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SubjectRe: [PATCH v2] binfmt_misc: pass info about P flag by AT_FLAGS
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Le 16/01/2020 à 03:20, YunQiang Su a écrit :
> From: YunQiang Su <ysu@wavecomp.com>
>
> Currently program invoked by binfmt_misc cannot be aware about whether
> P flag, aka preserve path is enabled.
>
> Some applications like qemu need to know since it has 2 use case:
> 1. call by hand, like: qemu-mipsel-static test.app OPTION
> so, qemu have to assume that P option is not enabled.
> 2. call by binfmt_misc. If qemu cannot know about whether P flag is
> enabled, distribution's have to set qemu without P flag, and
> binfmt_misc call qemu like:
> qemu-mipsel-static /absolute/path/to/test.app OPTION
> even test.app is not called by absoulute path, like
> ./relative/path/to/test.app
>
> This patch passes this information by the 3rd bits of unused AT_FLAGS.
> Then, in qemu, we can get this info by:
> getauxval(AT_FLAGS) & (1<<3)
>
> v1->v2:
> not enable kdebug
>
> See: https://bugs.launchpad.net/qemu/+bug/1818483
> Signed-off-by: YunQiang Su <ysu@wavecomp.com>
> ---
> fs/binfmt_elf.c | 6 +++++-
> fs/binfmt_elf_fdpic.c | 6 +++++-
> fs/binfmt_misc.c | 2 ++
> include/linux/binfmts.h | 4 ++++
> 4 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index f4713ea76e82..d33ee07d7f57 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -178,6 +178,7 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
> unsigned char k_rand_bytes[16];
> int items;
> elf_addr_t *elf_info;
> + elf_addr_t flags = 0;
> int ei_index;
> const struct cred *cred = current_cred();
> struct vm_area_struct *vma;
> @@ -252,7 +253,10 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
> NEW_AUX_ENT(AT_PHENT, sizeof(struct elf_phdr));
> NEW_AUX_ENT(AT_PHNUM, exec->e_phnum);
> NEW_AUX_ENT(AT_BASE, interp_load_addr);
> - NEW_AUX_ENT(AT_FLAGS, 0);
> + if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0) {
> + flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
> + }

Perhaps we also need a different flag in AT_FLAG than in interp_flag as
BINPRM_FLAGS_PRESERVE_ARGV0 is also part of the internal ABI?

Al?

Thanks,
Laurent

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