On Fri, Jan 29, 2021 at 12:22:41PM +0100, Mark Wielaard wrote:
> On Thu, Jan 28, 2021 at 08:25:20PM -0600, Paul A. Clarke wrote:
> > The subject commit, 3804e937b0e252a7e42632fe6d9f898f1851a49c, causes a
> > failure in the test suite for the IBM Advance Toolchain. The test in
> > question uses "perf probe" to set a tracepoint at "main" in a newly built
> > (with GCC 11) binary of "/bin/ld". With the patch applied, the command
> > enters an infinte loop, calling libdw1 functions but making no progress.
> >
> > The infinite loop can be found in the Linux kernel
> > tools/perf/utils/probe-finder.c:
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/util/probe-finder.c?h=v5.11-rc5#n1190
> >
> >
>
> The infinite loop is because off isn't updated to noff before calling
> continue in the while loop. Moving the last line of the loop off =
> noff; to the start of the loop should fix that.
I noticed that, too. I'll report that over on linux-perf-users.
(That code is about 10 years old, surprisingly.)
> Why the call to dwarf_offdie fails is unclear. Try printing the error
> using dwarf_errmsg (-1) when it returns NULL.
The message is not terribly helpful, to me anyway:
invalid DWARF
> If you also print out
> off (in hex) and the filename the dbg was created from you can inspect
> the file using [eu-]readelf --debug-dump=info to see how the DIEs look
> at that offset.
I'm not a DWARF/DIE expert at this point to know what to look for.
--
Contents of the .debug_info section:
Compilation Unit @ offset 0x0:
Length: 0x24 (32-bit)
Version: 5
Abbrev Offset: 0x0
Pointer Size: 8
<0><c>: Abbrev Number: 1 (DW_TAG_compile_unit)
<d> DW_AT_stmt_list : 0x0
<11> DW_AT_low_pc : 0x100089d4
<19> DW_AT_high_pc : 68
<1a> DW_AT_name : (indirect string, offset: 0x0): start.S
<1e> DW_AT_comp_dir : (indirect string, offset: 0x8):
/path/to/AT.../sources/glibc/csu
<22> DW_AT_producer : (indirect string, offset: 0x5c): GNU AS 2.36.50
<26> DW_AT_language : 32769 (MIPS assembler)
...
Is there an incompatibility introduced with DWARF5?
> BTW. Make sure you have elfutils libdw version 0.172 or newer when
> dealing with DWARF5. Latest elfutils release is 0.182.
SLES15SP2 has an older version:
$ rpm -qi libdw1
Name : libdw1
Version : 0.168
Release : 4.5.3
PC
