From: Omar Sandoval <osan...@fb.com>
Hello,
I recently encountered a bug that dwfl_addrmodule doesn't work correctly
for Linux kernel modules. This is because each section of a kernel
module is allocated independently, so sections from different kernel
modules may be intermixed. For example:
# cd /sys/modules
# cat ext4/sections/.init.text
0xffffffffc0f0f000
# cat ext4/sections/.bss
0xffffffffc1303e80
# cat kvm/sections/.init.text
0xffffffffc0f06000
# cat kvm/sections/.bss
0xffffffffc10d2340
This confuses dwfl_addrmodule/dwfl_addrsegment, which builds a lookup
table based on mod->low_addr and mod->high_addr. For relocatable files,
we should be using the addresses of each section, instead.
Patch 4 makes this change, but it needs some preparation. Patch 1 allows
us to distinguish between unloaded sections and sections loaded at zero.
This is necessary so that dwfl_addrmodule doesn't map, e.g., 0x123 to a
module with an unloaded section of size 0x200. Because indexing every
section creates many more lookup entries than we previously had, patch 3
separates the module lookup table from the dwfl_report_segment lookup
table. Finally, patch 2 is the patch I sent yesterday, included in this
series because it would conflict with the later patches.
If these patches are the wrong way to go about this, please consider
this a bug report. I'd be happy to test alternative fixes.
Thanks!
Omar Sandoval (4):
libdwfl: return error from __libdwfl_relocate_value for unloaded
sections
libdwfl: remove broken coalescing logic in dwfl_report_segment
libdwfl: store module lookup table separately from segments
libdwfl: use sections of relocatable files for dwfl_addrmodule
.gitignore | 1 +
libdwfl/ChangeLog | 30 +++++
libdwfl/derelocate.c | 24 +---
libdwfl/dwfl_addrmodule.c | 106 ++++++++++++++-
libdwfl/dwfl_getmodules.c | 14 +-
libdwfl/dwfl_module.c | 11 +-
libdwfl/dwfl_module_getsym.c | 3 +-
libdwfl/libdwfl.h | 20 +--
libdwfl/libdwflP.h | 42 ++++--
libdwfl/link_map.c | 7 +-
libdwfl/relocate.c | 9 +-
libdwfl/segment.c | 178 +++----------------------
tests/ChangeLog | 5 +
tests/Makefile.am | 6 +-
tests/dwfl-report-segment-contiguous.c | 82 ++++++++++++
15 files changed, 305 insertions(+), 233 deletions(-)
create mode 100644 tests/dwfl-report-segment-contiguous.c
--
2.24.0
