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Message-ID: <3fbb9319.20c8.198a1410186.Coremail.phoenix500526@163.com>
Date: Wed, 13 Aug 2025 10:27:28 +0800 (CST)
From: 赵佳炜 <phoenix500526@....com>
To: "Yonghong Song" <yonghong.song@...ux.dev>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH v7 2/2] selftests/bpf: Force -O2 for USDT selftests
to cover SIB handling logic
Sure.
The usdt_rip.c source code:
```C
// the usdt_rip.c file
#include <stddef.h>
#include <stdint.h>
#include "sdt.h"
static volatile char ti = 0;
int add(int a, int b) {
return a + b;
}
int (*add_ptr)(int, int) = add;
struct st{
int a;
char b;
};
volatile struct st t1 = {.a = 1, .b = 'a'};
static void __always_inline trigger_func() {
STAP_PROBE4(usdt_rip, rip_global_var, ti, add_ptr, t1.b, ti);
}
int main() {
trigger_func();
return 0;
}
```
The test/usdt_rip.c source code:
```C
// The test/usdt_rip.c file
static volatile char ti = 0;
```
The compiler option is `gcc -O2 -g usdt_rip.c test/usdt_rip.c -o usdt_rip`
My compiler version:
```bash
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 13.3.0-6ubuntu2~24.04' --with-bugurl=file:///usr/share/doc/gcc-13/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-13 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-libstdcxx-backtrace --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/gcc-13-fG75Ri/gcc-13-13.3.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-13-fG75Ri/gcc-13-13.3.0/debian/tmp-gcn/usr --enable-offload-defaulted --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu --with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.3.0 (Ubuntu 13.3.0-6ubuntu2~24.04)
```
At 2025-08-13 00:11:45, "Yonghong Song" <yonghong.song@...ux.dev> wrote:
>
>
>On 8/12/25 12:02 AM, 赵佳炜 wrote:
>> Yes, I've tried that but it didn't help. FYI:
>>
>> $ readelf -nsr usdt_rip
>>
>>
>> Relocation section '.rela.dyn' at offset 0x530 contains 9 entries:
>> Offset Info Type Sym. Value Sym. Name + Addend
>> 000000003df0 000000000008 R_X86_64_RELATIVE 1150
>> 000000003df8 000000000008 R_X86_64_RELATIVE 1110
>> 000000004008 000000000008 R_X86_64_RELATIVE 4008
>> 000000004018 000000000008 R_X86_64_RELATIVE 1160
>> 000000003fd8 000100000006 R_X86_64_GLOB_DAT 0000000000000000 __libc_start_main@...BC_2.34 + 0
>> 000000003fe0 000200000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_deregisterTM[...] + 0
>> 000000003fe8 000300000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ + 0
>> 000000003ff0 000400000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_registerTMCl[...] + 0
>> 000000003ff8 000500000006 R_X86_64_GLOB_DAT 0000000000000000 __cxa_finalize@...BC_2.2.5 + 0
>>
>>
>> Symbol table '.dynsym' contains 6 entries:
>> Num: Value Size Type Bind Vis Ndx Name
>> 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
>> 1: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _[...]@GLIBC_2.34 (2)
>> 2: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterT[...]
>> 3: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
>> 4: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMC[...]
>> 5: 0000000000000000 0 FUNC WEAK DEFAULT UND [...]@GLIBC_2.2.5 (3)
>>
>>
>> Symbol table '.symtab' contains 42 entries:
>> Num: Value Size Type Bind Vis Ndx Name
>> 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
>> 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS Scrt1.o
>> 2: 000000000000038c 32 OBJECT LOCAL DEFAULT 4 __abi_tag
>> 3: 0000000000000000 0 FILE LOCAL DEFAULT ABS usdt_rip.c
>> 4: 0000000000004021 1 OBJECT LOCAL DEFAULT 25 ti
>> 5: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
>> 6: 00000000000010a0 0 FUNC LOCAL DEFAULT 14 deregister_tm_clones
>> 7: 00000000000010d0 0 FUNC LOCAL DEFAULT 14 register_tm_clones
>> 8: 0000000000001110 0 FUNC LOCAL DEFAULT 14 __do_global_dtors_aux
>> 9: 0000000000004020 1 OBJECT LOCAL DEFAULT 25 completed.0
>> 10: 0000000000003df8 0 OBJECT LOCAL DEFAULT 21 __do_global_dtor[...]
>> 11: 0000000000001150 0 FUNC LOCAL DEFAULT 14 frame_dummy
>> 12: 0000000000003df0 0 OBJECT LOCAL DEFAULT 20 __frame_dummy_in[...]
>> 13: 0000000000000000 0 FILE LOCAL DEFAULT ABS damo.c
>> 14: 0000000000004022 1 OBJECT LOCAL DEFAULT 25 ti
>> 15: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
>> 16: 00000000000020d8 0 OBJECT LOCAL DEFAULT 19 __FRAME_END__
>> 17: 0000000000000000 0 FILE LOCAL DEFAULT ABS
>> 18: 0000000000003e00 0 OBJECT LOCAL DEFAULT 22 _DYNAMIC
>> 19: 0000000000002008 0 NOTYPE LOCAL DEFAULT 18 __GNU_EH_FRAME_HDR
>> 20: 0000000000003fc0 0 OBJECT LOCAL DEFAULT 23 _GLOBAL_OFFSET_TABLE_
>> 21: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __libc_start_mai[...]
>> 22: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterT[...]
