Hi Mark,
I just dumped out my executable (code was in my very first email):
$ eu-readelf -l myexec
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flg Align
PHDR 0x000040 0x0000000000400040 0x0000000000400040
0x0001f8 0x0001f8 R E 0x8
INTERP 0x000238 0x0000000000400238 0x0000000000400238
0x00001c 0x00001c R 0x1
[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
LOAD 0x000000 0x0000000000400000 0x0000000000400000
0x00079c 0x00079c R E 0x200000
LOAD 0x000de8 0x0000000000600de8 0x0000000000600de8
0x000247 0x000248 RW 0x200000
DYNAMIC 0x000df8 0x0000000000600df8 0x0000000000600df8
0x000200 0x000200 RW 0x8
NOTE 0x000254 0x0000000000400254 0x0000000000400254
0x000044 0x000044 R 0x4
GNU_EH_FRAME 0x00063c 0x000000000040063c 0x000000000040063c
0x000044 0x000044 R 0x4
GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000
0x000000 0x000000 RW 0x10
GNU_RELRO 0x000de8 0x0000000000600de8 0x0000000000600de8
0x000218 0x000218 R 0x1
Section to Segment mapping:
Segment Sections...
00
01 [RO: .interp]
02 [RO: .interp .note.ABI-tag .note.gnu.build-id .gnu.hash
.dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init
.plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame]
03 [RELRO: .init_array .fini_array .dynamic .got] .got.plt .data .bss
04 [RELRO: .dynamic]
05 [RO: .note.ABI-tag .note.gnu.build-id]
06 [RO: .eh_frame_hdr]
07
08 [RELRO: .init_array .fini_array .dynamic .got]
By looking at the output and the wiki link, the program headers do
contain virtual addresses but nothing explicit about .rodata. How can
I use libelf to figure the correct virtual memory address to "hello
world"?
But if I print out Elf64_Shdr::sh_addr (.rodata section header) +
offset to "hello world" in .rodata, I do see the output matches the
output of printf("%p\n", "hello world");
As you mentioned, it is not guaranteed, I wonder under what situation
Elf64_Shdr::sh_addr won't represent the virtual address of the
beginning of .rodata section.
Thanks in advance!
On Fri, Aug 31, 2018 at 7:33 PM Mark Wielaard <m...@klomp.org> wrote:
>
> On Fri, 2018-08-31 at 19:07 +0800, Henry C wrote:
> > Thanks for replying.
> >
> > I mean for example,
> > void myprintf(const char* ptr) {
> > printf("%p\n", ptr);
> > }
> >
> > int main() {
> > myprintf("hello world");
> > }
> >
> > Let's say the output is 0x403DE.
> >
> > Does it mean that Elf64_Shdr::sh_addr of the string table (of
> > .rodata)
> > + the offset of "hello word" within the string table is guaranteed to
> > be the virtual address 0x403DE? As I am not sure whether virtual
> > memory addresses of all string literals are defined/calculated when
> > ELF is created.
>
> No, that is not guaranteed. How data in an ELF file is mapped into
> memory is determined by the program headers (not the section headers).
> See also the picture showing the different ELF file data views in https
> ://en.wikipedia.org/wiki/Executable_and_Linkable_Format
>
> Cheers,
>
> Mark
