| Message ID | 20240329093356.276289-8-ardb+git@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: Avoid weak external linkage where possible | expand |
On Fri, Mar 29, 2024 at 2:35 AM Ard Biesheuvel <ardb+git@google.com> wrote: > > From: Ard Biesheuvel <ardb@kernel.org> > > If the BTF code is enabled in the build configuration, the start/stop > BTF markers are guaranteed to exist in the final link but not during the > first linker pass. > > Avoid GOT based relocations to these markers in the final executable by > providing preliminary definitions that will be used by the first linker > pass, and superseded by the actual definitions in the subsequent ones. > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > --- > include/asm-generic/vmlinux.lds.h | 2 ++ > kernel/bpf/btf.c | 4 ++-- > 2 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index e8449be62058..141bddb511ee 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -456,6 +456,8 @@ > * independent code. > */ > #define PRELIMINARY_SYMBOL_DEFINITIONS \ > + PROVIDE(__start_BTF = .); \ > + PROVIDE(__stop_BTF = .); \ should this be guarded by CONFIG_DEBUG_INFO_BTF condition? > PROVIDE(kallsyms_addresses = .); \ > PROVIDE(kallsyms_offsets = .); \ > PROVIDE(kallsyms_names = .); \ > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > index 90c4a32d89ff..46a56bf067a8 100644 > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -5642,8 +5642,8 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat > return ERR_PTR(err); > } > > -extern char __weak __start_BTF[]; > -extern char __weak __stop_BTF[]; > +extern char __start_BTF[]; > +extern char __stop_BTF[]; kernel/bpf/sysfs_btf.c also defines __weak externs for these symbols, you probably need to adjust that as well? Other than that looks good to me: Acked-by: Andrii Nakryiko <andrii@kernel.org> > extern struct btf *btf_vmlinux; > > #define BPF_MAP_TYPE(_id, _ops) > -- > 2.44.0.478.gd926399ef9-goog > >
On Fri, 29 Mar 2024 at 20:24, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Fri, Mar 29, 2024 at 2:35 AM Ard Biesheuvel <ardb+git@google.com> wrote: > > > > From: Ard Biesheuvel <ardb@kernel.org> > > > > If the BTF code is enabled in the build configuration, the start/stop > > BTF markers are guaranteed to exist in the final link but not during the > > first linker pass. > > > > Avoid GOT based relocations to these markers in the final executable by > > providing preliminary definitions that will be used by the first linker > > pass, and superseded by the actual definitions in the subsequent ones. > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > > --- > > include/asm-generic/vmlinux.lds.h | 2 ++ > > kernel/bpf/btf.c | 4 ++-- > > 2 files changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index e8449be62058..141bddb511ee 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -456,6 +456,8 @@ > > * independent code. > > */ > > #define PRELIMINARY_SYMBOL_DEFINITIONS \ > > + PROVIDE(__start_BTF = .); \ > > + PROVIDE(__stop_BTF = .); \ > > should this be guarded by CONFIG_DEBUG_INFO_BTF condition? > That shouldn't matter - the linker will not create the symbol unless an unsatisfied reference to it exists anywhere in the input. > > PROVIDE(kallsyms_addresses = .); \ > > PROVIDE(kallsyms_offsets = .); \ > > PROVIDE(kallsyms_names = .); \ > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > > index 90c4a32d89ff..46a56bf067a8 100644 > > --- a/kernel/bpf/btf.c > > +++ b/kernel/bpf/btf.c > > @@ -5642,8 +5642,8 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat > > return ERR_PTR(err); > > } > > > > -extern char __weak __start_BTF[]; > > -extern char __weak __stop_BTF[]; > > +extern char __start_BTF[]; > > +extern char __stop_BTF[]; > > kernel/bpf/sysfs_btf.c also defines __weak externs for these symbols, > you probably need to adjust that as well? > Yes, thanks for pointing that out. > Other than that looks good to me: > > Acked-by: Andrii Nakryiko <andrii@kernel.org> > Thanks! > > > extern struct btf *btf_vmlinux; > > > > #define BPF_MAP_TYPE(_id, _ops) > > -- > > 2.44.0.478.gd926399ef9-goog > > > >
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index e8449be62058..141bddb511ee 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -456,6 +456,8 @@ * independent code. */ #define PRELIMINARY_SYMBOL_DEFINITIONS \ + PROVIDE(__start_BTF = .); \ + PROVIDE(__stop_BTF = .); \ PROVIDE(kallsyms_addresses = .); \ PROVIDE(kallsyms_offsets = .); \ PROVIDE(kallsyms_names = .); \ diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 90c4a32d89ff..46a56bf067a8 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5642,8 +5642,8 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat return ERR_PTR(err); } -extern char __weak __start_BTF[]; -extern char __weak __stop_BTF[]; +extern char __start_BTF[]; +extern char __stop_BTF[]; extern struct btf *btf_vmlinux; #define BPF_MAP_TYPE(_id, _ops)