Le 02/03/2020 à 19:18, Lirong Yuan a écrit :
> On Mon, Mar 2, 2020 at 6:39 AM Laurent Vivier <laur...@vivier.eu> wrote:
>>
>> Le 21/02/2020 à 21:28, Lirong Yuan a écrit :
>>> This change adds the support for AT_EXECFN and AT_EXECFD auxval.
>>
>> Why do we need AT_EXECFD?
>>
>> AT_EXECFD is normally only used with binfmt_misc so I don't see any use
>> cases for it with QEMU.
>>
>> For AT_EXECFN, according to kernel commit
>>
>> 651910874633 execve filename: document and export via auxiliary vector
>>
>> It sould be like readlink("/proc/self/exe",), and thus I think we should
>> use realpath() like we have in syscall.c for TARGET_NR_readlink:
>>
>> 8843 case TARGET_NR_readlink:
>> ...
>> 8854 char real[PATH_MAX], *temp;
>> 8855 temp = realpath(exec_path, real);
>> ...
>>
>> Thanks,
>> Laurent
>>
>>>
>>> Signed-off-by: Lirong Yuan <yua...@google.com>
>>> ---
>>> linux-user/elfload.c | 13 +++++++++----
>>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
>>> index f3080a1635..7e0f3042f1 100644
>>> --- a/linux-user/elfload.c
>>> +++ b/linux-user/elfload.c
>>> @@ -1568,7 +1568,7 @@ struct exec
>>> ~(abi_ulong)(TARGET_ELF_EXEC_PAGESIZE-1))
>>> #define TARGET_ELF_PAGEOFFSET(_v) ((_v) & (TARGET_ELF_EXEC_PAGESIZE-1))
>>>
>>> -#define DLINFO_ITEMS 15
>>> +#define DLINFO_ITEMS 17
>>>
>>> static inline void memcpy_fromfs(void * to, const void * from, unsigned
>>> long n)
>>> {
>>> @@ -1888,11 +1888,14 @@ static abi_ulong loader_build_fdpic_loadmap(struct
>>> image_info *info, abi_ulong s
>>> return sp;
>>> }
>>>
>>> -static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,
>>> +static abi_ulong create_elf_tables(struct linux_binprm *bprm,
>>> struct elfhdr *exec,
>>> struct image_info *info,
>>> struct image_info *interp_info)
>>> {
>>> + abi_ulong p = bprm->p;
>>> + int argc = bprm->argc;
>>> + int envc = bprm->envc;
>>> abi_ulong sp;
>>> abi_ulong u_argc, u_argv, u_envp, u_auxv;
>>> int size;
>>> @@ -2032,6 +2035,8 @@ static abi_ulong create_elf_tables(abi_ulong p, int
>>> argc, int envc,
>>> NEW_AUX_ENT(AT_CLKTCK, (abi_ulong) sysconf(_SC_CLK_TCK));
>>> NEW_AUX_ENT(AT_RANDOM, (abi_ulong) u_rand_bytes);
>>> NEW_AUX_ENT(AT_SECURE, (abi_ulong) qemu_getauxval(AT_SECURE));
>>> + NEW_AUX_ENT(AT_EXECFN, info->file_string);
>>> + NEW_AUX_ENT(AT_EXECFD, bprm->fd);
>>>
>>> #ifdef ELF_HWCAP2
>>> NEW_AUX_ENT(AT_HWCAP2, (abi_ulong) ELF_HWCAP2);
>>> @@ -2870,8 +2875,8 @@ int load_elf_binary(struct linux_binprm *bprm, struct
>>> image_info *info)
>>> #endif
>>> }
>>>
>>> - bprm->p = create_elf_tables(bprm->p, bprm->argc, bprm->envc, &elf_ex,
>>> - info, (elf_interpreter ? &interp_info :
>>> NULL));
>>> + bprm->p = create_elf_tables(bprm, &elf_ex, info,
>>> + (elf_interpreter ? &interp_info : NULL));
>>> info->start_stack = bprm->p;
>>>
>>> /* If we have an interpreter, set that as the program's entry point.
>>>
>>
>
> Hi Laurent,
Hi Lirong,
> I added support for AT_EXECFD because I thought it might be useful to
> implement all types that getauxval could take as an argument.
> Would you prefer that it be removed?
I think providing the AT_EXECFD to the target binary could make it think
it has been run directly by binfmt_misc (as an interpreter itself), and
that is not the case (qemu is run by binfmt_misc and is the interpreter).
So I would prefer you remove it.
> For AT_EXECFN, there are two questions that we considered:
> 1) What should it return?
> Since QEMU is emulating running the guest program, the function should
> return the file name of the guest program (info->file_string), rather
> than the QEMU program itself, which we get from
> qemu_getauxval(AT_EXECFN).
>
> 2) Should it return the full path or as is?
> We tested the behavior of getauxval with a simple test program on
> Linux, and it turned out that it returned file path as is. For
> example,
> $ ./test
> getauxval(AT_EXECFN): ./test
> $ /usr/local/home/tmp/test
> getauxval(AT_EXECFN): /usr/local/home/tmp/test
If you have compared the result with the real one it's fine for me.
Resend tou patch without the AT_EXECFD part and it will be good.
Thanks,
Laurent
