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

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;

if ((st->bfd = bfd_openr(pc->debuginfo_file, NULL)) == NULL) error(FATAL, "cannot open object file: %s\n",