| Message ID | 20240409150132.4097042-8-ardb+git@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | kbuild: Avoid weak external linkage where possible | expand |
On Tue, Apr 9, 2024, at 17:01, Ard Biesheuvel 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 pass, and superseded by the actual definitions in the subsequent ones. > > Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so > that inadvertent references to this section will trigger a link failure > if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF. > > Note that Clang will notice that taking the address of__start_BTF cannot > yield NULL any longer, so testing for that condition is no longer > needed. > > Acked-by: Andrii Nakryiko <andrii@kernel.org> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Arnd Bergmann <arnd@arndb.de>
On Tue, Apr 09, 2024 at 05:01:36PM +0200, Ard Biesheuvel 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 pass, and superseded by the actual definitions in the subsequent ones. > > Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so > that inadvertent references to this section will trigger a link failure > if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF. > > Note that Clang will notice that taking the address of__start_BTF cannot > yield NULL any longer, so testing for that condition is no longer > needed. > > Acked-by: Andrii Nakryiko <andrii@kernel.org> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > --- > include/asm-generic/vmlinux.lds.h | 9 +++++++++ > kernel/bpf/btf.c | 4 ++-- > kernel/bpf/sysfs_btf.c | 6 +++--- > 3 files changed, 14 insertions(+), 5 deletions(-) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index e8449be62058..4cb3d88449e5 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -456,6 +456,7 @@ > * independent code. > */ > #define PRELIMINARY_SYMBOL_DEFINITIONS \ > + PRELIMINARY_BTF_DEFINITIONS \ > PROVIDE(kallsyms_addresses = .); \ > PROVIDE(kallsyms_offsets = .); \ > PROVIDE(kallsyms_names = .); \ > @@ -466,6 +467,14 @@ > PROVIDE(kallsyms_markers = .); \ > PROVIDE(kallsyms_seqs_of_names = .); > > +#ifdef CONFIG_DEBUG_INFO_BTF > +#define PRELIMINARY_BTF_DEFINITIONS \ > + PROVIDE(__start_BTF = .); \ > + PROVIDE(__stop_BTF = .); > +#else > +#define PRELIMINARY_BTF_DEFINITIONS > +#endif hi, I'm getting following compilation fail when CONFIG_DEBUG_INFO_BTF is disabled [jolsa@krava linux-qemu]$ make CALL scripts/checksyscalls.sh DESCEND objtool INSTALL libsubcmd_headers UPD include/generated/utsversion.h CC init/version-timestamp.o LD .tmp_vmlinux.kallsyms1 ld: kernel/bpf/btf.o: in function `btf_parse_vmlinux': /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5988: undefined reference to `__start_BTF' ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__stop_BTF' ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__start_BTF' make[2]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1 make[1]: *** [/home/jolsa/kernel/linux-qemu/Makefile:1160: vmlinux] Error 2 make: *** [Makefile:240: __sub-make] Error 2 maybe the assumption was that kernel/bpf/btf.o is compiled only for CONFIG_DEBUG_INFO_BTF, but it's actually: obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o I guess we just need !CONFIG_DEBUG_INFO_BTF version of btf_parse_vmlinux function jirka > + > /* > * Read only Data > */ > 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) > diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c > index ef6911aee3bb..fedb54c94cdb 100644 > --- a/kernel/bpf/sysfs_btf.c > +++ b/kernel/bpf/sysfs_btf.c > @@ -9,8 +9,8 @@ > #include <linux/sysfs.h> > > /* See scripts/link-vmlinux.sh, gen_btf() func for details */ > -extern char __weak __start_BTF[]; > -extern char __weak __stop_BTF[]; > +extern char __start_BTF[]; > +extern char __stop_BTF[]; > > static ssize_t > btf_vmlinux_read(struct file *file, struct kobject *kobj, > @@ -32,7 +32,7 @@ static int __init btf_vmlinux_init(void) > { > bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF; > > - if (!__start_BTF || bin_attr_btf_vmlinux.size == 0) > + if (bin_attr_btf_vmlinux.size == 0) > return 0; > > btf_kobj = kobject_create_and_add("btf", kernel_kobj); > -- > 2.44.0.478.gd926399ef9-goog > >
