| Re: [tcf-dev] Can't do address to line for ELF with debug info only |
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Hi Eugene, Thanks for the extra explanation. I understood the case, nothing has to be done. Just pointed out that TCF does not catch this kind of incorrect memory
maps and that it will try to use the debug file. But that is likely a problem in how we allow adding memory maps in Simics. The user binaries came from a Yocto build which likely does stripping in similar way to what you wrote. Thanks again, Andreas Hi Andreas, I feel like I did not explain it well. No changes are needed, because debug only files work just fine. The problem you described looks like a simple user error. Here are the steps to prepare and use debug only file: objcopy --only-keep-debug foo foo.debug strip -g foo objcopy --add-gnu-debuglink=foo.debug foo Then add foo (not foo.debug) to the memory map. In your case, it looks like user added foo.debug to memory map, which is wrong – it is not going to work. Regards, Eugene From:
tcf-dev-bounces@xxxxxxxxxxx <tcf-dev-bounces@xxxxxxxxxxx>
On Behalf Of Ragnerstam, Andreas EXTERNAL EMAIL Hi Eugene, Thanks for the information! For me it seems to work, at least for some simple cases, with only using a debug info file after applying the patch from the first mail. But I have only done simple testing and cannot find any documentation saying that
this should work.So I guess this is nothing we can assume works. The customer can produce non-stripped binaries and use them instead, so we can probably discard this issue. You might want to check the get_pheader_file_size which will allow the exec file to be the same as the debug only file. Regards, Andreas From:
tcf-dev-bounces@xxxxxxxxxxx <tcf-dev-bounces@xxxxxxxxxxx>
On Behalf Of Eugene Tarassov Hi Andreas, As far as I know, it is not possible to use debug info only ELF alone, without the exe ELF. The debug info file is incomplete, by design. It is meant to be used together with its exe file. You should put exe ELF into memory map, and let debugger to search and load debug info ELF using either “debug link” or “build ID” from the mapped ELF. Regards, Eugene From:
tcf-dev-bounces@xxxxxxxxxxx <tcf-dev-bounces@xxxxxxxxxxx>
On Behalf Of Ragnerstam, Andreas EXTERNAL EMAIL Hi Eugene, We, in the Simics team, are seeing a problem when having a debug only ELF file as the file in a MemoryRegion. Such a debug only ELF file can be created with “objcopy --only-keep-debug” for a ELF binary that contains DWARF
debug information. That will strip a lot of the data except debug information. This is something that Yocto will output. Seems TCF somewhat handles debug info files, the ELF_file struct has a debug_info_file member. And adding a debug info only ELF will be identified as such. The problem comes when performing address_to_line, which will
not work properly for such files. The reason is that elf_find_unit, in tcf_elf.c, gets the pheader_file_size from the debug info file, where the file_size != mem_size for the loadable segment. The get_pheader_file_size function tries to solve this by getting
the file_size from the executable binary, but in our case the exec binary (the file in the memory region) will be the debug info file, which is the same file as “file”. So there is no executable file pointing out a dwarf debug file in the memory map, which
that function assumes. The result will be that get_pheader_file_size returns the file_size of the file that is a debug_info_file. What we would like is that the mem size of the pheader is used instead of the file size. The mem size is what we put as size in the MemoryRegion struct. The following patch would solve our problems, but not sure it is good for the general case: --- a/agent/tcf/services/tcf_elf.c +++ b/agent/tcf/services/tcf_elf.c @@ -1763,3 +1763,3 @@ UnitAddressRange * elf_find_unit(Context * ctx, ContextAddress addr_min, Context pheader_address = get_debug_pheader_address(file, debug, p); - pheader_file_size = get_pheader_file_size(file, p, r); + pheader_file_size = r->size > 0 ? r->size : get_pheader_file_size(file, p, r); if (pheader_file_size == 0) continue; It uses that region size if such is specified and otherwise falls back to getting the pheader file size. Regards, Andreas Ragnerstam ---------------------------------------------------------------------- This e-mail and any attachments may contain confidential material for ---------------------------------------------------------------------- This e-mail and any attachments may contain confidential material for ---------------------------------------------------------------------- This e-mail and any attachments may contain confidential material for |