 component_idx=-1 >> [16] DECL_TAG 'tag_b' type_id=10 component_idx=-1 >> [17] DECL_TAG 'tag_a' type_id=10 component_idx=-1 >> [18] DECL_TAG 'member_a_tag' type_id=2 component_idx=0 >> [19] DECL_TAG 'member_b_tag' type_id=2 component_idx=1 >> [20] DECL_TAG 'param_x_tag' type_id=13 component_idx=0 >> [21] DECL_TAG 'param_y_tag' type_id=13 component_idx=1 >> [22] DECL_TAG 'func_add_tag' type_id=13 component_idx=-1 >> [23] DATASEC '.bss' size=0 vlen=2 >>           type_id=10 offset=0 size=4 (VAR 'multi_tag_var') >>           type_id=11 offset=0 size=4 (VAR 'global_var') >> $ bpftool btf dump file decl_tag.o | grep DECL_TAG >> [14] DECL_TAG 'global_var_tag' type_id=11 component_idx=-1 >> [15] DECL_TAG 'static_var_tag' type_id=0 component_idx=-1 >> [16] DECL_TAG 'tag_b' type_id=10 component_idx=-1 >> [17] DECL_TAG 'tag_a' type_id=10 component_idx=-1 >> [18] DECL_TAG 'member_a_tag' type_id=2 component_idx=0 >> [19] DECL_TAG 'member_b_tag' type_id=2 component_idx=1 >> [20] DECL_TAG 'param_x_tag' type_id=13 component_idx=0 >> [21] DECL_TAG 'param_y_tag' type_id=13 component_idx=1 >> [22] DECL_TAG 'func_add_tag' type_id=13 component_idx=-1 >> $ >> >> Three decl tags (struct_foo_tag, typedef_foo_tag and typedef_foo2_tag) >> are missing here: > > I'll double check, once I'm back from PTO. > >> struct foo { >>           int a __tag("member_a_tag"); >>           int b __tag("member_b_tag"); >> } __tag("struct_foo_tag"); >> >> /* tag on a typedef */ >> typedef struct foo foo_t1 __tag("typedef_foo_tag"); >> typedef struct {int foo2;} foo_t2 __tag("typedef_foo2_tag"); >> >> $ clang -O2 -g -target bpf -c decl_tag.c -o decl_tag.o >> $ bpftool btf dump file decl_tag.o >> [1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED >> [2] FUNC_PROTO '(anon)' ret_type_id=1 vlen=2 >>           'x' type_id=1 >>           'y' type_id=1 >> [3] FUNC 'add' type_id=2 linkage=global >> [4] DECL_TAG 'param_x_tag' type_id=3 component_idx=0 >> [5] DECL_TAG 'param_y_tag' type_id=3 component_idx=1 >> [6] DECL_TAG 'func_add_tag' type_id=3 component_idx=-1 >> [7] PTR '(anon)' type_id=8 >> [8] TYPEDEF 'foo_t1' type_id=10 >> [9] DECL_TAG 'typedef_foo_tag' type_id=8 component_idx=-1 >> [10] STRUCT 'foo' size=8 vlen=2 >>           'a' type_id=1 bits_offset=0 >>           'b' type_id=1 bits_offset=32 >> [11] DECL_TAG 'struct_foo_tag' type_id=10 component_idx=-1 >> [12] DECL_TAG 'member_a_tag' type_id=10 component_idx=0 >> [13] DECL_TAG 'member_b_tag' type_id=10 component_idx=1 >> [14] PTR '(anon)' type_id=15 >> [15] TYPEDEF 'foo_t2' type_id=17 >> [16] DECL_TAG 'typedef_foo2_tag' type_id=15 component_idx=-1 >> [17] STRUCT '(anon)' size=4 vlen=1 >>           'foo2' type_id=1 bits_offset=0 >> [18] FUNC_PROTO '(anon)' ret_type_id=1 vlen=2 >>           'f' type_id=7 >>           'g' type_id=14 >> [19] FUNC 'use' type_id=18 linkage=global >> [20] VAR 'global_var' type_id=1, linkage=global >> [21] DECL_TAG 'global_var_tag' type_id=20 component_idx=-1 >> [22] VAR 'multi_tag_var' type_id=1, linkage=global >> [23] DECL_TAG 'tag_a' type_id=22 component_idx=-1 >> [24] DECL_TAG 'tag_b' type_id=22 component_idx=-1 >> [25] DATASEC '.bss' size=0 vlen=2 >>           type_id=20 offset=0 size=4 (VAR 'global_var') >>           type_id=22 offset=0 size=4 (VAR 'multi_tag_var') >> $ bpftool btf dump file decl_tag.o | grep DECL_TAG >> [4] DECL_TAG 'param_x_tag' type_id=3 component_idx=0 >> [5] DECL_TAG 'param_y_tag' type_id=3 component_idx=1 >> [6] DECL_TAG 'func_add_tag' type_id=3 component_idx=-1 >> [9] DECL_TAG 'typedef_foo_tag' type_id=8 component_idx=-1 >> [11] DECL_TAG 'struct_foo_tag' type_id=10 component_idx=-1 >> [12] DECL_TAG 'member_a_tag' type_id=10 component_idx=0 >> [13] DECL_TAG 'member_b_tag' type_id=10 component_idx=1 >> [16] DECL_TAG 'typedef_foo2_tag' type_id=15 component_idx=-1 >> [21] DECL_TAG 'global_var_tag' type_id=20 component_idx=-1 >> [23] DECL_TAG 'tag_a' type_id=22 component_idx=-1 >> [24] DECL_TAG 'tag_b' type_id=22 component_idx=-1 >> >> DECL_TAG 'static_var_tag' type_id=0 component_idx=-1 is missing in llvm. >> This is execpted for llvm since 'static_var' is 'inlined' since it is >> value is 0 and the compiler optimization removed it in function use(). >> In llvm Dwarf->BTF conversion is very late and we only emit survived >> globals. >> >> gcc emits 'static_var_tag' probably in frontend. Emitting >> 'static_var_tag' is okay, just not used. >> >> I think gcc should support >>    - declaration tag for typedef, and >>    - declaration tag for the whole struct (like above 'struct_foo_tag') >> to be compatible with llvm. > > OK we will look into this. Thanks! > > Thx, > -Vineet >