| Message ID | 20210119221220.1745061-4-jolsa@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | dwarves,libbpf: Add support to use optional extended section index table | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Tue, Jan 19, 2021 at 2:15 PM Jiri Olsa <jolsa@kernel.org> wrote: > > For very large ELF objects (with many sections), we could > get special value SHN_XINDEX (65535) for elf object's string > table index - e_shstrndx. > > In such case we need to call elf_getshdrstrndx to get the > proper string table index. > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > --- > tools/lib/bpf/btf.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c > index 3c3f2bc6c652..4fe987846bc0 100644 > --- a/tools/lib/bpf/btf.c > +++ b/tools/lib/bpf/btf.c > @@ -863,6 +863,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > Elf_Scn *scn = NULL; > Elf *elf = NULL; > GElf_Ehdr ehdr; > + size_t shstrndx; > > if (elf_version(EV_CURRENT) == EV_NONE) { > pr_warn("failed to init libelf for %s\n", path); > @@ -887,7 +888,16 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > pr_warn("failed to get EHDR from %s\n", path); > goto done; > } > - if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) { > + > + /* > + * Get string table index from extended section index > + * table if needed. > + */ > + shstrndx = ehdr.e_shstrndx; > + if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx)) > + goto done; just use elf_getshdrstrndx() unconditionally, it works for extended and non-extended numbering (see libbpf.c). > + > + if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) { > pr_warn("failed to get e_shstrndx from %s\n", path); > goto done; > } > @@ -902,7 +912,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > idx, path); > goto done; > } > - name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name); > + name = elf_strptr(elf, shstrndx, sh.sh_name); > if (!name) { > pr_warn("failed to get section(%d) name from %s\n", > idx, path); > -- > 2.27.0 >
Em Tue, Jan 19, 2021 at 05:22:08PM -0800, Andrii Nakryiko escreveu: > On Tue, Jan 19, 2021 at 2:15 PM Jiri Olsa <jolsa@kernel.org> wrote: > > > > For very large ELF objects (with many sections), we could > > get special value SHN_XINDEX (65535) for elf object's string > > table index - e_shstrndx. > > > > In such case we need to call elf_getshdrstrndx to get the > > proper string table index. > > > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > > --- > > tools/lib/bpf/btf.c | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c > > index 3c3f2bc6c652..4fe987846bc0 100644 > > --- a/tools/lib/bpf/btf.c > > +++ b/tools/lib/bpf/btf.c > > @@ -863,6 +863,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > Elf_Scn *scn = NULL; > > Elf *elf = NULL; > > GElf_Ehdr ehdr; > > + size_t shstrndx; > > > > if (elf_version(EV_CURRENT) == EV_NONE) { > > pr_warn("failed to init libelf for %s\n", path); > > @@ -887,7 +888,16 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > pr_warn("failed to get EHDR from %s\n", path); > > goto done; > > } > > - if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) { > > + > > + /* > > + * Get string table index from extended section index > > + * table if needed. > > + */ > > + shstrndx = ehdr.e_shstrndx; > > + if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx)) > > + goto done; > > just use elf_getshdrstrndx() unconditionally, it works for extended > and non-extended numbering (see libbpf.c). Yeah, we even have this in tools/perf/util/symbol-elf.c: #ifndef HAVE_ELF_GETSHDRSTRNDX_SUPPORT static int elf_getshdrstrndx(Elf *elf __maybe_unused, size_t *dst __maybe_unused) { pr_err("%s: update your libelf to > 0.140, this one lacks elf_getshdrstrndx().\n", __func__); return -1; } #endif And a feature detection for that: [acme@five perf]$ cat tools/build/feature/test-libelf-getshdrstrndx.c // SPDX-License-Identifier: GPL-2.0 #include <libelf.h> int main(void) { size_t dst; return elf_getshdrstrndx(0, &dst); } [acme@five perf]$ Your implementation would provide a good fallback tho to avoid requiring updating to 0.140 :-) - Arnaldo > > + > > + if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) { > > pr_warn("failed to get e_shstrndx from %s\n", path); > > goto done; > > } > > @@ -902,7 +912,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > idx, path); > > goto done; > > } > > - name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name); > > + name = elf_strptr(elf, shstrndx, sh.sh_name); > > if (!name) { > > pr_warn("failed to get section(%d) name from %s\n", > > idx, path); > > -- > > 2.27.0 > >
On Tue, Jan 19, 2021 at 05:22:08PM -0800, Andrii Nakryiko wrote: > On Tue, Jan 19, 2021 at 2:15 PM Jiri Olsa <jolsa@kernel.org> wrote: > > > > For very large ELF objects (with many sections), we could > > get special value SHN_XINDEX (65535) for elf object's string > > table index - e_shstrndx. > > > > In such case we need to call elf_getshdrstrndx to get the > > proper string table index. > > > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > > --- > > tools/lib/bpf/btf.c | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c > > index 3c3f2bc6c652..4fe987846bc0 100644 > > --- a/tools/lib/bpf/btf.c > > +++ b/tools/lib/bpf/btf.c > > @@ -863,6 +863,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > Elf_Scn *scn = NULL; > > Elf *elf = NULL; > > GElf_Ehdr ehdr; > > + size_t shstrndx; > > > > if (elf_version(EV_CURRENT) == EV_NONE) { > > pr_warn("failed to init libelf for %s\n", path); > > @@ -887,7 +888,16 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > pr_warn("failed to get EHDR from %s\n", path); > > goto done; > > } > > - if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) { > > + > > + /* > > + * Get string table index from extended section index > > + * table if needed. > > + */ > > + shstrndx = ehdr.e_shstrndx; > > + if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx)) > > + goto done; > > just use elf_getshdrstrndx() unconditionally, it works for extended > and non-extended numbering (see libbpf.c). I did not see that, ok thanks, jirka > > > + > > + if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) { > > pr_warn("failed to get e_shstrndx from %s\n", path); > > goto done; > > } > > @@ -902,7 +912,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, > > idx, path); > > goto done; > > } > > - name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name); > > + name = elf_strptr(elf, shstrndx, sh.sh_name); > > if (!name) { > > pr_warn("failed to get section(%d) name from %s\n", > > idx, path); > > -- > > 2.27.0 > > >
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index 3c3f2bc6c652..4fe987846bc0 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -863,6 +863,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, Elf_Scn *scn = NULL; Elf *elf = NULL; GElf_Ehdr ehdr; + size_t shstrndx; if (elf_version(EV_CURRENT) == EV_NONE) { pr_warn("failed to init libelf for %s\n", path); @@ -887,7 +888,16 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, pr_warn("failed to get EHDR from %s\n", path); goto done; } - if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) { + + /* + * Get string table index from extended section index + * table if needed. + */ + shstrndx = ehdr.e_shstrndx; + if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx)) + goto done; + + if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) { pr_warn("failed to get e_shstrndx from %s\n", path); goto done; } @@ -902,7 +912,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, idx, path); goto done; } - name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name); + name = elf_strptr(elf, shstrndx, sh.sh_name); if (!name) { pr_warn("failed to get section(%d) name from %s\n", idx, path);
For very large ELF objects (with many sections), we could get special value SHN_XINDEX (65535) for elf object's string table index - e_shstrndx. In such case we need to call elf_getshdrstrndx to get the proper string table index. Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- tools/lib/bpf/btf.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)