[Bug binutils/20876] New: objdump is not aware about the build ID method to find detached debug info

[doko at debian dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20876

            Bug ID: 20876
           Summary: objdump is not aware about the build ID method to find
                    detached debug info
           Product: binutils
           Version: 2.28 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: doko at debian dot org
  Target Milestone: ---

[forwarded from https://bugs.debian.org/838875]

find_separate_debug_file is not aware of finding the detached debuginfo using
the Build-Id method.  It looks like when this was introduced, it was only done
for gdb, not for bfd in opncls.c(find_separate_debug_file).

$ readelf -n /bin/ls | grep 'Build ID'
    Build ID: 6774d0a9b81709df5c4dec5df14749c7b645ff7a

$ strace objdump --disassemble -S /bin/ls 2>&1 | grep debug
open("/bin/74d0a9b81709df5c4dec5df14749c7b645ff7a.debug", O_RDONLY) = -1 ENOENT
(No such file or directory)
open("/bin/.debug/74d0a9b81709df5c4dec5df14749c7b645ff7a.debug", O_RDONLY) = -1
ENOENT (No such file or directory)
open("/usr/lib/debug/bin/74d0a9b81709df5c4dec5df14749c7b645ff7a.debug",
O_RDONLY) = -1 ENOENT (No such file or directory)

$ dpkg -S 4d0a9b81709df5c4dec5df14749c7b645ff7a
coreutils-dbgsym:
/usr/lib/debug/.build-id/67/74d0a9b81709df5c4dec5df14749c7b645ff7a.debug

gdb documents this lookup as:

   * For the "build ID" method, GDB looks in the '.build-id'
     subdirectory of each one of the global debug directories for a file
     named 'NN/NNNNNNNN.debug', where NN are the first 2 hex characters
     of the build ID bit string, and NNNNNNNN are the rest of the bit
     string.  (Real build ID strings are 32 or more hex characters, not
     10.)

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