>> 23: 0000000000004000 0 NOTYPE WEAK DEFAULT 24 data_start
>> 24: 0000000000001160 8 FUNC GLOBAL DEFAULT 14 add
>> 25: 0000000000004020 0 NOTYPE GLOBAL DEFAULT 24 _edata
>> 26: 0000000000002004 1 NOTYPE WEAK HIDDEN 17 _.stapsdt.base
>> 27: 0000000000004010 8 OBJECT GLOBAL DEFAULT 24 t1
>> 28: 0000000000001168 0 FUNC GLOBAL HIDDEN 15 _fini
>> 29: 0000000000004000 0 NOTYPE GLOBAL DEFAULT 24 __data_start
>> 30: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
>> 31: 0000000000004008 0 OBJECT GLOBAL HIDDEN 24 __dso_handle
>> 32: 0000000000002000 4 OBJECT GLOBAL DEFAULT 16 _IO_stdin_used
>> 33: 0000000000004028 0 NOTYPE GLOBAL DEFAULT 25 _end
>> 34: 0000000000001070 38 FUNC GLOBAL DEFAULT 14 _start
>> 35: 0000000000004020 0 NOTYPE GLOBAL DEFAULT 25 __bss_start
>> 36: 0000000000001040 48 FUNC GLOBAL DEFAULT 14 main
>> 37: 0000000000004018 8 OBJECT GLOBAL DEFAULT 24 add_ptr
>> 38: 0000000000004020 0 OBJECT GLOBAL HIDDEN 24 __TMC_END__
>> 39: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMC[...]
>> 40: 0000000000000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@G[...]
>> 41: 0000000000001000 0 FUNC GLOBAL HIDDEN 11 _init
>>
>>
>> Displaying notes found in: .note.gnu.property
>> Owner Data size Description
>> GNU 0x00000020 NT_GNU_PROPERTY_TYPE_0
>> Properties: x86 feature: IBT, SHSTK
>> x86 ISA needed: x86-64-baseline
>>
>>
>> Displaying notes found in: .note.gnu.build-id
>> Owner Data size Description
>> GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
>> Build ID: eb615daa575687cc44edc1d339b27890c12c27f1
>>
>>
>> Displaying notes found in: .note.ABI-tag
>> Owner Data size Description
>> GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
>> OS: Linux, ABI: 3.2.0
>>
>>
>> Displaying notes found in: .note.stapsdt
>> Owner Data size Description
>> stapsdt 0x00000066 NT_STAPSDT (SystemTap probe descriptors)
>> Provider: usdt_rip
>> Name: rip_global_var
>> Location: 0x0000000000001058, Base: 0x0000000000002004, Semaphore: 0x0000000000000000
>> Arguments: -1@ti(%rip) 8@..._ptr(%rip) -1@...1(%rip) -1@ti(%rip)
>
>Could you share the complete source codes and compiler options which
>reproduce the above result?
>
>>
>>
>>
>> At 2025-08-12 13:06:40, "Yonghong Song" <yonghong.song@...ux.dev> wrote:
>>>
>>> On 8/10/25 1:55 AM, 赵佳炜 wrote:
>>>>
>>>> Hi Yonghong,
>>>>
>>>> I found another issue where symbols can be duplicated, and I’m not sure how to tell them apart.
>>>>
>>>> For example, I created two C files named usdt_rip.c and hello.c. Both define their own static ti variables, like:`static volatile char ti = 0;`.
>>>>
>>>> After compiling, I obtained an ELF file usdt_rip whose .symtab contains the following entries:
>>>>
>>>> $ readelf -s usdt_rip
>>>>
>>>> Symbol table '.symtab' contains 42 entries:
>>>> Num: Value Size Type Bind Vis Ndx Name
>>>> 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
>>>> 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS Scrt1.o
>>>> 2: 000000000000038c 32 OBJECT LOCAL DEFAULT 4 __abi_tag
>>>> 3: 0000000000000000 0 FILE LOCAL DEFAULT ABS usdt_rip.c
>>>> 4: 0000000000004021 1 OBJECT LOCAL DEFAULT 25 ti
>>>> 5: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
>>>> 6: 00000000000010a0 0 FUNC LOCAL DEFAULT 14 deregister_tm_clones
>>>> 7: 00000000000010d0 0 FUNC LOCAL DEFAULT 14 register_tm_clones
>>>> 8: 0000000000001110 0 FUNC LOCAL DEFAULT 14 __do_global_dtors_aux
>>>> 9: 0000000000004020 1 OBJECT LOCAL DEFAULT 25 completed.0
>>>> 10: 0000000000003df8 0 OBJECT LOCAL DEFAULT 21 __do_global_dtor[...]
>>>> 11: 0000000000001150 0 FUNC LOCAL DEFAULT 14 frame_dummy
>>>> 12: 0000000000003df0 0 OBJECT LOCAL DEFAULT 20 __frame_dummy_in[...]
>>>> 13: 0000000000000000 0 FILE LOCAL DEFAULT ABS damo.c
>>>> 14: 0000000000004022 1 OBJECT LOCAL DEFAULT 25 ti
>>>> 15: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
>>>> 16: 00000000000020d8 0 OBJECT LOCAL DEFAULT 19 __FRAME_END__
>>>>
>>>>
>>>> As you can see, there are two ti variables in the .symtab section. Their values are very close, making them hard to distinguish.
>>>>
>>>> I’m unsure how to handle this situation. Do you have any suggestions?
>>> Did you check relocations? Relocaitons should be able to point exact which symbol.
>>>
>>>> Thanks,
>>>> Jiawei Zhao
>>> [...]
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