| Message ID | 20210205134221.2953163-6-gprocida@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | ELF writing changes | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Fri, Feb 5, 2021 at 5:42 AM Giuliano Procida <gprocida@google.com> wrote: > > This is to avoid misaligned access to BTF type structs when > memory-mapping ELF objects. > > Signed-off-by: Giuliano Procida <gprocida@google.com> > --- I trust you did verify that it actually works in cases where previously .BTF was mis-aligned? Acked-by: Andrii Nakryiko <andrii@kernel.org> > libbtf.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/libbtf.c b/libbtf.c > index 9f4abb3..6754a17 100644 > --- a/libbtf.c > +++ b/libbtf.c > @@ -744,6 +744,14 @@ static int btf_elf__write(const char *filename, struct btf *btf) > goto out; > } > > + /* > + * We'll align .BTF to 8 bytes to cater for all architectures. It'd be > + * nice if we could fetch this value from somewhere. The BTF > + * specification does not discuss alignment and its trailing string > + * table is not currently padded to any particular alignment. > + */ > + const size_t btf_alignment = 8; > + > /* > * First we check if there is already a .BTF section present. > */ > @@ -821,6 +829,7 @@ static int btf_elf__write(const char *filename, struct btf *btf) > elf_error("elf_getshdr(btf_scn) failed"); > goto out; > } > + btf_shdr.sh_addralign = btf_alignment; > btf_shdr.sh_entsize = 0; > btf_shdr.sh_flags = 0; > if (dot_btf_offset) > -- > 2.30.0.478.g8a0d178c01-goog >
On Mon, 8 Feb 2021 at 22:30, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Fri, Feb 5, 2021 at 5:42 AM Giuliano Procida <gprocida@google.com> wrote: > > > > This is to avoid misaligned access to BTF type structs when > > memory-mapping ELF objects. > > > > Signed-off-by: Giuliano Procida <gprocida@google.com> > > --- > > I trust you did verify that it actually works in cases where > previously .BTF was mis-aligned? > Yes. :-) > Acked-by: Andrii Nakryiko <andrii@kernel.org> > > > libbtf.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/libbtf.c b/libbtf.c > > index 9f4abb3..6754a17 100644 > > --- a/libbtf.c > > +++ b/libbtf.c > > @@ -744,6 +744,14 @@ static int btf_elf__write(const char *filename, struct btf *btf) > > goto out; > > } > > > > + /* > > + * We'll align .BTF to 8 bytes to cater for all architectures. It'd be > > + * nice if we could fetch this value from somewhere. The BTF > > + * specification does not discuss alignment and its trailing string > > + * table is not currently padded to any particular alignment. > > + */ > > + const size_t btf_alignment = 8; > > + > > /* > > * First we check if there is already a .BTF section present. > > */ > > @@ -821,6 +829,7 @@ static int btf_elf__write(const char *filename, struct btf *btf) > > elf_error("elf_getshdr(btf_scn) failed"); > > goto out; > > } > > + btf_shdr.sh_addralign = btf_alignment; > > btf_shdr.sh_entsize = 0; > > btf_shdr.sh_flags = 0; > > if (dot_btf_offset) > > -- > > 2.30.0.478.g8a0d178c01-goog > > > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >
diff --git a/libbtf.c b/libbtf.c index 9f4abb3..6754a17 100644 --- a/libbtf.c +++ b/libbtf.c @@ -744,6 +744,14 @@ static int btf_elf__write(const char *filename, struct btf *btf) goto out; } + /* + * We'll align .BTF to 8 bytes to cater for all architectures. It'd be + * nice if we could fetch this value from somewhere. The BTF + * specification does not discuss alignment and its trailing string + * table is not currently padded to any particular alignment. + */ + const size_t btf_alignment = 8; + /* * First we check if there is already a .BTF section present. */ @@ -821,6 +829,7 @@ static int btf_elf__write(const char *filename, struct btf *btf) elf_error("elf_getshdr(btf_scn) failed"); goto out; } + btf_shdr.sh_addralign = btf_alignment; btf_shdr.sh_entsize = 0; btf_shdr.sh_flags = 0; if (dot_btf_offset)
This is to avoid misaligned access to BTF type structs when memory-mapping ELF objects. Signed-off-by: Giuliano Procida <gprocida@google.com> --- libbtf.c | 9 +++++++++ 1 file changed, 9 insertions(+)