http://sourceware.org/bugzilla/show_bug.cgi?id=13364
Bug #: 13364
Summary: ICF may not be as thorough as one would expect
Product: binutils
Version: 2.23 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: gold
AssignedTo: i...@airs.com
ReportedBy: mh-sourcew...@glandium.org
CC: ccout...@google.com
Classification: Unclassified
When linking Mozilla's libxul.so with GNU gold (GNU Binutils 2.22.51.20111010)
1.11 on ARM, with code built as Thumb-2, with either --icf=safe or --icf=all, a
lot of functions one would expect to be folded aren't.
I figured this when looking what 2 bytes long functions content could be, and
it turns out a lot (if not all) are just doing "bx lr", the ARM/Thumb
equivalent to "ret". But not all the functions doing so are folded:
$ objdump -t libxul.so | awk '$3=="F" && $5=="00000002" {print $1}'| sort |
uniq -c | sort -n
1 00390fc5
1 008545e9
1 0085463d
1 00854655
1 0085467d
1 0085c109
1 0093948d
1 00939cd1
1 0093be95
1 009498e9
1 0095ca4d
1 0095d79d
1 0095d7dd
1 00969ed9
1 0096dffd
1 00992691
1 009b90c9
1 009b90cd
1 009e6781
1 009e9ced
1 009f8649
1 00a18535
1 00a40001
1 00a5e30d
1 00a60f79
1 00a60f7d
1 00a66f35
1 00a680cd
1 00ab97f5
1 00ac57b1
1 00ac57b5
1 00aed3dd
1 00aed3e1
1 00afd821
1 00afd825
1 00b03575
1 00b03579
1 00b0357d
1 00b03581
1 00b089ad
1 00b089b1
2 003102d5
2 00854545
2 00854611
2 0085b105
2 0096bed9
2 009d9129
2 00a05855
2 00afd81d
3 003a6b77
3 00832181
3 00854505
4 00296963
41 00892571
721 001e98a5
(this list is with --icf=all, the --icf=safe list is longer)
Corresponding disassembly:
00390fc4 <_ZN14nsMenuBarFrame19LockMenuUntilClosedEb>:
390fc4: 4770 bx lr
008545e8 <_ZN7mozilla6layers29BasicShadowableContainerLayer7AsLayerEv>:
8545e8: 4770 bx lr
0085463c <_ZN7mozilla6layers25BasicShadowableImageLayer7AsLayerEv>:
85463c: 4770 bx lr
00854654 <_ZN7mozilla6layers25BasicShadowableColorLayer7AsLayerEv>:
854654: 4770 bx lr
0085467c <_ZN7mozilla6layers26BasicShadowableCanvasLayer7AsLayerEv>:
85467c: 4770 bx lr
0085c108 <_ZN7mozilla6layers17ContainerLayerOGL8GetLayerEv>:
85c108: 4770 bx lr
00296962 <_ZN13nsGridLayout216CastToGridLayoutEv>:
296962: 4770 bx lr
001e98a4 <JSD_JSContextInUse>:
1e98a4: 4770 bx lr
etc.
A few disassemble to something like:
0093948c <JS_AnchorPtr>:
93948c: 4770 bx lr
93948e: bf00 nop
but still have a size of 2 in the symbols table.
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