Hi Mark,
在 2023/5/22 05:14, Mark Wielaard 写道:
> Hi Ying,
>
> On Tue, May 16, 2023 at 03:34:01PM +0800, Ying Huang wrote:
>> 在 2023/5/16 14:46, Ying Huang 写道:
>>>>> libelf/elf_getdata.c: Some eu-utils use read-mmap method to map file,
>>>>> so we need to malloc and memcpy raw data to avoid segment fault. After
>>>>> modification, the correct value are saved in the malloced memory not in
>>>>> process address space.
>>>> Where do these segfaults show up?
>>> The screenshot of the segment error was not uploaded successfully in
>>> the last email, upload again.
> Sorry, the mailinglist seems to strip the image attachements.
>
>> huangying@Sleepygon:~/elf/elfutils_4$ src/elflint src/nm.o
>> Segmentation fault
>> huangying@Sleepygon:~/elf/elfutils_4$ src/elflint src/strip.o
>> Segmentation fault
> When running under gdb, what is the backtrace of the crash?
>
> Thanks,
>
> Mark
huangying@Sleepygon:~/elf/elfutils_4$ src/elflint src/nm.o
Segmentation fault (core dumped)
huangying@Sleepygon:~/elf/elfutils_4$ gdb src/elflint
...
(gdb) bt
#0 convert_data (type=ELF_T_RELA, size=24912, data=1, eclass=<optimized out>,
scn=0xaad3698f98) at elf_getdata.c:254
#1 __libelf_set_data_list_rdlock (scn=0xaad3698f98, wrlocked=<optimized out>)
at elf_getdata.c:515
#2 0x000000fff3862f14 in __elf_getdata_rdlock (scn=0xaad3698f98,
data=<optimized out>) at elf_getdata.c:622
#3 0x000000fff3862f54 in elf_getdata (scn=<optimized out>, data=<optimized
out>) at elf_getdata.c:640
#4 0x000000aaac571c9c in check_rela (ebl=0xaad369b120, ehdr=0xfffb9451b0,
shdr=0xfffb945008, idx=<optimized out>) at elflint.c:1500
#5 0x000000aaac574e40 in check_sections (ebl=0xaad369b120, ehdr=0xfffb9451b0)
at elflint.c:4198
#6 0x000000aaac5784ac in process_elf_file (only_one=<optimized out>,
size=<optimized out>, fname=<optimized out>, suffix=<optimized out>,
prefix=<optimized out>, elf=<optimized out>) at elflint.c:4842
#7 process_file (fd=<optimized out>, elf=<optimized out>, prefix=<optimized
out>, suffix=<optimized out>, fname=<optimized out>, size=<optimized out>,
only_one=<optimized out>) at elflint.c:241
#8 0x000000aaac5688fc in main (argc=<optimized out>, argv=0xfffb9455d8) at
elflint.c:174
...
If I did not malloc to scn->data_base, would occur Segment fault when we
want to operate this space "&scn->data_list.data.d". Because src/elflint use
read-mmap method to map file.
Show 10 lines of code "libelf/elf_getdata.c" starting at line 254:
huangying@Sleepygon:~/elf/elfutils_4$ cat libelf/elf_getdata.c | tail -n +254 |
head -n 10
for (int cnt = 0; cnt < nentries; cnt++)
{
Elf_Data_Scn *data_scn = (Elf_Data_Scn *) &scn->data_list.data.d;
Elf64_Rela *value = &((Elf64_Rela *) data_scn->d.d_buf)[cnt];
Elf64_Xword info = value->r_info;
value->r_info = (((info & 0xffffffff) << 32)
| ((info >> 56) & 0xff)
| ((info >> 40) & 0xff00)
| ((info >> 24) & 0xff0000)
| ((info >> 8) & 0xff000000));
Show elflint map method in src/elflint.c:
/* Create an `Elf' descriptor. */
Elf *elf = elf_begin (fd, ELF_C_READ_MMAP, NULL);
Thanks,
Ying