On Wed, 10 Apr 2024 at 10:22, Jiri Olsa <olsajiri@gmail.com> wrote: > > On Tue, Apr 09, 2024 at 05:01:36PM +0200, Ard Biesheuvel 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. > > > > Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so > > that inadvertent references to this section will trigger a link failure > > if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF. > > > > Note that Clang will notice that taking the address of__start_BTF cannot > > yield NULL any longer, so testing for that condition is no longer > > needed. > > > > Acked-by: Andrii Nakryiko <andrii@kernel.org> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > > --- > > include/asm-generic/vmlinux.lds.h | 9 +++++++++ > > kernel/bpf/btf.c | 4 ++-- > > kernel/bpf/sysfs_btf.c | 6 +++--- > > 3 files changed, 14 insertions(+), 5 deletions(-) > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index e8449be62058..4cb3d88449e5 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -456,6 +456,7 @@ > > * independent code. > > */ > > #define PRELIMINARY_SYMBOL_DEFINITIONS \ > > + PRELIMINARY_BTF_DEFINITIONS \ > > PROVIDE(kallsyms_addresses = .); \ > > PROVIDE(kallsyms_offsets = .); \ > > PROVIDE(kallsyms_names = .); \ > > @@ -466,6 +467,14 @@ > > PROVIDE(kallsyms_markers = .); \ > > PROVIDE(kallsyms_seqs_of_names = .); > > > > +#ifdef CONFIG_DEBUG_INFO_BTF > > +#define PRELIMINARY_BTF_DEFINITIONS \ > > + PROVIDE(__start_BTF = .); \ > > + PROVIDE(__stop_BTF = .); > > +#else > > +#define PRELIMINARY_BTF_DEFINITIONS > > +#endif > > hi, > I'm getting following compilation fail when CONFIG_DEBUG_INFO_BTF is disabled > > [jolsa@krava linux-qemu]$ make > CALL scripts/checksyscalls.sh > DESCEND objtool > INSTALL libsubcmd_headers > UPD include/generated/utsversion.h > CC init/version-timestamp.o > LD .tmp_vmlinux.kallsyms1 > ld: kernel/bpf/btf.o: in function `btf_parse_vmlinux': > /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5988: undefined reference to `__start_BTF' > ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__stop_BTF' > ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__start_BTF' > make[2]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1 > make[1]: *** [/home/jolsa/kernel/linux-qemu/Makefile:1160: vmlinux] Error 2 > make: *** [Makefile:240: __sub-make] Error 2 > > maybe the assumption was that kernel/bpf/btf.o is compiled only > for CONFIG_DEBUG_INFO_BTF, but it's actually: > > obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o > Interesting. I did build test this with and without CONFIG_DEBUG_INFO_BTF, but not with CONFIG_BPF_SYSCALL=y and CONFIG_DEBUG_INFO_BTF=n. > I guess we just need !CONFIG_DEBUG_INFO_BTF version of btf_parse_vmlinux > function > The below gives me a working build. --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5971,6 +5971,9 @@ struct btf *btf_parse_vmlinux(void) struct btf *btf = NULL; int err; + if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) + return ERR_PTR(-ENOENT); + env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN); if (!env) return ERR_PTR(-ENOMEM);
On Wed, Apr 10, 2024 at 10:37:42AM +0200, Ard Biesheuvel wrote: > On Wed, 10 Apr 2024 at 10:22, Jiri Olsa <olsajiri@gmail.com> wrote: > > > > On Tue, Apr 09, 2024 at 05:01:36PM +0200, Ard Biesheuvel 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. > > > > > > Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so > > > that inadvertent references to this section will trigger a link failure > > > if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF. > > > > > > Note that Clang will notice that taking the address of__start_BTF cannot > > > yield NULL any longer, so testing for that condition is no longer > > > needed. > > > > > > Acked-by: Andrii Nakryiko <andrii@kernel.org> > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > > > --- > > > include/asm-generic/vmlinux.lds.h | 9 +++++++++ > > > kernel/bpf/btf.c | 4 ++-- > > > kernel/bpf/sysfs_btf.c | 6 +++--- > > > 3 files changed, 14 insertions(+), 5 deletions(-) > > > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > > index e8449be62058..4cb3d88449e5 100644 > > > --- a/include/asm-generic/vmlinux.lds.h > > > +++ b/include/asm-generic/vmlinux.lds.h > > > @@ -456,6 +456,7 @@ > > > * independent code. > > > */ > > > #define PRELIMINARY_SYMBOL_DEFINITIONS \ > > > + PRELIMINARY_BTF_DEFINITIONS \ > > > PROVIDE(kallsyms_addresses = .); \ > > > PROVIDE(kallsyms_offsets = .); \ > > > PROVIDE(kallsyms_names = .); \ > > > @@ -466,6 +467,14 @@ > > > PROVIDE(kallsyms_markers = .); \ > > > PROVIDE(kallsyms_seqs_of_names = .); > > > > > > +#ifdef CONFIG_DEBUG_INFO_BTF > > > +#define PRELIMINARY_BTF_DEFINITIONS \ > > > + PROVIDE(__start_BTF = .); \ > > > + PROVIDE(__stop_BTF = .); > > > +#else > > > +#define PRELIMINARY_BTF_DEFINITIONS > > > +#endif > > > > hi, > > I'm getting following compilation fail when CONFIG_DEBUG_INFO_BTF is disabled > > > > [jolsa@krava linux-qemu]$ make > > CALL scripts/checksyscalls.sh > > DESCEND objtool > > INSTALL libsubcmd_headers > > UPD include/generated/utsversion.h > > CC init/version-timestamp.o > > LD .tmp_vmlinux.kallsyms1 > > ld: kernel/bpf/btf.o: in function `btf_parse_vmlinux': > > /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5988: undefined reference to `__start_BTF' > > ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__stop_BTF' > > ld: /home/jolsa/kernel/linux-qemu/kernel/bpf/btf.c:5989: undefined reference to `__start_BTF' > > make[2]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1 > > make[1]: *** [/home/jolsa/kernel/linux-qemu/Makefile:1160: vmlinux] Error 2 > > make: *** [Makefile:240: __sub-make] Error 2 > > > > maybe the assumption was that kernel/bpf/btf.o is compiled only > > for CONFIG_DEBUG_INFO_BTF, but it's actually: > > > > obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o > > > > Interesting. I did build test this with and without > CONFIG_DEBUG_INFO_BTF, but not with CONFIG_BPF_SYSCALL=y and > CONFIG_DEBUG_INFO_BTF=n. > > > I guess we just need !CONFIG_DEBUG_INFO_BTF version of btf_parse_vmlinux > > function > > > > The below gives me a working build. > > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -5971,6 +5971,9 @@ struct btf *btf_parse_vmlinux(void) > struct btf *btf = NULL; > int err; > > + if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) > + return ERR_PTR(-ENOENT); nice, so this basically eliminates the rest of the function, I did not know this would work build's fine now, thanks jirka > + > env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN); > if (!env) > return ERR_PTR(-ENOMEM);
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index e8449be62058..4cb3d88449e5 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -456,6 +456,7 @@ * independent code. */ #define PRELIMINARY_SYMBOL_DEFINITIONS \ + PRELIMINARY_BTF_DEFINITIONS \ PROVIDE(kallsyms_addresses = .); \ PROVIDE(kallsyms_offsets = .); \ PROVIDE(kallsyms_names = .); \ @@ -466,6 +467,14 @@ PROVIDE(kallsyms_markers = .); \ PROVIDE(kallsyms_seqs_of_names = .); +#ifdef CONFIG_DEBUG_INFO_BTF +#define PRELIMINARY_BTF_DEFINITIONS \ + PROVIDE(__start_BTF = .); \ + PROVIDE(__stop_BTF = .); +#else +#define PRELIMINARY_BTF_DEFINITIONS +#endif + /* * Read only Data */ 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) diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c index ef6911aee3bb..fedb54c94cdb 100644 --- a/kernel/bpf/sysfs_btf.c +++ b/kernel/bpf/sysfs_btf.c @@ -9,8 +9,8 @@ #include <linux/sysfs.h> /* See scripts/link-vmlinux.sh, gen_btf() func for details */ -extern char __weak __start_BTF[]; -extern char __weak __stop_BTF[]; +extern char __start_BTF[]; +extern char __stop_BTF[]; static ssize_t btf_vmlinux_read(struct file *file, struct kobject *kobj, @@ -32,7 +32,7 @@ static int __init btf_vmlinux_init(void) { bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF; - if (!__start_BTF || bin_attr_btf_vmlinux.size == 0) + if (bin_attr_btf_vmlinux.size == 0) return 0; btf_kobj = kobject_create_and_add("btf", kernel_kobj);