Re: [Crash-utility] [Patch] linux-2.6.22 on i386
| From: Dave Anderson <anderson(a)redhat.com>
| Ken'ichi Ohmichi wrote:
| > On linux-2.6.22, the external declaration of i386's __per_cpu_offset[]
| > is in include/asm-i386/percpu.h, and the definition of __per_cpu_offset[]
| > is in init/main.c:
| >
| > unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
| >
| >
| > There are their debugging information in the dwarf section, and the
| > definition's one includes the array length.
| > I explain by following output of the dwarfdump command.
| >
| > * The debugging information of "extern unsigned long
__per_cpu_offset[];"
| > There is not the attribute DW_AT_upper_bound and the crash utility cannot
| > get the array number.
| > <1><32685> DW_TAG_variable
| > DW_AT_name __per_cpu_offset
| > DW_AT_decl_file 83 include/asm/percpu.h
| > DW_AT_decl_line 48
| > DW_AT_type <32674>
| > DW_AT_external yes(1)
| > DW_AT_declaration yes(1)
| > <1><32674> DW_TAG_array_type
| > DW_AT_sibling <32685>
| > DW_AT_type <83>
| > <2><32683> DW_TAG_subrange_type
| >
| > * The debugging information of "unsigned long __per_cpu_offset[NR_CPUS]
__read_mostly;"
| > There is the attribute DW_AT_upper_bound and the crash utility can do it.
| > <1><58437> DW_TAG_variable
| > [a1][a1][a1][a1] DW_AT_name __per_cpu_offset
| > DW_AT_decl_file 1 init/main.c
| > DW_AT_decl_line 363
| > DW_AT_type <33>
| > DW_AT_external yes(1)
| > DW_AT_location DW_OP_addr 0xc03fd400
| > <1>< 33> DW_TAG_array_type
| > DW_AT_sibling <49>
| > DW_AT_type <56>
| > <2>< 42> DW_TAG_subrange_type
| > DW_AT_type <49>
| > DW_AT_upper_bound 31 <--- Here!
| >
| >
| > I thought get_array_length() should retry to get the array length from
| > the next if it could not get it. But I prefer your following idea because
| > it is simple and does not make other effects.
|
| I see. But as it stands now, the crash utility has no dwarfdump-like
| functions to pull out such data, but rather relies on gdb to do the
| dirty work. There's probably something in the gdb innards that could
| access it, but I'm not aware of it.
|
| But it's not that important...
This makes me quite suspicious. I assume that you are correct that
the problem is in gdb. It still feels like there is a serious problem
here: that the most complete definition is not being made available.
You have an effective work-around for __per_cpu_offset, but I wonder
how many other ways this same problem will come up.