Hi Shivang,
Sorry for the late. LGTM, so ack.
Thanks,
Tao Liu
On Mon, Jul 21, 2025 at 8:18 PM Shivang Upadhyay <shiva...@linux.ibm.com> wrote:
>
> Crash with GDB 16.2, the following warnings are printed:
>
> crash>
> crash: page excluded: kernel virtual address: c0000000022d6098 type:
> "gdb_readmem_callback"
> crash: page excluded: kernel virtual address: c0000000022d6098 type:
> "gdb_readmem_callback"
>
> This occurs because the elf_locate_base function in GDB 16.2
> attempts to read the address of the dynamic linker runtime
> structure, which is present in the .dynamic section of the
> executable. However, this section may be excluded from the
> dump by makedumpfile.
>
> The repeated calls to elf_locate_base were introduced by gdb
> commit [1] aebb370 ("gdb, solib-svr4: support namespaces in
> DSO iteration") via svr4_iterate_over_objfiles_in_search_order.
>
> To check whether the kernel includes DT_DEBUG information,
> prints were added inside crash::xfer_partial, which is
> called through elf_locate_base when reading from vmcore.
> Even when running crash on /proc/kcore, all output data was
> zero. This confirms that DT_DEBUG information is never
> present in the kernel image.
>
> `mod -S` continues to function correctly after the following
> patch:
>
> ...
> crash> mod -S
> Enable debuginfod for this session? (y or [n])
> MODULE NAME TEXT_BASE SIZE
> OBJECT FILE
> c0080000004a0300 dm_log c008000000480000 196608
> XXX/lib/modules/5.14.0-592.el9.ppc64le/kernel/drivers/md/dm-log.ko
> c0080000006d1100 sd_mod c008000000580000 196608
> XXX/lib/modules/5.14.0-592.el9.ppc64le/kernel/drivers/scsi/sd_mod.ko
> c0080000005c0080 dm_region_hash c0080000005a0000 196608
> XXX/lib/modules/5.14.0-592.el9.ppc64le/kernel/drivers/md/dm-region-hash.ko
> c008000000770700 sg c008000000620000 262144
> XXX/lib/modules/5.14.0-592.el9.ppc64le/kernel/drivers/scsi/sg.ko
> c008000000660500 dm_mirror c008000000640000 196608
> XXX/lib/modules/5.14.0-592.el9.ppc64le/kernel/drivers/md/dm-mirror.ko
> ...
>
>
>
> Commit e906eaca2b1a ("Fix the issue of "page excluded"
> messages flooding") attempted fix this by suppressing these
> warnings for regular users, but the warnings still appear
> when crash is started in debug mode.
>
> To fix this, remove the DT_DEBUG read call, from the
> elf_locate_base function in GDB that tries to read the
> .dynamic section, as this information is not useful for
> debugging kernel images in either dump or live kernel
> scenarios.
>
>
> [1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aebb370
>
> Cc: Tao liu <l...@redhat.com>
> Cc: Lianbo Jiang <liji...@redhat.com>
> Cc: Sourabh Jain <sourabhj...@linux.ibm.com>
> Signed-off-by: shivang.upadhyay <shiva...@linux.ibm.com>
> ---
> gdb-16.2.patch | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/gdb-16.2.patch b/gdb-16.2.patch
> index 151e4e2..7b79cdf 100644
> --- a/gdb-16.2.patch
> +++ b/gdb-16.2.patch
> @@ -1952,3 +1952,19 @@ exit 0
> }
>
> /* Remember the bfd indexes for the .text, .data, .bss and
> +--- gdb-16.2/gdb/solib-svr4.c.orig
> ++++ gdb-16.2/gdb/solib-svr4.c
> +@@ -742,11 +742,13 @@ elf_locate_base (void)
> + return extract_typed_address (pbuf, ptr_type);
> + }
> +
> ++#ifndef CRASH_MERGE
> + /* Find DT_DEBUG. */
> + if (gdb_bfd_scan_elf_dyntag (DT_DEBUG, current_program_space->exec_bfd (),
> + &dyn_ptr, NULL)
> + || scan_dyntag_auxv (DT_DEBUG, &dyn_ptr, NULL))
> + return dyn_ptr;
> ++#endif
> +
> + /* This may be a static executable. Look for the symbol
> + conventionally named _r_debug, as a last resort. */
> --
> 2.50.0
>
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