[Crash-utility] Re: [PATCH] symbols: use non-debug BFD to retrieve .rodata

Hi Jiri, On 8/14/26 2:06 PM, Jiri Slaby wrote: > When running crash on openSUSE, get_linux_banner_from_vmlinux() returns > success but fill the target buffer with all zero bytes (`\0`). > > This happens because `st->bfd` is initially opened for the main binary > (`vmlinux`), but is later overwritten with the debuginfo file > (`vmlinux.debug`) in `check_gnu_debuglink()`. In separate debug files, > `.rodata` has no content, so is marked only as `ALLOC` without > `SEC_HAS_CONTENTS`. > > When `bfd_get_section_contents()` is called on a section without > `SEC_HAS_CONTENTS`, BFD clears the buffer to zeros and returns TRUE. As > a result, `get_linux_banner_from_vmlinux()` thinks it successfully read > the banner, while it actually received zeroed bytes. > > Fix this by caching the original main executable's BFD (into > `st->bfd_orig`) before `st->bfd` gets swapped for the debuginfo file. > > `get_linux_banner_from_vmlinux()` will then fall back to `st->bfd_orig` > if present, ensuring `.rodata` contents are read from the binary that > actually contains the raw section data. > > Fixes #232. > > Signed-off-by: Jiri Slaby <jirislaby(a)gmail.com&gt; > Cc: Dave Young <yangrr.2009(a)tsinghua.org.cn&gt; > Cc: <ltao(a)redhat.com&gt; > Cc: <mpilaniy(a)redhat.com&gt; > --- > defs.h | 1 + > kernel.c | 5 +++-- > symbols.c | 1 + > 3 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/defs.h b/defs.h > index e3027e2b9141..e82af5bd5ed0 100644 > --- a/defs.h > +++ b/defs.h > @@ -2920,6 +2920,7 @@ struct symbol_table_data { > #ifdef GDB_5_3 > struct _bfd *bfd; > #else > + struct bfd *bfd_orig; > struct bfd *bfd; > #endif > struct sec *sections; > diff --git a/kernel.c b/kernel.c > index e53038d5d8db..521cdf5664ef 100644 > --- a/kernel.c > +++ b/kernel.c > @@ -12145,6 +12145,7 @@ check_vmcoreinfo(void) > static > int get_linux_banner_from_vmlinux(char *buf, size_t size) > { > + struct bfd *bfd = st->bfd_orig ? : st->bfd; > struct bfd_section *sect; > long offset; > ulong start_rodata; > @@ -12156,7 +12157,7 @@ int get_linux_banner_from_vmlinux(char *buf, size_t size) > else > return FALSE; > > - sect = bfd_get_section_by_name(st->bfd, ".rodata"); > + sect = bfd_get_section_by_name(bfd, ".rodata"); > if (!sect) > return FALSE; > > @@ -12168,7 +12169,7 @@ int get_linux_banner_from_vmlinux(char *buf, size_t size) > */ > offset = symbol_value("linux_banner") - start_rodata; > > - if (!bfd_get_section_contents(st->bfd, > + if (!bfd_get_section_contents(bfd, > sect, > buf, > offset, > diff --git a/symbols.c b/symbols.c > index a7ccdb101033..4b5585d62dba 100644 > --- a/symbols.c > +++ b/symbols.c > @@ -444,6 +444,7 @@ check_gnu_debuglink(bfd *bfd) > return FALSE; > > reset_bfd: > + st->bfd_orig = st->bfd; Nitpick:iIt is even better to add code comment here or in defs.h, eg: /* * Cache the original bfd in case it will be replaced by a separate debug * file. Debug files often lack section contents (e.g., .rodata is ALLOC * only), so we need the original binary to read actual data. */ Anyway, thanks for fixing the issue: Reviewed-by: Dave Young <yangrr.2009(a)tsinghua.org.cn&gt; > > if ((st->bfd = bfd_openr(pc->debuginfo_file, NULL)) == NULL) > error(FATAL, "cannot open object file: %s\n", -- Crash-utility mailing list -- devel(a)lists.crash-utility.osci.io To unsubscribe send an email to devel-leave(a)lists.crash-utility.osci.io https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/ Contribution Guidelines: https://github.com/crash-utility/crash/wiki