https://sourceware.org/bugzilla/show_bug.cgi?id=24809
Bug ID: 24809
Summary: eu-unstrip to drop SECTION symbols if section
.note.gnu.gold-version present
Product: elfutils
Version: unspecified
Status: NEW
Severity: enhancement
Priority: P2
Component: tools
Assignee: unassigned at sourceware dot org
Reporter: vries at gcc dot gnu.org
CC: elfutils-devel at sourceware dot org
Target Milestone: ---
Consider a hello world with debug info, linked using gold:
...
$ gcc hello.c -g -fuse-ld=gold -o hello
...
Now say we strip using objcopy, and then unstrip:
...
$ objcopy --only-keep-debug hello hello.debug
$ objcopy --strip-debug hello hello.stripped
$ eu-unstrip hello.stripped hello.debug -o hello.unstripped
...
Interestingly, the unstripped exec is larger than the original:
...
$ ls -la
-rwxr-xr-x 1 vries users 14104 15 jul 12:34 hello
-rwxr-xr-x 1 vries users 11528 15 jul 12:34 hello.debug
-rwxr-xr-x 1 vries users 8760 15 jul 12:34 hello.stripped
-rwxr-xr-x 1 vries users 14896 15 jul 12:34 hello.unstripped
...
Comparing section sizes, we get:
...
$ readelf -S -W hello | grep ']'| sed 's/\[ /[/' | egrep -v 'NULL|Name' | awk
'{print $2, $6}' > SIZE.1
$ readelf -S -W hello.unstripped | grep ']'| sed 's/\[ /[/' | egrep -v
'NULL|Name' | awk '{print $2, $6}' > SIZE.2
$ diff -u SIZE.1 SIZE.2
--- SIZE.1 2019-07-15 12:43:14.495608629 +0200
+++ SIZE.2 2019-07-15 12:43:07.743655249 +0200
@@ -35,6 +35,6 @@
.debug_ranges 000080
.debug_loc 00013e
.note.gnu.gold-version 00001c
-.symtab 0003c0
-.strtab 000213
+.symtab 000720
+.strtab 0001cf
.shstrtab 000190
...
That is, the .strtab section is slightly smaller, but the .symtab section
significantly larger.
The difference is because of the SECTION symbols, which ld normally adds, but
gold doesn't. However, objcopy adds them nevertheless:
...
$ readelf -s hello | grep -c SECTION
0
$ readelf -s hello.debug | grep -c SECTION
37
$ readelf -s hello.stripped | grep -c SECTION
30
$ readelf -s hello.unstripped | grep -c SECTION
37
...
It would be good if eu-unstrip could recognize the fact that the exec was
produced using gold (there seems to be a section .note.gnu.gold-version) and
drop those symbols (and likewise, objcopy should probably do the same).
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