https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105704
Bug ID: 105704
Summary: jump tables are not marked with @STT_OBJECT,
disassembly wrong
Product: gcc
Version: 11.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: jur at sysgo dot com
Target Milestone: ---
It seems that the compiler sometimes creates jump tables when using
switch/case. The generated output looks like (PowerPC e5500 output from
-save-temps):
addis 9,2,.LC0@toc@ha
rldic 3,3,2,46
.LVL15:
ld 8,.LC0@toc@l(9)
lwax 9,8,3
add 9,9,8
mtctr 9
bctr
.p2align 2
.align 2
.L6:
.long .L5-.L6
.long .L7-.L6
.long .L8-.L6
.long .L9-.L6
.long .L10-.L6
.long .L11-.L6
.long .L19-.L6
.long .L19-.L6
.long .L19-.L6
.long .L12-.L6
.p2align 4,,15
.L12:
.loc 1 159 0
ld 9,224(13)
The disassembly looks like:
ffffff800004a654: 7d 29 03 a6 mtctr r9
ffffff800004a658: 4e 80 04 20 bctr
ffffff800004a65c: 00 00 00 64 .long 0x64
ffffff800004a660: 00 00 01 a4 .long 0x1a4
ffffff800004a664: 00 00 02 d4 .long 0x2d4
ffffff800004a668: 00 00 01 d4 .long 0x1d4
ffffff800004a66c: 00 00 02 54 .long 0x254
ffffff800004a670: 00 00 01 04 .long 0x104
ffffff800004a674: ff ff fe b8 fmsub f31,f31,f26,f31
ffffff800004a678: ff ff fe b8 fmsub f31,f31,f26,f31
ffffff800004a67c: ff ff fe b8 fmsub f31,f31,f26,f31
ffffff800004a680: 00 00 00 64 .long 0x64
The problem is that the offset for the bctr is interpreted as fmsub
instruction.
There is something missing like:
.type .L6 @STT_OBJECT
This would declare it as data. But then you may need to declare the code after
this as STT_FUNC again.
The example code comes from an older GCC version, but it seems that the
behaviour did not change in GCC 11.3.0.
